Testing of PAA and Sodium Hypochlorite for Wet Weather Disinfection
- Jason Beck PE, Anthony Farina PE, W. James Gellner PE - Hazen and Sawyer
- Brian Clark, Barry Zerkle - City of Sidney, OH
A recent NPDES permit revision for the City of Sidney, OH Wastewater Treatment Plant (WWTP) included E. coli limits for all flows, including any overflows from the Equalization (EQ) Basins during wet weather events. The Sidney WWTP has an annual average capacity of 7.0 mgd and experiences wet weather influent flows as high as 36 mgd. Side by side dose response testing of peracetic acid (PAA) and sodium hypochlorite (hypo) was conducted on a blend of 75 percent secondary effluent and 25 percent raw influent to simulate wet weather flow characteristics. A C×T (effluent residual concentration × contact time) value of 150 mg-min/L was selected for both PAA and hypo to meet the proposed E. coli limits based on dose response testing. Effluent residual and total chemical demand were both 7.5 mg/L for both chemicals resulting in a total chemical dose of 15 mg/L at a contact time of 20 minutes. Hypo was selected for wet weather disinfection based on a cost evaluation (capital and annual chemical costs) that included sodium bisulfite for neutralization for both chemicals.
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