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重金属污染一直以来备受关注。砷作为高毒性污染物被广泛认知,矿山开采、冶炼、农业生产、制革、染料、化工等行业生产中往往会产生大量的砷[1-2]。As及其化合物随着径流、入渗等途径进入地下水中,污染水体,并通过不断累积对环境与人体健康造成威胁。在我国,对于砷的排放标准也有着严格的规定[3]。如何有效地处理含As地下水一直以来都是环境工程领域所关注的热点。
As的存在形式及其价态决定了As及其化合物的毒性[4]。As在水体中常以As(Ⅲ)和As(Ⅴ)的形态存在,而在还原条件下的地下水体中,又以As(Ⅲ)为主要存在形态。在目前的地下水As(Ⅲ)污染处理中,中和法[5]、混凝法[6-7]、吸附法[8-9]、离子交换法[10-11]、微生物法[12-13]、电化学法[14-15]均能取得良好的治理效果。但不断寻求提供高效,创新的处理方法,并作为现有地下水As(Ⅲ)污染处理技术的补充或替代仍然是十分必要的。已有研究[16]表明,As(Ⅲ)的毒性比As(Ⅴ)高出数十倍以上,并且迁移性更强,稳定性差,因此,将As(Ⅲ)氧化成更易吸附、稳定的As(Ⅴ)是实现As(Ⅲ)控制的可行途径。SORLINI等[17]研究了二氧化氯、次氯酸盐、高锰酸钾等氧化剂对水体中As的氧化效果,As(Ⅲ)的氧化效率能到达到80%~100%。吕杰蝉等[18]通过感应电芬顿法处理二甲基砷废水,在初始pH为3,电流密度为2 mA·cm−2,初始浓度为5 mg·L−1的条件下,4 h后去除率达到94.4%。LAN等[19]以FeCx/N掺杂的碳纤维复合材料作为催化剂,通过电芬顿反应对含二甲基砷废水进行高效处理,6 h后去除率达到96%。ZHANG等[20]通过非均相芬顿法对畜牧业中的有机砷化合物进行降解,处理3 h后降解率可达到80%以上。尽管对地下水中砷污染处理的研究较少,但这能为我们处理此类地下水提供新的思路,通过强氧化性的羟自由基(·OH)可将As(Ⅲ)氧化为更稳定、毒性低的As(Ⅴ),同时亦可减少使用化学氧化剂带来的风险与成本。
本研究设计了一种新型流通式电芬顿系统,用来处理含As(Ⅲ)地下水。考察了电流强度、pH、流速、曝气速率、电解质浓度等因素对去除效果的影响,并探讨了水体中共存离子的干扰作用及相关的反应机理。此外,对流通式电芬顿系统在连续运行条件下的性能进行了评估,以期为地下水As(Ⅲ)污染的治理提供参考。
流通式电芬顿系统对地下水中As(Ⅲ)的高效去除
High efficiency removal of As (Ⅲ) in groundwater by a flow through electro-Fenton system
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摘要: 为了高效处理地下水中的As(Ⅲ),设计了一种流通式电芬顿处理系统,考察了电流密度、pH、曝气速率、流速、电解质浓度以及共存离子等关键因素对As(Ⅲ)去除率的影响。此外,对电芬顿体系中As(III)的去除机理进行了分析,并对该系统在连续运行下的处理效果进行了评估。结果表明:在最佳反应条件下(电流密度为7.6 mA·cm−2、pH为6、流速为20 mL·min−1、曝气速率为80 mL·min−1、电解质浓度为100 mg·L−1),地下水中As(Ⅲ)的去除率接近100%,该系统可以在近中性的pH范围内发挥作用;在连续运行条件下,该系统能够保持良好的处理稳定性;在电芬顿反应体系中,·OH和HO2·能够共同促进As(III)的去除。水体中生成的As(Ⅴ)、Ni、Fe等能够在流通式系统中被过滤器有效地拦截,避免了二次污染的发生,污染水体得到净化。以上结果可为流通式电芬顿系统处理含As(Ⅲ)的地下水提供参考。Abstract: In order to provide a new solution for the efficient removal of As(Ⅲ) in groundwater, a flow-through electro-Fenton system was proposed in this study. The effects of key factors such as current density, pH, aeration rate, flow rate, electrolyte concentration, and coexisting ions on the removal efficiency of As(Ⅲ) were investigated. In addition, the As(Ⅲ) removal mechanism by the electro-Fenton system was analyzed, and the treatment effect of this system under continuous operation conditions was evaluated. The results showed that the removal efficiency of As(Ⅲ) in groundwater could reach nearly 100% under optimum conditions (current density of 7.6 mA·cm−2, pH 6, flow rate of 20 mL·min−1, aeration rate of 80 mL/min, electrolyte concentration of 100 mg·L−1). This system could have an important performance across a near-neutral pH range, and it could maintain good treatment stability under continuous running conditions. The mechanism studies indicated that ·OH and HO2· could promote As(Ⅲ) removal together by the electro-Fenton system. Moreover, the As(Ⅴ), Ni, Fe generated in this process could be effectively intercepted by the filter in the flow-through system, and the occurrence of secondary pollution was avoided, then the wastewater was purified. The above results could provide references for the efficient treatment of groundwater containing As(Ⅲ) by the flow-through electro-Fenton system.
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Key words:
- groundwater /
- As(Ⅲ) /
- flow-through electro-Fenton /
- removal mechanism /
- continuous operation
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