Impact of hydrogen peroxide on nitrite formation during UV disinfection

One concern with UV disinfection of water is the production of nitrite when polychromatic UV sources are utilized. Based on previous work, it was hypothesized that a small addition of hydrogen peroxide (H2O2) may be useful in controlling nitrite during UV disinfection. However, it was found that H2O2 addition (5 or 10 mg/L) during polychromatic UV irradiation of drinking water at doses used for disinfection significantly increases the levels of nitrite produced relative to solutions without H2O2. Enhancement rates ranged from approximately 15% to 40% depending upon pH and H2O2 concentration; the relative increase in the NO2- yield was greater at pH 6.5 than at pH 8.3. The observed effects are tentatively ascribed to a combination of enhanced superoxide production and increased hydroxyl radical scavenging when H2O2 is added. These results indicate that H2O2 cannot be used to control nitrite production during UV disinfection and that enhanced nitrite formation will occur if H2O2 is added during UV water treatment to achieve advanced oxidation of contaminants.