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Cl exist as NHCl2 +NH2Cl at the end of treatment Smell chlorine in pools (NHCl2 and NH2Cl)Not strong oxidant (about 50 times less efficient than free chlorine but has longer residual effect); prevent bacterial regrowth in the distribution system Ozone Extremely reactive oxidant (more powerful than chlorine)Disinfectant and oxidant Primary disinfectant (cannot maintain a residual)Due to high cost, ozone application is often used for a combination of operations, including disinfection, taste, odour and colour controlophysical Disinfection ultraviolet (UV)unit consists of UV light source enclosed in a sleeve made of quartzwater passes through a flow chamber; UV rays are emitted and absorbed into the stream rays destroy bacteria and inactivate many viruses Limitations may include water hardness, iron and manganese concentrations Filtration Heat Boiling eater inactivates essentially all microorganisms Method is energy intensive Only practical application is when individual users are required to boil their water Physical methods are not acceptable for secondary disinfection as they do not provide a persistent residual oPrimary disinfection – in water treatment plant oSecondary disinfection – in distribution system Disinfection By-Products (DBPs)oChemicals formed when certain disinfectants are added to water oFormed from reactions between strong oxidants (disinfectants) and natural organic matter in the water (e.g. THMs – trihalomathanes)oChemical breakdown of disinfectant (e.g. Chlorite and chlorate)oReactions with inorganics such as bromide (ozonation)find more resources at oneclass.comfind more resources at oneclass.com
oNew standards and testing requirements for othersphased in 2017-2020Arsenic: “The largest Mass Poisoning in History”oBangladesh (more than 100 million people affected)oWHO – max. permissible level for arsenic is 50 ug/l and recommends 10ug/oGroundwater wells oFiltering arsenic: buckets of river sand, pieces of cast iron and charcoal Point-of-use method to purify drinking water oInadequate sanitation increases user exposure to fecal pathogens and indirect exposure through water, food, soil or fliesoPOU treatments variety of technique that individual housholds can use: Ceramic filter, adding bleach, hypochlorate tablets, sunlight treatment, adding packets with flocculant and disinfectant Straining storage/settlement filtration Disinfection Municipal Sewage Treatment of Wastewater Treatment oPrimary treatment remove suspended and floating particles oSecondary treatment Decompose suspended organics oTertiary treatment Dissolved substances, mostly for nutrient N and P removal oHumber wastewater treatment plant Capacity 473,000 m3/day Population of 685,000oRow sewage skimmer in primary sedimentation final sedimentation Wastewater treatment for homes and small communities oHome treatment o