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The effectiveness of ultraviolet (UV) light irradiation for inactivation of nitrifyingbacteria is demonstrated in this study. The destruction of total chlorine and formation of nitritewere evaluated. Bench scale experiments were conducted, in which water with thenitrifying bacteria was passed through a low-pressure UV-lamp. UV-dose was varied bypassing water at different flow rates and by covering the portion of the lamp quartz sleevewith the aluminum foil. The approximate UV-dose range was estimated based on lampspecifications, water flow rate, and lamp coverage. UV-irradiated water was ammoniatedand stored in the dark bottles in the incubator at 15 and 25C for up to three weeks todetermine the effective dose and nitrifying bacteria regrowth. A UV dose estimated to beon the order of magnitude of 20 mJ/cmsup2/sup was optimal to inactivate nitrifying bacteria,minimize total chlorine destruction and nitrite formation. UV light doses reported hereshould 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 ongoingnitrification episode in a flow-through pilot water storage tank supplied withchloraminated water. Two application concepts were tested: UV-irradiation of thebulk water; and, UV-irradiation of the water collected at the tank walls with anaquarium squeegee. The water in both cases was recirculated into the nitrifying storagetank. An approximate UV-dose, turnover of UV-irradiated water recirculated through thewater storage tank (typically 7 days), and tap water turnover rate through the pilot tankwere varied. A limited number of pilot UV experiments conducted were not successfulin controlling an on-going nitrification episode. However, pilot tests demonstrated thatthe UV irradiation of the bulk water slowed down the uptake of ammonia. Severalconcepts were discussed, which could be tested to evaluate full-scale process feasibility. Includes 5 references, figures.

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Edition: Vol. - No. Published: 06/01/2006 Number of Pages: 16File Size: 1 file , 460 KB