title: Two-step chlorination: A new approach to disinfection of a primary sewage effluent.
abstract: Sewage disinfection aims at inactivating pathogenic microorganisms and preventing the transmission of waterborne diseases. Chlorination is extensively applied for disinfecting sewage effluents. The objective of achieving a disinfection goal and reducing disinfectant consumption and operational costs remains a challenge in sewage treatment. In this study, we have demonstrated that, for the same chlorine dosage, a two-step addition of chlorine (two-step chlorination) was significantly more efficient in disinfecting a primary sewage effluent than a one-step addition of chlorine (one-step chlorination), and shown how the two-step chlorination was optimized with respect to time interval and dosage ratio. Two-step chlorination of the sewage effluent attained its highest disinfection efficiency at a time interval of 19 s and a dosage ratio of 5:1. Compared to one-step chlorination, two-step chlorination enhanced the disinfection efficiency by up to 0.81- or even 1.02-log for two different chlorine doses and contact times. An empirical relationship involving disinfection efficiency, time interval and dosage ratio was obtained by best fitting. Mechanisms (including a higher overall Ct value, an intensive synergistic effect, and a shorter recovery time) were proposed for the higher disinfection efficiency of two-step chlorination in the sewage effluent disinfection. Annual chlorine consumption costs in one-step and two-step chlorination of the primary sewage effluent were estimated. Compared to one-step chlorination, two-step chlorination reduced the cost by up to 16.7%.
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; College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen, 518060, Hong Kong, 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. Electronic address: xiangru@ust.hk.
authors.forename: Xiangru
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Jingyi
authors.initials: J
authors.lastname: Jiang
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: Cie Fu
authors.initials: CF
authors.lastname: Yau
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
mesh_terms: D002713:Chlorine; D004202:Disinfectants; D004203:Disinfection; D054879:Halogenation; D012722:Sewage; D018508:Water Purification
chemical_list: D004202:Disinfectants; D012722:Sewage; D002713:Chlorine
keywords: DBPs; Disinfection; Disinfection efficiency; Synergistic effect; Two-step chlorination