Secondary disinfection ensures biosafety of domestic hot water and its impact on biofilm bacterial community

To ensure the biosafety of the domestic hot water system (DHWS) in the case of residual chlorine exhaustion and biofilm exfoliation, the secondary disinfection effects of chlorine alone or in combination with ultraviolet (UV) on microorganisms and its impact on biofilm bacterial community were investigated. A biofilm annular reactor was used to simulate DHWS conditions on a lab-scale and reproducibly. The results showed that even in the case of biofilm exfoliated into domestic hot water seriously, the chlorine combined with UV (chlorine-UV) disinfection could achieve high-level inactivation of suspended bacteria in a short time. Chlorine-UV disinfection effectively reduced the diversity of the bacterial community and affected bacterial community structure. It decreased the relative abundance of pathogenic bacteria, including Legionella, Staphylococcus. Chlorine-UV disinfection is suitable for the secondary disinfection of DHWS, which can ensure biosafety and effectively reduce bacterial contamination.