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Use of pulsed‐UV processes to destroy NDMA

Bench‐scale experiments were conducted to determine the effectiveness of using pulsed‐ultraviolet (UV) irradiation and pulsed‐UV/hydrogen peroxide (H2O2) processes to destroy N‐nitrosodimethylamine (NDMA). The effects of various UV and H2O2 dosages and source waters, as well as nitrate (NO3–) and initial NDMA concentrations, were investigated as control parameters for both completely mixed batch reactor and continuously stirred tank reactor tests. The presence of compounds that interfere with UV light (e.g., NO3–) and the formation of total trihalomethanes after pulsed‐UV treatment were also studied. Pulsed‐UV technology was highly effective for destroying NDMA. The pseudo–first‐order rate constants were calculated to be in the range of 1.4 to 12.2 min–1. This technology offers other benefits (e.g., disinfection) and can be applied directly to drinking water treatment. However, potential concerns in pulsed‐UV photolysis of NDMA include (1) the formation of undesirable chemicals as reaction intermediates and (2) possible reformation/regeneration of NDMA after chlorination of pulsed‐UV–treated effluent. Pulsed‐UV with a small amount of H2O2 could be used to control the reaction by‐products and to inhibit the reformation of NDMA by using hydroxyl radicals generated during an advanced oxidation process. In contrast, pulsed‐UV with a larger amount of H2O2 could inhibit NDMA decay by direct photolysis.