Feasibility of Ultraviolet Disinfection of WWTP Final (Blended) Effluent under Wet Weather Flow Conditions

Ultraviolet light (UV) disinfection has gained tremendous popularity in wastewater disinfection over the traditional chemical disinfection process using chlorine gas and other chlorine compounds for many reasons. Mainly, UV disinfection offers a safe process by eliminating the use of a dangerous gas and eliminates the production of toxic disinfection byproducts. UV also eliminates the need for chlorine residual removal (dechlorination) using another chemical reducing reagent. Thus, UV disinfection replaces two processes and eliminates completely the on-site storage of dangerous chemicals.The City of Warren Wastewater Treatment Plant (WWTP) is evaluating the feasibility of UV disinfection to replace its existing chlorine disinfection process and dechlorination process. A large plan nested in a residential area, Warren WWTP handles, by NPDES permit, 36 MGD of dry weather flow and up to 60 MGD of wet weather flow. The plant is a tertiary treatment facility that employs gravity filtration to achieve a tight NPDES permit effluent limits for BOD5 and ammonia. Because of the significant wet weather flow component, the UV disinfection process has to be carefully evaluated as to its effectiveness. UV light transmission can be a limiting factor to achieve final effluent disinfection permit requirement.The presentation will provide information useful to other treatment plants, particularly those with significant wet weather flow component, considering UV disinfection as a replacement of the traditional chlorine disinfection process. Specifically, the presentation will discuss, among other things, the following :○ Required testing to evaluate the UV transmission under worst case scenario of "blended" final effluent quality○ Various technology of UV disinfection form the perspective of lamp pressure and light intensity○ Impact of the process foot print and retrofit within the existing chlorine contact chamber○ Life cycle cost of the various UV technology (pressure/intensity)○ Impact on the plant hydraulic profile