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电化学氧化工艺(EO)为电化学高级氧化(EAOPs)工艺中用于去除废水中有机污染物的主要方法[1 − 2]. 阳极材料类型对去除效率有显著影响,如掺硼金刚石(BDD)、PbO2和Sb-SnO2电极,能高效产生物理吸附态的羟基自由基(·OH)[3 − 4];尺寸稳定阳极(DSA)具有较高稳定性,能优先产生化学吸附态的·OH,进而转化Cl−为高度氧化的活性物种,如Cl· (
$E^0_{{\mathrm{Cl}}^{\cdot}/{\mathrm{Cl}}^-} $ = 2.4 VNHE),Cl2·− ($E^0_{{\mathrm{Cl}}_2^{\cdot-}/{\mathrm{Cl}}^-} $ = 2.0 VNHE),和 ClO· ($E^0_{{\mathrm{ClO}}^{\cdot}/{\mathrm{Cl}}^-} $ = 1.5—1.8 VNHE),增强了水中污染物的氧化降解能力,有助于实现COD的电氧化去除[5 − 6].尽管氯离子对COD的电氧化去除有积极作用,但很少有研究考虑电氧化过程中所产生的氯氧离子(ClOx−)对性能评价的影响. 这些ClOx−不仅在COD测定中存在掩蔽效应,使得COD测定值偏低,导致对电氧化去除COD性能的过高评价[7-8]. 这种过高评价会使得真实的电催化效果无法达到预期目标. 这样的错误评价在预处理过程中会增大后续生化处理的压力,在深度处理阶段产生处理后的废水COD看似达标的假象[9]. 此外,电氧化产生的无机氯化副产物如ClO3−和ClO4−具有生物毒性. 排放这些含氯氧离子(ClOx−)的水不仅影响后续的生化处理过程,甚至会严重威胁到人类健康和生态系统安全[10 − 12]. 在电化学氧化过程中,有机物和氯(氧)离子除了在阳极处发生氧化反应外,已有研究证明在阴极处同样会发生直接还原和原子H*介导的间接还原[11]. 不同的阴极材料还原能力不同,同样会影响氯氧离子的生成. 然而,对于常见阴极材料对氯氧离子产生的具体影响仍未明确.
本研究旨在探究DSA电极体系处理含Cl−废水时,不同阴极材料对氯氧离子生成水平及其影响因素. 采用钛板、不锈钢和Cu/Zn等不同阴极材料构建DSA电化学氧化体系,模拟苯酚废水进行电催化氧化,并评估氯氧离子对COD的干扰水平. 通过考察不同电流密度对ClOx−产生、COD和TOC去除的影响;同时利用亚硫酸盐去除氯氧离子,测定电化学氧化体系内真实的COD去除性能. 最后,通过电化学分析和自由基清除实验,探究不同阴极材料在ClO3−和ClO−产生机理方面的差异. 这些研究结果有望为今后COD性能测定的干扰及氯氧离子的控制提供新的方法.
阴极材料对钛基金属氧化物阳极体系氯氧离子生成规律及COD去除性能影响评价
Effects of cathode materials on the oxychlorides generation laws in the DSA electrooxidation system and performance assessment of COD removal
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摘要: 金属氧化物阳极(DSA)体系对含氯废水进行电化学氧化会产生氯氧离子副产物,导致COD去除性能评价过高及污水达标的假象. 本文旨在探究不同阴极的DSA电氧化体系中氯氧离子的产生情况对COD、TOC测定的干扰. 在40 mA·cm−2电流密度下,经过180 min处理后,不同阴极对TOC的去除率基本相似,但对COD的表观去除率则依次为Ti(94%)、不锈钢(86%)、Cu/Zn阴极(74%),这与氯氧离子的产生量对应一致,即Ti阴极的氯氧离子副产物产出更多. 采用还原性能更强的Cu/Zn阴极或通过增加有机物苯酚的浓度均可显著抑制氯氧离子的生成. 使用亚硫酸盐还原去除氯氧离子(ClO−和ClO3−)后,COD去除效率均下降到相近水平,表明氯氧离子对COD的测定具有掩蔽效应. 对照实验中发现,ClO3−对COD测定的干扰比ClO−更明显. 通过研究氯氧离子在不同阴极的DSA电氧化体系下的产生情况及其对COD去除性能测定的干扰,引入了一种方便、绿色、有效的控制策略,为正确评价电氧化体系的COD去除性能提供新方法.Abstract: The Direct Solar Airflow (DSA) electrooxidation system, employed for the electrochemical oxidation of chlorine-rich wastewater, yields oxychlorides as byproducts. This can lead to an overestimation of Chemical Oxygen Demand (COD) removal efficiency and a misleading impression of compliant effluent. This study investigates the influence of oxychloride formation in the DSA electrooxidation system on COD and Total Organic Carbon (TOC) determination when utilizing various cathodes. After 180 minutes of treatment at a current density of 40 mA·cm−2, TOC removal was largely consistent across different cathodes. However, the apparent COD removal followed the order Ti (94%), stainless steel (86%), and Cu/Zn cathode (74%), corresponding to the production of oxychlorides; notably, the Ti cathode produced more Chlorine Dioxide (ClOx−) as byproducts. Oxychloride oxide production can be significantly mitigated using a Cu/Zn cathode with robust reducing capabilities and increasing the content of organic phenol. The removal of oxychlorides (ClO− and ClO3−) via sulfite reduction resulted in a decrease in COD removal efficiency to similar levels, suggesting a masking effect of chloroxylate ions on COD determination. In control experiments, it was observed that ClO3− interfered more significantly with COD determination than ClO−. By examining the generation of oxychlorides under DSA electrooxidation systems with different cathodes and their interference with COD removal performance determination, a convenient, green, and effective control strategy was introduced, providing a novel method for accurately evaluating COD removal performance of electrooxidation systems.
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Key words:
- electrochemical /
- oxychloride ions /
- cathode material /
- COD determination
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图 7 Ti (a); 不锈钢 (b)和Cu/Zn (c) 阴极分别在2 mmol·L−1 NaCl和1 mmol·L−1 NaCl + 1 mmol·L−1 ClO3−溶液中分别进行的CV扫描实验. 当电流密度为30 mA cm−2时, 在10 mmol·L−1 NaClO3和30 mmol·L−1 Na2SO4中用Ti (d); 不锈钢 (e) 和Cu/Zn (f) 阴极进行电化学还原ClO3−(Ti作为阳极)
Figure 7. CV scanning experiments of Ti (a); stainless steel (b) and Cu/Zn (c) cathodes in 2 mmol·L−1 NaCl and 1 mmol·L−1 NaCl + 1 mmol·L−1 ClO3− solution, respectively. Electrochemical reduction of ClO3− (Ti as anode) was carried out with Ti (d); stainless steel (e) and Cu/Zn (f) cathodes in 10 mmol·L−1 NaClO3 and 30 mmol·L−1 Na2SO4 when the current density was 30 mA cm−2
图 8 分别在2 mmol·L−1 NaCl和1 mmol·L−1 NaCl+1 mmol·L−1 ClO−溶液中对Ti (a); 不锈钢 (b) 和Cu/Zn (c) 阴极进行CV扫描实验. 当电流密度为30 mA cm−2时, 在20 mmol·L−1的NaClO中将ClO−还原成Cl−, 阴极为Ti (d); 不锈钢 (e) 和Cu/Zn (f) (Ti作为阳极)
Figure 8. CV scanning experiments were performed on Ti (a); stainless steel (b) and Cu/Zn (c) cathodes in 2 mmol·L−1 NaCl and 1 mmol·L−1 NaCl+1 mmol·L−1 ClO− solutions, respectively. Reduction of ClO− to Cl− in 20 mmol·L−1 NaClO at a current density of 30 mA cm−2 , cathodes of Ti (d); stainless steel (e) and Cu/Zn (f) (Ti as anode)
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