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Unformatted text preview: Department für Wasser-Atmosphäre-Umwelt Institut für Siedlungswasserbau, Industriewasserwirtschaft und Gewässerschutz CORROSIVE WATER Impact & Solutions for Rural Growth Centres Water Supply Systems in Developing Countries Case Study: Uganda Diplomarbeit zur Erlangung des akademischen Grades Diplomingenieur eingereicht von: PINTER, ERIK ROBERT Betreuer: HABERL RAIMUND, Univ.Prof. Dipl.-Ing. Dr.nat.techn. JUNG HELMUT, Dipl.-Ing. H9640242 18.01.2005 ‘Corrosion is a complex problem. It has been investigated for decades and is still incompletely understood.’ (LANGENEGGER, 1994) i (I) ACKNOWLEDGEMENTS Many people assisted and supported me during the elaboration of this thesis, both in Uganda and in Austria ‐ special thanks to all of you – without you, this would not have been possible. In particular, I want to thank Dipl.‐Ing. Helmut Jung for his confidence, honesty and fair comments and Univ. Prof. Dipl.‐Ing. Dr.nat.techn. Haberl for his flexible time schedule. Further, I would like to express my deepest appreciation to the staff of the South Western Towns Water & Sanitation Project and the Austrian Regional Bureau for Development Cooperation in Uganda, for their assistance during my field studies. Finally, I want to thank my family & my girlfriend for their unconditional support throughout the years of my studies. CORROSIVE WATER Erik PINTER, 2005 ii (II) ABSTRACT This thesis is focused on assisting the stakeholders in ‘the Water Sector’ in developing countries in the detection of aggressive / corrosive water, the process of creating sustainable designs and the operation & maintenance of water supply schemes in rural growth centres that are affected by aggressive / corrosive water. A ‘4‐Step approach’ was used during the field studies in the Southwest of Uganda. In the first step the extent & magnitude of corrosion in the area was documented. The second step ‐ the determination of the possible causes of corrosion – was done by focusing on the natural, technical and social aspects of the investigated water supply systems. During the third step, different corrosion control strategies were developed and assessed. The final (fourth) step was to evaluate the different corrosion control strategies concerning the set aims and objectives of this work. Based on the experiences gathered during the field studies and the implementation of the ‘4‐Step approach’, recommendations were given to three levels of stakeholders in the water sector: on a technical, an operational and a policy level. CORROSIVE WATER Erik PINTER, 2005 iii (III) TABLE OF CONTENTS (1) Introduction .............................................................................................1 (1.1) Justification for this Research ............................................................................................. 2 (1.2) Extent and Relevance of Corrosion in Uganda................................................................ 5 (1.3) Aims and Objectives of this Thesis.................................................................................... 7 (1.4) Outline ................................................................................................................................... 8 (2) Regional Background ..............................................................................9 (2.1) Uganda .................................................................................................................................. 9 (2.2) South Western Towns Water & Sanitation Project........................................................ 11 (2.3) Rural Growth Centres Water Supply and Sanitation Schemes in Uganda................ 12 (2.4) Hydrogeology of Uganda ................................................................................................. 14 (3) Technical & Scientific Background ......................................................16 (3.1) Corrosive / Aggressive Water .......................................................................................... 16 (3.2) Drinking Water Quality & Corrosion ............................................................................. 17 (3.2.1) Standards / Guidelines................................................................................................ 17 (3.2.2) Physicochemical Parameters...................................................................................... 21 (3.2.3) Chemical Parameters .................................................................................................. 24 (3.2.4) Bacteriology.................................................................................................................. 28 (3.3) Corrosion of Metals ........................................................................................................... 28 (3.3.1) Chemistry of Corrosion .............................................................................................. 28 (3.3.2) Forms of Corrosion...................................................................................................... 29 (3.4) Aggression of Cementitious Materials............................................................................ 31 (3.5) Existing Corrosion Indices................................................................................................ 32 (3.5.1) pH and Alkalinity........................................................................................................ 32 (3.5.2) Langelier Saturation Index (LSI) ............................................................................... 32 (3.5.3) Calcium Carbonate Precipitation Potential (CCPP) ............................................... 33 (3.5.4) Other corrosion indices............................................................................................... 33 (3.6) Corrosion Control Strategies ............................................................................................ 34 CORROSIVE WATER Erik PINTER, 2005 iv (3.6.1) Changing the Properties of the Corrosive Media ................................................... 35 (3.6.2) Creating a Barrier ........................................................................................................ 38 (3.6.3) Changing the Properties of the Corroded Material ................................................ 39 (4) Research Strategy & Methodology .......................................................41 (4.1) The 4 STEP Approach........................................................................................................ 41 (4.2) Tools..................................................................................................................................... 42 (4.2.1) Visual Investigations................................................................................................... 42 (4.2.2) Interviews ..................................................................................................................... 43 (4.2.3) Water Quality Analyses.............................................................................................. 43 (4.2.4) Calculations & Simulations ........................................................................................ 44 (4.3) Levels of Response............................................................................................................. 45 (4.3.1) Technical Level ............................................................................................................ 45 (4.3.2) Operational Level ........................................................................................................ 46 (4.3.3) Policy Level .................................................................................................................. 46 (5) Field Studies in Uganda ........................................................................47 (5.1) Geographical Area of the Field Studies .......................................................................... 47 (5.2) Implementation of the ‘4‐STEP Approach’ .................................................................... 49 (5.3) STEP 1: Document Extent & Magnitude of Corrosion ................................................. 49 (5.3.1) Existing Information ................................................................................................... 50 (5.3.2) Ecological Aspects / Corrosion Potential of the Water Supply ............................. 51 (5.3.3) Social aspects / User Complaints & Health.............................................................. 51 (5.3.4) Technical Aspects / Infrastructural deterioration ................................................... 54 (5.4) STEP 2: Determine Possible Causes of Corrosion ......................................................... 59 (5.4.1) Ecological Aspects / Water Quality........................................................................... 59 (5.4.2) Technical Aspects / Materials Design and Installation .......................................... 61 (5.4.3) Social Aspects / Workmanship .................................................................................. 62 (5.5) STEP 3: Develop and Assess Corrosion Control Strategies ......................................... 63 (5.5.1) Simulations ................................................................................................................... 63 (5.5.2) Field and Laboratory Research.................................................................................. 64 CORROSIVE WATER Erik PINTER, 2005 v (5.5.3) Secondary and Tertiary Effects of Corrosion Treatment ....................................... 68 (5.6) STEP 4: Evaluate Alternatives and Select Corrosion Control Strategy ...................... 69 (5.6.1) Evaluation Criteria ...................................................................................................... 69 (5.6.2) Rating, Ranking the Strategies................................................................................... 70 (6) Results & Discussion of the Field Studies ...........................................71 (6.1) STEP 1: Document Extent & Magnitude of Corrosion ................................................. 71 (6.2) STEP 2: Determine possible Causes of Corrosion ......................................................... 72 (6.3) STEP 3: Develop and Assess Corrosion Control Strategies ......................................... 74 (6.3.1) Aeration ........................................................................................................................ 74 (6.3.2) Filtration through Limestone..................................................................................... 75 (6.3.3) Lime dosing .................................................................................................................. 77 (6.3.4) Coating .......................................................................................................................... 79 (6.4) STEP 4: Evaluate Corrosion Control Strategies ............................................................. 79 (7) Recommendations.................................................................................82 (7.1) Recommendations for Policy Makers ............................................................................. 82 (7.2) Recommendations for Authorities & Institutions ......................................................... 84 (7.3) Recommendations for Planners & Implementers ......................................................... 85 (7.4) Recommendations for Operators & Owners.................................................................. 86 (7.5) Recommendations for the South Western Towns Water & Sanitation Project (swTwsP)..................................................................................................................................... 87 (8) Conclusions & Summary .......................................................................89 (9) Recommendations for Further Research..............................................91 (10) References ...........................................................................................92 (11) Appendix...............................................................................................96 (11.1) Hydrogeological Map of the Southwest of Uganda.................................................... 97 (11.2) Simulations done with STASOFT & WinWASI ........................................................... 98 (11.3) Water Quality Data of Rural Growth Centres & Potential Sources ........................ 106 CORROSIVE WATER Erik PINTER, 2005 vi (11.4) CEMFLEX Technical Data Sheet .................................................................................. 111 (11.5) Corrosion Test Specimen .............................................................................................. 113 CORROSIVE WATER Erik PINTER, 2005 vii (IV) LIST OF FIGURES Figure 1‐1 ‐ The corrosion cycle of steel (DAVIS, 2000)............................................................. 1 Figure 2‐1 – Map of Uganda – (WORLDATLAS, 2004) ............................................................. 9 Figure 2‐2 – Vertical representation of the weathered crystalline‐aquifer system, including locations of aquifers and construction of wells (TAYLOR et al., 2002) ....................... 15 Figure 3‐1 – Interrelationship of the chapters of the Guidelines for Drinking‐water Quality in ensuring drinking‐water safety (WHO, 2004) ............................................................ 19 Figure 3‐2 – Relationship between rock type and pH. The ranges indicate the limits of the 95% confidence intervals for the mean pH values. ()…Sample Size (LANGENEGGER, 1994).................................................................................................... 22 Figure 3‐3 – Relationship between rock type and the electrical conductivity (LANGENEGGER, 1994).................................................................................................... 23 Figure 3‐4 ‐ Different forms of Alkalinity and Acidity (KEMMER, 1979)............................. 26 Figure 3‐5 – Fundamental corrosion reaction (BRITS, 1998)................................................... 29 Figure 3‐6 – Uniform Corrosion (TIS‐GDV, 2004)..................................................................... 30 Figure 3‐7 – Pitting Corrosion (TIS‐GDV, 2004) ....................................................................... 30 Figure 3‐8 – Galvanic Corrosion (TIS‐GDV, 2004).................................................................... 30 Figure 3‐9 – Corrosion‐System Components............................................................................. 34 Figure 4‐1 – The 4‐Step Approach............................................................................................... 42 Figure 4‐2 – Natural, technical & social components of a water supply system affected by corrosion............................................................................................................................... 46 Figure 5‐1 – The 4‐StepApproach............................................................................................... 49 Figure 5‐2 – Water inside the break pressure tank along the distribution branch in Ryakarimira ......................................................................................................................... 53 Figure 5‐3 – Heavy Cement Degradation at the Sedimentation Chamber in Ryakarimira 56 Figure 5‐4 – Corroded pipes from the intake works in Ryakarimira..................................... 56 Figure 5‐5 – Collection Tank in Ryakarimira & Close‐up of crack at the outside of the tank ............................................................................................................................................... 57 Figure 5‐6 – The inside of the Tank in Ryakarimira ................................................................. 57 Figure 5‐7 – A valve box & a look inside the outlet pipe of the valve box through the valve (right) .................................................................................................................................... 58 CORROSIVE WATER Erik PINTER, 2005 viii Figure 5‐8 – Data for the water at Ryakarimira Source, calculated with STASOFT4 .......... 61 Figure 5‐9 – A GI coupling between stainless steel parts; A brass valve between GI fittings (right) .................................................................................................................................... 62 Figure 5‐10 – The experimental water treatment plant in Ryakarimira ................................ 65 Figure 5‐11 ‐ The application of CEMFLEX (SIKA, 2004)........................................................ 68 Figure 6‐1 ‐ Simulation of the Aeration in Ryakarimira usingSTASOFT .............................. 75 Figure 6‐2 ‐ Simulation of the Limestone filtration with STASOFT....................................... 76 Figure 6‐3 – Simulation of the lime dosing with STASOFT .................................................... 77 CORROSIVE WATER Erik PINTER, 2005 ix (V) LIST OF TABLES Table 2‐1 – Uganda: Key Figures UNDP (2004) .......................................................................... 9 Table 2‐2 ‐ Access to improved water supply sources in Uganda (MWLE, 2004) ............... 11 Table 2‐3 – Objectives of the swTwsP (SWTWSP, 2003).......................................................... 12 Table 3‐1 – Ugandan and WHO guidelines for drinking water ............................................. 20 Table 3‐2 – Advantages of Stabilisation according to Mackintosch et al. (1998).................. 37 Table 3‐3 – Experiences from the use of lime for final pH control (AWWA, 1996) ............. 38 Table 4‐1 – Measurement of different Water Quality Parameters at the swTwsP Laboratory............................................................................................................................ 43 Table 5‐1 – Water Quality Data from different points of the distribution network in Ryakarimira ......................................................................................................................... 51 Table 5‐2 – Statements and Concerns by Stakeholders in Ryakarimira ................................ 52 Table 5‐3 – Signs of Corrosion on the Water Supply Infrastructure in Ryakarimira........... 55 Table 6‐1 ‐ Evaluation of different Corrosion Control Strategies in the Context of this Research................................................................................................................................ 79 Table 7‐1 – Quality Criteria for stabilisation, LOEWENTHAL et al. (2004) ......................... 83 CORROSIVE WATER Erik PINTER, 2005 x (VI) LIST OF DEFINITIONS AND ABBREVIATIONS Alkalinity The proton (H+) accepting capacity relative to an equivalent solution of H2CO3. Also called H2CO3 alkalinity or alkalinity. (AWWA, 2002) Ca(OH)2 Calcium Hydroxide – hydrated / slaked lime CaCO3 Calcium Carbonate – limestone, marble CaO Calcium Oxide – quicklime CCDP Calcium Carbonate Dissolution Potential – indicates the theoretical amount of calcium carbonate that a water can dissolve before reaching saturation with respect to calcium carbonate CCPP Calcium Carbonate Precipitation Potential – indicates the theoretical amount of calcium carbonate that can precipitate from a water DVGW Deutsche Vereinigung des Gas‐ und Wasserfaches / The German Technical and Scientific Association for Gas and Water DWD Directorate of Water Development DWO District Water Officer GI Galvanised Iron GoA Government of Austria GoU Government of Uganda HDPE High Density Polyethylene HTN Handpump Technology Network MWLE Ministry of Water Lands and Environment NGO Non Governmental Organization NWSC National Water & Sewerage Corporation PE Polyethylene PEAP/PRSP Poverty Eradication Action Plan / Poverty Reduction Strategy Process pH the negative logarithm of the Hydogen Ion concentration CORROSIVE WATER Erik PINTER, 2005 xi PVC Polyvinyl chloride RGC Rural Growth Centre SKAT Swiss Centre for Development Cooperation in Technology and Management SO Scheme Operator swTws South Western Towns Water & Sanitation Project TDI tolerable daily intake USh Ugandan Shillings (€1 = USh2,200 – August, 2004) US$ United States Dollar (€1 = US$1.34 – September, 2004) WHO World Health Organization WRC Water Research Commission – South Africa CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 1 (1) INTRODUCTION Corrosion is a natural process. All natural processes tend towards the lowest possible energy state. Thus, for example, iron and steel frequently combine with oxygen and water, to form hydrated iron oxides (rust) in order to return to their lowest energy states. These hydrated iron oxides are similar in chemical composition to iron ore. Figure 1‐1 illustrates the corrosion cycle of steel products. Figure 1-1 - The corrosion cycle of steel (DAVIS, 2000) The total cost of corrosion to our economies is astronomical. In the United States of America, the total direct cost of corrosion was estimated at US$276 billion (~ €206 billion) per year, which is about 3.1% of the U.S. gross domestic product (GDP) in 1998. Among the five industrial sectors, having the largest direct corrosion impact the drinking water & sewer systems sectors were included. The total annual direct cost of corrosion for the USA’s drinking water and sewer systems was estimated to be US$36.0 billion (~ €26.9 billion). This cost was caused by the cost of replacing aging infrastructure, the cost of unaccounted‐for water through leaks, the cost of corrosion inhibitors, the cost of internal mortar linings, and the cost of external coatings and cathodic protection (FHWA, 2002). The costs of public infrastructure corrosion are usually born collectively by society, whereas corrosion in home and business plumbing directly falls on the individual owners. A survey by DVGW (The German Technical and Scientific Association for Gas and Water) amongst 1,130 water suppliers, showed that the need of engaging the DVGW in corrosion research was ranked at fifth place among the most needed services (DVGW, 2000). CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 2 In developing countries, the negative effects of corrosion are intensified, as economic poverty is a widespread problem. People in developing countries frequently do not have financial means to repair or replace damaged water supply infrastructure. This is one of the major causes for water supply systems in developing countries to fail completely, only a few years after construction, if not the government or other donors step in with financial support for the operation and maintenance. The main goal of any technical intervention in developing countries should be sustainability – especially with regard to operation and maintenance. (1.1) JUSTIFICATION FOR THIS RESEARCH Damage related to corrosion on the smaller or larger dimension is a substantial threat to water supply systems in developing countries. Many of these systems are financed by donor countries or donor organisations. These financial resources are usually dedicated to new investments – only a fracture of the money is available for operation and maintenance purposes. The investment costs are often carried by ‘donors’ or ‘development partners’. These investments are provided according to the framework of the corresponding organisations. In case of the Austrian Development Cooperation (ADC) – the official development assistance (ODA) of the Republic of Austria – the water and sanitation sector plays a major role in the bilateral development cooperation. The goal system of the water and sanitation sector within the ADC’s working framework within the official Water Sector Policy is shown below (BMAA, 2001): Goal of Austrian foreign policy: conflict prevention and international peace Goal of Austrian Development Cooperation: poverty eradication, … Goals of the Water & Sanitation Sector: water & sanitation for all, source protection, reliability, economy It is obvious that corrosion is a threat to all four goals of the water and sanitation sector as shown below, hence also threatens the achievement of the higher goals as listed above: water and sanitation for all (quantity & quality, equitable access ...) CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 3 protection of water resources (water, soil, vegetation, water balance ...) supply reliability (technical, operational, financial ....) cost effectiveness (investment, operation & maintenance ....). Each of these goals is put at risk by problems related to corrosive water, such as infrastructural degradation, water leakages, discolourations or increased iron levels in the supplied water. Therefore, a considerable amount of literature and research is covering corrosion problems and their impact and solutions in industrialised countries only. This research varies in the following socio‐geographic aspects: It focuses on development countries, where many of the assumptions made in studies in industrialised countries do not apply. A functional service network is substantial for any water supply system. In the industrialised world any type of spare part can be acquired within a few hours; costs of repairs are often cross‐ subsidised from other sectors. In developing countries the process of acquiring spare parts can be a near to impossible task for a rural community, if no appropriate support structures have been set in place. Due to general financial constraints within smaller communities, cross subsidies are not possible. The cost of spare parts compared to relative income is very high. It deals with rural growth centres (RGC). These are small dynamic settlements that are bigger than villages, yet cannot be regarded to as towns, because of missing infrastructure. In RGCs many people have shifted from farming to petty trade. The term ‘small towns’ is often used as a synonym for rural growth centres. Water supply systems in RGCs often consist of small centralised piped water supply systems with public stand posts, private or institutional yard and in‐house connections. Furthermore, it tries to analyse the situation of RGCs especially in remote areas, where infrastructural & organisational structures are especially weak and human skills as well as technical resources for water supply systems are hardly found. As these areas lack connections to infrastructure such as transport, grid CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 4 electricity supply and communication networks, often they are not integrated into surrounding support network. Although this research should apply to many cases of water supply systems in rural growth centres in developing countries throughout the world, the focus was set to be the South Western Towns Water & Sanitation Project (swTwsP) in the Southwest of Uganda, a project by the Ugandan Ministry of Water Lands & Environment (MWLE), which was initiated and is supported by the Austrian Development Cooperation (ADC) to make it as concrete as possible. The swTwsP was chosen as the focus of this research for the following reasons: instances of heavy corrosion emerged throughout the project area and threatened the achievement of the specific goals of the ADC as listed above the Water & Sanitation Sector is one of the four pillars in the bilateral development cooperation between Austria and Uganda – one third of the total budget of the ADC in Uganda will flow to this sector in the years 2003 to 2005 (BMAA, 2002). The three aspects: development countries, rural growth centres and remote areas apply to rural growth centres in Uganda, where the field study for this research was conducted. The problems related to corrosion of water distribution systems in developing countries are more severe than in distribution systems in industrialised countries. When users of a water and sanitation scheme in a rural growth centre are not supplied with water even for a small period of time, they are likely to switch back to their former, alternative, unsafe water sources such as rivers, unprotected springs or well. This imposes an immediate threat to human health. Although means of infrastructure in Uganda are constantly improving, it is still difficult for scheme operators of small water supply schemes in remote areas to get access to appropriate support in case of serious problems with their water supply systems. Standards regarding the corrosion of water supply infrastructure do not exist in Uganda. The process of involving ‘the private sector’ in government projects has advanced in the last years and is a substantial part of most programmes of official development assistance CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 5 (ODA). Therefore, standards become more and more important in terms of quality assurance in the implementation of government programmes. If planners do not include strategies for corrosion control in their designs, the (local) contractors or ‘private sector’ are hardly limited in the choice of the quality of materials they select or combine. In fact, contractors who choose to offer higher quality materials in public tenders loose jobs, as higher prices make their bids uncompetitive. (1.2) EXTENT AND RELEVANCE OF CORROSION IN UGANDA The corrosion of metals and aggression of cementitious materials in water supply systems can be linked to the occurrence of waters with low pH values, so‐called ‘acidic waters’. Low pH values in natural waters are usually caused by a deficit of calcium carbonates (CaCO3). Due to the local hydrogeology in Uganda (see Chapter (2.4)), water in parts of the country has a deficit of calcium carbonates (CaCO3) and can be regarded to as ‘soft acidic water’ with corrosive / aggressive properties. Many water supply schemes in Uganda are affected by these corrosive / aggressive waters. Problems that commonly occur in connection with the occurrence of these waters include the degradation of cement and mortar as well as the corrosion of metal parts. High operating costs and sometimes even the complete failure of a scheme within its design period to deliver potable water are consequences of this infrastructural degradation. In 1992, corrosion was detected as being a serious problem in the early stages of the (former) RUWASA (Rural Water & Sanitation East Uganda Project) project in eastern Uganda (RUWASA, 1998). Discolourations caused by corrosion by‐products lead to unacceptable high levels of iron in the supplied drinking water. The main cause was found to be the internal corrosion of the riser pipes of the handpumps. Several investigations concluded that the dominant factor in the corrosion process was aggressive carbon dioxide in the low pH water. As a result of the investigations, the design and materials of the used handpump type were changed. It was recommended that the galvanised iron rising mains and rods be replaced by stainless steel, which is not / less susceptible to acidic water. CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 6 Other studies carried out in the (former) RUWASA project area in 1993 found widespread corrosion of GI pipes with ‘no geographical limitation of corrosion and no correlation between corrosion and water chemistry’ (OKUNI, 2000). As a counter measure, the riser pipes and rods of more than 2400 handpumps were changed by RUWASA between 1993 and 2000. Simultaneously, trainings for the pump attendants were conducted. In 1999 demonstrations with PVC rising mains were carried out by SKAT/HTN, which were also found to be successful as a replacement for the GI parts. SKAT also mentions the corrosion problem in 1996 in the report ‘Uganda’s Water Sector Development: Towards Sustainable Systems’ (SKAT, 1996): ‘Within the rural water supply sector in Uganda corrosiveness is a widespread problem’. Also in the the South West of Uganda – where the field study for this thesis was carried out – reports by DWD (2000), the swTwsP (JERLICH, 2000) as well as the records of the swTwsP laboratory in Kabale show, that most of the groundwaters found in the seven districts covered by the swTwsP rarely have pH levels exceeding 6.5 – some even reaching pH levels of below 4.5. Unfortunately, amongst planners, implementers and operators of water supply schemes as well as authorities and policy makers there is (still) little awareness of the difficulties that are likely to arise due to the aggressiveness / corrosiveness of ‘soft acidic water’. Thus, in Uganda little/no data is available to quantify the economical disadvantage associated with these effects. The financial cost of corrosive/aggressive attack on distribution networks and water systems in Uganda has not been quantified yet. However, MACKINTOSCH (1998) indicates that ‘the financial cost of corrosive/aggressive attack is substantial’ under similar conditions in South Africa is substantial to municipalities. Only little attention is focused towards the protection and sustainability of newly designed water supply infrastructure; in most cases equipment that qualifies with the DWD‐’guidelines’ is used without further investigations whether the materials used may be susceptible to corrosion. After a few years noticeable problems (e.g. discolouration of the supplied water, leaks in tanks and pipes) are likely to develop, may result in failure of one or more parts, and finally the complete failure of the water supply system to deliver CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 7 potable water to the community, as the operators are not economically capable of rehabilitating the supply system. Many affected water supply schemes in Uganda are likely to fail without appropriate counter measures being set in the (very) near future. This research is understood as a contribution to initiate a discussion in the Water & Sanitation Sector regarding ‘corrosive water’ its ‘impact and solutions for rural growth centres’ water supply systems in developing countries’ – especially in Uganda, where serious problems are imminent. It should work as a model for other similar regions in developing countries. (1.3) AIMS AND OBJECTIVES OF THIS THESIS This thesis is focused on assisting the stakeholders in ‘the Water Sector’ in developing countries in the detection of aggressive / corrosive water, the process of creating sustainable designs and the operation & maintenance of small water supply schemes that are affected by aggressive / corrosive water. The scientific objectives of this paper are… 1. to provide tools for the assessment of problems related to corrosive / aggressive waters with a focus on rural growth centres water supply systems 2. to recommend preventative and/or remedial measures, once corrosion proves to be a widespread problem to describe preventive strategies for the design & management of water supply schemes in areas that are affected by corrosive/aggressive water to define technical solutions for problems related to corrosive / aggressive waters with a focus on rural growth centres water supply systems to evaluate these technical solutions with specific focus on implementation procedures, operation as well as maintenance efforts (& sustainability aspects) 3. to provide tools for appropriate & sustainable management of problems related to corrosive/aggressive water with a focus on small water supply schemes CORROSIVE WATER Erik PINTER, 2005 (1) Introduction 4. 8 to discuss relevant literature on corrosive/aggressive water and its implications with a focus on rural growth centres water supply systems (1.4) OUTLINE (1) Introduction provides a rationale for the research. The occurrences of corrosive water in the Ugandan context are highlighted. The aims and objectives are described. (2) Regional Background gives a brief background about the regional setting of the field study, regarding Uganda, Rural Growth Centres and the South Western Towns Water & Sanitation Project. (3) Technical & Scientific Background sums up the basics regarding corrosive / aggressive water, drinking water quality, the corrosion of metals and cementitious materials, corrosion indices and describes possible corrosion control strategies. (4) Research Strategy & Methodology provides an insight into the scientific methods and tools that were involved in the implementation of the field studies. The ‘4‐Step Approach’. (5) Field Studies in Uganda describes the detailed implementation of the ‘4‐Step Approach’. (6) Results & Discussion of the Field Studies sums the results of the field studies according to the ‘4‐Step Approach’ and interprets the significance of the results. (7) Recommendations sets out recommendations collated from other sections from this thesis. This chapter particularly focuses on recommendations for policy makers, authorities & institutions, planners & implementers, operators and owners. (8) Conclusions & Summary sums up the experiences gathered and the consequences of the achieved results. (9) Recommendations for Further Research lists topics for further research projects. CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 9 (2) REGIONAL BACKGROUND (2.1) UGANDA Uganda is an ethnically diverse nation situated in the equatorial East‐Africa (see Figure 2‐1). It gained independence from British rule in 1962. Its economy depends mainly on agricultural activities. Figure 2-1 – Map of Uganda – (WORLDATLAS, 2004) Uganda is considered being a country with ‘low human development’ by the UNDP – its human development index (HDI) – although not considered a comprehensive measure for development – being 0.493; ranking it at position 146 (1 being the highest rank) from a total of 177 countries (UNDP, 2004). Key figures of Uganda are listed in Table 2‐1. Table 2-1 – Uganda: Key Figures UNDP (2004) Indicator Value Land area 241,038 sq km Human Development Index (HDI) value 0.493 Human Development Rank 146 (out of 177) Population 25 Mio Life Expectancy at birth 45.7 years Annual population growth rate 3.5 % GDP per capita 1,390 USD Total Fertility Rate (births per woman) 7.1 Urban Population 12.2 % Adult Illiteracy Rate (ages 15 and above) 68.9 % Total Official Development Assistance (ODA) Received 637.9 Mio USD (11% of the GDP) Population with sustainable access to an improved water source 52 % Population with sustainable access to improved sanitation 79 % CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 10 Being a development country Uganda depends on Official Development Assistance (ODA) extended by foreign governments. According to OECD figures the ODA received in the year 2002 totals US$637.9 mio (~ €476.0 mio) or 11.0% of the Ugandan GDP (UNDP, 2004). The total flow of resources to the water sector in the financial year 2001/2002 was USh94.34 bn (~ €40.3 million), of which the contribution of the Government of Uganda was 29% (MWLE, 2004). The Austrian Development Cooperation (ADC) of the Ministry of Foreign Affairs – now implemented under the Austrian Development Agency (ADA) – disbursed €5.56 million to programme and project support in Uganda –, which equals 8.92% of the total programme and project aid (€62.32 million) of the Austrian ODA in the year 2002. Uganda is considered as a one of seven priority countries within the ADC (BMAA, 2002). The Water Sector in Uganda is quite diverse, with the government, NGOs, the Church, and others planning and implementing Water Supply & Sanitation Schemes in Rural Growth Centres. The main institutions responsible in the sector include (MWLE, 2004): Ministry of Water, Lands and Environment (MWLE) is responsible for formulating national policies and setting national standards. Directorate of Water Development (DWD) under the MWLE is responsible for managing water resources, water‐guidance, co‐ordinating and regulating all water and urban sanitation activities, as well as provision of support services to local governments and other service providers. National Water and Sewerage Corporation (NWSC) is an autonomous organisation that is responsible for delivery of water and sewerage services to 16 larger urban centres. District Councils co‐ordinate rural water and sanitation activities at the local level. Town councils co‐ordinate urban water and sanitation services in the smaller towns not managed by NWSC, either directly or working with private sector service providers. CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 11 The activities of the different stakeholders in the water sector are coordinated in an annual Joint Sector Review and a Joint Technical Review. The figures of the water coverage in Uganda for the year 2002 show a huge gap between rural and urban access (Table 2‐2). Table 2-2 - Access to improved water supply sources in Uganda (MWLE, 2004) Indicator National Rural Urban Percentage of people with access to improved water sources 68 % 60 % 80 % Groundwater is the most important source of potable water in Uganda, especially in rural areas, and provides about 80% or more of the water supply (BRITISH GEOLOGICAL SURVEY, 2001). (2.2) SOUTH WESTERN TOWNS WATER & SANITATION PROJECT This thesis is based on a field study that was mainly conducted in the seven districts Kabale, Kisoro, Ntungamo, Rukungiri, Kanungu, Bushenyi & Mbarara in the Southwest of Uganda, which form the area in which the South Western Towns Water & Sanitation Project (swTwsP) operates. The swTws Project is a project by the government of Uganda with support from the Austrian government. It is currently carried out under the ‘Rural Water Supply & Sanitation Programme’ under the DWD (Directorate of Water Development). Austria was the first bilateral donor to provide funds for the improvement of water supply and sanitation in 17 RGCs and Small Towns in the South West of Uganda under the ‘Rural Towns Water and Sanitation Programme’ (BMAA, 2002). Its overall goal is to ‘directly improve the quality of life of the poor’ as part of the fourth pillar of the PEAP/PRSP (Poverty Eradication Action Plan / Poverty Reduction Strategy Process) by implementing water and sanitation activities in 49 towns (500 ‐ 15000 inhabitants per town) (DWD, 2004). In its first phase from 1996 to 2002, water supply and sanitation schemes for 17 small towns were implemented. Within its ongoing second phase an additional 34 schemes are to be implemented until the end of the year 2007. CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 12 The project’s headquarters are located in the town of Kabale in Kabale district next to the offices of the Kabale District Water Officer and the Technical Support Unit 8. The objectives of the swTwsP are listed in Table 2‐3, below. Table 2-3 – Objectives of the swTwsP (SWTWSP, 2003) Objectives: Ensure water services for all users and equity of access. Make pumped water supply affordable for the community. Providing stand posts preferably within a distance of 250 m of all households serving between 250-500 people per outlet. Sustainability of water and sanitation schemes. Economic efficiency. Sensitive use and protection of water sources. Ensuring basic sanitation by promoting dehydration toilets or at least latrines with sanplats. Minimise faecal contaminated wastewater. Improving the sanitation situation in general incl. the treatment of all generated faecal matter contaminated wastewater. In order to accomplish the listed objectives, the following innovative approaches play a major role: Photovoltaic Pumping Systems Ecological Sanitation Participation, Mobilisation and Capacity Building. (2.3) RURAL GROWTH CENTRES WATER SUPPLY AND SANITATION SCHEMES IN UGANDA Rural Growth Centres (RGCs) are small settlements, which are very dynamic in their development. Compared to villages, the communities are more involved in petty trade than in agricultural activities. People in RGCs take advantage of links to nearby towns that have developed in the centre – migration to the RGCs is usually high. The major development constraints of RGCs are the following: lack of technical & managerial know‐how through structural and institutional constraints infrastructural deficiencies such as poor transportation and communications and CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 13 limited political commitment and poor governance. Rural Growth Centres (RGCs) in Uganda are defined by the DWD as communities with a population between 500 and 5000 inhabitants. Small Towns are centres with between 5000 and 15000 inhabitants. About 250 RGCs and approx. 55 Small Towns were identified by the DWD in the year 2002, which are to be considered under the ‘Rural Water & Sanitation Programme’. The GoU has stated that it wishes to ensure universal access to safe water supplies in urban areas by the year 2010 in addition to that by achieving financially self‐sustainable urban water sector, which is not reliable on on‐going subsidies from the government (DWD, 2002). The water supply of villages usually consists of point water sources like public stand posts or handpumps. People often have to walk longer distances to the water sources. In rural growth centres (RGC), households and businesses mostly depend on water vendors, if no adequate water supply system is existent. In case a water supply system is present, RGCs and small towns are usually supplied by small‐scale centralised water supply systems, which are owned by the community or town council and operated by private scheme operators. Theses schemes usually consist of a mechanised water supply system with public stand posts (which should be within a walking distance of the consumers), institutional stand posts (e.g. schools, health centres, churches) and optional in‐house‐connections. All stand posts are metered, so that the consumption can be charged by the tap attendants / water & sanitation boards according to the quantity withdrawn. The introduction of flat rates for drinking water has not been successful in RGC – communities had to switch back to the pay‐per‐quantity system, because of serious economic problems to autonomously maintain the scheme. RGC have only limited economic and human resources available, which make it difficult to maintain these schemes. Therefore, extensive training of the community and the operator is needed to ensure the sustainability of the water supply. Recent figures released by the Ministry of Water, Lands and Environment show that ‘over 30% of rural [water supply] systems in Uganda are non‐functional’ (MWLE, 2004). CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 14 Although piped water supplies in RGCs often may be appropriate, sewer systems are definitely not an appropriate means of disposing off wastewaters in RGCs in developing countries. Other sanitation systems like pit latrines and dry‐toilets are the current sanitation standard in Uganda’s RGCs. By the use of pit latrines, faeces and urine infiltrate into the surrounding environment and therefore are a danger to underlying water resources and – also – to a piped water supply system. Especially if the water supply is intermitted, the risk of contamination is high. In case of leakages (e.g. through corrosion of the system) in the supply system and an intermitted supply, pollution is likely to enter the system and cause a substantial threat to the consumers’ health. (2.4) HYDROGEOLOGY OF UGANDA The geology of an area has a direct effect on its underlying water resources and the water quality of its ground waters, as the water interacts with a variety of soils and rocks. According to BRITISH GEOLOGICAL SURVEY (2001) the geology of Uganda is dominated by ancient (Precambrian) crystalline rocks (granites), which constitute 90% of the land area. The remaining rock types are dominantly younger volcanic and sedimentary rocks. The crystalline rocks are generally covered by a layer of weathered material known as ‘regolith‘. The material varies from rock fragments near the interface with the bedrock to well‐weathered soil and hardened laterite at the ground surface. Typically, the height of the laterite layer is of the order of about 30 m. The typical regolith‐ system is shown in Figure 2‐2. CORROSIVE WATER Erik PINTER, 2005 (2) Regional Background 15 Figure 2-2 – Vertical representation of the weathered crystalline-aquifer system, including locations of aquifers and construction of wells (TAYLOR et al., 2002) The report also states, that groundwater quality varies highly within Uganda. Variations are seen both between different types of water sources (e.g. springs, tube wells) as well as between different rock types (regolith or crystalline bedrock). The ‘Hydrogeological Map of Uganda’ as presented in the Appendix (BRITISH GEOLOGICAL SURVEY, 1989) shows that the hydrogeology of South Western Uganda is dominated by ‘Precambrian formations’ that are partly or wholly granitised and ‘high to medium grade metamorphic formations’ with local and limited groundwater resources. The Rift Valley is characterised by ‘Pleistocene’, with essentially no ground water. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 16 (3) TECHNICAL & SCIENTIFIC BACKGROUND (3.1) CORROSIVE / AGGRESSIVE WATER Groundwaters vary significantly in composition from one point of withdrawal to another. Many groundwaters are at least mildly corrosive to iron and some severely attack iron and even more resistant metals. Corrosive water is a term used to describe ‘aggressive’ water that can dissolve materials with which it comes in contact. It can dissolve enough of these metals to create both aesthetic and health‐related problems in drinking water. Much research was done in South Africa regarding corrosive waters, as approximately forty percent of the surface waters are said to be ‘soft acidic waters’ with corrosive properties (MACKINTOSCH et al., 1998). The South African Water Quality Guidelines (DEPARTMENT OF WATER AFFAIRS AND FORESTRY, 1996) list the following types of water as being potentially corrosive: soft waters with little or no dissolved calcium bicarbonate, for example rain water waters with high concentrations of chloride or sulphate and waters with low or acidic pH values. MACKINTOSCH et al. (1998) describe ‘soft acidic ground and surface waters’ as typically being waters with low alkalinity (0‐25 mg/l as CaCO3) low calcium (0‐25 mg/l as CaCO3) and a low pH. Corrosion is a complex phenomenon that may be caused by a number of factors, either separately or in combination. Important chemical parameters with regard to corrosion are pH, alkalinity (HCO3‐), calcium, aggressive carbon dioxide, chloride, sulphate and oxygen.’ CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 17 Two major problems are likely to occur in relation to internal corrosion of water distribution systems: the failure of the distribution system – caused by the buildup of unwanted corrosion products and unwanted changes in water quality – caused by corrosion by‐products entering the water. (3.2) DRINKING WATER QUALITY & CORROSION The physical, chemical and microbiological characteristics of the water passing through the water distribution system greatly affects the corrosion rate of the materials. On the other hand, corrosion by‐products also affect the water quality. This chapter will bring light on the following issues concerning the different chemical and physical parameters that are of interest regarding corrosive waters: definitions: How are the different parameters defined? standards: Which international and national standards / guidelines exist? relevance: Why are the parameters relevant in the corrosion discussion? (AWWA, 1996) measurement: How are the parameters typically measured, within which time period do samples have to be analysed? (EPA, 2004) range in the field study area: What is the range of the parameters within the field study area? (Data from the South West of Uganda – see Appendix (11.3)) (3.2.1) Standards / Guidelines ‘The quality of drinking‐water is a universal health concern. Water is essential for life, but it can and does transmit disease in countries in all continents – from the poorest to the wealthiest.’ (WHO, 2004) In most countries of the world, the water quality of drinking water – that is water for human consumption – is regulated by national guidelines / standards. The basis for regulation and standard setting to ensure the safety of drinking water in most cases are CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 18 the WHO’s ‘Guidelines for Drinking Water Quality’, which are being published by the WHO at around ten years interval since 1958. The most current edition is the third edition of the guidelines from 2004. WHO Guidelines (WHO, 2004) The WHO states, that ‘safe drinking‐water, as defined by the Guidelines, does not represent any significant risk to health over a lifetime of consumption, including different sensitivities that may occur between life stages.’ The basis for the calculation of the WHO guideline values as is the tolerable daily intake (TDI) as ‘an estimate of the amount of a substance in food or drinking‐water, expressed on a body weight basis […], that can be ingested daily over a lifetime without appreciable health risk.’ Although the guideline values are based on studies which were conducted in temperate climatic conditions, it is assumed that the drinking‐water consumption patterns of the South West of Uganda vary inconsiderably so that the given guideline values are also valid for the area, where this research was carried out. According to the WHO guidelines, the basic requirements for drinking water are that it should be ‘free from pathogenic (disease causing) organisms […] incapable of causing corrosion or encrustation of the water supply system’. Apart from direct health impacts concerning corrosion like high lead and copper concentrations, there are also indirect impacts for health related to the degradation of piped water supplies: infrastructural damages and interruption of the water supply, and therefore the threat, that users in developing countries may turn back to other unprotected water sources leakages and the following intrusion of pollutants in case of low pressure zones or intermitted operation of the system. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 19 Since 1994 the guidelines have been undergoing a rolling revision. Although analytical monitoring has become a focus of assuring water quality, the current third edition of the guidelines is placing more emphasis on preventative management of water safety. The guideline therefore recommends the application of ‘water safety plans’ as a central element for drinking water safety (see Figure 3‐1). Figure 3-1 – Interrelationship of the chapters of the Guidelines for Drinking-water Quality in ensuring drinkingwater safety (WHO, 2004) Relevant chapters of the WHO guidelines in respect to the water quality parameters regarding corrosion of water distribution systems are Chapter 8: Chemical Aspects Chapter 10: Acceptability Aspects and Chapter 12: Chemical Fact Sheets. European Guidelines (EU, 1998) The EU – ‘COUNCIL DIRECTIVE 98/83/EC of 3rd November 1998 on the quality of water intended for human consumption’ provides guidelines for drinking water for the members of the European Union. In the annex of the directive a list of ‘Indicator Parameters’ is given, which are proposed for monitoring purposes. The parameters chloride, conductivity, hydrogen ion CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 20 concentration (pH), sulphate in this list are provided with the note that the given parametric values ensure that ‘the water should not be aggressive’. Ugandan Guidelines Defining water quality guidelines / standards in Uganda is a responsibility of the Ministry of Water, Lands and Environment. Below, the existing water quality policies operational in Uganda are listed: Urban water supplies are based on the Uganda National Standards for Drinking (potable) Water (1994). World Health Organization (WHO) Guidelines, 2004 used with due consideration to specific local conditions and water use habits. Rural water Supplies are based on the Uganda National Water Quality Guidelines (1996). During the time this research was carried out, only interim values set by the Directorate of Water Development in 1995 were available (DWD, 1995). In some instances, the values of the WHO guideline values were modified to allow higher concentrations of certain parameters. A comparison of the Ugandan and WHO drinking water guidelines is given in Table 3‐1. Table 3-1 – Ugandan and WHO guidelines for drinking water Parameter Ugandan guidelines (1995) Guideline Value Maximum allowable WHO guidelines (2004) Guideline Value concentration Temperature (°C) - - Acceptable 5.5 – 8.5 5.0 – 9.5 - - - - 1,000 1,500 - 10 30 (5 Acceptability) Total Alkalinity (mg/l) as CaCO3 - - - Total Hardness (mg/l) as CaCO3 600 800 (500 Acceptability) Calcium (mg/l) - - - Magnesium (mg/l) - - - Total Iron (mg/l) 1.0 2.0 (0.3 Acceptability) Manganese (mg/l) 1.0 2.0 0.4 Chloride (mg/l) 250 500 (250 Acceptability) pH (pH Units) Electrical Conductivity (µS/cm) Total Dissolved Solids (mg/l) Turbidity (NTU) CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 21 Parameter Ugandan guidelines (1995) Guideline Value Maximum allowable WHO guidelines (2004) Guideline Value concentration Sulphates (mg/l) Dissolved Oxygen (mg/l) 250 500 (250 Acceptability) - - - Some of the values set by the DWD are beyond the proposed values given by the WHO. An important statement for the Water Sector in Uganda regarding water quality guidelines can be found in the ‘Water Supply Manual’ (DWD, 1995) which states: ‘In general, water quality guidelines should always be applied with common sense, particularly for small community and rural water supply schemes where the choices for sources and the opportunities for treatment are limited.’ (3.2.2) Physicochemical Parameters Groundwater Temperature Corrosion represents a group of chemical reactions. Water temperature can be an important factor in corrosion, as the oxidation and diffusion rates of metals generally increase with temperature. Increases in temperature affect the chemical and physical composition and properties of waters, the properties of deposits and the actual behaviour of metal itself. Although temperature can have a dramatic effect on the solubility, the temperatures, which are likely to be encountered in a water distribution system, are normally within a narrow range (RINGAS et al, 1999). Hence, this factor is of minor importance in this study. Measurement: The temperature has to be analysed immediately on‐site, using a thermometer. Standards: No guideline value for temperature is provided by the WHO, although it is mentioned, that high water temperature enhances the growth of microorganisms, and may increase taste, odour, colour and corrosion problems. Range: The range of the observed temperatures in the field study area was between 14.8°C and 28.1°C. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 22 Hydrogen Ion Concentration (pH) The pH is the ratio between hydrogen (H+) and hydroxide (OH‐) ions in a solution and is defined as the negative normal logarithm of the hydrogen ion activity (aH+). Since the hydrogen activity in water is about equal to the hydrogen concentration (cH+), the pH can be defined as pH = ‐ log10 [cH+] (LANGENEGGER, 1994). At 25°C, the pH of pure water is 7 (neutral point). That means that OH‐ and H+ in the solution are in equal quantities and the solution is at equilibrium. At a pH > 7 the solution is referred to as being basic or alkaline. A pH < 7 means that there are excess H+ ions in solution – the solution is acidic. The cause for acidic waters often is excess carbon dioxide (CO2) – the pH of a water will decrease when carbon dioxide is formed and will increase when CO2 is destroyed. Waters with low pH values clearly increase corrosion rates by providing a supply of hydrogen ions (see Chapter (3.3.1)). Waters with high pH values may protect pipes and decrease corrosion rates (AWWA, 1996). Therefore, the pH is one of the most useful indicators of corrosion and can be measured relatively easily in the field. A report on ‘Groundwater Quality and Handpump Corrosion in Africa’ by LANGENEGGER (1994) states that the most important factor for the pH of groundwater is the lithology of the aquifer (see Figure 3‐2). Figure 3-2 – Relationship between rock type and pH. The ranges indicate the limits of the 95% confidence intervals for the mean pH values. ()…Sample Size (LANGENEGGER, 1994) Standards: No health‐based guideline value is proposed by the WHO for pH. Nevertheless, it is noticed that pH values greater than 11 may cause eye irritations and CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 23 exacerbation of skin disorders. The pH usually has no direct impact on consumers, but is regarded to as one of the most important operational water quality parameters. The optimum value required usually being in the range of 6.5 ‐ 8. The guideline value for pH in the Ugandan guidelines is defined as the range of 5.5 – 8.5; the maximum allowable concentration is set as 5.0 – 9.5. Range: The pH values of sources in the areas of the field study range from 4.1 (Rubuguri) to 7.7 (Kabirizi). Measurement: The pH has to be measured immediately on‐site using a pH meter. The pH is related to the temperature. Electrical Conductivity (EC) The electrical conductivity (EC) is a measure of the ability of water to conduct an electrical current, and thus is an indication of the total amount of dissolved ions in water, usually expressed in microSiemens per centimetre (μS/cm) at 25°C. It is useful in the determination of water quality and is easily measured on‐site. The major constituents contributing to the EC are the hardness components calcium (Ca2+) and magnesium (Mg2+). Nitrate, chloride and sulphate may also make a significant contribution to the EC. The parameter ‘Total Dissolved Solids’ (TDS) is closely related to the EC and can be calculated by multiplication of the EC by an empirical factor. High EC / TDS tend to increase corrosion rates (AWWA, 1996). LANGENEGGER (1994) also documented a close relationship between the electrical conductivity and the underlying geology (see Figure 3‐3). Figure 3-3 – Relationship between rock type and the electrical conductivity (LANGENEGGER, 1994) CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 24 Standards: There is no proposed WHO guideline value. The WHO states, that the TDS is not of health concern at levels found in drinking water, but that it may affect acceptability of the drinking water. Range: The range of measured values was between 30 μS/cm (Rubuguri) and 600 μS/cm (Muhanga). Measurement: The electrical conductivity can be measured within 28 days after sampling, if the sample is kept refrigerated at 4°C. Turbidity Turbidity is caused by suspended matter in the water, such as mineral particles (silt, clay, corrosion products, etc.), soluble organic compounds, microorganisms, and other microscopic organisms and particles. Turbidity is thus a measure of water clarity and an indicator of its optical properties. Corrosion can affect the turbidity of water through the dissolution of ferric iron from metallic infrastructure. Standards: No health based value has been given by WHO, although a value of less than 5 NTU is mentioned as to usually be acceptable by consumers. Measurement: The most frequently used method to determine the turbidity is the nephelometric method, which involves the use of a turbidimeter and provides data in nephelometric units (NTU). It is easily measured in the field. The turbidity has to be measured within 48 hours if the sample is kept refrigerated. (3.2.3) Chemical Parameters Iron Iron (Fe) can be present in waters in three states, namely as dissolved ferric iron (Fe3+), as ferrous iron (Fe2+) or as suspended iron hydroxides. On exposure to the atmosphere, ferrous iron of groundwaters oxidises to ferric iron causing a reddish‐brown colour. Fe2+ is quite well soluble in water, especially in the presence of CO2: FeCO3 + CO2 + H2O → Fe2+ + 2 HCO3‐. Hence, high iron contents in pumped / piped water are quite common because of corrosion of steel and cast iron pipes. Iron may precipitate a protective film on the interior of metallic pipes (AWWA, 1996). CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 25 WHO Standards: No health‐based guideline value for iron in drinking water is proposed. Usually there is no noticeable taste at iron concentrations below 0.3mg/l. At levels above 0.3mg/l iron stains laundry and plumbing fixtures. Interim Ugandan Standards: For total iron, the guideline value was set at 1.0mg/l, the maximum allowable concentration at 2.0mg/l. Measurement: Iron has to be measured within 6 months after sampling. Range: The observed iron values in the field study area were between 0.0mg/l and 3.5mg/l (Ishasha) Dissolved Oxygen, Carbon Dioxide The concentration of Dissolved Oxygen (O2) is an important factor in both the chemistry and microbiology of water. It is one of the most important factors influencing the rate of corrosion for all metals, as it is a direct participant in the corrosion reaction, acting as a cathode‐accepting electron. Therefore, it increases the rate of many corrosion reactions. Furthermore, dissolved oxygen can destroy the protective hydrogen film, which can form on many metals. (AWWA, 1996) The dissolved oxygen concentration is highly dependent on the temperature of the groundwater. Carbon Dioxide (CO2) forms a weak acid known as carbonic acid (H2CO3) in water. However, CO2 corrosion rates are greater than the effect of carbonic acid alone. The effect of carbon dioxide is closely linked with the bicarbonate content. In the presence of carbon dioxide, iron is quite well soluble in water: FeCO3 + CO2 + H2O → Fe2+ + 2 HCO3‐. It has been suggested that the major source for CO2 in the groundwater is from CO2 in the microbiologically active vadose zone in the soil layer. Rainwater picks up CO2 from the enriched air in the topsoil, as the water percolates downward through the vadose zone (LANGENEGGER, 1994). Standards: No health‐based values by the WHO are recommended. Range: The found values for dissolved oxygen were between 2mg/l and 6mg/l. Measurement: The dissolved oxygen content has to be analysed immediately on‐site. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 26 Total Hardness, Calcium, Magnesium Total Hardness is defined as the sum of the Calcium and Magnesium concentrations, expressed in mg calcium carbonate (CaCO3) per litre. Depending on pH and alkalinity, hardness above about 200mg/l may lead to scaling in plumbing and results in an increase in soap required to produce lather. Calcium may precipitate as calcium carbonate and may provide protection and reduced corrosion rates, but it can also cause turbidity and excessive scaling (AWWA, 1996). Soft waters contain low concentrations of calcium. With a total hardness of less than 100mg/l these waters may lead to aggressive / corrosive water qualities. Standards: No health based guideline value for total hardness is proposed by the WHO. Range: The range of total hardness values found within the South West of Uganda was between 12mg/l and 320mg/l (Buyanja). Measurement: The hardness, calcium and magnesium contents can be measured using titrymetric procedures up to 6 months after sampling. Alkalinity (Acidic Capacity) The Alkalinity of water is defined as its capacity to neutralise acids. The main ions that contribute to the alkalinity are carbonate (CO32‐), bicarbonate (HCO3‐) and hydroxide (OH‐). It is therefore taken as an indication of the concentration of these constituents. The various types of alkalinity can be seen in Figure 3‐4. Figure 3-4 - Different forms of Alkalinity and Acidity (KEMMER, 1979) CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 27 The calcium concentration and the alkalinity, predominantly determine the saturation pH (pHs) of a water. Regarding corrosion, the major water quality factors that determine whether precipitate forms a protective scale on iron, are the pH and alkalinity. Alkalinity may help in the forming of a protective coating and it helps to control pH changes. Low to moderate alkalinity reduces corrosion of most materials (AWWA, 1996). Standards: No standards regarding the alkalinity were defined. Measurement: The alkalinity can be analysed within 14 days, if the sample is kept refrigerated. Range: The values for alkalinity in the area of the field study were between <5mg/l as CaCO3 and 184mg/l as CaCO3 (Buyanja). Sulphate, Chloride Sulphate is a common constituent of water and usually arises from the dissolution of mineral sulphates in soils and rocks. The consumption of excessive amounts of sulphate usually results in diarrhoea. Excessive concentrations of sulphate increase the corrosion rate of metals (AWWA, 1996). Chloride is also a common constituent in water. Chloride accelerates the corrosion rate of iron and other metals, depending on the alkalinity of the water. It is assumed that chloride will take the place of oxygen in any corrosion process, as it is an effective oxidising agent. Standards: No health based guideline value for sulphate was proposed by the WHO. Levels of below 350mg/l were found not to influence the taste of the water. No health based guideline value for Chloride is proposed by the WHO, although values above 250mg/l were found to be increasingly likely to be detected by taste. Measurement: The parameters chloride and sulphate can be measured within 28 days after sampling, if the sample is kept refrigerated (chloride can be kept without cooling). Range: The range of chloride in the field area was between 5.4mg/l and 19.0mg/l (Muhanga). The range of sulphates was between 2.0mg/l and 156mg/l (Ruhaama). CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 28 (3.2.4) Bacteriology The bacteriological parameters of water were not relevant in the context of this research, but is a useful means for the determination of probable contamination of a piped water supply that is affected by corrosion. (3.3) CORROSION OF METALS The distribution system is the most expensive part of a water supply system. Maintenance and replacement of corroded infrastructure impose unnecessary economic costs on water suppliers and ultimately on the users. Corrosion can become a problem if metallic infrastructure of the water supply system stays in direct contact with water. This report focuses on both the undesired corrosion of ferrous materials such as galvanised iron as well as on the aggression of concrete (see Chapter (3.4)). (3.3.1) Chemistry of Corrosion Corrosion is the attack of the surface of materials by chemical processes. According to ISO 1979 corrosion is defined as the ‘physicochemical interaction between a metal and its environment which results in changes in the properties of the metal’ (AWWA, 1996). This definition also agrees with the German standard DIN 50900. Chemical corrosion occurs, where any metal is in direct contact with an oxidising agent (e.g. oxygen, hydrogen, carbon dioxide, chloride). Electrochemical corrosion is the most common form of corrosion. Hereby metal is being destructed by electron transfer reactions, which require the presence of an electrochemical cell with an anode, a cathode and an electrolyte. Dissolution of metal occurs at the anode where the corrosion current enters the electrolyte and flows to the cathode (see Figure 3‐5). CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 29 Figure 3-5 – Fundamental corrosion reaction (BRITS, 1998) The general reaction that occurs at the anode is the dissolution of metal as ions: M → Mn+ + en‐ (Where M = metal involved; n = valence of the corroding metal species; e = electrons). The number n of electrons lost at the anode must equal the number n of electrons gained at the cathode. For example, if iron (Fe) were exposed to aerated, corrosive water, the reaction at the anode would be 2Fe → 2Fe2+ + 4e‐ (anodic reaction). At the same time, reduction of oxygen would occur at the cathode: O2 + 2H2O + 4e‐ → 4(OH‐) (cathodic reaction). The overall reaction can be summarised as 2Fe + O2 + 2H2O → 2Fe2+ + 4(OH‐). After dissolution, ferrous iron Fe2+ will generally oxidise to ferric iron Fe3+, which will combine with the hydroxide ions OH‐ formed at the cathode. The product of this reaction is called ‘rust’ (FeOOH or Fe2O3 ∙ H2O). Similarly, other metals will form corrosion products e.g. corroded zinc will form the corrosion product Zn(OH)2. The driving force for all corrosion processes is a tendency to approach the most stable energy state. (3.3.2) Forms of Corrosion Several corrosion forms can be differentiated according to AWWA (1996). The different forms of corrosion depend on several factors: the material to become corroded, the construction of the system, scale and oxide film formation, as well as hydraulic conditions. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 30 Although there are several, different forms of corrosion – only the forms relevant in the context of this thesis are summarised below. Uniform Corrosion Uniform Corrosion is also known as general, surface or overall corrosion. In case of uniform corrosion of a single metal surface, the surface may be referred to as a ‘polyelectrode’: there is continuous shifting of microgalvanic cells on the metal surface. Figure 3-6 – Uniform Corrosion (TIS-GDV, 2004) Examples of uniform corrosion are the attack on metals by acids and bases. Figure 3‐6 shows the effect of uniform corrosion on a metal surface. The corrosion rate is nearly constant throughout the metal surface. Localised Corrosion (Pitting Corrosion) Localised attack resulting in pitting is the local concentration of corrosion, either in very little spots or over relatively large areas. Usually the anodic region is small compared to the cathodic area. Localised corrosion is one of the most destructive forms of corrosion. Corrosion to the point of failure occurs rather rapidly; therefore, the rate of pitting is more important than the size or number of pits. Figure 3-7 – Pitting Corrosion (TIS-GDV, 2004) In Figure 3‐7 the effect of pitting corrosion on a metal surface is shown. Galvanic Corrosion Galvanic corrosion occurs in places where two dissimilar metals or alloys are electrically connected and exposed to a corrosive environment. The less noble metal serves as the anode and therefore deteriorates, while the more noble metal serves as a cathode and is therefore protected (see Figure 3‐8). Figure 3-8 – Galvanic Corrosion (TIS-GDV, 2004) CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 31 The tendency of metals / alloys to be anodic or cathodic can be derived from the ‘galvanic series’. The rate of galvanic corrosion is increased by the greater differences in the electrical potential between two metals. The corrosion rate of galvanic corrosion is usually much higher than that of normal electrochemical corrosion. Other forms of Metal Corrosion Other forms of corrosion that were not found relevant during this research are Intergranular / Intercrystalline Corrosion Microbially Influenced Corrosion and Concentration Cell Corrosion. (3.4) AGGRESSION OF CEMENTITIOUS MATERIALS Many drinking water systems contain infrastructure with cement‐based materials such as concrete. Aggression is the process, where water attacks the cement matrix. The aggression of these materials depends mainly on the amount of calcium carbonate‐ aggressive carbon dioxide or the CCPP (Calcium Carbonate Precipitation Potential – see also Chapter (3.5.3)) as well as the amounts of sulphate and chloride of the water. If the water is undersaturated with calcium carbonates, the free lime [Ca(OH)2] at the surface will react with carbonate species in the water and form calcium carbonate (CaCO3) precipitate, which is dissolved in the water. The result of an attack on the cement‐based material – by leaching free lime, calcium aluminates and silicates out of the cement matrix – is the decrease of the mechanical stability and may result in the eventual failure of the structure. This type of corrosive attack can be prevented by changing the chemical characteristics of the water in such a manner that it does not dissolute CaCO3, as it becomes slightly supersaturated with respect to CaCO3. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 32 (3.5) EXISTING CORROSION INDICES The corrosivity of water can be predicted with ‘corrosion indices’, which are based on the chemical composition of the water. Although the prediction of corrosion by the use of corrosion indices is useful, the complexity of the corrosion processes makes it necessary to test and monitor corrosion on‐ site using corrosion test specimen (see Appendix (11.4)). These direct methods of determining corrosion rates are based on weight loss measurements and often require very long periods of time (up to 24 months). Strictly speaking, the term ‘corrosion index’ is misleading, as most indices are just used to indicate the possibility of calcium carbonate (CaCO3) to precipitate from the water, in which case corrosion protection may occur by the creation of a calcium carbonate coating. The calculation of the CCPP is the only ‘index’ with which the precise amount of CaCO3 that may precipitate or dissolve, as well as the equilibrium pH and alkalinity can be calculated (BRITS et al., 1998). Both qualitative and quantitative assessments regarding the corrosiveness / aggressiveness of water can be done by the determination of different corrosion indices. Qualitative parameters just predict the tendency, whether water is going to precipitate or dissolve CaCO3, quantitative parameters also predict how much CaCO3 is going to be precipitated. (3.5.1) pH and Alkalinity The pH may be regarded as a basic, but easy method of determining whether a water is aggressive / corrosive or not. Water with a pH above 9.5 will not be corrosive to metal structures, as long as no major concentrations of sulphates or chlorides are present. The pH can be easily assessed in the field using a pH meter. (3.5.2) Langelier Saturation Index (LSI) The LSI is (still) one of the main qualitative parameters to evaluate corrosive properties of water in respect to concrete and steel. It is defined as LSI = pH ‐ pHs (Where: pH is the pH CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 33 of the water; pHs is the saturation pH at the calcium carbonate equilibrium). The pHs can be determined by the marble test (DIN 380404‐C10‐M4). Several studies by the Water Research Commission (WRC) show that the Langelier Saturation Index does not coincide with corrosion rates of pipe materials (RINGAS, 1999) and is therefore not regarded as being suitable for the measurement of corrosivity. According to EDWARDS (2004) the use of the Langelier index belongs to ‘principles discredited for more than a decade […] as a viable guide to corrosion control’. It was therefore not used in this research. (3.5.3) Calcium Carbonate Precipitation Potential (CCPP) The CCPP is an index used for the evaluation of water quality goals, which are necessary to provide corrosion protection through the formation of a calcium carbonate scale (see Chapter (3.6)). The CCPP describes both the tendency whether water is going to dissolve or precipitate CaCO3 as well as the quantity of CaCO3 in mg/l that may be dissolved or precipitated for a given water. According to AWWA (1996) the CCPP is defined as ‘the quantity of CaCO3 that theoretically can be precipitated from oversaturated waters or dissolved by undersaturated waters during equilibration’. For undersaturated waters the CCPP is negative, for oversaturated waters it is positive. The CCPP can be determined by the use of diagrams (e.g. Modified Caldwell‐Lawrence Diagrams) or calculated using computerised water chemistry models (e.g. StaSoft, WinWASI) as its calculation is very complex. The necessary parameters for its determination are calcium as mg/l Ca2+, alkalinity as mg/l CaCO3, the pH, temperature in °C and total dissolved solids (TDS) in mg/l. The CCPP is valid over the whole range of pH values. (3.5.4) Other corrosion indices Other corrosion indices include the Ryznar index (RI), Larson index (LI), Riddick index (RI), Driving force index (DFI), momentary excess index (ME), aggressive index (AI), and are not further discussed in this research. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 34 (3.6) CORROSION CONTROL STRATEGIES Achieving calcium carbonate saturation is considered the principal means of corrosion control in water distribution systems containing iron and cementitious materials. If the water is supersaturated with calcium carbonate, the pipe will be coated with an eggshell‐ like calcium carbonate coating that protects the pipe from corrosive attack. If the water is undersaturated with calcium carbonate, this coating will not form and the water will be regarded to as non‐scale forming or corrosive. A treated water with a calcium carbonate precipitation potential (CCPP) of about 4 mg/l (measured as CaCO3) is recommended to promote the formation of a protective calcium carbonate coating (LOEWENTHAL et al., 2003). The basic ‘corrosion system’ as shown in Figure 3‐9 consists of two elements: the corrosive media (e.g. acidic water) the corroded matix (e.g. iron). By direct contact of these two elements, corrosion is will occur on the interface. Figure 3-9 – Corrosion-System Components Three straight strategies to control corrosion can be thought of: changing the properties of the corrosive media (e.g. changing the properties of the drinking water to a non‐corrosive nature) changing the properties of the corroded/degraded material (e.g. the judicious use of materials for infrastructure) CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 35 creating a barrier between the corrosive media and the potentially corroded material (e.g. through the protection of the infrastructure with coatings) and alternatively, combinations of these strategies are also possible. (3.6.1) Changing the Properties of the Corrosive Media Corrosive water can be changed to a state, where it has no damaging influence on the water supply infrastructure. Especially for existing water supply systems with soft, acidic waters as their sources, these methods may be the only option of effective corrosion control. MACKINTOSCH (1998) describes the principal component of measures to prevent corrosive and/or aggressive attack by soft, acidic waters, as being the chemical conditioning, or ‘stabilisation’ of the water. Stabilisation of the water requires adjusting the chemical characteristics of the water to an extent that: calcium and alkalinity > 50 mg/l as CaCO3 6.5 < pH < 9.5 and calcium carbonate precipitation potential (CCPP) of about +4mg/l as CaCO3 (a slight supersaturation with CaCO3). Complete stabilisation will terminate aggressive attack of cementitious materials and corrosive attack of metals, although protection of iron will only occur if a dense precipitate scale is formed on the metal surface adjacent to water. Corrosion problems that arise from soft acidic waters are often treated by increasing the buffer capacity and the concentration of divalent cations like calcium and magnesium. The methods that are available for attaining the slightly supersaturated water quality are listed below. Alternative Sources If possible, the easiest way to avoid corrosion problems in (future) water distribution systems is not to design water supply systems that use corrosive water as a source. Whenever this option is possible it should be given priority to any other measures of corrosion control. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 36 Aeration In waters with high levels of dissolved carbon dioxide (carbonic acid) present, aeration for stripping the excess carbon dioxide reduces the ratio of [H2CO3]/[HCO3‐], which results in an increased pH, and therefore lesser aggressiveness / corrosiveness of the water. Depending on the stripping technology used and the raw water quality, carbon dioxide concentrations can be reduced to less than 5mg CO2/l by aeration (MACKINTOSCH et al., 1998). Types of aerating technologies include natural draft aeration, forced draft aeration, spray aeration, pressure aeration and packed tower aeration. Filtration through Limestone (CaCO3) or half-burnt dolomite limestone (MgO·CaCO3) Filtration through limestone is one of the oldest technologies for the stabilisation of acidic waters and is a commonly used water treatment technology in industrialised countries. A limestone reactor or filter is a bed of granular limestone through which water passes. The process simulates the natural underground processes that occur when water passes through limestone deposits. The process is well suited for smaller water supply systems, because there is no need to feed chemicals, and it cannot result in overdosing. These filters are used widely in small water supply facilities in many areas of North America and Europe. In most cases, they are low cost and operation is simple. By filtration through naturally occurring solid calcium carbonate or limestone, water will react with the CaCO3 of the limestone until it reaches the equilibrium pH. The dissolution of calcium carbonate firstly forms carbonic acid, which reacts with water and forms hydrogen carbonates. This reaction can be summarised as follows: CaCO3 + CO2 + H2O ↔ Ca2+ + 2HCO3‐. The driving force in this process is the natural dissolution force of the water – expressed as the CCDP or negative CCPP. According to MACKINTOSCH et al. (1998) ‘such stabilisation significantly reduces the aggressive and corrosive properties of the water, making the water essentially non‐aggressive to cement concrete, non‐corrosive to copper, and significantly less corrosive to iron.‘ He lists several advantages of this ‘partial stabilisation’ over the traditional use of powdered lime and carbon dioxide (see Table 3‐2). CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 37 Table 3-2 – Advantages of Stabilisation according to Mackintosch et al. (1998) Advantages The water treats itself, taking up calcium and alkalinity to satisfy equilibrium requirements. The pH is controlled naturally at desirable upper limits. The process is robust and problem-free, with low supervision and maintenance requirements. Lime dosing equipment is notoriously troublesome, and impractical in small-scale water treatment plants. Limestone is significantly cheaper than lime. Complicated dosing of expensive carbon dioxide is not required. Chemical cost of stabilisation is greatly reduced. The German DVGW (DVGW‐W 214 T.2) has made recommendations for the design of alkaline media filters. Typically, limestone based filters can be run either downstream or upstream and either as wet or dry. Filter aggregates usually have diameters of between 0.7mm and 3.0mm. Refilling of the material should be done, when the height of the filter material has been reduced by 10%. The half‐burnt filter media, such as half burnt limestone (MgO∙CaCO3) is more frequently used in water treatment systems in industrialised countries, as the amount of filter media used is halved and the necessary contact time is reduced (resulting in smaller volumes). The following reaction takes place: MgO∙CaCO3 + 3CO2 +2H2O → Ca2+ + Mg2+ + 2HCO3‐. Dosing of Calcium Hydroxide (Ca(OH)2) – hydrated lime By adding quicklime (CaO) or hydrated lime (Ca(OH)2) in the form of lime milk (~10 percent Ca(OH)2) or lime water (~1 percent Ca(OH)2) to water, the corrosive water reacts such that the alkalinity and the pH of the water are being raised. The reaction is as follows: Ca(OH)2 + 2CO2 → Ca(HCO3)2. Overdosage of lime will result in the increase of the pH above the equilibrium pH. Experiences from the use of lime for pH control in water utilities are summarised in Table 3‐3. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 38 Table 3-3 – Experiences from the use of lime for final pH control (AWWA, 1996) Experiences: a relatively inexpensive chemical increases pH and calcium for soft water requires large investments in chemical dosing equipment can increase turbidity and aluminium in treated water unless there is good control of particulates can cause dust problems if special precautions are not taken can clog dosing equipment In practice, the dosage of the quicklime solution proves to be hard. In industrialised countries, the process of dosing the solution is normally done by the use of special dosage pumps (e.g. membrane pumps). Inhibitors In case corrosion problems cannot be overcome by pH control or pH and alkalinity control, the use of inhibitors can be an option – along with pH control. Corrosion inhibitors are chemicals that are dosed in small quantities to obtain a passivating film to block electrochemical corrosion. Orthophosphates and silicate chemicals form passivating films on anodic sites to suppress the electrochemical corrosion reactions. The WHO in its third edition of the Water Quality Guidelines (WHO, 2004) states that there is no guarantee that silicates and polyphosphates will inhibit corrosion, but that they may act by ‘masking’ the effects of corrosion, rather than by preventing it. An interesting article by VON FRAUNHOFER (2000) shows potential corrosion inhibition properties of tobacco, a plant that is widespread in many equatorial countries. (3.6.2) Creating a Barrier If it is not possible to change the properties of the corrosive water, another option is to create a barrier between the corrosive water and the potentially corrodible infrastructure. This can be accomplished by the application of coatings on the infrastructure as well as through cathodic protection. Coatings Coatings provide a barrier between the (corrosive) water and the (corrodible) infrastructure. CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 39 Coatings in pipes are usually mechanically applied either when the pipes are being manufactured, in the field before the pipe is installed or even after service – which is much more expensive. The most common types of pipe coatings are coal‐tar, enamels, epoxy paints, cement mortar and polyethylene. Typical types of coatings for water storage tanks are coal‐tar paints, enamels, vinyl and epoxy (AWWA, 1996). Cathodic Protection Cathodic protection is an electrical method for the protection of metallic structures from corrosion. The principle of cathodic protection is to suppress the corrosion current that causes damage in a corrosion cell and force the current to flow to the metal structure that has to be protected. Thus, the corrosion is prevented. There are two basic methods of cathodic corrosion protection: the first method uses an impressed current, which uses an external direct current power source to power the electrodes. The second method uses a sacrificial anode, such as magnesium or zinc anodes, which are connected to the structure to provide the cathodic protection current. Cathodic corrosion is not regarded as a feasible means of corrosion control of entire water supply systems, as it is very expensive. Its primary target of use is the protection of single water storage tanks or pipes that are affected by external corrosion. (3.6.3) Changing the Properties of the Corroded Material Another way of corrosion protection is the choice of corrosion resistant materials for the infrastructure. According to LANE AND NEFF (1969; cited by AWWA, 1996) materials selection is the ‘first line of defence’ in corrosion control in water distribution systems. Some of the corrosion resistant materials, which are relevant to water supply infrastructures, are described below. Polyethylene (PE) In research done by RINGAS (WRC, 1999) several non‐metallic piping materials and coatings were tested according to their corrosion abilities in corrosive / aggressive waters. It was found, that non‐metallic piping such as HDPE, PP and polycarbonate were suitable to convey potable water. They showed good performance after 42 months of testing, CORROSIVE WATER Erik PINTER, 2005 (3) Technical & Scientific Background 40 although it was noted that the corrosion products from the metallic pipes did adhere to the non‐metallic pipe surface and hence, negatively affect the hydraulic properties of the pipes. Polyvinylchloride (PVC) It has been reported that corrosion of PVC plumbing components is also possible and likely to result in dangerous amounts of vinyl chloride in the drinking water (SWISTOCK et al., 2001). Stainless Steel (SS) Steels with an amount of free chromium contents of more than 11 percent, do normally not form red rust. The resistance of stainless steel to corrosion comes from a protective coating that forms on its surface. This coating is a ‘passive’ film that is resistant to further oxidation or other forms of chemical attack and is produced by the combination of oxygen, water and constituents of the steel. Although this protective film may just be monomolecular in thickness, it is generally protective in oxidising environments. However, stainless steels are subject to corrosion by halogen salts, primarily chlorides. CORROSIVE WATER Erik PINTER, 2005 (4) Research Strategy & Methodology 41 (4) RESEARCH STRATEGY & METHODOLOGY (4.1) THE 4 STEP APPROACH During a literature review to develop an appropriate approach for the field study of this thesis, a six‐step approach was found in ‘Internal Corrosion of Water Distribution Systems’ by AWWA (1996). AWWA is recommending the following procedure when conducting a corrosion control study and implementing its findings. The six recommended steps are: 1. Document extent and magnitude of corrosion. 2. Determine possible causes of corrosion. 3. Develop and assess corrosion control alternatives. 4. Evaluate alternatives and select corrosion control strategy. 5. Document findings in engineering report. 6. Implement corrosion control and monitor effectiveness. Several of the recommended points of the detailed description of the six‐step procedure by AWWA were not found to fit within the framework of this research and therefore had to be adapted. Some aim specifically on copper, zinc, cadmium and lead, which have shifted into the focus of many investigations in the last few years, because of increasing health problems in respect to these elements in industrialised countries. It was not possible to test for these parameters during the time the field studies in Kabale were conducted. These parameters were therefore not covered in this research. This is considered a valid simplification, as these materials – apart from zinc – were not used in the water supply systems that were investigated in the area of the field study. Some of the proposed procedures of the six‐step approach did not seem achievable in the field study due to the limited technical, financial and skilled human resources in the area of the field study, as compared to industrialised countries. CORROSIVE WATER Erik PINTER, 2005 (4) Research Strategy & Methodology 42 The discussions in this thesis are understood as a contribution to the steps one to five of the ‘original’ six‐step approach. The fifth step to ‘document findings in an engineering report’ is done by completing this thesis. The sixth step is the task of the responsible bodies, as addressed in Chapter (7): Recommendations. A ‘4‐step approach’ was therefore chosen, which is outlined in Figure 4‐1. Figure 4-1 – The 4-Step Approach (4.2) TOOLS Several tools were used in order to implement the 4 Step Approach, during the field study. (4.2.1) Visual Investigations Visual investigations were conducted of several water supply schemes, in particular to determine the deteriorating effects of corrosive water on the water supply infrastructure. As far as possible, the impressions from the field observations were captured using photographic equipment. The attempt to provide reference measures (mostly a reference object) if necessary was made, to give the viewer of the pictures an impression about the original dimensions of the portrayed objects. CORROSIVE WATER Erik PINTER, 2005 (4) Research Strategy & Methodology 43 Physical properties that could not be captured in pictures are described in words. (4.2.2) Interviews Semi‐structured interviews with various stakeholders of the investigated schemes were conducted at different occasions, including the scheme operator users of the supplied water South Western Towns Water & Sanitation Project (swTwsP) staff South Western Umbrella of Water & Sanitation (swUws) staff. Due to the local circumstances, the discussions were of informal nature and are therefore not statistically analysable. Records of important information were created during the interviews and are provided in the relevant context. (4.2.3) Water Quality Analyses A substantial part of the field studies required the analysis of various physical and chemical water quality parameters. Therefore, it was necessary to ensure the correct determination of the different physical and chemical parameters. The analysis of as many parameters as possible was done on‐site. An overview of the different parameters, measuring methods and equipment used at the South Western Towns Water & Sanitation Project Laboratory, as well as the range and error margins of the methods are provided in Table 4‐1. Table 4-1 – Measurement of different Water Quality Parameters at the swTwsP Laboratory Parameter Equipment / Method Brand Range / Unit On-Site? Yes / No Physicochemical Parameters: Temperature pH Meter WTW 0-25°C Y pH pH Meter WTW 0 – 14 pH units Y Electrical Conductivity Electrical conductivity 0 – 19990 µS/cm Y <5 – 2000 NTU Y Meter Turbidity Turbidity meter CORROSIVE WATER Erik PINTER, 2005 (4) Research Strategy & Methodology 44 Chemical Parameters: Alkalinity Titration HACH <5 - 400mg/l as CaCO3 Y Calcium Titration Standard Methods mg/l as CaCO3 N Magnesium Titration Standard Methods mg/l as CaCO3 Iron (II) Photometer MERCK N 2+ N 3+ N 10-150mg/l as Fe Manganese Photometer MERCK 0.5-10mg/l as Mn Dissolved Oxygen Titration HACH mg/l as O2 Chloride Photometer Sulphate Photometer MERCK MERCK Y 1.0 – 15.0mg/l as Cl 24 mg/l as SO - N N The analyses were done together with the Water Quality Analyst of the swTwsP, Mr. Julius Byamugisha, an experienced chemist in his field. For the determination of the corrosion index calcium carbonate precipitation potential (CCPP) the computer programs WinWASI and STASOFT 4 were used (see Chapter (4.2.4)). (4.2.4) Calculations & Simulations Several calculations were done as a part of the assessment of the corrosive properties of the water sources using the software programs WinWASI 3.0 and STASOFT 4 especially regarding the calculation of the corrosion indexes. In Chapter (5.5) ‘STEP 3: Develop and Assess Corrosion Control Strategies‘ the two listed computer programs were used to determine changes in the water quality that can be taken to limit the corrosive properties of the waters. WinWASI 3.0 The program WinWASI is a computer program that allows a number of calculations of different water treatment techniques. The calculations with WinWASI require a full analysis of at least the parameters magnesium, sodium, potassium, chloride, nitrate and sulphate (BIESER UND PARTNER). At the time of the field study, the manual of WinWASI was only available in German, which made it very difficult for the chemist of the swTws project to work with the program, despite the fact that the program interface was in English. CORROSIVE WATER Erik PINTER, 2005 (4) Research Strategy & Methodology 45 STASOFT 4 Stasoft 4 allows to calculate and display the changes in chemical composition of any given water resulting from the application of a succession of treatment processes. The effect of any change in initial water composition or treatment is immediately shown on the screen. Calculations regarding the carbonic system of a given water with the program STASOFT 4 were possible with any combination of at least two of the parameters: pH, alkalinity, acidity, CO2‐acidity and total carbonic species (MORRISON et al., 2000). (4.3) LEVELS OF RESPONSE In order to ensure the effect of this research, an attempt is made, to give recommendation to the different relevant stakeholders, according to the results from the field study. Most of the field work relating to the chosen ‘4‐Step Approach’ was done on a technical, and some work on an operational level. From the experiences gathered on these two levels, recommendations and conclusions for the policy level will be drawn. According to the ‘Aims and Objectives of this Thesis’ (Chapter (1.3)), this research aims at giving recommendations on three action levels of the Water Sector: a ‘broader’ policy level an operational level and a technical level The very important user level was left out in the discussion, as piped water suppliers are understood as providing a service to the paying users. Hence, the users have the right not to be negatively affected by measures taken to control corrosion in a water supply system. (4.3.1) Technical Level Different strategies to control corrosion‐related problems were discussed in Chapter (3.6). These strategies were formulated on a technical level. For a technology in the context of the Water Sector, it has to be seen in relation to natural, social and technical components. This systematic approach is addressed in the Water CORROSIVE WATER Erik PINTER, 2005 (4) Research Strategy & Methodology 46 Sector Policy of the Austrian Development Cooperation (BMAA, 2001). An attempt to capture the impacts of corrosive water on these components was done in Figure 4‐2. Figure 4-2 – Natural, technical & social components of a water supply system affected by corrosion Sustainable technologies have to be affordable, manageable and adaptable. The recommendations for the technical level are therefore going to focus on small‐scale technical solutions for the sustainable management of water supply systems in RGCs. (4.3.2) Operational Level Regarding the operational level, this thesis concentrates on necessary operation and maintenance issues for the successful implementation of different corrosion control strategies for water supply schemes in rural growth centres, which are affected by corrosive water. (4.3.3) Policy Level Rural Growth Centres (RGCs) have to be seen within a system consisting of universities, government administration, government legislation and the private sector. On one hand, the water supply systems in RGCs are decentralised (which can be seen as a positive development), on the other hand they are hardly integrated into the broader Water Sector framework. This thesis therefore tries to provide recommendations on the policy level, which will allow the integration of water supply systems in RGCs into regional and sub regional structures. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 47 (5) FIELD STUDIES IN UGANDA The field study for this research was conducted in the South West of Uganda with the support of the South Western Towns Water & Sanitation Project (swTwsP). The field study was based on a ‘4‐Step Approach’ that was derived from a six step approach for the conduction of corrosion control strategies (AWWA, 1996) which was modified to fit the specific needs of this research, in regard to the focal points: development countries, rural growth centres and remote areas. The Results of the Field Studies are discussed in Chapter (6). The recommendations are outlined in Chapter (7) of this thesis. (5.1) GEOGRAPHICAL AREA OF THE FIELD STUDIES The field studies were conducted together with the South Western Towns Water & Sanitation Project (swTwsP) in Kabale ‐ Uganda, during a stay from March 2002 to October 2003. Kabale is a town situated in the Southwest of Uganda. The region is characterised by hilly, mountainous areas. The average altitude of the subregion is around 1900m, the highest peak that is located at the Ugandan – Rwandan border near Kisoro town is Mt. Muhavura (4127m). The general geology of the subregion is provided in the hydrogeological map in Appendix (11.1). The dominant rock types are Precambrian formations; Pleistocene formations in the region of the rift valley. The Precambrian rocks are generally considered as being acidic or intermediate – based on the acidic/basic rock classification system, which is dependent on the silica content of the rocks. Groundwater originating from such aquifers was generally found to be aggressive, with a pH below 7 (LANGENEGGER, 1994). The soils of Kabale district are generally acidic, in some cases the acidity of the soils can closely be related to the environmental geology. An increase in the acidity of the soils that was related to leaching of the soils has been detected by NEMA (1997) throughout the last years. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 48 Several occurrences of corrosion were reported by the South Western Towns Water & Sanitation Project (swTwsP) – especially leaking tanks were suspected to be related to occurrences of water with low pH values and thereby related to possible corrosion. The scheme affected mostly by corrosion, was the water supply scheme in Ryakarimira – a small town in Kabale district at the border to Rwanda. Ryakarimira was chosen to be the focal point of this investigation, as all of the aspects relevant to this research were obvious in its case: 1. Ryakarimira is a Rural Growth Centre in a Developing Country – it has about 1700 inhabitants. 2. It is located in a Remote Area in the far south of Uganda, in a hilly region bordering Rwanda. Infrastructure is deficient. There are only murrum roads, no grid‐power supply, no fixed‐line phone connections. 3. The piped water supply scheme is affected heavily by Corrosive Water. Some information about the scheme is provided in the excursus in the box, below. Excursus: The water supply system in Ryakarimira The water supply system in Ryakarimira is operational since May 1999. About 3000 people live in the area of the scheme and almost all of them actually use the water from the scheme, due to the lack of alternative sources. The only available water sources apart from rainwater are lake Bunyonyi (a lake that is located a few hundred metres in altitude below the town) and a few seasonal streams in the surrounding hills. The infrastructure consists of four protected spring eyes, a 1.5m³ sedimentation tank, a 40m³ collection tank, a solar pumping station with 72 panels, a standby diesel pump, a GI pipeline, Steel reservoir tank of 90m³, GI gravity pipeline, HDPE pipes, 5 institutions (sub-county, health-centre, primary- and secondary school, technical institute), 3 public tap-stands, a Water office with solar heated public showers and ecological sanitation toilets. A distribution branch attached to a break pressure tank supplies Rokure Primary School with water. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 49 (5.2) IMPLEMENTATION OF THE ‘4-STEP APPROACH’ According to Chapter (4), a ‘4‐Step Approach’ was chosen for the fieldwork of this thesis. The four steps are described in the following four subchapters. The Results & Discussion of the Field Studies in Chapter (6) are also arranged accordingly: Figure 5-1 – The 4-Step Approach The four steps will be outlined in a figure on the right side at the beginning of each of the following subchapters. The current step is highlighted to give guidance through the process. (5.3) STEP 1: DOCUMENT EXTENT & MAGNITUDE OF CORROSION In order to meet the objectives set, it was necessary to gain an understanding on the extent of corrosion in the affected water supply systems. The first step in the chosen approach (see figure on the left) was to document the extent & magnitude of corrosion in the area of the field study. Relevant data was gathered by a desk study of existing literature, field visits, the conduction of interviews as well as through extensive water quality analysis in the region of the field study. By conducting a literature survey of existing documents regarding corrosion within the area, a CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 50 basic idea of the further necessary assessment was gotten. Thereafter the data from the literature study was refined by field visits to further assess the effects of corrosive waters on the following three components: ecological component: the water itself social component: the users, owners and operators technical component: the infrastructure. (5.3.1) Existing Information In the library of the South Western Towns Water & Sanitation Project, several documents regarding the corrosivity of waters in the area were found. The main data / information sources were: the records of the swTwsP laboratory, containing data of water quality analyses of the existing schemes and potential sources for future schemes implemented under the swTwsP a report by the Directorate of Water Development (DWD) Laboratory in Entebbe (DWD, 2000) about the water quality in four of the small towns a report by Jerlich (JERLICH, 2000) about the ‘Corrosive Properties of Drinking Water Sources in the South West of Uganda’. private communications with the staff. From reports of the swTwsP staff and the investigations reported by JERLICH, it was well known that corrosion within the supplied towns was seen as a problem by the implementers (swTwsP), operators (Scheme Operator) and users. This observation was also confirmed by SCHWARZ‐HERDA (2003). Due to the low alkalinity and pH of some waters, these waters were regarded as being heavily corrosive to the water supply infrastructure. Especially in several of the reservoir tanks cracks had developed, which were supposedly linked to the occurrence of acidic waters (see Figure 5‐5). In the RGC Ryakarimira, where the pH of the water at the source is especially low (pH 4.5), the tank was said to be in a pitiful state with water gashing out CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 51 of steadily enlarging cracks. Project staff was reporting of the fear of the population in that particular town that the tank ‘may burst, anytime’. As the reports from the town of Ryakarimira showed the significance of the problems related to corrosion in the area, and it was located in a close distance to the swTwsP headquarters and (more importantly) the laboratory, it was chosen to be the main subject of the investigations for this report. (5.3.2) Ecological Aspects / Corrosion Potential of the Water Supply As mentioned in Chapter (5.3.1), investigations into the problem of corrosive water had already been carried out by the swTwsP team in the year 2000 and were documented in reports by DWD (2000) and JERLICH (2000). In the town of Ryakarimira, water samples from several points of the water supply system were taken in an attempt to evaluate changes in water quality parameters that could be related to corrosion. The analysis of the samples showed that the water at the stand posts – when compared to the source – had higher values for pH, electrical conductivity, alkalinity, calcium and magnesium (see table Table 5‐1). This led to the assumption that the water had dissolved calcite (CaCO3) from the walls of the collection tank as an effect of aggression, whereas these values were raised. Similar observations were also made in the above‐mentioned technical report from the DWD laboratory. Table 5-1 – Water Quality Data from different points of the distribution network in Ryakarimira Sampling point pH Temp Alkalinity EC Ca Mg Turbidity (°C) (as CaCO3) (µS/cm) (as CaCO3) (as CaCO3) (NTU) Source 4.50 16.8 <5 210 30.0 40.0 <5 Collection Tank 5.08 17.3 - - - - <5 Distribution Tank 5.23 17.9 - - - - <5 Stand post 5.70 19.2 10 230 48.0 58.0 5 (5.3.3) Social aspects / User Complaints & Health After the assessment of the ecological aspects concerning the corrosion potential of the water supply, the next task, according to the ‘4‐Step Approach’ was to document impacts of corrosion on the water consumers, related to the direct use of the provided drinking water. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 52 An interview with the Scheme Operator Mr. Bernard Bigwero revealed that there were concerns by the community that the degradation of the system eventually may lead to the complete failure of the town’s water supply system. Apart from issues that were linked to corrosion, an overall satisfaction with the system was expressed, as it was working on a 24 hours a day and 7 days a week basis, since its completion in May 1999, with no major break‐downs. Because of the general high satisfaction of the customers with the water supply system and the limited alternative water resources in the area, it is assumed, that the readiness of the people to maintain their system was very high. This was also expressed in the willingness of the people to pay double the usual amount for the supplied water, in case the standby diesel pump had to be used to pump water (e.g. if the photovoltaic pumping fails to pump enough water to the reservoir for several days, in case of reduced solar radiation). Statements and concerns given by the scheme operator and other users are summarised in Table 5‐2. Table 5-2 – Statements and Concerns by Stakeholders in Ryakarimira Comments by Stakeholders Fear of the population (esp. the scheme operator) the tank may break apart, because of enlarging cracks in the collection tank Fear that the transmission line may burst, because of degradation / corrosion Problems disassembling / reassembling GI pipes of the transmission & distribution pipelines – ‘it is not possible to rejoin them again after disconnecting them’ The first flush of water being tapped in the morning at the stand posts is reddish / brownish An institution along a distribution branch pipeline is experiencing problems with discoloured water Aesthetics and Consumer Perception By‐products of water supplies with corroding infrastructures due to corrosive water often include dissolved iron. This can be noticed by the consumers as reddish discolourations, staining and taste problems of the supplied water, and may lead to user complaints. In Ryakarimira interviews with the scheme operator revealed that the first flush of water at the stand posts in the morning usually was of reddish‐brownish colour. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 53 An analysis of the turbidity levels at different sampling points showed increasing turbidity levels – from the source to the stand posts. This was obviously due to the corrosion of the galvanised iron pipes in the transmission and distribution lines, as well as due to the corrosion of the distribution tank (see table Table 5‐1). Compared to the (interim) national and international guideline values of drinking water quality, the iron values were found to be within all relevant guideline values, although they cause an aesthetic problem in the water supply. Although discolourations of the supplied water were reported, this did not necessarily lead to a decrease in user acceptance. This may be due to the fact that the town of Ryakarimira does not have other easily accessible (drinking) water resources apart from precipitation during the rainy season. Other water resources include lake Bunyonyi, from where water has to be carried a few hundred meters in elevation to the town using foot paths. Therefore, user acceptability in Ryakarimira is generally very high and no major complaints due to the instances of discolouration were (yet) to be reported. The first flush at the stand posts is usually disregarded or given away for free for non‐drinking / non‐ cooking purposes by the tap attendants. After the first flush, the water stays clear with no further discolourations throughout the day. In a break‐pressure tank on a distribution branch to an institutional stand post (Rukore Primary school), extremely turbid and reddish/brownish water was observed (Figure 5‐2). The school had already complained about the discoloured water to the scheme operator. This shows, that under the special circumstances of water supply systems in remote areas in developing countries, the high acceptability of users towards discolourations and other corrosion side effects, may lead to a neglect of the corrosion problems by the water supply operators. The users do not have other choices, than to accept the water as it is supplied. Figure 5-2 – Water inside the break pressure tank along the distribution branch in Ryakarimira CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 54 Health Aspects All water quality parameters that were analysed in the supplied towns of the South Western Towns Water & Sanitation Project (swTwsP) were found to be within the relevant Ugandan guidelines (see Chapter (3.2)), apart from the pH values in some of the towns. As the waters found in the region of the field study partly are very acidic, one question to be answered was, whether the direct consumption of the soft, acidic water was a possible health issue. As shown in Chapter (3.2) no guideline values for the pH and the hardness of drinking water are proposed in the latest edition of the WHO’s Drinking Water Quality Guidelines. One concern is though stated: ‘there is some indication that very soft waters may have an adverse effect on mineral balance, but detailed studies were not available for evaluation.’ (WHO, 2004). In relation to the ingestion of acidic waters and possible health concerns, one also has to mention the pH values of other popular beverages like beer (pH 3.3‐4.7) or coke (pH 3.0) (CORROSION DOCTORS, 2004). Typical by‐products of corrosion by corrosive / aggressive waters of water supply systems in industrialised countries are Lead and Copper (AWWA, 1996). Lead is rarely present in tapped water as a result of its dissolution from natural sources. Rather, its presence is primarily from corrosion of the interior of plumbing containing lead in pipes, solder, fittings or the service connections to homes. The primary source for copper in water supply systems mostly is the corrosion of the interior of copper plumbing. Health related concerns regarding lead and copper include neurological effects, therefore the guideline values of 0.01mg/l for lead and 2mg/l for copper were proposed by the WHO (2004). It was neither possible to get data, nor to analyse parameters of the health‐related corrosion by‐products lead and copper. Nevertheless, as both lead and copper were not used in any of the water supply infrastructures in the investigated towns, these parameters were not further investigated in this study. (5.3.4) Technical Aspects / Infrastructural deterioration Several field trips to Ryakarimira were made in an attempt to gather information about the technical extent & magnitude of corrosion in this specific water supply scheme. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 55 Samples of all major parts of the technical infrastructure were investigated including pipes, valves, tanks, the pump and the stand posts. Observations of a first investigation are listed in Table 5‐3. Table 5-3 – Signs of Corrosion on the Water Supply Infrastructure in Ryakarimira component of distribution system possible indications of corrosion sedimentation tank degradation of mortar lining GI inlets and outlets: uniform corrosion collection tank leaking tank, cracks on the inside of the tank degradation of the inner mortar lining, where in contact with water cracks on the outside of the tank GI inlets, outlets & overflow: uniform corrosion pump inside the collection tank no signs of corrosion clamps to fix the pump on the concrete floor: uniform & pitting corrosion valves no signs of corrosion – but galvanic corrosion on the adjoined GI pipes transmission line (pressure) internal corrosion: uniform corrosion of the GI pipes distribution tank internal corrosion: uniform & pitting corrosion of the Steel tank distribution line (gravity) internal corrosion: uniform corrosion of the GI pipes pressure break tank degradation of the inner mortar lining, where in contact with water corrosion of the inlet, outlet pipes stand posts no major signs of corrosion Field Observations of Corrosion The whole water supply system was part of the investigation. Starting from the source, the following components of the supply system were examined, following the flow of the water through the scheme: sedimentation chamber (the source intake works) collection tank (brick‐masonry), from where the water is pumped 160m in altitude using photovoltaic pumping transmission pipe (GI) and valves (BR or SS) along the transmission pipe distribution tank (steel plate) distribution pipe (mainly HDPE) stand posts. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 56 The sedimentation chamber at the source intake was constructed out of bricks and plastered with cement mortar. The water at the intake works was found to be very clear and of good taste. The areas that stayed in direct contact with water in the sedimentation chamber were affected by heavy degradation. The vertical wall on which the water from the inlet was gashing onto, was discoloured and the flow of the water had left noticeable marks in the mortar. The cement layer, beneath the constant water line was also obviously affected by the water. This could be seen beneath the constant water level, where the cement mortar had been degraded by nearly 2 mm in comparison to the mortar above the waterline (see Figure 5‐3). Figure 5-3 – Heavy Cement Degradation at the Sedimentation Chamber in Ryakarimira An interview with the scheme operator revealed that some of the pipes in the system had had to be replaced after a period of only two years after installation. He specifically mentioned the former inlet pipes from the spring catchment to the sedimentation chamber, which are shown in Figure 5‐4below. Figure 5-4 – Corroded pipes from the intake works in Ryakarimira CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 57 The collection tank below the spring showed a large number of cracks on the outside (see Figure 5‐5). The tank was leaking – yet the scheme operator claimed that the leakage from some of the cracks had reduced over the past few months. This was related to the buildup of calcium deposits at the outside of the tank, which had formed white calcium carbonate layers at the outside of the cracks. Figure 5-5 – Collection Tank in Ryakarimira & Close-up of crack at the outside of the tank After emptying the tank, the interior of the tank was investigated. The inner walls of the tank showed a very similar pattern of cracks as the ones observed on the outside. All galvanised iron pipes and fittings inside the tank were corroded. At the line of the overflow of the tank, the degradation of the cement mortar on the walls could easily be noticed. The material below the highest water level was very soft, wet and the aggregates of the mortar could easily be felt, whereas the mortar above the highest water level was dry, hard, and smooth. In Figure 5‐6 the effects of scraping the wall with a pen in a vertical motion from above the highest water line to below the waterline can be seen. In the lower part, the pen left a deep groove. Figure 5-6 – The inside of the Tank in Ryakarimira The submersible pump and some fittings to connect the pump to the transmission pipe were the only metal parts inside the tank that were not affected by corrosion. They were CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 58 found to be made out of stainless steel, and therefore not vulnerable to corrosive attack by the water. An attempt was made to ‘have a look inside’ the galvanised iron transmission line leading from the pump to the collection tank, to get an idea about the internal state of the pipe. The scheme operator feared to disconnect pipes along the transmission line, because he believed it would not be possible to reconnect the pipes again afterwards. Therefore, it was decided to open a washout valve along the transmission line to have a look inside the transmission pipe (see Figure 5‐7). After opening the valve to empty the pipe, the water flowing out of the pipe was clear for some minutes, but later changed its colour to reddish‐brown and became turbid. The inside of the pipe was observed by taking photographs through the washout pipe and the valve. As shown in Figure 5‐7 below, the interior of the transmission pipe was attacked by uniform corrosion. Figure 5-7 – A valve box & a look inside the outlet pipe of the valve box through the valve (right) The water inside the steel plate distribution tank was of slightly redish‐brownish colour. The inner sides of the steel plates as well as the steel supporting structure showed signs of localised / pitting corrosion, where they stayed in direct contact with the water. The distribution line was made of high density polyethylene (HDPE) which is not vulnerable to possible corrosion and was therefore not further investigated. The stand posts showed signs of corrosive attack on taps. The water was found to be clear with no objectionable taste or odour. As noticed in Chapter (5.3.3) the scheme operator had reported the occurrence of reddish‐brown water at the first flush from the taps in the morning. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 59 (5.4) STEP 2: DETERMINE POSSIBLE CAUSES OF CORROSION After the documentation of the extent & magnitude of the corrosion problems, the next step was to determine the possible causes of corrosion in the region of the field study. This was accomplished by both a desk study, laboratory research and a number of computational simulations, to find the cause of the corrosion problems. Again, the water supply system in the town of Ryakarimira was the focus of the study. Reports from DWD and Jerlich (as mentioned in Chapter (5.3.1) ‘Existing Information’) had already led to the conclusion, that the soft, acidic nature of the waters was the cause for the extensive corrosion problems in the area. The task was to further verify and quantify these statements. The data required for this assignment was gotten from the water quality database from the swTwsP laboratory as well as refined by data from additional field visits. The task was to find the answer to the question what the primary causative factors of corrosion in the area were. (5.4.1) Ecological Aspects / Water Quality Data from the water quality database at the swTwsP laboratory is gathered during the quarterly seasonal sampling, which includes the chemical, physical and microbiological analysis of samples from all water supply schemes implemented under the swTwsP, as well as samples from potential sources for future supply systems. The samples were taken and analysed by the project’s laboratory in Kabale. As far as possible, parameters were determined directly on‐site. The dataset for each town includes samples from the source and stand posts of each water supply scheme. Additional samples from collection or distribution tanks were taken and analysed where it was found to be appropriate. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 60 The samples were analysed by the water quality analyst of the project, Mr. Julius Byamugisha, using the methods of analysis as outlined in Chapter (4.2.3) ’Water Quality ’. It was found that many ground water sources within the project area have very low pH values, the lowest pH value (4.1 pH units) was found at Rubuguri source in Kisoro district, the highest pH value (7.7 pH units) was found in Kabirizi (see Appendix (11.3)). To assess the effect of the water quality on the corrosion, it was necessary to calculate a quantitative corrosion parameter in addition to the existent water quality parameters. The calcium carbonate precipitation potential (CCPP) was chosen, as several studies regard to it as the main representative corrosion index (LOEWENTHAL, 2004). The available datasets proved to be insufficient for the calculation of the CCPP. To overcome this lack of data, further test kits for the determination of alkalinity and free oxygen had to be procured locally. This (finally) allowed the on‐site testing of most of the crucial water quality parameters for the determination of the corrosion risk using the CCPP. Namely, the parameters pH, temperature, electrical conductivity, free oxygen and alkalinity were measured directly on‐site. Carbonate hardness, magnesium hardness, sulfate and chloride had to be analysed from the laboratory in Kabale. The methods used to determine the different water quality parameters are listed in Chapter (4.2.3) ’Water Quality ’. After introducing the ‘new’ parameter alkalinity, it was possible to determine the CCPP of the water. The CCPP was calculated for all waters where sufficient data was available, by the use of the computer program STASOFT 4. The calculations done, showed that the water in Ryakarimira had a surplus of free aggressive carbon dioxide of 443.1mg/l. In the column labelled ‘Initial Water’ in Figure 5‐8 the natural properties of the water found in Ryakarimira can be seen, in the column labelled ‘EqAirCaMg’ the properties the water would have at equilibrium with respect to carbon dioxide in the gaseous phase and solid‐phase calcium carbonate and magnesium hydroxide are listed. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 61 NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: InitialEqAirCaMg Water pp Atm 0.00035 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 23.8 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 16.0 7.0 7.19 5.0 CO2 CaCO3 443.1 -475.9 5.1 -4.9 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 0.74 160 Carbonic Species CaCO3 PP Figure 5-8 – Data for the water at Ryakarimira Source, calculated with STASOFT4 The results of the calculations for selected water supply schemes that have either already been implemented under the swTwsP, or are yet to be implemented are shown in the Appendix (11.3). (5.4.2) Technical Aspects / Materials Design and Installation The data needed for this chapter was collected from design reports of the water supply schemes form records at the swTwsP, as well as from field visits and personal communications. Quality of Materials The materials used in the water supply schemes that had been designed by the swTwsP were: galvanised iron (GI) for pipes and fittings poly vinyl chloride (PVC) for pipes high‐density polyethylene (HDPE) for pipes brass (BR) for valves and stainless steel (SS) for pumps and a limited number of fittings. In the first phase of the swTwsP, the majority of the laid pipes were GI‐pipes, which were manufactured and procured locally. The installed brass valves were made in Europe. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 62 It was assumed by the swTwsP staff, that inferior quality of the galvanised pipes could be one reason for the extensive interior corrosion of these pipes. This can be ruled out, as field observations by LANGENEGGER (1994) show that under moderately to highly corrosive groundwater conditions (pH < 6.5) the quality of galvanisation does not have a significant impact on the resistance to corrosion. The material will definitely corrode. Dissimilar metals The connection of two dissimilar materials to each other creates a galvanic cell. The electrical potential of this cell depends on the status of the two metals in the galvanic series. The greater the electrical potential is, the greater is the corrosion potential (see Chapter (3.3.2)). Only few occurrences, where dissimilar metals were joined, were observed during the field studies. In Ryakarimira, brass valves were directly connected to galvanised iron pipes. Inside the collection tank, the submerged photovoltaic‐powered pump was connected to the galvanised iron pipes using stainless steel reducers (see Figure 5‐9). It was not possible to determine the exact reason of corrosion at these incidences, but probably galvanic corrosion plays a major role in the corrosion of the GI‐pipes next to the brass valves as shown in Figure 5‐9. Figure 5-9 – A GI coupling between stainless steel parts; A brass valve between GI fittings (right) (5.4.3) Social Aspects / Workmanship Well trained, experienced plumbers and masons are hard to be found in rural growth centres and especially in remote areas in Uganda. The construction works of the swTwsP are usually given to private contractors through public tenders. The variety of people involved in these works is high and the quality of the works usually varies from one CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 63 contractor to another. All construction sites are constantly being supervised on a full‐time basis by experienced staff of the swTwsP. Therefore, shoddy work has been said to been ruled out within the water supply schemes, implemented by the swTwsP under its second phase. (5.5) STEP 3: DEVELOP AND ASSESS CORROSION CONTROL STRATEGIES After determining the possible causes of corrosion within the field area and especially in the town Ryakarimira – being the focal point of the field study – the next logical step was to develop and assess corrosion control alternatives. The necessary data for this task was gathered from field and laboratory testing, which followed an extensive literature survey. The research of relevant literature revealed different strategies of controlling corrosion problems (see Chapter (3.6)), whereas special attention was turned to solutions that would allow sustainable operation and maintenance in the context of this research (developing countries, rural growth centres and remote areas). (5.5.1) Simulations The corrosion evaluations on paper were done in order to assess the potential corrosion control possibilities as described in Chapter (3.6) ‘Corrosion Control Strategies’. A number of simulations were done to find out the parameters, that best describe the corrosion risk of the investigated systems. Simulations to find the equilibrium pH, amount of calcium carbonate (CaCO3) to neutralise the pH, amount of free carbon dioxide (CO2), … were done using two different software packages: WinWASI 3.0 from BIESER UND PARTNER and STASOFT 4 from MORRISON et al. (2000). CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 64 The two computer programs are described in Chapter (4.2.4). The calculations done involved: corrosivity / aggressiveness of the water equilibrium pH of the water amount of lime to get equilibrium pH amount of quicklime to get equilibrium pH aeration possibilities. The detailed results can be found in the Appendix (11.2). (5.5.2) Field and Laboratory Research After the literature survey and the corrosion evaluations done on paper, it was decided to do several field tests to investigate the usability of several methods of corrosion control. The major part of the field‐testing was done in the water supply scheme in Ryakarimira in the time from August 2002 to September 2003. The following technologies to change the water quality to a non‐corrosive / less‐corrosive nature were tested (compare with Chapter (3.6.1)): aeration of the water in order to strip the excess carbon dioxide filtration through limestone in order to stabilise the water lime dosage to obtain a higher pH value and hardness. The following technology was tested in order to create a barrier between the infrastructure and the corrosive water to protect the infrastructure (compare with Chapter (3.6.2)): application of a coating inside the collection tank. An experimental treatment plant was set up in Ryakarimira (see Figure 5‐10). The location of the source intake works proved to be an ideal testing site for the different CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 65 methods, also as the water had to be treated before it could do harm to the following water supply infrastructure. To keep away major influence by wind, sunshine and precipitation, the area was roofed with iron sheets. Figure 5-10 – The experimental water treatment plant in Ryakarimira Aeration By aeration of water the excess carbon dioxide is stripped away, which leads to a higher calcium carbonate precipitation potential (CCPP), a higher pH value and consequently to a less corrosive nature of the water. In addition, dissolved oxygen is introduced into the water. In an attempt to evaluate the effect of natural draft aeration on the water in Ryakarimira, six showerheads and one perforated PVC pipe were installed above two plastic basins and connected to a plastic sedimentation basin after the inlet of the source. The perforated pipe was created by drilling holes into a 1½‐inch PVC pipe. The height of the drop from the outlets of the showerhead to the bottom of the basins was about 35cm, the height from the perforated pipes about 45cm – with hardly any pressure at the outlets of the showerheads and the perforated pipes. Filtration through Limestone By the filtration through limestone, the natural process of an underground passage through limestone deposits is simulated, whereby the water dissolves the calcium carbonate of the limestone, until the saturation pH value is reached. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 66 Limestone was procured from a limekiln in Busanza in Kisoro district, at the border to the Democratic Republic of Congo. The procurement proved to be difficult and the first attempt to buy limestone failed as the people at the plant were only allowed to sell the final product: slaked lime. After negotiations with the plant owner, a pickup full of limestone was purchased and transported to the experimental treatment plant in Ryakarimira on a four hours trip on rough roads. The limestone was crushed by hand to pieces of a size of about 3 ‐ 4cm. Thereafter the limestone was filled into one of the two basins underneath the aeration unit to cover the bottom of the basin to a height of approximately 10cm. The second basin was left without any limestone for comparison purposes. Lime dosing The option of dosing hydrated lime as a means of positively affecting the calcium carbonate equilibrium of the acidic water was considered, as it proved to be quite difficult to get appropriate limestone (see above) in the area. Whereas slaked lime (for building purposes) is easily available at many local markets throughout the country. A dosing unit, which had formerly been used to dose Aluminium Sulphate, was acquired from National Water & Sewerage Corporation (NWSC) at a price of USh 400,000 (~ €181.8). It was in good condition, but came without proper connections and fittings, and was not calibrated. Especially the (significant) floating valve for the inlet was missing. A (low precision) floating valve was locally purchased and installed; the inlets and outlets were connected by flexible PVC tubes, and the unit was recalibrated. The inlet of the unit was connected to an elevated 1m³ (1000l) polyethylene tank; the outlet was fixed to the outlet of one of the aeration basins. The placement of the filtration unit within the experimental treatment plant in Ryakarimira can be seen in Figure 5‐10, above. It was decided to use limewater, a 1% lime solution (10kg lime per 1000l water), as this was convenient for the scheme operator to prepare, without special need for additional measuring devices. The rate was determined by the capacity of the storage tank for the limewater, as well as the necessary service interval. The refilling of the 1000l tank with water from the source takes about 35 minutes, as the yield of the spring in Ryakarimira is CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 67 only 0.5l/s. A dosage rate of 3.0ml/s was therefore chosen, to allow continuous dosing for around three and a half days, before the scheme operator would have to refill the 1000l tank with limewater. Coating In order to protect the heavily affected brick‐masonry collection tanks throughout the area of the field study, and to gather experience with this type of corrosion protection, it was decided to apply a protective coating on the inside of the collection tank in Ryakarimira. An ‘acrylic based emulsion which improves the water resistance and adhesion of Portland cement based composites’, namely CEMFLEX from a company in Kampala was chosen (see Appendix (11.4)). The company had already offered this solution to prevent the further leaking of the water tanks to the swTwsP several years before. By that time, the offer was denied, mainly due to two reasons, namely high costs, and the fear that unknown compounds of the product could be dissolved in the drinking water and cause a potential threat to the consumers’ health. Due to these reasons, data regarding the water quality of the water in Ryakarimira was sent to the company in order to get an assurance that the product would not be a potential threat to the health of the water consumers and an estimate of the suspected lifetime under the local water quality conditions. The company assured that there were no hazardous constituents in the product, and referred to a brewery that was using the product for the protection of their (beer) storage tanks. Concerning the estimated lifetime, the product was said to provide complete waterproofness for at least two years under the local conditions. After that time a new layer of the coating onto the might be needed. The CEMFLEX coating was applied in August 2003. This was done after replastering both the inside and outside of the tank. As a standby diesel pump was available on‐site, it was possible to temporarily connect the diesel pump directly to the sedimentation chamber, so that the continuous supply of the centre during the time of the renovation of the tank was ensured. The scheme operator CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 68 had to manually pump to the collection tank using the diesel pump for around two hours per day, during the four weeks of construction. Both the inner and outer layers of plaster from the walls and the floor were completely removed, then reapplied. Thereafter, the plaster was left for curing for seven days. The CEMFLEX coating was applied on top of the inner plaster, by mixing CEMFLEX waterproofing slurry on site, soaking the CEMFLEX fabric in the solution before fixing them on the inner tank walls and the floor (see figure Figure 5‐11). After an instruction by the swTwsP team, this work was done by the scheme operator in only three days. Figure 5-11 - The application of CEMFLEX (SIKA, 2004) The SIKA coating was easy to apply. After the application, it was left for curing for another seven days. The tank was washed thoroughly, refilled once and then washed again, until the water was finally redistributed using the ‘old’ system with the photovoltaic pump. (5.5.3) Secondary and Tertiary Effects of Corrosion Treatment During water treatment in order to reduce the corrosion potential of the corrosive water (by raising the pH, alkalinity), other water quality parameters are also affected. By stabilising the water by filtration through limestone or lime dosing, the hardness of the water increases due to the dissolution of limestone or lime (see Appendix (11.2) & Chapter (6.3)). Excursus: Hardness in Buyanja In the town of Buyanja people started to complain about hardness. The water sources the community had traditionally used were soft waters in comparison to the source that was used for the piped water supply system. A major complaint was the increased use of soap for washing compared with the softer waters that were formerly used. During a visit of the minister of Water, Lands and Environment a member of the community asked the minister to provide them with a water treatment plant, in order to soften their water. CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 69 (5.6) STEP 4: EVALUATE ALTERNATIVES AND SELECT CORROSION CONTROL STRATEGY After conducting the field and laboratory research, the different corrosion control strategies as described in Chapter (3.6) ‘Corrosion Control Strategies’ had to be evaluated according to their usability in the context of this research. Therefore, it was firstly necessary to introduce evaluation criteria, based on the data that was gathered during the field and laboratory research as described in Step 3 (Chapter (5.5)). Then the alternatives were rated and ranked according to these criteria using data from field and laboratory research, as well as from the literature review (Chapter (6.4)). (5.6.1) Evaluation Criteria The selection of the evaluation criteria for choosing an appropriate technology was firstly done according to WEDC (1998) using the ‘SHTEFIE approach’, whereas the selection of a sustainable technology follows a three stage process and has to comply with issues that are grouped in the SHTEFIE criteria, namely Social, Health, Technological, Economic, Financial, Institutional and Environmental issues. This approach was not found to be useful in the context of this research, as consistent information regarding the effects of the corrosion control strategies to the ‘SHTEFIE’ issues was not available. The required information was not determinable, as all of the tested technologies probably influence all issues in a very complex manner. Especially, the prediction of health impacts of the different technologies proved to be extremely hard. Therefore, following evaluation criteria were selected, to rate the different corrosion control strategies: performance: the performance with respect to corrosion prevention investment costs: the initial cost of the necessary technical infrastructure CORROSIVE WATER Erik PINTER, 2005 (5) Field Studies in Uganda 70 training needs: measure of the necessary training for the stakeholders involved in the operation and maintenance of the technology operation & maintenance: necessary activities to ensure the proper working of the infrastructure (including replacements) operating costs: the operating costs necessary to run the system without break downs appropriateness: was the technology found to be appropriate within the context of this research. (5.6.2) Rating, Ranking the Strategies The rating was done due to the experiences and data gained by the implementation of the different corrosion control strategies in the field, as well as through the ongoing literature review. The values were only done on a ‘verbal’ basis, whereas the reference point was a scheme without any corrosion control measures set and with materials that are prone to degradation by corrosive water (e.g. the scheme in Ryakarimira). CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 71 (6) RESULTS & DISCUSSION OF THE FIELD STUDIES (6.1) STEP 1: DOCUMENT EXTENT & MAGNITUDE OF CORROSION Regarding the Extent and Magnitude of Corrosion it was found, that corrosion / aggression of water supply infrastructure was a widespread problem in the investigated water supply schemes. Damages of the infrastructure were observed and a relationship between low pH values (hence low CCPP) of the water, and the extent / severeness of corrosion damage in the investigated water supply systems was observed. The economic situation of the water supply schemes (operational level) does not allow a continuous rehabilitation of the damaged infrastructure. Eventually the operators will not be able to pay for the costs associated with the degradation of their systems. The water supply (technical level) will collapse and will not further be maintained, so that people will have to use other (unprotected) sources of water. This is an apparent threat to the goals of the Water & Sanitation Sector and hence, to the goals of the Austrian Development Cooperation (policy level), as described in Chapter (1.1). Under the current circumstances, it may be feared that the water supply systems in the two rural growth centres Ryakarimira and Rubuguri will break down, before the design life has been reached, due to the highly aggressive / corrosive nature of the water, and the low economic capability of the operators. During the sampling for the water quality analyses as well as for laboratory test, it was experienced that it was hard to get representative water quality samples from the source areas for analysis to the laboratory. As the roads in the area are quite rough (remote areas), some values that were measured on‐site were impossible to be reproduced in the laboratory later on – so that it was hard to perform laboratory‐size experiments. Although the samples were taken and handled with great care and according to international standards, especially the parameters alkalinity and pH proved to be very unstable and values from repeated measurements in the laboratory in Kabale deviated significantly – even after a few hours. CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 72 Therefore, it was aimed at measuring all parameters with relevance to the calcium carbonate equilibrium directly on‐site, and at performing on‐site experiments only. This was partly accomplished by the additional procurement of an alkalinity test kit. The magnesium and carbonate hardness values were measured later on in the swTwsP laboratory. (6.2) STEP 2: DETERMINE POSSIBLE CAUSES OF CORROSION One cause of corrosion in the investigated water supply systems was found to be the corrosive / aggressive nature of the waters. Waters throughout the area of the field study were found to be – to a certain extent – corrosive / aggressive. As can be seen from the water quality analyses of the sampled areas in Appendix (11.3), the pH values from the majority of samples was below 7.0, the alkalinity of most samples was very low. The waters can therefore be regarded to as soft, acidic waters with corrosive / aggressive properties. The CCPP from all sources in the area was found to be negative and therefore the waters were undersaturated in respect to calcium carbonate. The cause of corrosion in the drinking water supply systems investigated is a combination of high concentrations of excessive, dissolved carbon dioxide, low alkalinity and low pH values. The waters found in water supply schemes that were affected by corrosion had pH values far from the equilibrium pH values. Other possible water constituents like sulphate or chloride that could have lead to increased corrosion, were not observed in concentrations that would have a large impact on corrosion of the water supply infrastructure. The design and selection of materials of the water supply schemes was not done in respect to the corrosive nature of the water. Materials that are prone to corrosion were used extensively throughout all of the investigated water supply systems e.g. galvanised iron for pipes, cementitious materials for the tanks and intake works. Bad materials and shoddy workmanship were also found to be a (indirect) reason for the damage related to corrosive water. The cracks in the brick‐masonry tanks in the towns Kebisoni, Buyanja, Kisiizi, Kambuga, Muhanga and Ryakarimira (see Figure 5‐5) that were supposedly linked to corrosion, were found to be related to the use of improper materials and bad workmanship (MINK, 2004). It was assumed that due to corrosive CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 73 water and unprofessional application, the plaster on the interior walls of the tanks had become penetrable and water had leaked through the plastering to the burnt bricks. As the locally manufactured bricks were of inferior quality, the bricks started to swell under the influence of the permanent penetration of the water, hence causing the formation of cracks. Although the corrosive nature of the waters in the area of the field study had already been documented by DWD (2000) and by the investigations done by the swTwsP team (JERLICH, 2000), this research was the first attempt to include a quantitative corrosion index of the corrosion potential in a research regarding the waters in the Southwest of Uganda. Although an attempt was made to correlate the location of the investigated sources in respect to different soil systems and geological aspects with their corrosivity, it was not possible to find an apparent relationship between the location and the corrosivity ‐ as expressed through the CCPP. The computer program WinWASI in the version 3.0 proved to be hard to use under the conditions during the field study, as the determination of all of the required parameters for a proper simulation was not possible by the swTwsP laboratory. The program gave ambiguous results in cases, where both the m‐ and p‐values had been determined. Furthermore, the documentation of the software was available in German only, and some of the required parameters were described using the German nomenclature. Hence, it was not easy to use for the swTwsP staff. The program STASOFT 4 was therefore acquired as an alternative means of finding a method to determine the corrosivity of the waters under investigation. It was possible to determine both the CCPP as well as to simulate a number of processes regarding the calcium carbonate equilibrium. It proved to be applicable in the context of this investigation and was easy to use. CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 74 (6.3) STEP 3: DEVELOP AND ASSESS CORROSION CONTROL STRATEGIES The field study for the different methods of corrosion prevention revealed both strengths and weaknesses of the following corrosion control technologies: aeration filtration through limestone lime water dosing coating. Especially reactions regarding the operational and social aspects were hard to predict in advance. The field study allowed some interesting insights into these aspects. The effect of the different corrosion control strategies on the water were merely monitored using pH measurements on‐site, available water quality data from former analyses, and by simulating the processes using the computer software STASOFT (see Chapter (4.2.4)). Measurements were taken throughout the duration of the field study at an uncounted number of occasions. The given water quality values are assumed to be representative, as the source in Ryakarimira hardly showed any changes in the water quality characteristics throughout the seasons. The yield of the spring was constant at 0.5l/s and the effects of the tested corrosion control strategies proved to be very stable during the period of the field studies. Therefore, a statistical evaluation of the taken measurements was not necessary. (6.3.1) Aeration The field study revealed that a simple aeration unit as the type installed in Ryakarimira is a technology that can easily be installed, operated and managed in water supply systems in rural growth centres. The experimental aeration unit in Ryakarimira increased the pH of the water from 4.50 pH units to 4.64 pH units. By comparison with the simulations done with STASOFT (see Figure 6‐1), it can be seen that this increase in 0.14 pH units equals to a carbon dioxide stripping of about 140mg/l. This results in an increase of the calcium carbonate CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 75 precipitation potential (CCPP) by approximately 93.3mg/l as CaCO3 (from ‐475.9 to ‐382.6mg/l as CaCO3). The parameters calcium and magnesium (hardness) remained unchanged. NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: Initial Water CO2 mg/l 100.0% -140.0 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 24.0 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 16.0 7.0 4.64 5.0 CO2 CaCO3 443.1 -475.9 303.1 -382.6 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 339.63 161 Carbonic Species CaCO3 PP Figure 6-1 - Simulation of the Aeration in Ryakarimira using STASOFT Some of the technical problems that were encountered using aeration were the: growth of algae in the holes of the showerheads and / or blockage of these after some time. As the algae grow and their length increases, the distance of the drop reduces, as it slides down on the algae until it reaches its end. corrosion on the outside of the fittings of the showerheads, if water from the perforated pipe trickles over them. (6.3.2) Filtration through Limestone The installation of the limestone filtration unit was easy, as the only thing needed was a structure that could be used as a filtration chamber for the aggregates. For that purpose, the installed basins proved to be adequate. The procurement of limestone was difficult, as – due to the local geology – limestone is not readily available in Uganda. The only places that are known to provide limestone in Uganda are: Kasese, Mbale and Busanza; Busanza being in a very remote area and Mbale, and Kasese being a distance of several hundred kilometres away from the investigated water supply schemes. Transport costs of limestone in Uganda are therefore high. This has to be taken in consideration as an important cost factor in economic calculations. CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 76 The filtration through limestone proved to be easily manageable, as no special measures had to be taken by the scheme operator to ensure the proper operation of the filtration unit. The only necessary action involved the cleaning of the top filter layer in case of algae growth. The pH in the basins with aeration and limestone contact increased from pH 4.50 from the raw water to a pH of 4.93, compared to a value of pH 4.64 after aeration only. Assuming the effect of the aeration was the same in both cases, this change in pH – according to simulations done with STASOFT (see Figure 6 2) – would result from approximately 7mg/l of dissolved limestone, hereby increasing the CCPP by 7mg/l (from ‐382.6 to ‐ 375.6mg/l CaCO3). The calcium content was slightly increased, by the dissolution of the limestone. NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: Initial Water CO2 mg/l 100.0% -140.0 CaCO3 mg/l 100.0% 7.0 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 24.0 17 25.1 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 16.0 7.0 4.64 5.0 18.8 7.0 4.94 12.0 CO2 CaCO3 443.1 -475.9 303.1 -382.6 306.2 -375.6 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 339.63 161 336.13 168 Carbonic Species CaCO3 PP Figure 6-2 - Simulation of the Limestone filtration with STASOFT This minor increase in the CCPP was related to the very short contact time of only about one minute due to the little quantity of filter material that was available, as well as the relatively big size of the aggregates. Yet, studies by MACKINTOSCH et al (1998) show the huge potential of the stabilisation of soft, acidic waters by limestone in combination with aeration under similar conditions in South Africa. After several weeks, a reduction of the filtration material could be noticed. In this situation, the scheme operator would have to fill the unit up to the original level with fresh limestone material again. This was not possible during the experimental phase, as there were no excess limestone aggregates left for the refilling of the chambers. No major technical and operational problems were noticed during the investigation. CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 77 (6.3.3) Lime dosing Although the performance of the lime‐dosing unit was promising, there were many technical and social problems related to the operation of the unit, as the operation & maintenance of the unit was very labour intensive compared to the other technologies. By dosing a 1% lime solution at a rate of 3ml/sec, it was possible to raise the pH of the water from 4.64 pH units (after aeration) to 5.55 pH units. According to the simulation done with STASOFT (Figure 6‐3) this change in pH would mean a dosing of approximately 30mg/l of Ca(OH)2, yet a quantity of 60mg/l was supposed to be dosed. The reason for this difference was due to impurities in the procured lime, as well as the inadequate (manual) mixing of the limewater and the short contact time of the water before the measurement of the pH. An increase of the CCPP from ‐382.6mg/l to ‐328.3mg/l as CaCO3 was calculated, hence a difference of 54.3mg/l as CaCO3. The calculated water showed more than double the calcium content as before. NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: Initial Water CO2 mg/l 100.0% -140.0 Ca(OH)2 mg/l 100.0% 30.0 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 24.0 17 31.0 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 16.0 7.0 4.64 5.0 32.2 7.0 5.55 45.5 CO2 CaCO3 443.1 -475.9 303.1 -382.6 303.1 -328.3 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 339.63 161 299.10 208 Carbonic Species CaCO3 PP Figure 6-3 – Simulation of the lime dosing with STASOFT Several problems with the lime dosing procedure were identified during the investigations – technical aspects as well as social aspects are listed below. Technical aspects: The rate of outflow of the unit decreased after a few days as the V‐notch of the outlet started to get clogged. This was fixed by telling the scheme operator to regularly (twice a week) clean the V‐notch of the dosing unit. CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 78 The unit was very sensitive to even very small vertical movements. A completely level surface and a fixed mounting is therefore essential. The floating valve stopped working properly after about three weeks because the mechanism was clogged by coagulating lime. This was fixed by telling the scheme operator to keep the mechanism sound by regularly applying the float valve. The flexible PVC tube for the inlet of the dosing unit after some time bent to an extent that the lime solution could not flow into the unit anymore – this was fixed by supporting the tube by a piece of thick wire. The purity of the used lime was poor and was apparently dirtied by a lot of stones and other aggregates. These started to settle in the 1m³ PE Tank. Analysis at the swTwsP laboratory showed that the purity of the lime was at around 75% only. An attempt to buy a sack of lime in Kabale town failed because the 25 kg sack of ‘white powder’, which was bought at USh 10,000 (~ €4.54) from a local merchant, was found definitely not to be lime. It was assumed that the white powder in the sack was flour – probably cassava‐flour. Tests carried out at the swTwsP laboratory showed that the content of calcium hydroxide Ca(OH)2 in the ‘lime’ was nil. Social aspects: After some weeks, the scheme operator abandoned the lime‐dosing unit. He failed to mix the lime solution regularly, when no regular visits by the investigation team were carried out. The regular filling of the unit was too time intensive and he did not see the necessity in carrying out this activity, as it was only part of an experiment, and the benefits to the community (and him) were not obvious. There were complaints by users that the consumption of soap had increased. The soap did not form a lather as easily as before the experiment was carried out. (see also excursus: Hardness in Buyanja, where similar complaints were heard, because a source with moderately hard water was used to supply the town). CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 79 This increase in hardness was as a secondary effect of the filtration through limestone, as the calcium concentration was increased due to the dissolving limestone. (6.3.4) Coating One month after the complete renovation of the tank, and after the SIKA coating had been applied, the tank was leaking again. The cracks at the outside of the tank had redeveloped. Due to time constraints, it was not possible to reinspect the interior of the tank in order to find the possible cause for the reoccurring leakage. (6.4) STEP 4: EVALUATE CORROSION CONTROL STRATEGIES The evaluation of the different corrosion control strategies was done due to the results, gathered from the steps 1 to 3 and was merely done on a ‘verbal’ basis. The results can be found in Table 6‐1. high Notes - Appropriateness Operation and - Operating costs Training Needs Strategy Investment Cost - Corrosion Control Maintenance Performance Table 6-1 - Evaluation of different Corrosion Control Strategies in the Context of this Research None Corrosion at full scale very high - degradation of the system (leaks, discolourations, (corrosive water, GI failure of the system) pipes) Changing the water quality Alternative Sources low to low to none low none Y high very high Aeration medium low low medium none Y basic aeration Filtration through medium low to low low low to Y procurement of limestone limestone to high high Dosing of quicklime medium very high alternative sources medium high very high high was difficult N to high Use of inhibitors medium non-corrosive water as does not work in rural growth centres ? ? high high N to high CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 80 Barriers Coatings low medium none low low Y the performance of the tested coating was low Cathodic Protection medium high high medium ? N only for protection of parts of the infrastructure Changing the Material Properties Sound Material very high Selection low to none none none Y high GI low medium material selection according to water quality medium low high Y if no other measures are taken, GI will corrode PE very high low low medium none Y prone to vandalism, can not be used at pressures exceeding 16 bar Stainless high very high medium very low none N Steel PVC only for parts of the system very high medium low medium none Y prone to vandalism, can not be used at pressures exceeding 16 bar The evaluation of the different corrosion control strategies that were tested during the field study showed that the first choice should be to avoid the use of corrosive water for a water supply system in a rural growth centre. The second choice should be the design of water supplies using corrosion resistant materials. Hereby, the choice of HDPE pipes may be a big opportunity, although careful workmanship during the connection of the pipes is substantial, to prevent leakages at the joints / couplings. If case of existing water supplies, where corrosive water is present and the use of corrosion resistant materials has not been taken care of, the only corrosion control strategy is to change the properties of the corrosive water. In this case, both aeration and the filtration through limestone proved to be easily manageable technologies. Limitations in the use of limestone filtration were found, due to difficulties in the access to limestone aggregates in Uganda. Provided the existence of an appropriate support structure that could help in the procurement and delivery of the limestone aggregates, this technology could suit the CORROSIVE WATER Erik PINTER, 2005 (6) Results & Discussion of the Field Studies 81 needs of the RGCs that were found to be heavily affected by corrosive water in the field study. The installation costs are low, the operation and maintenance can easily be done by the local scheme operators. The operational costs could be kept low by a support structure with a central storage of limestone. CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 82 (7) RECOMMENDATIONS Most of the field work (Chapter (5)) relating to the chosen ‘4‐Step Approach’ was done on a technical, and some work on an operational level. From the results (Chapter (6)) of the gathered experiences on these two levels, recommendations and conclusions for the policy level are drawn. Therefore, based on the results of the field research and literature review, recommendations are given on all three levels, addressing the respective stakeholders, as discussed in Chapter (4.3): the policy level (policy makers) the operational level (authorities & institutions, operators & owners) the technical level (planners & implementers, operators). (7.1) RECOMMENDATIONS FOR POLICY MAKERS The following recommendations for the policy level can be given: Policy Makers must be aware of the impact, which the corrosion of water supply systems has on the development of a region. Adequate Water Supply is a major factor in improving life standards and the economic development of a country. Corrosion is a threat to the goals of the Water & Sanitation Sector (see Chapter (1.1)) and therefore has to be taken into consideration, accordingly. Hence, policy makers should demand information about the economic impact of corrosion to argue and set up proper counter measures. Existing laws, by‐laws and standards for the Water Sector have to be revised, and new laws, by‐laws and standards to be developed concerning the aspects of corrosion control in water supply systems. The main goal should be to ensure the technical & operational safety of the water supply schemes. National drinking water quality guidelines should include specific practices and parameters regarding the use of corrosive waters ‐ The South African Water Quality Guidelines (DEPARTMENT OF WATER AFFAIRS AND FORESTRY, 1996) could apply helpful in this context. CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 83 The Water Sector Policy must define the necessity of any water supply system to cover independently the operation and management costs, without financial assistance by the government. This would ensure proper planning methods concerning the longevity of water supply infrastructures and stability against corrosive water hence, minimising the economic impact of corrosion on the national economy. Financial support must only be given to projects, which ensure the sustainable design & implementation of water supply solutions concerning the technical & operational infrastructure. This would ensure that the standards and guidelines are followed by the planners & implementers. At the same time, the easy access to adequate financial resources for projects that fulfil the set criteria has to be supported. Mobilise the population to claim their rights as consumers. Users should be enabled to take (legal) action, if private infrastructure is damaged due to the corrosivity of the supplied waters or due to corrosion by‐products in the water supply. Research to improve the planning, implementation, operation & management of water supply systems should be encouraged and financed. A sector wide approach to include all involved stakeholders in the development of new methods regarding these aspects is recommended. The ‘quality criteria for stabilisation’ as seen in Table 7‐1, given by LOEWENTHAL et al. (2004) should be included in guidelines regarding the construction of water supply systems. Table 7-1 – Quality Criteria for stabilisation, LOEWENTHAL et al. (2004) Guideline No. Criteria for prevention of aggression: Guideline 1: The chemical state of the water needs to be adjusted to a state of slight supersaturation with respect to CaCO3; a precipitation potential of about 4 mg/l is recommended Guideline 2: For waters with sulphate content in excess of 350 mg/l (as SO4), the cement material used in the conduit should have a tricalcium aluminate content of less than 5.5%. CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 84 Guideline No. Criteria for prevention of corrosion: Guideline 1: The bulk water should be saturated or slightly supersaturated with respect to CaCO3 (where cement type pipes form part of the distribution system, the criteria covering nonaggression for cement material will automatically satisfy the criteria for metal pipes.) Guideline 2: Calcium and alkalinity values should not be less than about 50 mg/l (expressed as CaCO3). This is to ensure that sufficient cathodic carbonate film is deposited. Guideline 3: The WRC (1981) suggests waters be regarded as potentially corrosive when either the chloride or sulphate concentration exceeds 50 mg/l. The higher the chlorides and sulphates are above this limit, the greater should be the consideration given to substituting metal conduits with conduits of cement type or plastic material, or metal pipes must be lined internally with cement or some other inert coating material. Guideline 4: Flow velocities less than ca. 0.2 m/s are to be avoided and flow velocities of greater than 1 m/s are to be preferred. Any design feature that would give rise to dead ends in the system should also be avoided. Where low flow velocities are unavoidable in the system, the conduits should be made from cement type or plastic materials. Guideline 5: The dissolved oxygen concentration in the water should be greater than 4 mg/l (as O2). (7.2) RECOMMENDATIONS FOR AUTHORITIES & INSTITUTIONS Following recommendations for authorities are provided: Capacity building of authorities & institutions to assess the problems, to develop and implement solutions concerning the impact of corrosive water on water supply schemes is recommended. The development and implementation of adequate methods for the impact assessment, as well as methods for corrosion control in water supply systems is a basic need. Corrosion monitoring programs to assess the occurrences and impact of corrosive water on water supply systems in rural growth centres have to be implemented. Instances of corrosion in water supply systems as well as the occurrences of corrosive water should be assessed, interpreted and documented. The results of this assessment should influence the process of regional planning e.g. through the development of corrosion risk maps, based on the occurrences of corrosive water. CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 85 The input of knowledge into the corrosion discussion should be made possible by encouraging, financing and assisting further research on the topic, as well as through the participation in international conferences regarding corrosion Awareness about the impacts of corrosion on water supply systems must be created amongst planners, implementers, operators and owners of water supply systems. This could be achieved by the conduction of regular workshops. Quality assurance to ensure the compliance of planning to implementation procedures with laws, by‐laws and standards has to be accomplished. Therefore, capacity building at the authorities is needed to enable proficient consultations and supervision of planners and implementers. Regular evaluations and sharing of experiences regarding the practicability and effectiveness of laws, by‐laws and standards amongst stakeholders is recommended. This could be achieved by the conduction of regular workshops. The results of the different activities at this level should be used to evaluate the laws, by‐laws and standards at the policy level. (7.3) RECOMMENDATIONS FOR PLANNERS & IMPLEMENTERS From the results of the field study several recommendations for planners and implementers can be given: The water quality for any projected water supply system must be analysed regarding its corrosiveness towards different materials before the actual planning phase starts. The use of corrosive waters for drinking water supply systems has to be avoided, as far as possible. In case the use of corrosive water is unavoidable, the design and material selection has to be done accordingly: only corrosion resistant materials should be used. In case the use of corrosion resistant materials is not possible, although the water is corrosive, an appropriate water treatment should be chosen. Aeration CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 86 and the filtration through limestone were identified as being possible corrosion control strategies in the context of this research. The use of lime dosing has to be avoided. Water supply systems should strictly be designed for a 24 hours a day and 7 days a week (‘24/7’) based water supply. This is to ensure, that no low‐pressure zones develop, that could allow the infiltration of pollution. This would lead to the users shifting back to unprotected water sources due to interrupted or contaminated supply services. Corrosion test specimen (see Appendix (11.5)) should be included throughout the system at easily accessible points (e.g. rising pipe at tank inlet, standposts) in water supply systems, which use corrosive water. This allows the operators & owners to assess the actual state of internal corrosion of the infrastructure. Planners & Implementers should study the local market for water supply materials to be aware of new developments and alternative products for material selection. Hence, forcing the producers and suppliers of water supply components to further improve their products and develop new alternatives The active co‐operation in the development of standards together with authorities and institutions is a necessity for the usability and efficiency of the standards. Water Safety Plans should be introduced for piped water supply schemes in rural growth centres. Instances of corrosion should be treated with high priority. The development of water safety plans for water supply systems is a central element for drinking water safety in the WHO’s third edition of the Drinking water Quality Guidelines (WHO, 2004; see Chapter (3.2.1)). (7.4) RECOMMENDATIONS FOR OPERATORS & OWNERS The recommendations for operators and owners are as follows: Leak detection is recommended as a means to assess possible corrosion damages. Leaks as well as intermitted water supply allow the infiltration of CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 87 pollutants from the surrounding environment in case of low pressure in the system, and therefore have to be avoided. Corrosion test specimen have to be included throughout the water supply system, if it is affected by corrosive water. This allows both the assessment of the internal degradation of the water supply infrastructure, as well as the evaluation of the applied corrosion control strategies. Instances of heavy infrastructural degradation due to corrosive waters have to be monitored and reported to the relevant authorities and institutions. This allows an economic impact assessment by the operators, owners and authorities, which can lead to the choice of a corrosion control strategy. An appropriate corrosion control strategy should be chosen to prevent corrosion damage. Operators and Owners should define the problems that are related to corrosive water in their water supply schemes to allow the formulation of necessary research demand for corrosion control research. Water Safety Plans should be introduced for piped water supply schemes in rural growth centres. Instances of corrosion should be treated with high priority. The development of water safety plans for water supply systems is a central element for drinking water safety in the WHO’s third edition of the Drinking water Quality Guidelines (WHO, 2004; see Chapter (3.2.1)). (7.5) RECOMMENDATIONS FOR THE SOUTH WESTERN TOWNS WATER & SANITATION PROJECT (SWTWSP) Following recommendations can be given to the swTwsP, where the field studies for this research were conducted: In the RGCs that are affected heavily by corrosive waters such as Ryakarimira and Rubuguri, the installation of a limestone stabilisation unit, as shown by MACKINTOSCH et al. (1998) is recommended, when a support structure for the easy access to limestone aggregates is ascertained. Under the current CORROSIVE WATER Erik PINTER, 2005 (7) Recommendations 88 circumstances, it is feared that the systems in Ryakarimira and Rubuguri will break down, before the design life. The cost related to degradation of infrastructure in RGCs affected by corrosive water should be quantified. For the design of new schemes, where the use of corrosive water cannot be avoided, special care must be taken towards proper material selection. An engineer of the swTwsP should present this research at a relevant conference (e.g. IWA or WEDC conference) to initiate further discussion and research on this issue. CORROSIVE WATER Erik PINTER, 2005 (8) Conclusions 89 (8) CONCLUSIONS & SUMMARY Sustainable water supply is a major factor in improving life standards and the economic development of a country. Corrosion is a threat to the water supply infrastructure and hence, the goals of sustainable water supply. Especially in developing countries, where economic poverty is widespread and financial means to rehabilitate infrastructure are not available, corrosive water is an immense threat to water supply schemes of rural growth centres in remote areas. The failure of many schemes to deliver potable water throughout their design life is imminent. The field studies for this thesis were done in the time from March 2002 to September 2003 – in the Southwest of Uganda. The methodology consisted of a ‘4‐Step Approach’ with the following four steps: Step 1: Document Extent & Magnitude of Corrosion Step 2: Determine Possible Causes of Corrosion Step 3: Develop & Assess Corrosion Control Strategies Step 4: Evaluate Corrosion Control Strategies. The field studies showed that the impact of corrosive water on the visited water supply systems in rural growth centres was obvious. The infrastructure was severely attacked / corroded in several instances, thereby being a substantial threat to the concerned water supply schemes. Due to economic situation of these schemes, a continuous rehabilitation of the degraded infrastructure is not possible. By the development of low‐pressure zones, the infiltration of pollutants that may cause health problems is possible. Eventually the water supply systems will collapse. Therefore, corrosion is a direct threat to the main goals of the Water & Sanitation Sector. The causes of corrosion damages were found to be due to three reasons, namely the aggressive / corrosive nature of the water, the inappropriate use of materials and CORROSIVE WATER Erik PINTER, 2005 (8) Conclusions 90 shoddy workmanship, as an indirect reason for damages related to corrosion. Four corrosion control technologies (aeration, filtration through limestone, dosing of quicklime, application of a coating) were tested during the field study at an experimental treatment plant in one of the affected water supply schemes. This revealed both technical and operational (social) strengths and weaknesses of the four technologies, on which the following evaluation of the corrosion control strategies is based. The ranked corrosion control strategies in the context of this work can be summarised as follows: (1): avoid the use of corrosive water for water supply systems as far as possible (2): use corrosion resistant materials if (1) is not possible (3): apply water treatment, if both (1) and (2) are not possible. (4): the continuous monitoring of the corrosive attack to set appropriate counter measures Regarding point (3) the field studies showed, that aeration and the filtration through limestone proved to be possible choices. According to the results of the field study, recommendations were given on three ‘levels of response’: a technical level, an operational level and a policy level. Therefore, the aims and objectives of this thesis were met, as concerning the occurrence of corrosive water in rural growth centres in developing countries it was possible to: provide tools for the assessment of the problems related: in Chapter (4) recommend preventative or remedial measures: in Chapters (6) & (7) provide tools for appropriate & sustainable management of problems: in Chapter (7) discuss relevant literature on corrosive/aggressive water: throughout this thesis. CORROSIVE WATER Erik PINTER, 2005 (9) Recommendations for Further Research 91 (9) RECOMMENDATIONS FOR FURTHER RESEARCH There is a huge field for further research. Research to document and differentiate the different forms of corrosion / aggression, as observed in water supply systems in rural growth centres, to allow engineers and other professionals the easy determination of the experienced corrosion forms. Background: it was extremely difficult to get proper practical descriptions, of how the different forms of corrosion can be recognised in the field. Further research is needed to determine whether a relationship exists between the geology in Uganda and the corrosivity of water sources as expressed through the CCPP or the pH value, which can then be applied in a risk assessment to generate risk maps for corrosive water. A study to quantify the cost of corrosion in rural growth centres in Uganda is proposed. CORROSIVE WATER Erik PINTER, 2005 (10) References 92 (10) REFERENCES AWWA (American Water Works Association Research Fund), DVGW (DVGW Technologiezentrum Wasser): Internal Corrosion of Water Distribution Systems, American Water Works Association, 2nd Edition, Denver (1996) BIESER UND PARTNER: Bedienungshandbuch WinWASI 3.0 BMAA (BUNDESMINISTERIUM FÜR AUSWÄRTIGE ANGELEGENHEITEN – Sektion Entwicklungszusammenarbeit VII/A): Wasserversorgung und Siedlungshygiene – Sektorpolitik der Österreichischen Entwicklungszusammenarbeit, Wien (2001) BMAA (BUNDESMINISTERIUM FÜR AUSWÄRTIGE ANGELEGENHEITEN – Sektion Entwicklungszusammenarbeit VII/A): Country Programme Uganda 2003–2005, Wien (2002) BMAA (BUNDESMINISTERIUM FÜR AUSWÄRTIGE ANGELEGENHEITEN – Sektion Entwicklungszusammenarbeit VII/A): ADC Statistics: http://www.bmaa.gv.at/up‐ media/689_pph_2002_engl.pdf, Date of visit: 8th September, 2004 BRITISH GEOLOGICAL SURVEY: Hydrogeologic Map of Uganda, 1989 BRITISH GEOLOGICAL SURVEY: Groundwater Quality: Uganda, 2001 BRITS, A.G., J. C. GELDENHUYS, A. M. KOK and D. A. BAXTER: The effect of water quality and chemical composition on the corrosion of mild steel pipelines, WRC Report No. 259/1/98, WRC, Pretoria (1998) CORROSION DOCTORS: Corrosion by Beer, http://www.corrosion‐doctors‐ .org/FoodIndustry/Beer‐corrosion.htm, Date of Visit: 3rd July, 2004 DAVIS, J.R.: Corrosion: Understanding the Basics, ASM International, Ohio (2000) DEPARTMENT OF WATER AFFAIRS AND FORESTRY: South African Water Quality Guidelines (second edition). Volume 1: Domestic Use, Pretoria (1996) DVGW (Deutsche Vereinigung des Gas‐ und Wasserfaches e.V. Technisch‐ wissenschaftlicher Verein): DVGW‐Forschungsprogramm Wasser 2000‐2005, Stuttgart (1999) CORROSIVE WATER Erik PINTER, 2005 (10) References 93 DWD (Directorate of Water Development): National and International guidelines for drinking water & effluents, MWLE, Kampala (1995) DWD (Directorate of Water Development): Water Supply Manual, MWLE, Kampala (1995) DWD (Directorate for Water Development): Assessment of Water Quality in four small towns in Southwestern Uganda, Technical Report for swTwsP, unpublished project report, 2000 DWD (Directorate of Water Development): Issues Paper No. 3, Small Towns Water Supply and Sanitation, Joint GoU / Donor Review of the Water and Sanitation Sector, Kampala (2002) DWD (Directorate of Water Development), http://www.dwd.co.ug/urban‐programmes‐ .php, date of visit: 24th July, 2004 EDWARDS, M.: Controlling corrosion in drinking water distribution systems: a grand challenge for the 21st century, Water Science and Technology, Vol. 49, No. 2, pp 1–8, IWA Publishing (2004) EU. COUNCIL DIRECTIVE 98/83/EC of 3 November 1998 on the quality of water intended for human consumption, Official Journal of the European Communities, Vol. 330, pp 32‐54, Brussels (2004) FHWA (Federal Highway Administration): Corrosion Costs and Preventative Strategies in the United States, Report FHWA‐RD‐01‐156, US Department of Transportation Federal Highway Administration (2002) JERLICH K.: Corrosive Properties of drinking water sources in the South West of Uganda, unpublished project document, 2000 KEMMER, F.: The NALCO water handbook, McGraw‐Hill, Inc., USA (1979) LANGENEGGER, O.: Groundwater Quality and Handpump Corrosion in Africa, UNDP (1994) CORROSIVE WATER Erik PINTER, 2005 (10) References 94 LOEWENTHAL, R.E., I. Morrison and M.C. Wentzel: Control of corrosion and aggression in drinking water systems, Water Science and Technology Vol. 49, No 2, pp 9–18, IWA Publishing (2004) MACKINTOSCH, G. S., H. A. VILLIERS, G. J. DU PLESSIS, R. E. LOEWENTHAL and U. KORNMULLER: Stabilization of Soft Acidic Waters with Limestone, WRC Report No. 613/1/98, WRC, Pretoria (1998) MINK, A.: Report by Alfred Mink on the first visit to the South Western Towns for the Water and Sanitation Programme in Kabale, Uganda from 22–31 0ctober, 2003, Unpublished project report, 2003 MORRISON, I. and R. E. LOEWENTHAL: STASOFT 4, Water Research Commission, South Africa (2000) MWLE (Ministry of Water, Lands and Environment): Water and Sanitation in Uganda – Measuring Performance for Improved Service Delivery, MWLE, Kampala (2004) NEMA (National Environment Management Authority): District State of Environment Report – Kabale, MWLE, Kampala (1997) OKUNI, P.: Developments in addressing the corrosion problem in Uganda, Paper Presented at the HTN 2000 Workshop Held at the Krishna Oberoi Hotel, Hyderabad, Andhra Pradesh, India, 06 – 10 March (2000) RINGAS, C., F. J. STRAUSS, J. GNOINSKI and B.G. CALLAGHAN: Research on the Effects of Varying Water Quality on the Corrosion of Different Pipe Materials in the PWVS/Klerksdorp Areas, WRC Report No. 254/1/99, WRC, Pretoria (1999) RUWASA: Corrosion Study Report: A Study on Corrosion of Hand Pump in Ruwasa Project, unpublished project document, Mbale (1998) SCHWARZ‐HERDA, C.: Anwendung von Akteursnetzwerken in der Wasserversorgung – an den Beispielen Oberösterreich und Uganda, Diplomarbeit, Universität für Bodenkultur, Wien (2003) SIKA: Product Data Sheet – CEMFLEX (Provisional) Universal Water Proofer and Bonding Agent, 2004 CORROSIVE WATER Erik PINTER, 2005 (10) References 95 SKAT (Swiss Centre for Development Cooperation in Technology and Management): HTN Working Paper: WP 02/96: Ugandaʹs Water Sector Development: Towards Sustainable Systems (1996), Source: http://www.wateraid.org/other/startdownload‐ .asp?openType=forced&documentID=199, Date of Visit: 7th August, 2004 SWISTOCK, B. R., W. E. Sharpe and P. D. Robillard: Corrosive Water Problems, Agricultural and Biological Engineering Fact Sheet F‐137, University Park, PA 16802. 4 pp, (2001) SWTWSP (South Western Towns Water & Sanitation Project): Objectives of the swTws Project, http://iwga‐sig.boku.ac.at/swtws/swtws1_e.htm, Date of Visit: 3rd July, 2004 TAYLOR, R. and K. HOWARD: A tectono‐geomorphipc model of the hydrology of deeply weathered crystalline rock: Evidence from Uganda, Hydrogeology Journal 8, pp 279‐294, Springer Verlag (2000) TIS‐GDV (Transport Information Versicherungswirtschaft), Service – Gesamtverband der Deutschen http://www.tis‐gdv.de/tis_search/contentansicht‐ .jsp?vipoid=171, Date of Visit: 5th August, 2004 UNDP: Human Development Report 2004, UNDP (2004) VON FRAUNHOFER, J. A.: Inhibiting Corrosion with Tobacco, Advanced Materials & Processes, Vol. 158, 2, pp 33‐37, ASM International (2000) WEDC, Technical Brief No. 49: Choosing an appropriate technology, WEDC Loughborough University, Leicestershire (1998) WHO (World Health Organization): Guidelines for Drinking‐water Quality, Vol. 1, 3rd Edition, WHO, Geneva (2004) WORLDATLAS, http://www.worldatlas.com/webimage/countrys/africa/ug.htm, Date of visit: 7th August, 2004 CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 96 (11) APPENDIX (11.1) Hydrogeological Map of the Southwest of Uganda .....................................................97 (11.2) Simulations done with STASOFT & WinWASI...........................................................98 (11.3) Water Quality Data of Rural Growth Centres & Potential Sources ........................106 (11.4) CEMFLEX Technical Data Sheet....................................................................................111 (11.5) Corrosion Test Specimen ................................................................................................113 CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 97 (11.1) HYDROGEOLOGICAL MAP OF THE SOUTHWEST OF UGANDA PB…Precambrian – partly granitised and metamorphosed formations, predominantly argillites PC…Precambrian – wholly granitised and high to medium grade metamorphic formations PLR…Pleistocene - Recent CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 98 (11.2) SIMULATIONS DONE WITH STASOFT & WINWASI The following pages present simulations done with STASOFT & WinWASI. In the simulations done with STASOFT, each column from the left to the right in the figures represents one calculation. Starting from the left, the parameters of the ‘Initial Water’ are shown. From the second column onwards, every column represents the addition of one ‘treatment process’ to the water in the respective left column. Therefore, the values in the line ‘Amount’ have to be cumulated from the left to the right for every treatment process. The effect of carbon dioxide stripping by aeration on the pH and other water quality parameters of the water in Ryakarimira (STASOFT): NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: Initial Water CO2 mg/l 100.0% -100.0 CO2 mg/l 100.0% -100.0 CO2 mg/l 100.0% -100.0 CO2 mg/l 100.0% -50.0 CO2 mg/l 100.0% -50.0 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 24.0 17 24.0 17 23.9 17 23.9 17 23.9 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 16.0 7.0 4.59 5.0 16.0 7.0 4.72 5.0 16.0 7.0 4.93 5.0 16.0 7.0 5.10 5.0 16.0 7.0 5.44 5.0 CO2 CaCO3 443.1 -475.9 343.1 -411.6 243.1 -334.1 143.1 -233.6 93.1 -167.6 43.1 -83.3 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 385.11 161 271.40 160 157.69 160 100.84 160 43.98 160 Carbonic Species CaCO3 PP CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 99 The addition of calcium carbonate (CaCO3) by the filtration through limestone to the water in Ryakarimira to raise the pH, affecting other water quality parameters (STASOFT): NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: Initial Water CaCO3 mg/l 100.0% 20.0 CaCO3 mg/l 100.0% 20.0 CaCO3 mg/l 100.0% 20.0 CaCO3 mg/l 100.0% 20.0 CaCO3 mg/l 100.0% 20.0 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 27.4 17 30.9 17 34.4 17 37.9 17 41.4 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 24.0 7.0 5.09 25.0 32.0 7.0 5.34 45.0 40.0 7.0 5.51 65.0 48.0 7.0 5.63 85.0 56.0 7.0 5.73 105.0 CO2 CaCO3 443.1 -475.9 451.9 -455.9 460.7 -435.9 469.5 -415.9 478.3 -395.9 487.0 -375.9 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 488.82 184 478.82 207 468.82 231 458.82 254 448.82 278 Carbonic Species CaCO3 PP The addition of calcium hydroxide (Ca(OH)2) by lime dosing to the water in Ryakarimira to raise the pH, affecting other water quality parameters: (STASOFT): NAME: RYAKARIMRA SOURCE TREATMENT PROCESS: Unit: Purity of Process Chemical: Amount: Initial Water Ca(OH)2 mg/l 100.0% 10.0 Ca(OH)2 mg/l 100.0% 10.0 Ca(OH)2 mg/l 100.0% 10.0 Ca(OH)2 mg/l 100.0% 10.0 Ca(OH)2 mg/l 100.0% 10.0 PARAMETERS (mostly mg/l) Temperature C Conductivity mS/m 17 24.0 17 26.3 17 28.7 17 31.0 17 33.4 17 35.8 Calcium, dissolved Ca Magnesium, dissolved Mg pH Alkalinity CaCO3 16.0 7.0 4.50 5.0 21.4 7.0 4.96 18.5 26.8 7.0 5.20 32.0 32.2 7.0 5.37 45.5 37.6 7.0 5.49 59.0 43.0 7.0 5.59 72.5 CO2 CaCO3 443.1 -475.9 443.1 -458.9 443.1 -441.8 443.1 -424.7 443.1 -407.5 443.1 -390.3 CO2-Acidity CaC03 Total Dissolved Solids 498.82 161 485.31 176 471.81 192 458.30 208 444.79 224 431.28 240 Carbonic Species CaCO3 PP CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 100 Water Chemical Calculations for Calcium Carbonate Saturation in accordance to DIN 38404 - C 10-R-3 for Individual Waters WinWASI 3.0 University of Natural Resources and Applied Life Sciences, Vienna Thesis: Corrosive Water Names Employer Analytical institute Sampling place/Sampling date Sampling point/Sample name Name of results Date File name Input data Temperature of evaluation (te) Temperature of pH-measuring (tpH) Temperature of titration (tt) Oxygen [O2] Conductivity at 25°C Ionic strength pH m-value p-value Acid-Neutralization Capacity pH4,3 Base-Neutralizing Capacity pH8,2 Acid-Neutralization Capacity pH8,2 Base-Neutralizing Capacity pH4,3 Dissolved inorganic carbon (DIC) Calcium [Ca2+] Magnesium [Mg2+] Sodium [Na+] Potassium [K+] Ammonium [NH4+] Iron-II [Fe2+] Manganese-II [Mn2+] Barium [Ba2+] Strontium [Sr2+] Chloride [Cl-] Nitrate [NO3-] Nitrite [NO2-] Sulphate [SO42-] Orthophosphat [PO43-] Total phosphat Fluoride [F] Activated silica [SiO2] Dissolved organic carbon [DOC] Calculated data Temperature of evaluation (te) Oxygen [O2] pH value (at evaluation temperature) m-value p-value tCO3 (as C) Buffer intensity Ionic strength Total hardness Carbonate hardness Charge-balance Charge-balance relative Calcium [Ca2+] Magnesium [Mg2+] Sodium [Na+] Potassium [K+] Ammonium [NH4+] Iron-II [Fe2+] Manganese-II [Mn2+] Barium [Ba2+] Strontium [Sr2+] Chloride [Cl-] Nitrate [NO3-] Nitrite [NO2-] Sulphate [SO42-] Orthophosphat [PO43-] Total phosphat Fluoride [F] Activated silica [SiO2] Dissolved organic carbon [DOC] Total dissolved solids [TDS] CORROSIVE WATER South Western Towns Water & Sanitation Project Ryakarimira Source - Kabale District [°C] [°C] [°C] [mg/l] [mS/m] [mmol/l] 16.800 16.800 16.800 17.000 4.500 [mmol/l] [mmol/l] [mmol/l] [mmol/l] [mmol/l] [mmol/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [°C] [mg/l] [mmol/l] [mmol/l] [mg/l] [mmol/l] [mmol/l] [°eH] [°eH] [mmol/l] [%] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] 0.183 mit CO2-Ausblasung 1.550 12.010 16.020 0.000 0.000 0.000 10.000 0.025 0.100 NC4,3 / pH NC4,3 / NC8,2 16.800 16.800 NC8,2 / pH 16.800 4.500 0.130 -12.398 150.478 0.448 2.906 6.710 0.570 5.313 0.130 -1.555 20.238 0.297 2.878 6.710 0.470 4.500 -0.013 -1.554 18.510 0.124 2.909 6.710 0.070 12.010 16.020 12.010 16.020 12.010 16.020 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 10.000 10.000 10.000 0.025 0.025 0.025 47.922 46.213 39.352 Erik PINTER, 2005 (11) Appendix 101 Calcit saturation at evaluation temperature pHC (Calcit saturation) pHL (Langelier und Strohecker) pH (Calcit solvency 5 mg/l) Delta-pH Saturation Index SI(Calcit) D (Calcit saturation) [mg/l] Bounded carbon dioxide [mg/l] Aggressive carbon dioxide [mg/l] Free carbon dioxide [mg/l] Corrosion quotients (DIN 50930) S1 (wide pitting) S2 (zinc) S3 (copper) 7.506 9.511 7.521 10.345 -2.018 -4.917 541.632 0.007 544.196 544.203 -2.194 -4.198 136.562 0.004 68.238 68.242 -3.021 -5.845 137.971 0.000 66.943 66.943 -11.657 -10.036 -11.675 2.742 2.742 2.742 18.016 400.713 0.079 17.843 118.498 0.169 18.035 120.861 0.027 <1 >2 >2 Saturation indexes Bariumsulphate [BaSO4] Calciumsulphate [CaSO4] Calciumfluoride [CaF 2] Magnesiumhydroxide [Mg(OH) 2] SiO2 (amorph) Strontiumsulphate [SrSO4] Additional data Ionic strength (Conductivity) Ionic strength (Species) Concuctivity at 25 °C (calculated) D (Calcit saturation at 60°C) Total Alkalinity Cation quotient 6.518 9.417 [mmol/l] [mmol/l] [mS/m] [mg/l] [mmol/l] Evaluation for calcit saturation and examination of validity range Concerning Calcit the water is aggressive aggressive aggressive The charge-balance is in equilibrium Temperature (-10°C < te < 90°C) yes yes yes Concentrations (< 100 mmol/l) yes yes yes Conductivity (< 1200 mS/m) yes yes yes Ionic Strength (< 200 mmol/l) yes yes yes pH (1< pH < 13) yes yes yes m-value (-100 mmol/l < m < 100 mmol/l) yes yes yes The charge-balance cannot be computed, because not all necessary ion concentrations for the charge-balance according to DIN 38404 are available! CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 102 Evaluation of corrosion risk according to DIN 50930 University of Natural Resources and Applied Life Sciences, Vienna Thesis: Corrosive Water WinWASI 3.0 Names Employer Name of water Name of results Date File name Calculated data Temperature of evaluation (te) Oxygen [O2] pH value (at evaluation temperature) m-value p-value tCO3 (as C) Buffer intensity Ionic strength Total hardness Carbonate hardness Calcium [Ca2+] Magnesium [Mg2+] Sodium [Na+] Potassium [K+] Ammonium [NH4+] Iron-II [Fe2+] Manganese-II [Mn2+] Barium [Ba2+] Strontium [Sr2+] Chloride [Cl-] Nitrate [NO3-] Nitrite [NO2-] Sulphate [SO42-] Orthophosphat [PO43-] Total phosphat Fluoride [F] Activated silica [SiO2] Dissolved organic carbon [DOC] Total dissolved solids [TDS] Ryakarimira Source - Kabale District [°C] [mg/l] [mmol/l] [mmol/l] [mg/l] [mmol/l] [mmol/l] [°eH] [°eH] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] Calcit saturation at evaluation temperature pHC (Calcit saturation) pHL (Langelier und Strohecker) pH (Calcit solvency 5 mg/l) Delta-pH Saturation Index SI(Calcit) D (Calcit saturation) [mg/l] Bounded carbon dioxide [mg/l] Aggressive carbon dioxide [mg/l] Free carbon dioxide [mg/l] Corrosion quotients (DIN 50930) S1 (wide pitting) S2 (zinc) S3 (copper) <1 >2 >2 not fulfilled ! not fulfilled ! not fulfilled ! not fulfilled ! 0.000 Wide pitting and pitting corrosion = < 1.00 0.000 S1=(Cl-+2 SO42-) / Total Alkalinity 0.000 The risk of wide pitting and pitting corrosion is small, because S1<1! 10.000 Hot-dip galvanized iron-based materials (DIN 50930 Part 3) 0.025 Uniform general corrosion ! CO2 = 12.36 < 0.70 [mmol/l] Total Alkalinity = 0.08 > 1.00 [mmol/l] not fulfilled ! not fulfilled ! For formation of protective coatings the concentration of Carbondioxid is too high and the concentrations of Hydrogen Carbonate and Carbonate are too low! 47.870 Wide pitting and pitting corrosion ! 6.518 Total Alkalinity = 0.08 > 2.00 [mmol/l] 29.412 S1=(Cl +2 SO4 ) / Total Alkalinity = < 1.00 Calcium [Ca2+] = 0.30 > 0.50 [mmol/l] -2.018 -4.912 because the concentration of Oxygen is < 0,1 mg/l. 541.576 and the concentrations of Hydrogen Carbonate and Carbonate are too low! 0.007 544.161 544.168 Selective corrosion S2=(Cl-+2 SO42-)/ NO3= The risk of selective corrosion is increased! not fulfilled ! not fulfilled ! ! > 2.00 not fulfilled ! Copper and copper-base alloy (DIN 50930 Part 5) Pitting corrosion ! S3=Total Alkalinity / SO42= > 2.00 Saturation indexes Bariumsulphate [BaSO4] Calciumsulphate [CaSO4] Calciumfluoride [CaF2] Magnesiumhydroxide [Mg(OH)2] SiO2 (amorph) Strontiumsulphate [SrSO4] Additional data Ionic strength (Conductivity) Ionic strength (Species) Concuctivity at 25 °C (calculated) D (Calcit saturation at 60°C) Total Alkalinity Cation quotient Unalloyed and low-alloy iron-base materials (DIN 50930 Part 2) 16.800 Uniform general corrosion ! Oxygen[O2] = 0.00 > 3.00 [mg/l] 4.500 pH = 4.50 > 7.00 0.130 Total Alkalinity = 0.08 > 2.00 [mmol/l] 2+ -12.398 Calcium [Ca ] = 0.30 > 0.50 [mmol/l] 150.478 0.449 None of the conditions for formation of protective coatings is fulfilled! 2.906 6.710 0.570 Due to the low concentration of Oxygen (<0,02 mg/l) also in warm water 12.010 corrosion elements cannot develop! 16.020 Due to the low concentration of Oxygen Iron-II ions may be soluted! not fulfilled ! -11.653 The risk of pitting corrosion in warm water isincreased! Due to an Oxygen concentration lower than 0,1 mg/l [mmol/l] [mg/l] [mS/m] [mg/l] [mmol/l] Rust-resistant steel (DIN 50930 Part 4) 2.742 Knife-line corrosion S1=(Cl-+2 SO42-) / Total Alkalinity = < 0.50 18.015 400.713 For soldered joints made by siver-containing hard solders there is no 0.079 risk for knife-line corrosion! The charge-balance cannot be computed, because not all necessary ion concentrations for the charge-balance according to DIN 38404 are CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 103 Evaluation of corrosiveness to concrete according to DIN 4030 University of Natural Resources and Applied Life Sciences, Vienna Thesis: Corrosive Water WinWASI 3.0 Names Employer Name of water Name of results Date File name Calculated data Temperature of evaluation (te) Oxygen [O2] pH value (at evaluation temperature) m-value p-value tCO3 (as C) Buffer intensity Ionic strength Total hardness Carbonate hardness Calcium [Ca2+] Magnesium [Mg2+] Sodium [Na+] Potassium [K+] Ammonium [NH4+] Iron-II [Fe2+] Manganese-II [Mn2+] Barium [Ba2+] Strontium [Sr2+] Chloride [Cl-] Nitrate [NO3-] Nitrite [NO2-] Sulphate [SO42-] Orthophosphat [PO43-] Total phosphat Fluoride [F] Activated silica [SiO2] Dissolved organic carbon [DOC] Total dissolved solids [TDS] Ryakarimira Source - Kabale District [°C] [mg/l] [mmol/l] [mmol/l] [mg/l] [mmol/l] [mmol/l] [°eH] [°eH] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] Calcit saturation at evaluation temperature pHC (Calcit saturation) pHL (Langelier und Strohecker) pH (Calcit solvency 5 mg/l) Delta-pH Saturation Index SI(Calcit) D (Calcit saturation) [mg/l] Bounded carbon dioxide [mg/l] Aggressive carbon dioxide [mg/l] Free carbon dioxide [mg/l] Corrosion quotients (DIN 50930) S1 (wide pitting) S2 (zinc) S3 (copper) 0.000 0.000 0.000 10.000 0.025 47.870 6.518 9.412 -2.018 -4.912 541.576 0.007 544.161 544.168 <1 >2 >2 Saturation indexes Bariumsulphate [BaSO4] Calciumsulphate [CaSO4] Calciumfluoride [CaF2] Magnesiumhydroxide [Mg(OH)2] SiO2 (amorph) Strontiumsulphate [SrSO4] Additional data Ionic strength (Conductivity) Ionic strength (Species) Concuctivity at 25 °C (calculated) D (Calcit saturation at 60°C) Total Alkalinity Cation quotient Evaluation of the degree of corrosiveness to concrete according to DIN 4030 16.800 Limits for evalution of corrosiveness Degree of corrosiveness pH = 4.50 < 4.50 very strongly corrosive 4.500 Aggressive CO2 = 544.2 > 100 [mg/l] very strongly corrosive 0.130 Ammonium [NH4+] = 0.0 < 15 [mg/l] not corrosive 2+ -12.398 Magnesium [Mg ] = 16.0 < 300 [mg/l] not corrosive 150.478 Sulphate [SO42-] = < 200 [mg/l] not corrosive 0.449 Total evaluation very strongly corrosive 2.906 6.710 0.570 Explanations: 12.010 The water is strongly corrosive to concrete. 16.020 -11.653 [mmol/l] [mg/l] [mS/m] [mg/l] [mmol/l] 2.742 18.015 400.713 0.079196177 The charge-balance cannot be computed, because not all necessary ion concentrations for the charge-balance according to DIN 38404 are CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 104 Dimensioning of marble filters for deacidification University of Natural Resources and Applied Life Sciences, Vienna Thesis: Corrosive Water WinWASI 3.0 Names Employer Treatment plant Treatment step Name of raw water Name of results Date File name Input Data Input data Nominal capacity Daily output (NC4,3 / pH) 16.01.05 Results [m³/h] [m³/d] 2.000 Quantity of filter material (min) 45.000 Consumption of filter material pH Plant Data Filtration rate (max) Height of filter layer (max) Height of filter layer (min) Number of filters in parallel Filter material Effective size of grain (otional) Consumption until recharge Safety-reserve Calculated data Temperature of evaluation (te) Oxygen [O2] pH value (at evaluation temperature) m-value p-value tCO3 (as C) Buffer intensity Ionic strength Total hardness Carbonate hardness Calcium [Ca2+] Magnesium [Mg2+] Sodium [Na+] Potassium [K+] Ammonium [NH4+] Iron-II [Fe2+] Manganese-II [Mn2+] Barium [Ba2+] Strontium [Sr2+] Chloride [Cl-] Nitrate [NO3-] Nitrite [NO2-] Sulphate [SO42-] Orthophosphat [PO43-] Total phosphat Fluoride [F] Activated silica [SiO2] Dissolved organic carbon [DOC] Total dissolved solids [TDS] 6.000 Empty Bed Contact Time (EBCT) [m/h] [m] [m] 2.000 2.000 0.500 1 Marmor 6,0/10,0 mm [mm] [%] [%] 16.800 4.500 0.130 -12.398 150.478 0.448 2.906 6.710 0.570 12.010 16.020 399.539 6.518 9.417 -2.018 -4.917 541.632 0.007 544.196 544.203 [m³] [m³] [d] [%] 0.025 47.922 13.04 0.00 0.00 100.00 [m/h] [m] [m] [m²] 10.000 0.025 0.30 1.97 2.90 6.61 0.000 0.000 0.000 10.000 391.1310113 [min] 6.000 4.548 -10.189 177.013 7.242 9.248 22.170 15.920 100.555 16.020 0.000 0.000 0.000 18.25 [t] 9.95 [kg/d] Treated Water 16.800 6.518 7.158 7.106 -0.518 -1.158 320.469 31.147 417.245 448.393 -11.657 [mmol/l] [mmol/l] [mg/l] [mmol/l] [mmol/l] [°eH] [°eH] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] -8.726 <1 >2 >2 Saturation indexes Bariumsulphate [BaSO4] Calciumsulphate [CaSO4] Calciumfluoride [CaF2] Magnesiumhydroxide [Mg(OH)2] SiO2 (amorph) Strontiumsulphate [SrSO4] Additional data Ionic strength (Conductivity) Ionic strength (Species) Concuctivity at 25 °C (calculated) D (Calcit saturation at 60°C) Total Alkalinity Cation quotient Filter material/filter 8.000 Throughput/recharge 0.000 Operation time/recharge 0.000 Safety of dimensioning Raw Water [°C] [mg/l] Calcit saturation at evaluation temperature pHC (Calcit saturation) pHL (Langelier und Strohecker) pH (Calcit solvency 5 mg/l) Delta-pH Saturation Index SI(Calcit) D (Calcit saturation) [mg/l] Bounded carbon dioxide [mg/l] Aggressive carbon dioxide [mg/l] Free carbon dioxide [mg/l] Corrosion quotients (DIN 50930) S1 (wide pitting) S2 (zinc) S3 (copper) Filtration rate Height of filter layer Filter diameter Filter surface 13.04 [m³] 221.12 [g/m³] [mmol/l] [mg/l] [mS/m] [mg/l] [mmol/l] 2.742 18.016 400.713 0.079 57.340 179.603 4.473 Die Temperatur liegt außerhalb des Gültigkeitsbereichs (3°C - 16°C). CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 105 Water chemical calculations for calciumcarbonate saturation in accordance to DIN 38404 - C 10-R-3 for additives WinWASI 3.0 University of Natural Resources and Applied Life Sciences, Vienna Thesis: Corrosive Water Names Employer Treatment plant Treatment step Name of raw water Name of results Date5 File name Additive Ca(OH)2 Calculated data Temperature of evaluation (te) Oxygen [O2] pH value (at evaluation temperature) m-value p-value tCO3 (as C) Buffer intensity Ionic strength Total hardness Carbonate hardness 2+ Calcium [Ca ] Magnesium [Mg2+] + Sodium [Na ] + Potassium [K ] + Ammonium [NH4 ] 2+ Iron-II [Fe ] Manganese-II [Mn2+] Barium [Ba2+] Strontium [Sr 2+] Chloride [Cl-] Nitrate [NO 3-] Nitrite [NO 2 ] Sulphate [SO42-] Orthophosphat [PO43-] Total phosphat Fluoride [F] Activated silica [SiO 2] Dissolved organic carbon [DOC] Total dissolved solids [TDS] Ryakarimira Source - Kabale District Value Type Calcit solvency [°C] [mg/l] CORROSIVE WATER Raw Water 16.800 Treated Water 16.800 4.500 0.130 -12.398 150.478 0.448 2.906 6.710 0.570 12.010 16.020 6.697 8.762 -3.766 150.478 6.095 15.083 36.920 30.670 185.001 16.020 0.000 0.000 0.000 0.000 0.000 0.000 10.000 10.000 0.025 0.025 47.922 736.334 6.518 9.417 -2.018 -4.917 541.632 0.007 544.196 544.203 6.687 6.679 6.662 0.010 0.018 -4.810 173.160 -7.092 166.068 -7.375 <1 >2 >2 Saturation indexes Bariumsulphate [BaSO4] Calciumsulphate [CaSO4] Calciumfluoride [CaF2] Magnesiumhydroxide [Mg(OH)2] SiO2 (amorph) Strontiumsulphate [SrSO4] Additional data Ionic strength (Conductivity) Ionic strength (Species) Concuctivity at 25 °C (calculated) D (Calcit saturation at 60°C) Total Alkalinity Cation quotient Added Quantity 319.804 [mg/l] -11.657 [mmol/l] [mmol/l] [mg/l] [mmol/l] [mmol/l] [°eH] [°eH] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] Calcit saturation at evaluation temperature pHC (Calcit saturation) pHL (Langelier und Strohecker) pH (Calcit solvency 5 mg/l) Delta-pH Saturation Index SI(Calcit) D (Calcit saturation) [mg/l] Bounded carbon dioxide [mg/l] Aggressive carbon dioxide [mg/l] Free carbon dioxide [mg/l] Corrosion quotients (DIN 50930) S1 (wide pitting) S2 (zinc) S3 (copper) Target Value -5.000 [mmol/l] [mg/l] [mS/m] [mg/l] [mmol/l] 2.742 18.016 400.713 0.079 93.513 -109.253 8.702 Erik PINTER, 2005 (11) Appendix 106 (11.3) WATER QUALITY DATA OF RURAL GROWTH CENTRES & POTENTIAL SOURCES The following pages list the chemical analyses of the South Western Towns Water & Sanitation Project Laboratory, which were done during the field studies. In the last three columns, the calculated values for the Carbon Dioxide content, the Calcium Carbonate Precipitation Potential, and the Total Dissolved Solids can be found. These values could only be calculated for samples for which the Alkalinity had been tested, after the procurement of an Alkalinity Test Kit in August 2002. CORROSIVE WATER Erik PINTER, 2005 *)...values given as mg/l of CaCO3 ND...not done NG...not given CORROSIVE WATER TNTC...too numerous to be counted ND 0.2 <0.1 1.4 <0.1 <0.1 0.3 0.2 <0.1 0.3 3.5 3.6 2.9 1.5 1.1 0.5 1.3 0.9 ND 1.1 0.8 0.0 0.1 4.6 3.1 1.6 1.9 2.1 1.8 2.4 0.2 0.3 ND 0.3 0.1 0.6 0.6 0.1 0.1 0.1 0.1 0.1 <0.1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND 1.1 0.0 0.0 0.0 0.1 0.1 0.1 <0.1 <0.1 ND <0.1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND [CFU/100ml] [mg/l] *) ND ND ND 60 ND 110 ND 410 ND 130 ND 100 ND 110 ND 78 146 100 70 ND 200 ND 250 ND 120 ND 148 ND 44 ND 80 ND 46 ND 70 ND 70 ND 76 ND 56 ND 16 ND 57 250 3376 19330 314 910 374 820 40 340 66 70 64 90 84 200 104 170 60 110 ND 170 280 420 6.3 6.8 7.0 7.1 7.3 6.8 7.1 7.3 6.3 7.2 6.7 6.0 6.7 6.9 6.6 6.5 6.0 5.8 6.9 7.1 6.0 ND 7.5 7.7 9.0 7.3 8.1 7.5 8.0 8.0 6.2 6.1 6.0 6.4 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 0 200 20 300 40 100 100 40 <5 <5 <5 <5 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 1 ND 1 0 0 0 0 5 0 0 0 0 5 2 TNTC TNTC 0 0 TNTC TNTC 0 ND 0 TNTC TNTC 50 ND TNTC TNTC 0 1 0 1 ND ND ND ND ND ND ND ND 92 46 140 136 104 38 28 24 20 20 14 38 38 12 19 442 44 124 36 22 42 28 50 30 ND 104 Total dissolved solids ND 1.1 ND 1.3 0.9 1.0 1.1 1.0 1.7 1.8 2.0 1.6 2.7 1.5 1.6 1.5 1.9 1.5 1.4 1.6 1.5 1.8 0.0 8.9 1.9 4.4 2.6 2.9 2.9 ND 1.7 1.8 ND 1.7 [CFU/100ml] Calcium Carbonate Precipitation Potential ND 1.0 1.2 0.7 1.2 0.6 0.6 0.8 0.2 <0.3 0.3 0.2 0.4 0.5 0.5 0.1 0.1 0.0 0.2 0.0 0.1 ND ND 12.0 0.3 1.8 0.6 1.2 1.0 0.7 0.1 0.1 ND .1` [NTU] Carbon Dioxide ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND [-] Temperature ND 0.00 0.04 0.02 0.02 0.02 0.02 0.03 0.40 0.03 0.03 0.04 0.10 0.04 0.03 0.04 0.06 0.03 0.04 0.02 0.03 ND ND 0.28 0.04 0.06 0.09 0.12 1.00 0.06 0.03 0.03 ND 0.02 [µS/c m] Dissolved Oxygen S0005 19.0 ND S0006 7.0 ND S0016 7.0 ND S0019 8.0 ND S0022 7.0 ND S0025 8.0 ND S0021 7.0 ND S0024 7.0 ND S0037 10.0 ND S0038 9.0 ND S0049 8.0 ND S0041 8.0 ND S0039 11.0 ND S0045 7.0 ND S0046 7.0 ND S0053 7.0 ND S0052 7.0 ND S0047 6.0 ND S0040 6.0 ND S0043 10.0 ND S0051 8.0 ND S0056 6.0 ND NW&SC 47.0 ND S0064 110.0 >300 S0073 10.0 115.0 S0072 11.0 130.0 S0065 8.0 11.0 S0074 9.0 29.0 S0063 9.0 26.0 S0066 8.0 77.0 S0071 7.0 80.0 S0070 7.0 94.0 S0069 ND ND S0067 6.0 2.0 [mg/l] *) Alkalinity [mg/l] Magnesium (Mg) [mg/l] Calcium Hardness Fluoride (F-) [mg/l] Feacal Coliforms Ammonium (NH4+) [mg/l] Total Coliforms Iron (Fe) [mg/l] Turbidity Manganese (Mn) [mg/l] pH Phosphorous (PO4 3-) [mg/l] Electrical Conductivity Nitrate (NO3-) [mg/l] Total Hardness Nitrite (NO2-) [mg/l] swTwsP Lab No Sulfate (SO4 2-) 30-Apr-01 18-May-01 24-May-01 1-Jun-01 1-Jun-01 1-Jun-01 1-Jun-01 1-Jun-01 21-Aug-01 27-Sep-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 10-Oct-01 5-Nov-01 9-Jan-02 25-Feb-02 25-Feb-02 25-Feb-02 25-Feb-02 25-Feb-02 25-Feb-02 25-Feb-02 26-Feb-02 26-Feb-02 26-Feb-02 26-Feb-02 Chloride (Cl-) Date of Sampling [mg/l] *) [mg/l] *) [mg/l] [˚C] calc. [mg/l] calc. [mg/l] *) calc. [mg/l] 120 ND ND 113.1 -16 168 54 24 60 114 16 110 16 56 26 50 56 38 18 4 38 2934 270 250 4 44 22 56 54 30 107 Muhanga source Rubuguri source Kihiihi source Buyanja Artesian well Kambuga Katembe1 Kebisoni source 11 Kihiihi source Kisiizi source Hamurwa source Kabirizi source Buyanja Artesian well Buyanja Office tapstand Ishasha Shallow Well Kambuga katembe 1 Kambuga Katembe 1&11 Kebisoni Reservoir tanks Kebisoni source 11 Kihiihi source Kihiihi tapstand Rwashamaire Kitimba Rwashamaire Nyakigoye Rubuguri source Bunagana Borehole CD2703 Rwenshama Hand dug hole Rwenshama Lake edward Rwenshama lake edward bank Rwenshama R.ncwera Rwenshama R.ncwera Distrib.lower Rwenshama R.ncwera Distrib.upper Rwenshama R.ncwera Lake outlet Rwerer kabwoma kashenyi prot.spring Rwerer kabwomaprot.spring upper Rwerere Kabwoma prot.spring lower Rwerere Kigarama(Artesian well) Date of Sampling and Analysis Scheme Scheme P.O. Box 75 Kabale, UGANDA (11) Appendix South Western Towns Water and Sanitation Project Water Quality Database 176 Erik PINTER, 2005 South Western Towns Water and Sanitation Project *)...values given as mg/l of CaCO3 ND...not done NG...not given TNTC...too numerous to be counted CORROSIVE WATER Nitrite (NO2-) Nitrate (NO3-) Phosphorous (PO4 3-) Manganese (Mn) Iron (Fe) Ammonium (NH4+) Fluoride (F-) Total Hardness Electrical Conductivity pH Turbidity Total Coliforms Feacal Coliforms Calcium Hardness Magnesium (Mg) Alkalinity Dissolved Oxygen Temperature Carbon Dioxide Calcium Carbonate Precipitation Potential Total dissolved solids S0068 S0077 S0076 S0078 S0079 S0075 S0093 S0093 S0095 S0096 S0097 S0098 S0099 S0100 S0102 S0103 S0101 S0108 S0109 S0110 S0104 S0105 S0106 S0107 S0111 S0112 S0113 S0114 S0120 s0117 S0118 S0115 S0116 S0124 Sulfate (SO4 2-) 26-Feb-02 1-Mar-02 1-Mar-02 1-Mar-02 1-Mar-02 1-Mar-02 14-Jun-02 14-Jun-02 14-Jun-02 17-Jun-02 17-Jun-02 17-Jun-02 17-Jun-02 17-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 21-Jun-02 25-Jun-02 25-Jun-02 25-Jun-02 25-Jun-02 25-Jun-02 27-Jun-02 Chloride (Cl-) swTwsP Lab No [mg/l] Date of Sampling [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] [mg/l] *) [µS/c m] [-] [NTU] [CFU/100ml] [CFU/100ml] [mg/l] *) [mg/l] *) [mg/l] *) [mg/l] [˚C] calc. [mg/l] calc. [mg/l] *) calc. [mg/l] 7.0 17.0 17.0 16.0 18.0 20.0 15.0 16.0 15.0 10.0 9.0 8.0 9.0 10.0 8.0 8.0 8.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 10.0 11.0 10.0 10.0 8.0 6.0 6.0 6.0 6.0 6.0 95.0 266.0 198.0 158.0 161.0 238.0 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.03 0.05 0.04 0.07 0.05 0.06 0.04 0.05 0.03 0.02 0.03 0.04 0.02 0.02 0.03 0.03 0.04 0.04 0.02 0.03 0.03 0.60 0.20 0.02 0.02 0.03 0.02 0.03 0.12 0.10 0.20 0.07 0.06 0.10 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.2 0.5 0.1 0.2 0.7 0.1 0.1 0.2 0.2 0.1 0.1 0.2 0.2 0.3 0.1 0.1 <0.05 0.1 0.1 0.2 <0.05 0.2 0.0 0.2 0.2 <0.05 0.1 <0.05 0.2 ND ND 1.4 0.5 0.3 1.7 ND 2.4 1.8 2.8 1.9 1.9 2.3 2.0 1.9 2.8 2.5 2.6 2.4 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.1 ND ND ND <0.1 1.7 3.1 1.2 1.0 1.1 0.0 0.0 <0.1 0.0 0.0 0.1 0.1 0.1 <0.1 0.2 <0.1 0.1 <0.1 <0.1 <0.1 0.0 0.0 0.0 <0.1 <0.1 <0.1 <0.1 3.5 0.1 0.0 0.0 <0.1 0.0 <0.1 0.1 <0.1 <0.1 0.0 <0.1 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 0.1 0.1 <0.13 <0.13 <0.13 0.2 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 <0.13 0.2 0.0 0.0 0.0 0.0 0.0 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 60 532 450 318 498 762 202 212 206 100 152 224 160 172 64 76 108 54 34 42 46 36 12 40 60 90 62 106 260 36 46 36 38 50 70 500 540 840 410 780 470 510 470 240 240 240 250 280 120 130 120 100 80 70 80 28 30 60 10 240 170 220 270 90 90 90 90 ND 6.2 7.4 7.3 6.8 8.0 7.7 5.8 6.0 6.1 6.3 6.3 6.3 6.3 6.2 7.5 7.7 7.3 9.0 8.9 8.9 8.7 8.9 8.9 8.6 4.6 4.4 4.3 5.7 6.6 6.4 6.4 6.3 6.4 ND <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 1 10 0 0 TNTC 0 0 0 0 0 0 0 0 0 0 0 0 3 3 4 2 0 18 2 0 0 1 ND TNTC ND 23 ND 24 79 24 280 246 278 320 446 124 150 120 44 74 58 116 114 40 42 26 22 10 16 26 28 6 10 12 52 30 48 180 14 12 16 12 14 36 252 204 40 178 316 78 62 86 56 78 166 44 58 24 34 82 32 24 26 20 8 6 30 48 38 32 58 80 22 34 20 26 36 108 Rwerere kyamisinde prot. spring Rubaare akatojO surface flow Rubaare akatojoprot.spring Rubaare health centre bore hole Rubaare Omuyanja stream Rubare diary bore hole Muhanga Reservoirtank Muhanga source Muhanga tapstand Hamurwa source springlet 1 Hamurwa source springlet 11 Hamurwa source springlet 111 Hamurwa tapstand Karukara tapstand Kabirizi Reservoir tank Kabirizi source Kabirizi tapstands Karengyere rain tank 1 Karengyere rain tank 1 Karengyere rain tank 11 Muko(akatojo)rain tank 1 Muko(akatojo)rain tank 11 Muko(akatojo)rain tank 111 Muko(akatojo)rain tank 1V Ryakarimira source springlet 1 Ryakarimira source springlet 11 Ryakarimira source springlet 111 Ryakarimira tapstand Ishasha Shallow Well Kihiihi collection tank Kihiihi Res tank kihiihi Sed.tank Kihiihi tapstand Kambuga katembe 1 Date of Sampling and Analysis Scheme Scheme P.O. Box 75 Kabale, UGANDA (11) Appendix Water Quality Database Erik PINTER, 2005 *)...values given as mg/l of CaCO3 ND...not done NG...not given CORROSIVE WATER TNTC...too numerous to be counted ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 0.3 0.3 0.4 0.5 0.5 ND ND ND ND ND ND ND ND ND ND 1.0 0.9 0.7 0.3 0.5 0.5 ND ND ND ND ND ND ND ND ND ND ND ND ND 0.6 1.4 1.5 0.4 1.7 0.1 0.2 0.3 0.4 0.2 0.1 0.1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 2.6 2.4 4.7 2.1 2.8 1.9 2.0 1.8 1.8 1.9 1.8 1.8 1.9 1.8 1,9 <0.1 0.0 0.1 0.6 1.3 1.7 ND ND ND ND ND ND ND ND ND ND ND ND ND <0.1 0.4 0.9 0.2 0.2 0.4 0.1 0.1 0.1 0.3 0.1 0.1 0.1 0.1 0.0 0.0 <0.1 <0.13 0.0 0.0 0.0 ND ND ND ND ND ND ND ND ND ND ND ND ND 0.1 1.1 0.3 0.1 0.1 ND 0.0 0.0 0.2 0.0 0.1 ND 0.1 0.1 0.1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 90 100 70 310 314 320 ND 50 36 40 48 72 52 34 34 40 16 22 60 246 310 300 192 516 206 134 50 50 96 78 552 38 58 102 290 170 460 580 420 420 70 120 70 90 180 160 100 80 80 90 40 30 10 490 510 530 530 890 ND 80 60 90 100 80 1200 40 40 190 ND 76.0 140.0 193.0 58.0 156.0 ND ND ND ND ND ND 187.0 ND ND ND [CFU/100ml] 7.8 8.2 6.8 6.9 7.0 6.9 7.3 7.1 6.3 6.2 7.8 <5 <5 <5 <5 25 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 75 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 6.8 6.7 6.8 6.9 8.9 7.9 9.3? 6.8 6.9 7.0 6.3 6.1 6.5 6.9 6.7 6.7 6.6 6.8 6.6 6.8 6.6 6.1 Total dissolved solids 0.10 0.10 0.10 0.08 0.08 0.09 ND ND ND ND ND ND ND ND ND ND ND ND ND 0.04 0.07 0.40 0.05 0.03 0.03 0.05 0.09 0.05 0.04 0.05 0.02 0.03 0.01 0.03 [NTU] Calcium Carbonate Precipitation Potential ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND [-] Carbon Dioxide 6.0 6.0 6.0 8.0 8.0 8.0 ND ND ND ND ND ND ND ND ND ND ND ND ND 14.0 14.0 20.0 14.0 24.0 19.0 6.2 7.4 7.3 5.7 5.4 23.0 7.0 7.0 9.0 [µS/c m] Temperature [mg/l] *) Dissolved Oxygen [mg/l] Alkalinity Total Hardness [mg/l] Magnesium (Mg) Fluoride (F-) [mg/l] [mg/l] *) [mg/l] *) [mg/l] [˚C] calc. [mg/l] calc. [mg/l] *) calc. [mg/l] 200 200 6 4 21.7 22.6 221.4 211.7 -34.3 -23.5 389.0 323.0 100 120 80 60 40 5 6 6 2 3 22.1 22 21.6 22 22.2 116.8 132.8 84.8 107.9 90.7 -40.8 -32.8 -22.8 -96.4 -95.1 328 342 355 355 596 60 40 40 60 40 150 20 20 40 3 3 2 2 3 3 5 5 3 20 20 20 20 20 23.5 20.1 19.2 20 67.6 51.3 51.3 82.7 47.9 195.1 24 27.9 98 -30.6 -36.4 -36.4 -61 -28.5 -63.9 -17.7 -25.1 -118.8 130 55 60 100 78 804 39 54 127 Calcium Hardness Ammonium (NH4+) [mg/l] Feacal Coliforms Iron (Fe) [mg/l] Total Coliforms Manganese (Mn) [mg/l] Turbidity Phosphorous (PO4 3-) [mg/l] pH Nitrate (NO3-) [mg/l] Electrical Conductivity Nitrite (NO2-) S0123 S0122 S0121 S0126 S0127 S0129 S0125 S0131 S0132 S0133 S0130 S0134 S0135 S0141 S0139 S0140 S0137 S0138 S0136 S0144 S0145 S0146 S0142 S0143 S0048 S0151 S0149 S0150 S0148 S0147 S0152 S0159 S0160 S0162 Sulfate (SO4 2-) 27-Jun-02 27-Jun-02 27-Jun-02 28-Jun-02 28-Jun-02 28-Jun-02 28-Jun-02 29-Jun-02 29-Jun-02 29-Jun-02 29-Jun-02 29-Jun-02 29-Jun-02 16-Jul-02 16-Jul-02 16-Jul-02 16-Jul-02 16-Jul-02 16-Jul-02 4-Sep-02 4-Sep-02 4-Sep-02 4-Sep-02 4-Sep-02 10-Oct-02 21-Oct-02 21-Oct-02 21-Oct-02 21-Oct-02 21-Oct-02 10-Dec-02 9-Jan-03 9-Jan-03 10-Jan-03 Chloride (Cl-) swTwsP Lab No [mg/l] Date of Sampling [CFU/100ml] [mg/l] *) 50 60 50 190 170 184 0 22 10 14 20 32 28 28 10 28 6 10 32 176 186 160 120 268 116 52 14 14 24 32 320 10 18 38 40 40 20 120 144 136 ND 18 ND TNTC ND 18 ND 2 ND 6 ND 129? ND ND ND 0 ND 0 ND 5 ND 0 ND 5 ND TNTC ND 0 ND 0 ND 0 ND 0 ND 0 ND 0 ND TNTC ND 5 ND 26 TNTC 40 61 26 ND 0 70 1 23 2 25 0 76 4 TNTC 0 62 0 2 0 TNTC 0 TNTC 3 28 26 26 28 40 24 6 24 12 10 12 28 70 124 140 72 248 90 82 36 36 72 46 232 28 40 64 Erik PINTER, 2005 109 Kambuga Katembe11 Kambuga Reservoir tank Kambuga tapstands Buyanja office tapstand Buyanja Reservoir tank Buyanja Artesian well Kisiizi source Kebisoni Reservoir tanks Kebisoni source 1 Kebisoni source 11 Kebisoni tapstand Rwashamaire Kitimba Rwashamaire Nyakigoye Kabwohe Katagata Distribution tank Kabwohe Katagata source A Kabwohe Katagata source B Rubuguri catholic parish tapstand Rubuguri kashija tapstand Rubuguri Reservoir tanks Kitarisibwa protected spring Kitarisibwa shallow well 1 Kitarisibwa shallow well 11 Ruhama (Nyakihimbura) Ruhama(Kyabakazi) Muhanga source Kashenshero (Kibaale) Kashenshero Rushoroza spring Kashenshero( Karebo protected spring) Mitooma Hand dug well Mitooma spring Rubaare consultant sample Bugongi(Katebe 1) Bugongi(Katebe 11) Rwenanura (Kabungo) Date of Sampling and Analysis Scheme Scheme P.O. Box 75 Kabale, UGANDA (11) Appendix South Western Towns Water and Sanitation Project Water Quality Database 0.1 0.1 0.1 0.2 0.1 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.2 0.0 0.1 0.1 0.0 0.1 0.1 0.0 0.1 0.1 0.1 0.0 0.1 0.1 0.1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND [˚C] calc. [mg/l] calc. [mg/l] *) calc. [mg/l] 3 3 ND ND ND ND ND ND ND ND 22.3 21.3 20 20 20 20.5 21.6 20.2 20.7 21.7 73.7 164 238.9 876.8 163.3 147.4 49.3 118.3 88.6 81.6 -77.2 -146.3 -282.5 -653.6 -207.8 -216.9 -68.5 -75.2 -64.2 -56.7 100 362 60 34 67 29 38 253? 198? 136? ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 19.5 82.9 16.8 446.9 16.8 72.4 24.6 44.5 20.2 37.6 27.3 182.5 22.5 37.0 23.4 38.1 21.3 36.6 25.2 43.7 23.7 130.3 24.2 42.5 27.1 46.6 23.7 66.9 28.1 44.3 14.6 1628.7 21.9 81.3 -90.0 -482.4 -39.4 -21.2 -9.2 -11.2 -6.3 -8.5 -6.1 -16.5 -35.4 -16.3 -25.9 -28.2 -21.1 -925.0 -57.7 415.4 140.7 140.7 107.2 56.0 294.8 93.8 68.1 73.7 842.4 978.2 154.1 107.2 107.8 68.2 35.5 200 [NTU] [CFU/100ml] [CFU/100ml] [mg/l] *) [mg/l] *) TNTC TNTC 40 20 3 0 15 45 9 6 TNTC 1 TNTC 4 10 2 20 6 TNTC 5 14 2 TNTC ND TNTC 10 TNTC 20 50 0 16 9 0 5 0 0 10 1 0 0 2 0 20 2 0 0 0 0 1 0 0 0 50 ND 2 4 5 0 0 0 42 100 26 14 18 8 14 168 130 52 74 136 108 130 20 64 40 12 164 28 30 20 206 180 66 30 60 28 12 74 62 70 22 12 24 18 24 112 90 90 92 118 120 74 44 66 32 38 60 32 16 24 108 424 20 30 46 18 26 64 40 80 40 20 40 20 20 80 60 60 40 120 160 155.1 <5 60 40 40 180 40 40 40 40 120 40 40 60 40 <5 60 [mg/l] [mg/l] *) [µS/c m] [-] 104 170 48 26 42 26 38 280 220 142 166 254 228 204 64 130 72 50 224 60 46 44 314 604 86 60 106 46 38 138 150 540 90 50 100 10 50 ND ! ND ! ND ! 540 700 790 620 210 210 160 80 440 140 80 110 720 1460 230 160 160 100 30 300 6.3 6.2 5.6 4.7 5.8 5.5 6.1 6.5 6.5 6.6 6.6 7.2 6.8 6.2 4.5 6.8 6.9 7.5 7.1 7.6 7.4 7.7 6.9 6.9 7.0 6.8 6.9 6.9 4.1 6.6 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND Total dissolved solids 0.0 0.0 0.1 0.0 0.1 0.0 0.0 0.1 0.1 0.2 0.5 0.8 0.5 0.2 0.1 0.2 0.2 0.2 0.2 0.1 0.2 0.1 0.2 0.2 0.2 0.1 0.5 0.1 0.1 Calcium Carbonate Precipitation Potential 1.9 1.8 1.8 1.9 1.9 1.8 1.9 3.3 2.5 2.1 2.7 2.4 2.4 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND Carbon Dioxide ND ND ND ND ND ND ND 0.2 0.1 0.1 0.2 0.2 0.1 0.2 0.1 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.2 0.2 0.2 0.1 0.2 0.1 Temperature ND ND ND ND ND ND ND ND ND ND Dissolved Oxygen 0.04 0.05 0.01 0.04 0.02 0.01 0.05 0.02 0.02 0.01 0.05 0.02 0.05 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.01 0.03 0.06 0.01 0.01 0.02 0.01 0.01 Alkalinity ND ND ND ND ND ND ND ND ND ND [mg/l] Magnesium (Mg) 9.0 15.0 7.0 6.0 6.0 6.0 6.0 16.0 15.0 10.0 9.0 8.0 10.0 19.0 12.0 11.0 9.0 6.0 8.0 7.0 8.0 7.0 20.0 126.0 9.0 8.0 9.0 6.0 7.0 [mg/l] *) Calcium Hardness [mg/l] Feacal Coliforms [mg/l] Total Coliforms Ammonium (NH4+) [mg/l] Turbidity Iron (Fe) [mg/l] pH Manganese (Mn) [mg/l] Electrical Conductivity Phosphorous (PO4 3-) [mg/l] Total Hardness Nitrate (NO3-) [mg/l] Fluoride (F-) Nitrite (NO2-) S0164 S0163 S0166 S0165 S0167 S0169 S0168 S0170 S0171 S0172 S0174 S0173 S0174 S0189 S0188 S0190 S0191 S0176 S0186 S0187 S0180 S0181 S0182 S0183 S0184 S0185 S0178 S0179 S0177 S0192 Sulfate (SO4 2-) 10-Jan-03 10-Jan-03 13-Jan-03 13-Jan-03 13-Jan-03 14-Jan-03 14-Jan-03 4-Feb-03 4-Feb-03 4-Feb-03 19-Feb-03 19-Feb-03 19-Feb-03 3-Mar-03 4-Mar-03 6-Mar-03 7-Mar-03 11-Mar-03 12-Mar-03 12-Mar-03 12-Mar-03 12-Mar-03 12-Mar-03 12-Mar-03 12-Mar-03 12-Mar-03 13-Mar-03 13-Mar-03 18-Mar-03 15-Apr-03 Chloride (Cl-) swTwsP Lab No Date of Sampling and Analysis Scheme Rwenanura (kitembe) Rwenanura Town (protected spring) Katete (Kishuro) Katete (Mpangango) Katete (Omukayanja) Kanyatorogo(Kijanga) Kanyatorogo(Ruhonwa) Rwahi (Rwamahwa) Rwahi(Nyarubumba) Rwahi(Rubira) Rushare(Akanara Hund dug well) Rushare(Hospital)Borehole Rushere (Borehole DWD13792) Muhanga source Ryakarimira combined sample Hamurwa source Kabirizi source Karengyere rain tank 1 Buyanja office tapstand Kambuga Tank Kebisoni tapstand Kisiizi tapstands Ndago1 Ndago11 Rwashamaire Kitimba reservoir tank Rwashamaire Nyakigoye tapstand Ishasha treatment plant Kihiihi source Rubuguri source Ruhama (Nyakihimbura) [mg/l] Date of Sampling >5 <5 <5 <5 <5 <5 <5 Scheme P.O. Box 75 Kabale, UGANDA (11) Appendix South Western Towns Water and Sanitation Project Water Quality Database 110 *)...values given as mg/l of CaCO3 ND...not done NG...not given CORROSIVE WATER TNTC...too numerous to be counted Erik PINTER, 2005 (11) Appendix 111 (11.4) CEMFLEX TECHNICAL DATA SHEET CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 112 CORROSIVE WATER Erik PINTER, 2005 (11) Appendix 113 (11.5) CORROSION TEST SPECIMEN The Test Method employs removable, tared pipe inserts, which are installed in a plastic piping assembly tailored to provide the same surface and flow conditions as in a normal metal piping system. Proper dimensions are provided throughout, so that streamline flow (no‐flow distortion) results, and corrosion and scale formed on the inserts will be the same as that occurring in the metal piping system being tested. Steel, galvanized steel, and soldered copper and copper inserts have been found to provide meaningful corrosion test results by this test method. Figure - A Corrosion Test Specimen (ASTM, 1999) Reference: ASTM (American Society for Testing and Materials): Standard Test Methods for Corrosivity of Water in the Absence of Heat Transfer (Weight Loss Methods), Designation: D 2688 – 94 (Reapproved 1999), West Conshohocken, 1999 CORROSIVE WATER Erik PINTER, 2005 ...
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This note was uploaded on 05/18/2010 for the course FUR WASSE H9640242 taught by Professor Erikrobert during the Spring '05 term at University of the Punjab.

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