Managing Microbial Contamination in Urban Watersheds

Abstract

This paper describes different approaches for controlling pathogen contamination in urban watersheds for contamination resulting from point or diffuse sources. Point sources of pathogens can be treated by a disinfection technology of known effectiveness, and a desired reduction of microbial concentration is usually achieved. Diffuse sources of pathogens are commonly managed with the use of structural and nonstructural best management practices (BMPs). The primary function of BMPs is reduction of flow volume, sediment, and/or nutrients, while reduction of pathogens is a secondary function and not always quantified. Disinfection technologies for pathogen control are presented here for point sources resulting from urban wet-weather flow (WWF) such as combined sewer overflow (CSO), sanitary sewer overflow (SSO), and stormwater, as all components of WWF carry significant loads of fecal and pathogen contamination that should be prevented from entering an urban receiving water body. Further, since issuance o f the National CSO Control Policy, CSO has become the most frequently disinfected and studied type of urban WWF. Thus, discussion of WWF disinfection is largely based on studies conducted on CSO. However, disinfection of SSO and of collected and confined stormwater is feasible, though seldom implemented. Known implementation examples of disinfecting CSO, SSO, stormwater, and dry-weather runoff are discussed. BMPs, structural and nonstructural, are a set of practices to control and manage the quality and quantity of urban runoff, a diffuse source. There are two basic types of structural BMPs. One BMP type requires erection of a structure to control stormwater quality, and the second BMP type requires management of the sewerage system. Examples of BMPs requiring a structure are dry and wet ponds, constructed