AWWA ACE54301

The formation of nitrite (NO2-) during ultraviolet (UV) irradiation of laboratory water containing nitrate was studied as a function of irradiation wavelength, pH, and natural organic matter (NOM) concentration to determine how these parameters affect NO2-yields during UV disinfection of drinking water with polychromatic, medium-pressure (MP) Hg lamps. Yields of NO2- increase with decreasing wavelength and are higher at pH 8 than at pH 6. In the absence of NOM, the NO2- production rate decreases with time, but this effect can be eliminated or reversed by low or high concentrations of NOM, respectively. Also, addition of NOM leads to increased overall NO2- yields. When the full spectrum MP Hg lamp was used to deliver germicidally relevant UV doses, NO2-concentrations remained well below the US maximum contaminant level (MCL) of 1ppm-N, even with nitrate initially present at its MCL of 10 ppm-N. Under current US regulations, NO2- formation should not pose a significant problem for water utilities during UV disinfection of drinking water with MP Hg lamps. Includes 20 references, figures.