Ch3_1 disinfection

Ch3_1 disinfection - Chapter 3-1 Disinfection s s Water or...

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Chapter 3-1 Disinfection Water or wastewater processes for controlling microbial contaminants to prevent the transmission of waterborne disease through the infection by pathogenic microorganisms. Necessity of disinfection (disinfection credits): Giardia lamblia Removals Virus Removals Filter Process Maximum Turbidity (NTU) (log)  (%)  (log)  (%)  Conventional: coagulation, flocculation, sedimentation, rapid rate (granular) filtration 0.5 2.5 99.3 2.0 99.0 Direct filtration: coagulation, rapid rate (granular) filtraton 0.5 2.0 99.0 1.0 90.0 Slow sand filtration 1.0 2.0 99.0 2.0 99.0 Diatomaceous earth filtration 1.0 2.0 99.0 1.0 90.0 Total (including disinfection) -- 3.0 99.9 4.0 99.99 Source:EPA, 1989.
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Particulate Impurities in Water 0.1 0.001 0.01 100 10 1.0 0.0001 Size ( μ m) Flocculated particles Dissolved particles Suspended particles Colloids Protozoan Bacteria Algae Organic molecules Dissolve ions Viruses SETTLING Enough? Sand Filter Post-filtered particles Need Disinfection
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Disinfection (cont.) Concept: Inactivation of microorganisms by physical or chemical processes Physical processes: Heat, salinity, ultrasonic, ultraviolet (UV)-radiation and gamma-radiation. Chemical processes: Chlorination, Chloramination, Ozonation, and other oxidants. Sterilization Disinfection Sterilization: Complete killing all forms of life. Disinfection: Inactivating pathogenic microorganisms. It is not necessarily to kill pathogenic microorganisms. Some bacteria are still respiring after disinfection while the bioassay indicates no detectable one.
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Disinfection (cont.) Indicator organism: Serving as a surrogate to indicate the water quality with respect to the relative quantities of all forms of pathogens. Drinking water standard In the WHO standard (the HK standard), the maximum acceptable concentrations of indicators for water are: Total coliform bacteria (Total coli): 0~10 / 100 mL of water or Escherichia coli ( E. coli ): 0 / 100 mL of water. To be used: Giardia, Cryptosporidium, and coliphage. Table 6.2 Virus-Coliform Ratios for Sewage and Polluted Surface Water Virus Coliform Virus/Coliform Ratio Sewage 500/100 mL 46 × 10 6 /100 mL 1:92,000 Pollutated surface water 1/100 mL 5 × 10 4 /100 mL 1:50,000 Source : Robeck et al. (1962) How?
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Disinfection (cont.) Characteristics of ideal disinfectants: Capable of inactivating; Non-toxic to humans, domestic animals, or aquatic species; Should not generate harmful disinfection by-products (DBPs); Easy and safe to store, transport, and dispense.
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This note was uploaded on 09/13/2011 for the course CIVL 242 taught by Professor Gh during the Fall '09 term at HKUST.

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Ch3_1 disinfection - Chapter 3-1 Disinfection s s Water or...

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