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

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

4. 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

6. Parts of Water Treatment Coagulation Flocculation Sedimentation Filtration Disinfection

7. Methods of Disinfection Heat Boiling Radiation UV light Chemical Chlorine Alternatives

8. Factors Effecting Chlorination ›Concentration ›Contact Time ›Temperature ›pH ›& Foreign Substance concentration

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

12. Chlorine Reactions Cl 2 + H2OH2OHOCl + + H+H+ Cl - HOClH+H+ + ClO - Means that in solution it remains in Equilibrium Hypochlorous acidHydride ionHypochlorite ion ChlorineWaterHypochlorous acidChloride ionHydride ion

13. Chlorine Reactions Oxidation –Cleaves molecules Substitution –Replaces elements in a molecule RCHO + HOCl  RCO 2 H + H + + Cl - OH * + HOCl  *CHCl 3 + other Products Figure 5 (Johnson, 1983) Resorcinol Chloroform

15. Disinfection By-Products Most of the research and concern is about THMs THMs (Trihalomethanes) –Chloroform (CHCl 3 ) –Bromodichloromethane (CHBrCl 2 ) –Dibromochloromethane (CHBr 2 Cl) –Bromoform (CHBr 3 )

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

17. THM Precursors Source Examples 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) Table 2 (Johnson, 1983)

18. Alternatives to Chlorine Ozone –O3–O3 Chlorine Dioxide –ClO 2 Chloramines –NH 2 Cl,NHCl 2, NH 4 Cl

19. Chlorine Strong disinfectant Lasting “Residual” THM Production Treated water is “toxic” Ozone Powerful Oxidant Lacks “residual” Bromate formation Need secondary disinfectant, can be expensive Chlorine Dioxide Good disinfectant Must be prepared “on-site” by products: Chlorate and Chlorite Lacks “residual” ClO 2 presence reduces THM formation Chloramines Weak disinfectant Little THM Production Treated water is “toxic”

20. THM Control Methods Potassium Permanganate (KMnO 4 ) –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

21. 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

22. THE END