The Role of High Rate Treatment in Addressing Wet Weather Flows

Many municipalities are faced with major capital projects to mitigate the impact of wet weather overflows on receiving waters. Frequently, the costs and effectiveness of removing rain derived infiltration/inflow (RDI/I) or conveying and treating peak flows is not practical. The result has been a shift toward storage and/or treatment of excess flows and discharge to receiving streams. The focus of this paper is on the role of High Rate Treatment (HRT) as a tool to control the impacts on receiving streams caused by sanitary or combined sewer overflows (SSO, CSO).While many municipalities are considering treatment options, the development of appropriate design standards has varied significantly and has been inconsistently implemented as a result of varying interpretation by state and federal regulatory authorities. Many facilities have been constructed under the auspices of pilot facilities with a variety of unit processes over a wide range of design flows.This paper discusses three key issues associated with HRT:Current interpretation of several State and USEPA Regional regulatory agencies regarding the appropriateness of HRT for CSO and SSO applications.The performance results of several constructed CSO and SSO HRT Facilities that have operating experience.The role of HRT in future applications.