title: Three-step effluent chlorination increases disinfection efficiency and reduces DBP formation and toxicity.
abstract: Chlorination is extensively applied for disinfecting sewage effluents, but it unintentionally generates disinfection byproducts (DBPs). Using seawater for toilet flushing introduces a high level of bromide into domestic sewage. Chlorination of sewage effluent rich in bromide causes the formation of brominated DBPs. The objectives of achieving a disinfection goal, reducing disinfectant consumption and operational costs, as well as diminishing adverse effects to aquatic organisms in receiving water body remain a challenge in sewage treatment. In this study, we have demonstrated that, with the same total chlorine dosage, a three-step chlorination (dosing chlorine by splitting it into three equal portions with a 5-min time interval for each portion) was significantly more efficient in disinfecting a primary saline sewage effluent than a one-step chlorination (dosing chlorine at one time). Compared to one-step chlorination, three-step chlorination enhanced the disinfection efficiency by up to 0.73-log reduction of Escherichia coli. The overall DBP formation resulting from one-step and three-step chlorination was quantified by total organic halogen measurement. Compared to one-step chlorination, the DBP formation in three-step chlorination was decreased by up to 23.4%. The comparative toxicity of one-step and three-step chlorination was evaluated in terms of the development of embryo-larva of a marine polychaete Platynereis dumerilii. The results revealed that the primary sewage effluent with three-step chlorination was less toxic than that with one-step chlorination, indicating that three-step chlorination could reduce the potential adverse effects of disinfected sewage effluents to aquatic organisms in the receiving marine water.
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China. Electronic address: xiangru@ust.hk.
authors.forename: Xiangru
authors.initials: X
authors.lastname: Zhang
authors.affiliation: College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518060, China. Electronic address: yangmt@szu.edu.cn.
authors.forename: Mengting
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Jiaqi
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Wanxin
authors.initials: W
authors.lastname: Li
authors.affiliation: Department of Civil and Environmental Engineering, Imperial College London, London, UK.
authors.forename: Nigel J D
authors.initials: NJD
authors.lastname: Graham
authors.affiliation: Department of Civil Engineering, The University of Hong Kong, Hong Kong, China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Li
authors.affiliation: College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
mesh_terms: D000818:Animals; D001965:Bromides / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry*; D004202:Disinfectants / Q000737:chemistry*; D004203:Disinfection / Q000379:methods*; D054879:Halogenation; D011077:Polychaeta / Q000187:drug effects / Q000196:embryology; D012722:Sewage / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity; D018508:Water Purification / Q000379:methods*
chemical_list: D001965:Bromides; D004202:Disinfectants; D012722:Sewage; D014874:Water Pollutants, Chemical; D002713:Chlorine
keywords: DBPs; Disinfection byproducts; Disinfection efficiency; Three-step chlorination; Toxicity