WATER PLANT OPERATOR TRAINING PROGRAM

Factors influencing THM formation temperature pH precursor concentration (TOC, UV-absorbence) chlorine dose and residual contact time THM Reduction Strategies Option Advantages Potential Disadvantages Capital Costs THM Levels Comments 1. Chlorine deferral           a) post sedimentation simple slime disinfection zebra mussels low lower little change to current operating procedures will be required chlorine contact tanks may be necessary b)post filtration simple slime / mudballs disinfection contact time zebra mussels low to med lower little change to current operating procedures will be required chlorine contact tanks will be necessary 2. Change disinfectant           a) chlorine dioxide simple health effects of DBPs may be greater than for THMs zebra mussels low very low disinfection by-products may be subject to future regulations the effect on zebra mussels is not yet clear potential foul odour b)ozone   health effects of DBPs may be greater than for THMs complex technology high operating costs zebra mussels high very low disinfection by-products may be subject to future regulations the feasibility for zebra mussel control is not clear at this time c)pre-chlorination simple disinfection contact time zebra mussels disinfection compromised? med low large chlorine contact tanks will be necessary d)post-chlorination simple more persistent residual in the distribution system post-chlorine dosage may be lower at present possible nitrification in the distribution system low lower   3. Powdered activated carbon simple also removes other organics generates large amount of waste (dosage dependent) operating costs may be high low low carbon is added during flocculation on an "as needed basis" and is used only once will prompt immediate need for waste treatment facilities 4. Granular activated carbon           a)biologically active SIMPLE ALSO REMOVES OTHER ORGANICS OPERATING COSTS MAY BE HIGH MED low carbon will be replaced / regenerated periodically not biologically active simple also removes other organics operating costs may be high med low carbon will be replaced / regenerated periodically (more often than in 4a) 5. Aeration post-filtration also removes other visible organics complex high low moves an undesirable substance from water to air