title: Bromate formation in bromide-containing water through the cobalt-mediated activation of peroxymonosulfate.
abstract: Bromate formation in bromide-containing water through the cobalt (Co)-mediated activation of peroxymonosulfate (PMS) was investigated. Increasing the PMS dosage and the cobalt dosage increased the formation of bromate and bromate yields of up to 100% were recorded under the test conditions. The bromate yield increased to a maximum as the pH rose from 2.7 to 6 before decreasing by over 90% as the pH rose further from 6 to above 9. The bromate formation is a two-step process involving free bromine as a key intermediate and bromate as the final product. In the first step, apart from the known oxidation of bromide to free bromine and of free bromine to bromate by sulfate radicals (SO4(-)), Co(III) produced from the oxidation of Co(II) by PMS and SO4(-) also oxidizes bromide to free bromine. The contribution of Co(III) to the bromate formation was verified with the addition of methanol and EDTA, a radical scavenger and a Co(III) ligand, respectively. In the presence of methanol, free bromine formation increased with increasing Co(II) dosage but no bromate was detected, indicating that Co(III) oxidized bromide to form free bromine but not bromate. In the presence of both EDTA and methanol, no free bromine or bromate was detected, as Co(III) was stabilized by EDTA to form the Co(III)EDTA(-) complex, which could not oxidize bromide. Mathematical simulation further suggested that Co(III) outweighed SO4(-) to oxidize bromide to free bromine. On the other hand, SO4(-) is essential for the oxidation of free bromine to bromate in the second step. In real water, the presence of NOM significantly decreased the bromate formation but caused the brominated organic DBP formation with high quantity. This is the first study to demonstrate the significant bromate formation in the Co/PMS system and the substantial contribution of Co(III) to the formation.
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Zhaobing
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Yingying
authors.initials: Y
authors.lastname: Xiang
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Li
authors.initials: L
authors.lastname: Ling
authors.affiliation: School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, SYSU-HKUST Research Center for Innovative Environmental Technology (SHRCIET), School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China. Electronic address: fangjy3@mail.sysu.edu.cn.
authors.forename: Jingyun
authors.initials: J
authors.lastname: Fang
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. Electronic address: cechii@ust.hk.
authors.forename: Chii
authors.initials: C
authors.lastname: Shang
authors.affiliation: Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, OH 45221-0012, United States.
authors.forename: Dionysios D
authors.initials: DD
authors.lastname: Dionysiou
mesh_terms: D001959:Bromates / Q000737:chemistry*; D001965:Bromides / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D001959:Bromates; D001965:Bromides; D010545:Peroxides; C038288:peroxymonosulfate; D003035:Cobalt
keywords: Advanced oxidation processes; Bromate; Oxidation by-products; Sulfate radicals; Transition metals; Water treatment