Enhanced removal strategy towards organic matter with low coagulability: Immediate entrapment and complexation of oxidized intermediates by the hybrid ozonation-coagulation process

Shiyi Hu; Xin Jin; Mengwen Liu; Yao Li; Yadong Wang; Yixiong Wei; Pengkang Jin; Xiaochang C Wang

doi:10.1016/j.jhazmat.2023.133288

Enhanced removal strategy towards organic matter with low coagulability: Immediate entrapment and complexation of oxidized intermediates by the hybrid ozonation-coagulation process

J Hazard Mater. 2024 Mar 5:465:133288. doi: 10.1016/j.jhazmat.2023.133288. Epub 2023 Dec 27.

Authors

Shiyi Hu¹, Xin Jin², Mengwen Liu¹, Yao Li¹, Yadong Wang¹, Yixiong Wei¹, Pengkang Jin³, Xiaochang C Wang¹

Affiliations

¹ School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an, Shaanxi 710055, China.
² School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China. Electronic address: jinxin@xjtu.edu.cn.
³ School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, Xi'an, Shaanxi 710055, China; School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China. Electronic address: pkjin@xjtu.edu.cn.

PMID: 38154182
DOI: 10.1016/j.jhazmat.2023.133288

Abstract

The existence of dissolved organic matter (DOM) with low coagulability poses great challenges for conventional coagulation (CC) in water treatment. As a kind of typical organochlorine pesticide, 2,4-dichlorophenoxyacetic acid (2,4-D) cannot be efficiently removed by CC. To enhance the 2,4-D removal, ozonation was applied with coagulation. The hybrid ozonation-coagulation (HOC) achieved 60.61% DOC removal efficiency, which was obviously higher than pre-ozonation coagulation (POC) (45.83%). Synchronous fluorescence spectroscopy revealed stronger complexation between modified 2,4-D and coagulants during the HOC than that in subsequent coagulation of the POC process. During the HOC process, ozone promoted the formation of polymeric Al species, such as Al_b. To investigate the 2,4-D removal mechanism, γ-Al₂O₃/O₃ process with the same oxidation ability as the HOC was established. 2,4-D was oxidized step-by-step to 2,4-dichlorophenol, 4,6-dichlororesorcin, 3,5-dichlorocatechol, 2-chlorohydroquinone, 4-chlorocatechol, 1,2,4,5-tetrahydroxybenzene, pentahydroxybenzene and oxalic acid in γ-Al₂O₃/O₃ process. However, during the HOC process, these oxidized intermediates were readily complexed by coagulants and accumulated in flocs. Especially 1,2,4,5-tetrahydroxybenzene and pentahydroxybenzene, completely complexed by AlCl₃•6H₂O hydrolysates as soon as being formed. Immediate entrapment and complexation between coagulant hydrolysates and 2,4-D oxidized intermediates inhibited the generation of small-molecular-weight organics such as oxalic acid, which enhanced the removal of organics with low coagulability.

Keywords: 2,4-Dichlorophenoxyacetic acid; Hybrid ozonation-coagulation process; Hydrolysed metal coagulants; Immediate entrapment and complexation.