Recently there has been considerable concern in California about the detection of N-nitrosodimethylamine (NDMA) in drinking water at levels as high as 900 ppt. NDMA was found to be a carcinogen in animals and assessed as a Class 1 carcinogen. 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.
NDMA is thermally stable in aqueous solutions. Conventional methods such as biological treatment, air stripping and activated carbon are not effective for NDMA treatment. NDMA is photochemically labile, so advanced oxidation technologies that are 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 contaminated groundwater.
In this paper, the selection and scale-up considerations for UV systems designed to destroy NDMA are reviewed. A fundamental part of UV system selection involves an evaluation of medium pressure and low pressure UV systems. The differences between medium pressure and low pressure systems are discussed and system costs are compared.