UV Enhanced Chlorination of Sewage against "Tailing" Phenomenon

Combined disinfection with UV radiation and chlorination was investigated to reduce the tailing extent in chlorination of secondary effluent. Impacts of exposure sequences to UV and chlorination, pH, dosage of chlorine and UV dose on kinetic curves of E. coli was evaluated. Suspended solids significantly affect the extent of "tailing" phenomenon. Reduction of SS considerably increased the log-kill in tailing region. Combined disinfection with UV radiation and chlorination substantially increased the disinfection rate by 1.08-1.25 times in fast-order region, and consequently increased the log-kill by 2-2.5 level in tailing region. The synergistic effects of combined disinfection with UV radiation and chlorination were confirmed. UV-HOCl sequence resulted in higher inactivation rate than HOCl-UV sequence. Lowering pH and/or increasing chlorine dosage magnified the enhancements in first-order disinfection rate, and shortened the starting time of tailing region. Variation in UV dose had no significant effects on starting time of tailing region.