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NDMA Removal and Reformation Prevention

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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, as an antioxidant additive for lubricants, and as a softener of copolymers in the rubber industry. It is also 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 part per trillion (ppt) concentration in drinking water. The California Department of Health Services (DHS) has established an action level of 10 ppt.

Orange County Water District (OCWD) detected NDMA in two drinking water supply wells in excess of the 10 ppt action level and in reclaimed water from Water Factory 21 “ treated through lime treatment, recarbonation, and filtration followed by either granular activated carbon (GAC) or reverse osmosis (RO)” in levels exceeding 100ppt. Analysis of NDMA data collected over a period of one year for each unit process at Water Factory 21 indicated that NDMA is not removed by these advanced treatment processes to any appreciable levels. This evaluation also indicated that cellules acetate and thin film composite RO membranes NDMA removal efficiencies are <10% and about 50%, respectively. 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.

Because of its soluble characteristics, NDMA cannot be absorbed by activated carbon and is not removed from water using air stripping. However, UV photolysis and advanced oxidation (UV/peroxide) has been successful. UV destruction pilot tests at OCWD, conducted using flow through pilot scale and full scale low- and medium-pressure UV systems as well as natural sunlight, demonstrated that UV photolysis is effective in destruction of NDMA. UV/peroxide treatment of RO permeate resulted in an electrical energy per order (EEO) in the range of 0.2 to 0.6 kWh/ 1000 gallons for full scale UV systems compared to EEO of 1.5 kWh/1000 gallons or higher for pilot scale systems. This indicates that understanding of the hydraulic behavior of UV systems is critical in sizing the UV oxidation facilities. Hydrogen peroxide addition improved NDMA removal efficiencies and reduces reformation potential after chlorination with free chlorine. Sunlight exposure was very effective and reduced NDMA levels from 500 ppt to <1ppt in three hours.
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Document Type: Research Article

Publication date: 2004-01-01

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