State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, P.O. Box 2603#, No. 73, Huanghe Road, Nangang District, Harbin 150090, P. R. China.
Environ Sci Technol. 2020 Apr 7;54(7):4573-4582. doi: 10.1021/acs.est.9b05929. Epub 2020 Mar 20.
Low temperature presents a challenge to wastewater treatment in the winters of cold regions. In the electrochemical oxidation (EO) process, the interfacial Joule heating (IJH) effect results in interfacial temperature higher than that of bulk electrolytes, which would alleviate the negative impact of low water temperature on organic oxidation occurring within the boundary layer of the anode. This study investigated the electrochemical oxidation of the representative recalcitrant organic pollutant, i.e., phenol, -chlorophenol (-CP), and 2,4-dichlorophenoxyacetic acid (2,4-D) on titanium suboxide (TiSO) anode at a low water temperature (8.5 ± 1 °C). At a low current density of 2 mA cm, the IJH effect was insignificant and thus had a slight impact on interfacial temperature, leading to a low-efficiency and incomplete organic removal via direct electron transfer (DET) oxidation. Increasing the current density to 20 mA cm promoted the working up of the IJH effect and thus resulted in a dramatic increase in the interfacial temperature from 8.1 to 38.7 °C. This almost eliminated the negative impact of low temperature on the abatement of organic pollutants as though the low temperature of the bulk solution did not interact with interfacial reactions at all. This was indicated by the oxidation rates of 0.158 min (phenol), 0.084 min (-CP), and 0.070 min (2.4-D) at a temperature of 8.5 ± 1 °C, the values being almost comparable to that obtained at room temperature (23.5 ± 1 °C). Both theoretical and experimental results demonstrated that the extent to which the low- and room-temperature cases deviated from each other was positively correlated with the activation energy of organic pollutants when reacting with OH. The improvement of organic oxidation at low temperature should result from the compensation of the IJH effect, giving rise to higher OH reactivity, more activated organic molecules, and enhanced mass transfer. This study may prompt new possibilities to develop an IJH effect-based electrochemical manner for decentralized water decontamination in cold regions.
低温给寒冷地区的污水处理带来了挑战。在电化学氧化（EO）过程中，界面焦耳加热（IJH）效应导致界面温度高于电解质本体温度，这将减轻低温对阳极边界层内有机物氧化的负面影响。本研究在低温（8.5±1°C）条件下，采用钛亚氧化物（TiSO）阳极对代表性难降解有机污染物，即苯酚、-氯苯酚（-CP）和 2,4-二氯苯氧乙酸（2,4-D）进行电化学氧化。在低电流密度 2 mA cm-2 时，IJH 效应不明显，对界面温度影响较小，通过直接电子转移（DET）氧化，有机物去除效率低且不彻底。将电流密度提高到 20 mA cm-2 可促进 IJH 效应的发展，从而使界面温度从 8.1°C急剧升高至 38.7°C。这几乎消除了低温对有机物去除的负面影响，就好像低温的本体溶液与界面反应完全没有相互作用一样。这一点从在 8.5±1°C 温度下氧化速率分别为 0.158 min（苯酚）、0.084 min（-CP）和 0.070 min（2.4-D）可以看出，其值几乎与在室温（23.5±1°C）下获得的值相当。理论和实验结果都表明，低温和室温情况下的偏离程度与有机物与 OH 反应的活化能呈正相关。低温下有机物氧化的改善应该是由于 IJH 效应的补偿，导致 OH 反应性更高、更多的活性有机分子和增强的传质。本研究可能为在寒冷地区开发基于 IJH 效应的电化学分散式水净化方法提供新的可能性。
