NDMA DESTRUCTION AND DISINFECTION WITH UV IRRADIATION FOR INDIRECT POTABLE REUSE IN CALIFORNIA

This paper presents the experience of two Southern California water agencies in addressing concerns with N-nitrosodimethyamine (NDMA) in recycled water for indirect potable reuse. The West Basin Municipal Water District (WBMWD) owns and operates 7.5 million gallons per day (mgd) of advanced water treatment facilities for indirect potable reuse via injection into Los Angeles County's West Coast Basin Barrier Project. The Orange County Sanitation and Water Districts (OCSD and OCWD, respectively) operate wastewater treatment and reclamation facilities in Fountain Valley, California, including Water Factory 21 (WF-21), which recycles approximately 5 mgd, also via indirect potable reuse in OCWD's seawater intrusion barrier. OCWD is also designing a major new advanced treatment facility, the Groundwater Replenishment (GWR) Project, as a joint project with OCSD, that will replace WF-21 and produce 70 mgd of high-purity recycled water from secondary effluent now discharged to the Pacific Ocean. This paper presents results of WBMWD and OCWD evaluations of alternatives for meeting the goals of the California Department of Health Services (DHS) with respect to pathogen reduction and concentrations of NDMA in the recycled water, and summarizes design criteria developed for disinfection and NDMA destruction using ultraviolet (UV) irradiation. While both OCWD/OCSD and WBMWD have also been actively investigating sources of NDMA in the wastewater treatment processes and related mitigation, this paper is limited to investigation of UV irradiation for NDMA destruction and disinfection.