Fate of NDMA in Tertiary Water Reclamation Plants

N-nitrosodimethylamine (NDMA) is an emerging contaminant that can be formed from wastewater disinfection using chlorine. The California Department Health Services has set a notification level of 10 ng/L for NDMA due to its carcinogenic potency and mobility in groundwater. This paper summarizes the efforts of the Sanitation Districts of Los Angeles County (Sanitation Districts) on the evaluation of the occurrence and fate of NDMA at Sanitation Districts' water reclamation plants. These plants typically include primary sedimentation, activated sludge process with biological nitrogen removal, secondary sedimentation, media filtration, disinfection using chloramines, and dechlorination before discharge.Bench-, pilot-, and full-scale studies were conducted at two water reclamation plants operated by the Sanitation Districts to evaluate NDMA formation and destruction. Results from these studies indicated: (1) influent NDMA concentrations fluctuate over a wide range; (2) the biological treatment process is capable of removing some influent NDMA; (3) use of chlorinated effluent to prepare cationic polymer solution for application in settling enhancement and foam control results in formation of high levels of NDMA; (4) chloramination increases NDMA concentrations significantly, but chlorination using free chlorine does not; and (5) ultraviolet (UV) disinfection of media filtered secondary effluent can result in 30 to 40% of incidental NDMA destruction.