Synergistic effects of UV and chlorine in bacterial inactivation for sustainable water reclamation and reuse

Disinfection is a necessity in water and wastewater treatment and reclamation. This study examined the inactivation of a disinfectant resistant but widely existed opportunistic pathogen in reclaimed water, Staphylococcus aureus (S. aureus), by sequential UV and chlorine disinfection or simultaneous UV and chlorine disinfection (UV/Cl). It was identified that UV/Cl greatly promoted the inactivation efficacy and inhibited photoreactivation of S. aureus by the generation of free radicals (i.e. center dot OH and center dot Cl), - which reached a 7-log(10) reduction at UV and chlorine doses of 18 mJ/cm(2) and 2 mg-Cl/L, respectively. The changes of bacterial viability and morphology and the increase of extracellular ATP concentration confirmed the enhancement of cell membranes damages (>21.4 %) due to free radicals generated in UV/Cl process, which caused a dramatic reduction in metabolic activity and suppressed the photoreactivation. Furthermore, this study demonstrated that UV/Cl effectively removed heterotrophic plate count bacteria and aromatic organic fluorophores in reclaimed water samples. This study is of significant theoretical and applicable importance in guaranteeing safe microbial levels for water reclamation and reuse.

Automated summary

This study investigated the effectiveness of sequential or simultaneous UV and chlorine disinfection in inactivating disinfectant resistant Staphylococcus aureus in reclaimed water. The study found that simultaneous UV and chlorine disinfection significantly enhanced the inactivation efficacy by generating free radicals, which caused damages to cell membranes and suppressed bacterial metabolic activity and photoreactivation. UV/Cl also effectively removed heterotrophic bacteria and aromatic organic fluorophores.