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Water Treatment: Disinfection Processes

Water Treatment: Disinfection Processes. Current Technology vs. Alternatives. Water Treatment. Why?. To minimize the amount potentially harmful organisms in the water. To make the water aesthetically acceptable (look and taste good). Regulations. Safe Water Drinking Act

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Water Treatment: Disinfection Processes

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  1. Water Treatment: Disinfection Processes Current Technology vs. Alternatives

  2. WaterTreatment Why? To minimize the amount potentially harmful organisms in the water To make the water aesthetically acceptable (look and taste good)

  3. Regulations • Safe Water Drinking Act • 1979, amended 1986 • Standard techniques • Sets Maximum Contamination Levels for THMs (100 ppm) • Surface Water Treatment Rule (SWTR) • 1989 • required disinfection and filtration of surface water sources to remove pathogens • Disinfection/Disinfection By-Product Rule • lowers the MCL of THMs to 80 ppm

  4. Parts of Water Treatment • Coagulation • Flocculation • Sedimentation • Filtration • Disinfection

  5. MethodsofDisinfection • Heat • Boiling • Radiation • UV light • Chemical • Chlorine • Alternatives

  6. Factors Effecting Chlorination • Concentration • Contact Time • Temperature • pH • & Foreign Substance concentration

  7. Chlorine • Strong Disinfectant • Lasting “Residual” • THM Production • Treated water is “toxic”

  8. Chlorine Reactions Cl2 H2O HOCl H+ Cl- + + + Chlorine Water Hypochlorous acid Hydride ion Chloride ion HOCl H+ ClO- + Hypochlorous acid Hydride ion Hypochlorite ion Means that in solution it remains in Equilibrium

  9. Chlorine Reactions • Oxidation • Cleaves molecules • Substitution • Replaces elements in a molecule RCHO + HOCl RCO2H + H+ + Cl- OH * + HOCl  *CHCl3+ other Products OH Chloroform Resorcinol Figure 5 (Johnson, 1983)

  10. Disinfection By-Products • Most of the research and concern is about THMs • THMs (Trihalomethanes) • Chloroform (CHCl3) • Bromodichloromethane (CHBrCl2) • Dibromochloromethane (CHBr2Cl) • Bromoform (CHBr3)

  11. THM Formation Equation Precursors (humic substances and Bromide) Free Chlorine + Other Halogenated & non- halogenated By-Products THMs +

  12. Plants Algae Man Fulvic and Humic Acid Degradation Products like resorcinol. Plant pigments Algae Biomass Amino acids (i.e.. uracil) Industrial Effluents (i.e.. Phenols) THM PrecursorsSource Examples Table 2 (Johnson, 1983)

  13. Alternatives to Chlorine • Ozone • O3 • Chlorine Dioxide • ClO2 • Chloramines • NH2Cl,NHCl2, NH4Cl

  14. Chlorine Chloramines • Weak disinfectant • Little THM Production • Treated water is “toxic” • Strong disinfectant • Lasting “Residual” • THM Production • Treated water is “toxic” Chlorine Dioxide Ozone • Powerful Oxidant • Lacks “residual” • Bromate formation • Need secondary disinfectant, can be expensive • Good disinfectant • Must be prepared “on-site” • by products: Chlorate and Chlorite • Lacks “residual” • ClO2 presence reduces THM formation

  15. THM Control Methods • Potassium Permanganate (KMnO4) • Strong oxidant • Effective for taste and odor problems • oxidizes iron and manganese • controls some THM precursors • Enhanced Coagulation • Modifications of conventional treatment like pH and Coagulant dose • Performs better in TOC removal than most other methods

  16. Conclusions • Regulations result from ongoing research • Changes in treatment occur when regulations change • Any kind of “treatment” is going to have some kind of side effect, whether it be by-products or limitations in efficiency • Which of the side effects is worse? Until everything about each possible alternative is known, the true answer to that question will remain definitively unanswered. • Chlorine appears to be the most well rounded choice for disinfection, and will most probably remain the main disinfectant for most treatment plants

  17. THE END

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