Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/5516
Title: Degradation of synthetic organic compounds by sulfate- and hydroxyl radical-based advanced oxidation processes
Authors: Wang, Yuru
Keywords: Water -- Purification.
Water chemistry.
Hong Kong Polytechnic University -- Dissertations
Issue Date: 2012
Publisher: The Hong Kong Polytechnic University
Abstract: Currently, the contamination of water sources by synthetic organic compounds (SOCs) is one of the concerning environmental issues faced throughout the world, leading to a great interest in developing alternative treatment technologies for the removal of SOCs in aqueous medium. Among the existing SOCs, dyes and herbicides contribute to a large portion of the confirmed toxic organics and thus have to be removed prior to the discharge of the treated water. Against the background, the primary objective of this research work is to explore sulfate- and hydroxyl radical based advanced oxidation processes (AOPs) for the elimination of dyes and herbicides in water and wastewaters. Firstly, an oxidation process using sulfate radical (SO₄.⁻) activated by Fe(II)-mediated Oxone® process (FO) were evaluated by monitoring the degradation of a Xanthene dye Rhodamine B (RhB) in an aqueous solution. The effects of reactant dosing sequence, Fe(II)/Oxone® molar ratio and concentration, solution pH, and inorganic salts on the process performance were investigated. Total RhB removal was obtained within 90 min under an optimal Fe(II)/Oxone® molar ratio of 1:1. The RhB degradation was found to be a two-stage kinetics, consisting of a rapid initial decay and a subsequent retarded stage. Additionally, TOC study indicates that stepwise addition of Fe(II) and Oxone® can notably improve the process performance by about 20%, and the retention time required can be greatly reduced compared with the conventional one-off dosing method. On the other hand, it was found that the rapid depletion as well as the slow regeneration of Fe(II) in the above FO process usually terminates the production of SO₄.⁻ and limits the decay rate. To tackle with the problem, a novel electrochemically enhanced FO process (i.e. EFO) was proposed. In this oxidation process, once an electric current is applied between the anode (an iron sheet) and the cathode (a graphite bar), a predetermined amount of Oxone® is added to the reactor. Ferrous ions generated from the sacrificed Fe anode mediate the generation of SO₄.⁻ through the decomposition of Oxone®. The EFO process was evaluated in terms of a selected herbicide 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) degradation in aqueous solution. Experimental results demonstrated that low solution pH facilitated the system performance due to the dual effects of weak Fenton's reagent generation and persulfate ion generation, whereas the process was inhibited at basic pH levels through non-radical self-dissociation of Oxone® and the formation of Fe(OH)₃. The active radicals involved in the EFO process were identified. The EFO process demonstrates a very high 2,4,5-T degradation efficiency (over 90% decay within 10 min), which justifies the novel EFO a promising process for herbicide removal in water.
Currently, the contamination of water sources by synthetic organic compounds (SOCs) is one of the concerning environmental issues faced throughout the world, leading to a great interest in developing alternative treatment technologies for the removal of SOCs in aqueous medium. Among the existing SOCs, dyes and herbicides contribute to a large portion of the confirmed toxic organics and thus have to be removed prior to the discharge of the treated water. Against the background, the primary objective of this research work is to explore sulfate- and hydroxyl radical based advanced oxidation processes (AOPs) for the elimination of dyes and herbicides in water and wastewaters. Firstly, an oxidation process using sulfate radical (SO₄.⁻) activated by Fe(II)-mediated Oxone® process (FO) were evaluated by monitoring the degradation of a Xanthene dye Rhodamine B (RhB) in an aqueous solution. The effects of reactant dosing sequence, Fe(II)/Oxone® molar ratio and concentration, solution pH, and inorganic salts on the process performance were investigated. Total RhB removal was obtained within 90 min under an optimal Fe(II)/Oxone® molar ratio of 1:1. The RhB degradation was found to be a two-stage kinetics, consisting of a rapid initial decay and a subsequent retarded stage. Additionally, TOC study indicates that stepwise addition of Fe(II) and Oxone® can notably improve the process performance by about 20%, and the retention time required can be greatly reduced compared with the conventional one-off dosing method. On the other hand, it was found that the rapid depletion as well as the slow regeneration of Fe(II) in the above FO process usually terminates the production of SO₄.⁻ and limits the decay rate. To tackle with the problem, a novel electrochemically enhanced FO process (i.e. EFO) was proposed. In this oxidation process, once an electric current is applied between the anode (an iron sheet) and the cathode (a graphite bar), a predetermined amount of Oxone® is added to the reactor. Ferrous ions generated from the sacrificed Fe anode mediate the generation of SO₄.⁻ through the decomposition of Oxone®. The EFO process was evaluated in terms of a selected herbicide 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) degradation in aqueous solution. Experimental results demonstrated that low solution pH facilitated the system performance due to the dual effects of weak Fenton's reagent generation and persulfate ion generation, whereas the process was inhibited at basic pH levels through non-radical self-dissociation of Oxone® and the formation of Fe(OH)₃. The active radicals involved in the EFO process were identified. The EFO process demonstrates a very high 2,4,5-T degradation efficiency (over 90% decay within 10 min), which justifies the novel EFO a promising process for herbicide removal in water.
Description: xxi, 167, 1 leaves : ill. ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P CEE 2012 Wang
URI: http://hdl.handle.net/10397/5516
Rights: All rights reserved.
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