Inactivation of chlorine-resistant bacterial spores in drinking water using UV irradiation, UV/Hydrogen peroxide and UV/Peroxymonosulfate: Efficiency and mechanism

Although the quality of drinking water is extremely important for human health, the widespread use of chlorine disinfection results in the formation of chlorine-resistant bacteria which seriously threatens human health. Therefore, there is a need for an effective method for the inactivation of chlorine-resistant bacteria in drinking water. In this study, three methods, i.e., ultraviolet irradiation (UV) and two UV-based advanced oxidation processes (UV-AOPs) (UV/hydrogen peroxide, UV/H₂O₂ and UV/peroxymonosulfate, UV/PMS) were studied for the inactivation of Bacillus cereus (B. cereus) due to their high capability for the degradation of emerging contaminants. The inactivation rate of B. cereus species was 2-log lower than that of Escherichia coli (E. coli) at 1 mg/L NaClO. The spores were more chlorine-resistant than other growing cells because of their structure and chemical composition. A strong linear relationship was identified between the UV dosage and the inactivation rate. When the UV dosage was increased to 180 mJ/cm², an inactivation rate of over 3-log was observed. Furthermore, H₂O₂ and PMS at 20 mg/L decreased the consumption of UV radiation to 140 mJ/cm² and 120 mJ/cm², respectively. According to the DNA and protein concentration analysis, the UV-AOPs prevented the regrowth of chlorine-resistant bacteria and its spores in drinking water within 24 h. The flow cytometry and scanning electron microscopy results showed that UV/H₂O₂ and UV/PMS treatment methods destroyed the particle characteristics of the spores and caused the release of intracellular materials due to the damage of the cell membrane and the cytoplasm. Among these three methods, the best inactivation effect was achieved by UV/PMS followed by UV/H₂O₂ and then UV alone.