Abstract
• UV/chlorine was conducted under different pH and UV wavelength for disinfection. • Flow cytometer was used to quantify bacterial membrane or DNA damage by UV/chorine. • UV/chlorine showed enhanced kinetics of bacterial DNA damage than UV or Cl 2 alone. • Bacterial DNA damage during UV/chlorine are highly depended on the CT FAC values. • ΔUVA254 can be used to predict bacterial membrane damage during UV/chlorine. The UV photolysis of chlorine (UV/chlorine) produces a suite of radical species and has been proposed as a novel water treatment process for advanced oxidation and enhanced disinfection purposes. In this study, the kinetics and efficacy of membrane/DNA damage to B. subtilis and autochthonous bacteria during UV/chlorine treatment were investigated under different pH and irradiation wavelengths (254 nm Hg lamp vs 275 nm LEDs) with flow cytometer analysis. Compared to UV irradiation or chlorination alone, the UV/chlorine showed the enhanced kinetics and efficacy of cell membrane or DNA damage to B. subtilis . These enhancements by UV/chlorine might be primarily attributed to the in-situ generation of radical species HO • and Cl • around intracellular DNA. With pH increasing from acidic to alkaline, the UV254/chlorine showed the decreased kinetics of cell membrane or DNA damage to B. subtilis while the UV275/chlorine exhibited the increased cell membrane and DNA damage kinetics due to the higher chlorine photolysis rates. When the chlorine dose was not excess, the DNA damage of B. subtilis were highly depended on the cumulative exposures of free available chlorine ( CT FAC ). During UV275/chlorine in the presence of natural organic matter, the cell membrane damage also showed linear correlations with the decreases of UV absorbance at 254 nm (UVA254), and about 20–25% decrease of UVA254 indicates a sufficient cell membrane damage. Using the CT FAC values and decrease of UVA254, this study has provided the surrogate indicators for fast determining the minimal chlorine dose for sufficient inactivation of bacteria by UV/chlorine treatment.
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