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N-nitrosodimethylamine (NDMA) is a potent carcinogen and historically was associated with the production of rocket fuels until the mid 1970s. It is also used as an antioxidant additive for lubricants, a softener of copolymers in the rubber industry, and is found in trace amounts in cured meat products such as bacon and smoked fish. The additional lifetime cancer risk of 1 in 1,000,000 in humans is estimated to be posed by a 1.4 parts per trillion (ppt) concentration in drinking water. The California Department of Health Services (DHS) has established an interim action level of 20 ppt and is considering a future action level as low as 2 ppt. In water treatment and wastewater treatment plants, most NDMA generating reactions occur between a source of nitrite and a secondary, tertiary or quaternary amine in a mildly acidic solution. Amine sources that have been identified as precursors for NDMA include dimethylamine (DMA) and tetramethylthiuram disulfide (thiram). Polymers (polyelectrolytes) used in water and wastewater treatment as coagulant aids are also a potential amine source. Many herbicides contain the DMA salt. Thiram is used in seed fungicides and animal repellents. Orange County Water District (OCWD) of Fountain Valley, California detected NDMA in two drinking water supply wells in excess of the 20 ppt interim action level and in reclaimed water from Water Factory 21 (WF 21) that was treated through lime treatment, recarbonation, and filtration followed by either granular activated carbon (GAC) or reverse osmosis (RO) in levels exceeding 100 ppt. Analysis of NDMA data collected over a period of one year for each unit process at WF 21 indicated that NDMA is not removed by these advanced treatment processes to any appreciable levels. Chlorination, on the other hand, resulted in formation/reformation of NDMA. As a result, OCWD conducted NDMA destruction and formation/reformation prevention studies and pilot testing for reducing the NDMA levels. This paper presents a summary of NDMA sources, a survey of treatment literature, results of pilot studies for the destruction of NDMA at OCWD, and an evaluation of formation/reformation control options. Includes reference, tables, figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 20File Size: 1 file , 480 KB