AWWA ACE63253

The effectiveness of ultraviolet (UV) light irradiation for inactivation of nitrifying bacteria is demonstrated in this study. The destruction of total chlorine and formation of nitrite were evaluated. Bench scale experiments were conducted, in which water with the nitrifying bacteria was passed through a low-pressure UV-lamp. UV-dose was varied by passing water at different flow rates and by covering the portion of the lamp quartz sleeve with the aluminum foil. The approximate UV-dose range was estimated based on lamp specifications, water flow rate, and lamp coverage. UV-irradiated water was ammoniated and stored in the dark bottles in the incubator at 15 and 25ºC for up to three weeks to determine the effective dose and nitrifying bacteria regrowth. A UV dose estimated to be on the order of magnitude of 20 mJ/cm² was optimal to inactivate nitrifying bacteria, minimize total chlorine destruction and nitrite formation. UV light doses reported here should be used only in relative terms; no attempt was made to measure the exact dose. Pilot scale experiments evaluated the feasibility of the UV light for the control of an ongoing nitrification episode in a flow-through pilot water storage tank supplied with chloraminated water. Two application concepts were tested: UV-irradiation of the bulk water; and, UV-irradiation of the water collected at the tank walls with an aquarium squeegee. The water in both cases was recirculated into the nitrifying storage tank. An approximate UV-dose, turnover of UV-irradiated water recirculated through the water storage tank (typically 7 days), and tap water turnover rate through the pilot tank were varied. A limited number of pilot UV experiments conducted were not successful in controlling an on-going nitrification episode. However, pilot tests demonstrated that the UV irradiation of the bulk water slowed down the uptake of ammonia. Several concepts were discussed, which could be tested to evaluate full-scale process feasibility. Includes 5 references, figures.