title: Probing the radical chemistry in UV/persulfate-based saline wastewater treatment: kinetics modeling and byproducts identification.
abstract: The effect of Cl(-) on the oxidative degradation of Acid Orange 7 (AO7) was investigated in UV/S2O8(2-) system to elucidate the chlorination pathways in saline wastewaters. Lower amount of Cl(-) as well as Br(-) enhanced the decoloration of AO7, but such promotion effect reduced gradually with the increasing halide ion dosage. The dye mineralization was found to be inhibited by Cl(-), especially under acidic conditions. Results of kinetics modeling demonstrated that the fraction of different oxidizing radicals largely depended on the content of Cl(-). At the initial pH of 6.5, Cl2(-) was much more abundant than SO4(-). The significance of Cl2(-) for AO7 degradation increased with the increasing Cl(-) concentration and overwhelmed that of SO4(-) at [Cl(-)]>1mM. Without Cl(-), SO4(-) was the predominant radical for AO7 degradation under acidic conditions, while OH prevailed gradually at higher pH. Under high salinity conditions, more OH can be formed and contributed to the dye degradation especially in alkaline medium, leading to higher destruction efficiency of AO7. Several chlorinated byproducts were detected in the presence of chloride ions, and SO4(-)/Cl2(-)-based degradation pathways of AO7 were proposed. This work provides further understanding of the complex reaction mechanisms for SO4(-)-based advanced oxidation processes in chloride-rich environments.
authors.affiliation: Provincial Key Laboratory of Oil & Gas Chemical Technology, College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing 163318, China; College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
authors.forename: Ruixia
authors.initials: R
authors.lastname: Yuan
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China. Electronic address: zhaohuiwang@dhu.edu.cn.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
authors.forename: Yin
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Provincial Key Laboratory of Oil & Gas Chemical Technology, College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing 163318, China.
authors.forename: Baohui
authors.initials: B
authors.lastname: Wang
authors.affiliation: Provincial Key Laboratory of Oil & Gas Chemical Technology, College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing 163318, China.
authors.forename: Simeng
authors.initials: S
authors.lastname: Gao
mesh_terms: D001391:Azo Compounds / Q000737:chemistry; D001557:Benzenesulfonates / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D004396:Coloring Agents / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D012965:Sodium Chloride / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D001557:Benzenesulfonates; D002712:Chlorides; D004396:Coloring Agents; D005609:Free Radicals; D012965:Sodium Chloride; D013440:Sulfides; D062065:Wastewater; C051552:persulfides; C014722:2-naphthol orange
keywords: Chloride ion; Chlorinated byproducts; Kinetic modeling; Sulfate radical