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Dual Disinfection of Wastewater Effluent With Peracetic Acid (PAA) and Sodium Hypochlorite: A Full Scale Pilot Study
Citation:
Garg, A., V. Namboodiri, S. Islam, M. Nemade, B. Murugesan, A. Ouermi, AND B. Smith. Dual Disinfection of Wastewater Effluent With Peracetic Acid (PAA) and Sodium Hypochlorite: A Full Scale Pilot Study. WEFTEC 2019, Chicago, IL, September 21 - 25, 2019.
Impact/Purpose:
Peracetic acid(PAA) is an attractive alternative to chlorination can alleviate certain permit concerns such as high levels of DBPs, effluent toxicity, high total dissolved salts and quenching agent needs. Many utilities in US are currently interested in PAA treatment to reduce/eliminate the use of chlorination/ultraviolet (UV) and also to improve treatment efficiency. Combining PAA and chlorination disinfection approaches (Dual-disinfection) take advantages of each technologies such as cost reduction, improved treatment efficiency, elimination of post chlorine quenching treatment and less permit violations. This practical treatment approach may find application in future municipal wastewater treatment in all over US.
Description:
New NPDES permit for the City of Cincinnati’s Mill Creek wastewater treatment plant (MCTP) for the summer months limits the weekly and monthly geometric average for E. coli at 240 and 126 CFU/100 mL, respectively. In order to achieve this goal cost effectively a dual-disinfection approach was developed and is being implemented. At present, the plant uses sodium hypochlorite for disinfection but with the new permit limits existing hypochlorite dosing/outfall contact systems may not be adequate. Significant addition of new contact tanks and use of a quenching agent to eliminate chlorine residuals creates need for large infrastructural investment. A dual-disinfection of wastewater approach was developed and evaluated in our lab and tested at full scale field pilot level. In this study, secondary effluent was pre-treated with peracetic acid (PAA) before chlorination to assess the treatment efficiencies of PAA and hypochlorite individually and in combination to inactive E. coli to meet new permit regulations.For the bench scale study, samples of secondary effluent before disinfection were collected from the plant and treated with PAA (0.75 – 1.5 mg/L) or hypochlorite (1.0 – 2.5 mg/L) individually or in combination, either simultaneously or sequentially. The sequential addition of PAA and hypochlorite was found to be the most effective disinfection method, with a 2.79 log reduction after twenty minutes and a 3.02 log reduction after forty minutes.A full-scale pilot system was installed to investigate the treatment efficiency of dual disinfection scenario using PAA in combination with sodium hypochlorite. The pilot study supported the lab studies that sequential addition of low doses of PAA and NaOCl provides better disinfection with low residual compared to individual disinfectant at higher doses. This study demonstrates a novel way to disinfect wastewater by combining two distinct oxidizers PAA and hypochlorite to achieve the new NPDES permit compliance in a cost-effective way.