WATER ENVIRONMENT RESEARCH FOUNDATION PROJECT 00-HHE-6 IDENTIFYING AND COMMUNICATING THE BENEFITS AND RISKS OF DISINFECTING WET WEATHER FLOWS

The primary objective of this project was to identify and communicate the benefits and risks of disinfecting wet weather flows by evaluating available disinfection technologies and identifying disinfection by-products and their potential risks to aquatic and human life. A decision-making framework was developed that could be used as a model to guide combined sewer overflow (CSO) sanitary sewer overflow (SSO) and stormwater (SW) disinfection control policies.This project was implemented as a case study in collaboration with the Onondaga County Department of Water Environment Protection (Syracuse, NY). A literature review was completed that identified appropriate disinfection technologies and the associated disinfection by-products. A disinfection demonstration was conducted to verify findings of the literature review and fill data gaps. The data collected during this project were used by local stakeholders to select the most appropriate technologies. Information regarding the benefits and risks of disinfecting wet weather flows was also presented to the public during a public workshop.Chlorination/dechlorination, chlorine dioxide, ozone and UV were deemed to be the most appropriate technologies for disinfection of wet weather flows and consequently they were piloted during the disinfection demonstration. All four technologies achieved the U.S. EPA's bacteria criteria objectives. Ozone and UV did not produce residuals or by-products and did not result in effluent aquatic toxicity as measured through WET testing. Chlorination/dechlorination and chlorine dioxide did produce residuals and disinfection by-products including THMs, HAAs, chlorite and chlorate. With the exception of chlorite, these by-product concentrations were less than drinking water standards. Chlorination/dechlorination and chlorine dioxide did result in effluent aquatic toxicity as measured through WET testing, but the toxicity appeared to be related to residual chlorine in the case of chlorination/dechlorination and residual chlorine dioxide and chlorite in the case chlorine dioxide. Residuals can easily be controlled through proper dechlorination in a full-scale application. The chlorite was a by-product of the particular chlorine dioxide production method; this could be avoided by a generation method that produces a chlorite-free product, which would be more appropriate for a full-scale application.Based on findings from the literature review and disinfection demonstration, hazards associated with wet weather flow disinfection appear low, but the potential for public opposition can be high. Therefore proper communication planning is required to include stakeholders in the decision-making process as well as to perform public outreach. Stakeholders were included throughout the project through workshops and a public