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目前,新污染物已被发现广泛存在于水体环境当中,由于其在环境中的持久性,并且具有致突变、致畸变和致癌的“三致”风险,受到了研究人员的高度关注。有研究表明,以布洛芬(ibuprofen IBP)、阿特拉津(atrazine ATZ)、乐果(dimethoate DIM)以及三氯乙酸(trichloroacetic acid TCAA)为代表的新型污染物多次在地表水中被检出[1-2]。在日常生活中,人们往往忽略这些微量有机污染物对健康产生的不利影响,但长期接触或摄入这类化合物会对人体产生难以预料的影响[3]。饮用水是人类接触新污染物的直接途径,在日常洗漱和饮用过程中都会直接接触和摄入未完全去除的微污染物。
因此,必须将微污染物充分去除后饮用。常规的传统工艺如混凝、沉淀、消毒等,虽然能去除水体的浊度和色度等,但却无法将水体中的有机物彻底截留或降解[4],对于微克、纳克级别物质的去除效率更是十分有限。虽然大量采用纳滤和反渗透膜可以截留水中的污染物,但也大大提高了水处理成本,截留后产生的浓水也会成为新的污染来源。针对这一现状,本研究结合“分质供水”理念,对人体直接接触和摄入的饮用水进行深度处理,在减少水处理成本的基础上提高家庭端水质。
光电氧化被认为是一种具有应用前景的水处理技术,通过施加外部偏压减少光生电子和空穴的复合,提高量子效率,可以在提高降解率的同时降低能耗,具有绿色、高效的特点。能高效分离光电子空穴和具有出色的光吸收特性的半导体电极是光电催化体系的首选电极,如TiO2、ZnO、BiVO4和MOFs电极。其中,TiO2基电极因其具有良好的光学性能和低毒性成为最常用的光电电极。研究者采用Ru0.3Ti0.7O2作为光电阳极,这种电极既具有RuO2的电化学特性,又具有TiO2的光催化特性,其矿化效率(38%)高于仅在电催化过程中的矿化效率(<10%)[5]。本研究选用具有良好光活性的TiO2-IrRu电极,钌铱金属由于其优异的导电性能和长时间的工作寿命而被作为一种电极涂层,以此来增加电极材料的稳定性和电催化活性。与传统光电阳极相比,该电极具有物化性质稳定、氧化能力强、安全无害的特点[6]。
目前,光电技术已被证实对低浓度的有机污染物也有非常高的降解效能[7-10],但由于能耗较高,不适用于大规模的饮用水处理。本研究提出将光电催化技术用于分质供水的末端水处理,选用性能稳定、无毒无害的TiO2-IrRu电极为光电催化阳极材料,采用自来水配置水样模拟实际水体,以4种污染物为模型污染物分析光电氧化系统的污染物降解情况和能耗,并通过布洛芬的降解路径,计算降解过程的毒性变化。
光电氧化降解饮用水中有机污染物的效能
Performance of photoelectro-oxidation process on the degradation of organic pollutants in drinking water
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摘要: 针对地表水中普遍存在的有机污染物现状和常规水处理工艺无法去除有机污染物的问题,以紫外光电氧化技术为基础,提出了以“分质供水”为目标的末端深度水处理工艺。与单独电解和光解相比,电化学氧化与紫外耦合技术可以将布洛芬、阿特拉津、三氯乙酸、乐果的降解率在15 min内分别提高到92.5%、98.1%、71.0%和94.6%,并且能耗有所降低。电流和光强对光电氧化降解有机污染物有促进作用,但污染物初始质量浓度、Cl−、HCO3−和天然有机物(HA)和污染物去除率呈反比关系。在此基础上,以布洛芬为污染物代表,测定了布洛芬的中间产物,并计算了降解中间体的毒性变化,发现光电氧化明显降低了布洛芬的毒性。Abstract: In view of the present situation of organic pollutants in surface water and the problem that these organic pollutants cannot be effectively removed by the conventional water treatment technology, a deep end water treatment technology based on ultraviolet (UV) irradiation with electrochemical technology was proposed for dual water supply. Compared with electrolysis or UV irradiation alone, photoelectro-oxidation process coupled with UV irradiation could increase the degradation rates of ibuprofen, atrazine, trichloroacetic acid and dimethoate to 92.5%, 98.1%, 71.0% and 94.6% in 15 min, respectively, and could reduce the energy consumption. The increase of current and light intensity accelerated the degradation of organic pollutant by photoelectro-oxidation process. However, the initial concentration of pollutants、Cl−、HCO3− and organic matter (HA) were inversely proportional to the removal rates of these pollutants. Moreover, ibuprofen was taken as the representative pollutant, its intermediate products were determined and their toxicity changes were calculated. It was found that photoelectron-oxidation significantly reduced the toxicity of ibuprofen.
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表 1 实验所用自来水水质参数
Table 1. Water quality parameters of tap water
pH 浊度/
NTU电导率/
(μS·cm−1)TOC/
(mg·L−1)总碱度/
(mg·L−1)总硬度/
(mg·L−1)6.8~7.2 0.2~0.3 170~230 1.2~1.8 100~110 100~120 表 2 4种污染物动力学常数k值
Table 2. Parameters of reaction kinetics of four pollutants
污染物
名称k /min−1 E UV E-UV IBP 0.015 7 0.117 3 0.182 6 ATZ 0.034 6 0.219 2 0.368 0 TCAA 0.036 2 0.053 3 0.092 1 DIM 0.119 5 0.104 2 0.177 1 表 3 不同工艺能耗对比
Table 3. Comparison of energy consumption of different processes
表 4 不同实验参数下IBP的反应动力学k值
Table 4. The parameters of IBP reaction kinetics under different experiment parameters
min−1 电流/A 光强/LUX 初始质量浓度/(µg·L−1) 0.30 0.30 0.35 2 210 3 352 4 566 20 40 80 0.156 2 0.182 6 0.217 0 0.083 0 0.122 0 0.182 6 0.359 6 0.259 9 0.182 6 表 5 不同水质参数下IBP的反应动力学k值
Table 5. The parameters of IBP reaction kinetics under different water quality parameters
min−1 HCO3−/(mmol·L−1) Cl−/(mmol·L−1) HA/(mg·L−1) 0 5 10 0 5 10 0 0.5 1 0.182 6 0.146 8 0.127 7 0.182 6 0.148 3 0.124 9 0.182 6 0.158 3 0.131 5 -
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