The overall purpose of this research was to investigate the typical types of chemically enhanced backwash by-products (CEBBPs) produced in the chemically enhanced backwash (CEB) process and the influence of variability of CEB factors on typical CEBBPs in the adsorption-ultrafiltration process. Moreover, health risk assessment was utilized to assess the potential adverse health effects from exposure to effluent after the optimal online CEB. The results of the study found the NaClO backwash reagent could react with organic matter to produce CEBBPs, including 9 kinds of volatile halogenated organic compounds (VHOCs) and 9 kinds of haloacetic acids (HAAs) during the CEB process. After a comprehensive consideration of the influence of a single factor on the CEBBPs formation and membrane cleaning effect, the optimal CEB parameters were 6 min of BD, 120 min of BI, 30 L/(m2·h) of BF and 50 mg/L of RC. Under the optimum CEB cleaning parameters, the effluent does not pose a non-carcinogenic risk and posed potential carcinogenic risk to local residents. The lifetime carcinogenic risk (LCR) value for HAAs (6.68E-06) is very close to the LCR value of CEBBPs (6.78E-06), indicating that the HAAs are the main substances in the effluent after CEB.

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