Evaluating Peracetic Acid for Wet Weather Disinfection at the Metropolitan Sewer District of Greater Cincinnati Wet Weather Facilities

Metropolitan Sewer District of Greater Cincinnati (MSDGC) has implemented a program to identify and evaluate new, emerging technologies for the management and control of combined sewer overflows (CSOs). In 2016 and 2017, MSDGC, with technical and logistical support from Hazen and Sawyer, evaluated peracetic acid (PAA) for high-rate disinfection use in wet weather treatment applications. The evaluation included bench scale testing at two (2) wet weather flow sites, and a conceptual evaluation for full-scale implementation. The focus of the study was MSDGC’s SSO 700 Storage and Treatment Facility. The facility includes three storage tanks followed by a ballasted flocculation high rate treatment system and ultraviolet disinfection. Overflows from the storage tank are blended with treated effluent prior to discharge. Bench scale testing was performed to evaluate the PAA doses and contact times required to provide a three to four log reduction in Escherichia coli in storage tank overflows. Based on bench scale testing, a CT value of approximately 150 mg/L * minutes was found to effectively and consistently achieve the identified disinfection target.