Inactivation of microorganisms in drinking water using combined treatment with ultraviolet and sodium persulfate

This paper examines the combined UV irradiation and sodium persulfate treatment for disinfection of microorganisms in drinking water. By comparison, the effect of UV irradiation and sodium persulfate inactivating on Bacillus subtilis spores was applied through individual and combined treatment. B. subtilis spores were selected as the surrogate bacteria for these inactivation experiments. As comparison, first, the inactivating effect of UV/sodium persulfate on Escherichia coli was investigated. A 7.24 log reduction was achieved after 10 min exposure to 0.113 mW/cm2 and 0.5 mM sodium persulfate. The results showed that sodium persulfate alone caused barely any inactivation effect on B. subtilis spores, where only 0.98 log inactivation was achieved at 0.5 mM sodium persulfate during 10 min contact time. B. subtilis spores can be inactivated by UV irradiation to a certain extent, which reached 3.50 log at a UV dose of 68 mJ/cm2. The synergistic disinfection of UV and sodium persulfate was proved to be the optimal combined treatment methods which reached a 4.30 log inactivation. Ultrastructural changes caused by UV/sodium persulfate process were observed by transmission electron microscopy which showed that the cell wall became blurred and the inner cytoplasm was indistinguishable, followed by a complete leakage of the cytoplasmic content.