Removal and Destruction of NDMA and NDMA Precursors during Wastewater Treatment
Year Released: 2006
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board
Total Investment: $358,500 (Cash: $350,000, In-Kind: $8,500)
Principal Investigators: Dr. Michael Kavanaugh, Malcolm Pirnie, and Dr. David Sedlak, UC Berkeley
N-nitrosodimethylamine (NDMA) is a probable human carcinogen with a California drinking water notification level of 10 ng/L. In response to growing scrutiny of NDMA impacts, wastewater utilities that are practicing water reuse may need to evaluate NDMA sources, formation, removal and advanced treatment processes specific to NDMA in order to reliably and cost-effectively reduce concentrations in the final product water.
Goals and Objectives
The three-year project investigates the formation and removal of NDMA and NDMA precursors during wastewater treatment at facilities where indirect potable reuse is practiced. The project objectives were:
- To assess the importance of industrial sources of NDMA and NDMA precursors entering wastewater treatment plants.
- To understand the fate of NDMA precursors and NDMA during conventional treatment processes.
- To understand NDMA formation during conventional and advanced treatment.
- To select and validate a model to predict NDMA destruction using UV technology.
- To communicate research results to water utility personnel and other environmental professionals.
Composite samples were collected from seven wastewater treatment facilities in a range of settings (<2% to 18% industrial discharges), trunklines and industrial discharges to assess the importance of industrial sources, activated sludge treatment, chloramination, microfiltration (MF), reverse osmosis (RO) and UV treatment on NDMA and NDMA precursor concentrations. The benefits of pre-forming monochloramines prior to addition to wastewater were examined at pilot-scale. Samples were collected from six non-potable reuse facilities to survey NDMA occurrence and conduct laboratory studies quantifying the effect of chloramine dose and NDMA precursor concentration on NDMA formation. A theoretical photolysis model was developed to predict electricity requirements as a function of water quality, reactor configuration, and presence of H2O2. Predictions were compared with results from a pilot-scale UV system.
Findings and Conclusions
The findings presented in this report are significant to the water industry. The information provides utilities practicing water reuse with a scientific framework for managing NDMA at wastewater treatment plants and assessing the need for additional testing, potential improvements to existing treatment processes, and the need for advanced treatment.
This report provides utilities practicing indirect potable reuse with a scientific framework for managing NDMA and assessing the need for additional testing, improvements to existing treatment processes, and the need for advanced treatment. Advanced MF/RO/UV treatment effectively removes NDMA and NDMA precursors. Utilities without advanced treatment can reduce NDMA effluent concentrations via source control measures; avoiding chloramination (i.e., practicing nitrification prior to chlorine addition); pre-forming monochloramine by mixing chlorine, then ammonia, into a dosing tank; lowering chloramine dose without compromising the system’s ability to meet microbial targets; or using an alternative disinfection process such as UV treatment.