You are here:
Dual-Disinfection of Wastewater Effluent with Combined Peracetic Acid (PAA) and Sodium Hypochlorite Treatment: A Full-Scale Pilot Study at Mill Creek Plant
Citation:
Namboodiri, V. AND A. Garg. Dual-Disinfection of Wastewater Effluent with Combined Peracetic Acid (PAA) and Sodium Hypochlorite Treatment: A Full-Scale Pilot Study at Mill Creek Plant. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-21/000, 2021.
Impact/Purpose:
This detailed full-scale field study evaluated the effectiveness of combining Peracetic acid (PAA) and chlorination for municipal secondary effluent disinfection. Preliminary full-scale treatment studies using this dual-disinfection approach show that this approach is very effective for municipal wastewater disinfection. Major advantages of this novel method are the low residual oxidant content, better treatment efficiency and low environmental impact compared to individual treatments. This first full-scale field study on Combining PAA with chlorination has the potential to lower chlorine usage by reducing chlorinated disinfection byproducts in the discharge and avoiding the need for an expensive dechlorination step. PAA additions to the existing municipal wastewater treatment train requires only very low capital investment. Economic savings can be expected from the reduction of capital expenses needed for dechlorination and chlorination storage needs. In addition, PAA can be used to support several municipal facilities that uses chlorination to achieve any changing NPDES regulatory requirements without increasing chlorination.
Description:
In 2018, while renewing the permit for Metropolitan Sewer District of Greater Cincinnati’s (MSDGC) Mill Creek Treatment Plant (MCTP), the Ohio Environmental Protection Agency (OEPA) made key changes. These changes included replacing fecal coliforms with E. coli as the monitoring biomarker for secondary effluent disinfection during the recreational season (May 1– October 31). In addition, the weekly and monthly E. coli limits were set to 240 colony-forming units (CFU)/100mL and 126 CFU/100mL, whereas in the old permit limits were 400 CFU/100mL and 200 CFU/100mL respectively. The total maximum oxidant residual (0.33 mg/L) remained unchanged in the new permit. These changes in the permit prompted MSDGC to reevaluate its capabilities and assess challenges in meeting new permit requirements. A review of the E. coli data collected during the fall of 2018 at MCTP revealed that under current treatment conditions, MSDGC would consistently fail to meet the revised permit’s weekly and monthly E. coli limits. One solution was to increase chlorination and dechlorinate after treatment to keep the total oxidant level below 0.33mg/L. The dechlorination step would need new contact tanks and sodium bisulfate addition, which could cause sodium pollution. The construction of new tanks would require large capital investments (20-30 million dollars). This prompted MSDGC to collaborate with USEPA to search for new and alternative disinfection methods, including the use of peracetic acid (PAA). This report describes dual-disinfection, the process of combining two distinct disinfectants to achieve synergistic results. We found combining PAA with sodium hypochlorite is more effective at inactivating E. coli than either PAA or sodium hypochlorite on their own. This novel approach has achieved a greater degree of E. coli inactivation while keeping the oxidant residual below 0.33 mg/L. The use of low doses of PAA and NaOCl in dual disinfection strategy can reduce the cost of treatment while helping the plant stay in compliance.