AWWA ACE91024

This paper presents results of a two-phased pilot test to evaluate two high-rate contact clarifiers and high-rate filters for compliance with the new EPA Surface Water Treatment Rule (SWTR) for turbidity, Giardia (and Cryptosporidium) cyst removal; 2) to determine the oxidant demand of the raw water; and 3) to demonstrate the ability of the processes to achieve disinfection requirements of the new SWTR while meeting a total THM goal of 20 ug/l. Additional tests were run to determine whether disinfection goals could be accomplished in the pre- ozonation process or whether a separate ozonation stage would be required for disinfection, and to determine residual levels of iron, manganese and aluminum in the treated water. The results of the study are discussed under the headings of particle reduction, control of microorganisms, control of trihalomethanes, and production of other disinfection byproducts. The study showed that the high rate treatment process can comply with the SWTR. Ozonation was shown to be effective as a pre-oxidant and as a disinfectant. The study showed that the 20 ug/l THM goal cannot be met if free chlorine is used as the final disinfectant.