Implementing Local Limits for the Control of WWTP Effluent Ultraviolet Transmittance

Local limits are developed to implement site-specific prohibitions to protect against the discharge of pollutants at a quantity or rate that may cause pass-through or interference at (or otherwise detrimentally impact) a POTW. 40 CFR Part 403 requires certain POTWs to develop local limits when they develop a pretreatment program and to maintain and enforce these limits for pollutants of concern (POCs). Ultraviolet light is increasingly being used as a means for disinfecting municipal wastewater treatment plant effluent. Compounds responsible for lowering effluent ultraviolet transmittance (UVT) can interfere with UV disinfection and thus may be considered to be POCs appropriate for control through the use of local limits.In this paper, several possible approaches for developing local limits for UVT are described. Actual local limits for UVT developed for industrial discharges for two POTWs in Washington State, and initial monitoring results for industries from one City, are provided.