Application of a Medium Pressure UV System for the Treatment of N-Nitrosodimethylamine (NDMA)
N-nitrosodimethylamine (NDMA) was first detected in 1990 as a problem pollutant in drinking water wells at levels as high as 3,000 ppt in Elmira, Ontario, Canada. The waste from a large chemical plant over many years had led to the contamination of the drinking water wells for the community. After extensive evaluation and testing, it was determined that UV photolysis was the most effective treatment method which led to the installation of a Calgon 270 kW Rayox® UV system in 1991. The system has been continuously treating water to this day. At about the same time, NDMA was found in the drinking water on an Indian reserve in Ontario, and a similar UV system was installed to remove NDMA from that water. Since then NDMA has been detected as a pollutant in ground waters, surface waters, industrial effluents and wastewaters in many jurisdictions. Many sources have been identified, including chemical plants that manufacture pesticides and herbicides, rubber manufacturing plants, rocket fuel manufacturing plants and wastewater treatment plants.
Recently there has been considerable concern in California about the detection of NDMA in drinking water feed wells at levels as high as 900 ppt. NDMA was found to be a carcinogen in animals and assessed as a Class 1 carcinogen by the USEPA. It is currently listed as a priority pollutant on the US EPA National Priorities List. California has set an 'action level' of 20 ppt for NDMA and treatment systems are required to treat to the detection limit of 2 ppt.
NDMA is often produced as a byproduct in the industrial use of dimethylamine (DMA). DMA is a semi-volatile organic chemical that is soluble in water and has been commercially used for several decades. For example, from the mid 1950's till April, 1976, it was manufactured and used as an intermediate in the production of 1,1-dimethylhydrazine, a storable liquid rocket fuel that contained approximately 0.1% NDMA as an impurity. In addition 1,1-dimethylhydrazine oxidizes to produce NDMA. DMA is also used for the inhibition of nitrification in soil, as a plasticizer for rubber and polymers, as a solvent in the fiber and plastics industry, an antioxidant, a softener of copolymers, and as an additive to lubricants. DMA is used in rubber processing where it reacts with nitrite to produce NDMA which can be present as a contaminant in the final rubber product.
N-nitrosodimethylamine is also present in many other products such as tobacco smoke and a variety of foods such as cheeses, soybean oil, canned fruit, various meat products, bacon, various cured meat, cooked ham, milk, fish and fish products, apple brandy, and other alcoholic beverages including beer.
NDMA is thermally stable in aqueous solutions, and conventional methods such as biological treatment, air stripping, and activated carbon are not effective for NDMA treatment. Since NDMA is photochemically labile, advanced oxidation technologies, based on irradiation with ultraviolet (UV) light, have been promoted for the removal of NDMA in contaminated waters. Direct UV photolysis readily destroys the compound and has been used commercially for over 10 years for the treatment of NDMA in contaminated groundwater.
In direct UV photolysis, a high powered lamp emits UV radiation through a quartz sleeve into the contaminated water. The photons of light are absorbed by NDMA resulting in breaking of the N-N bond in the molecule. The destruction of NDMA is therefore dependent upon the amount of UV light which is applied to the contaminated water and the UV wavelengths emitted by the lamp.