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为改善农村公共卫生和环境质量,我国开展了农村厕所革命的工作[1]。虽然多年厕改已取得阶段性成效,但一些农村仍存在诸如化粪池污水缺乏专人收集处理、村级污水处理站运行不畅等问题,这不仅影响“厕所革命”实效,还造成了“二次污染”[2]。主流的分散式改厕由于其化粪池的污水主要由群众自行处理,一些农户或因不会处理、无处处理、处理麻烦等原因,将化粪池污水直接排入农村沟渠、农田;由于现有生化工艺运行管理困难等问题,导致了部分农村污水处理设施处于非正常运行或停止运行的状态[3]。而且,分散式改厕主要靠生物菌、三格化粪池自然降解等方式处理污水,部分技术尚不成熟,且后续管护比较复杂,导致污水处理站排水存在富营养化问题[4]。因此,亟需开发一种高效易操作的技术助力农村摆脱当前厕所存在的困境。
农村生活污水 (包括厕所黑水) 分散排放且水量总体较小、水质波动较大,传统生物处理工艺较难运行,且常规的混凝澄清池面临加药和絮体后处理等问题。电化学氧化技术具有较高的催化降解能力,且无需添加外源药剂、反应条件温和、操作简单、易于自动化运行[5-6]。电化学净水装置体积小、水力停留时间短、处理效果稳定,并且控制方便、启动快捷、无二次污染,适合处理农村分散式污水。该技术可以利用析氯反应原位产生活性氯,有效氧化污水中的化学需氧量 (chemical oxygen demand,COD) 和氨氮,同时高效灭活水中病原微生物,电化学氧化工艺解决了农村厕所黑臭排水富营养化和排放安全性的问题[7-8]。在既定的配置和设计理念下保持电极材料的长期使用寿命是电催化工艺研发的重点,特别是对于在厕所黑臭水的恶劣水质条件下运行的基于氧化涂层的析氯氧化技术工艺。形稳电极 (dimensionally stable anodes,DSA) 具有导电性能好、电催化活性高、抗腐蚀能力强以及制备方法简单等优点[9-10],且由于其具有良好的尺寸稳定性而被广泛应用于环境保护、电镀、电合成、电催化等领域的生产实践中。而铱系阳极是较为理想的电解析氯用电极材料,具有良好的电催化活性和极高的电化学稳定性[11-12]。目前,常用到的铱系电极有Ti/IrTa、Ti/RuIrTi、Ti/RuTiIrSn等。电极涂层与金属基体间的结合强度是影响氧化物阳极稳定性的一个非常重要的因素,而钛阳极产品基体的表面预处理工艺直接影响涂层与基体的结合效果[13]。制定并优化适当的钛阳极基体预处理工艺,对钛阳极产品的后续电化学性能以及使用寿命至关重要[14]。然而,钛基铱钽涂层阳极存在服役失效的问题,使用寿命不够长,需要提高电极制备工艺的稳定性,改善析氯活性[15]。因此如何合理调配涂层与Ti基体,关系到电极的析氯性能、化学稳定性和使用寿命,进一步影响电化学氧化净水工艺的运行成本和农村厕所黑臭污水的处理效果。
在本研究中,通过探究钛基底的预处理方式、不同比例和组成的氧化物涂层涂覆方法以及电极的烧结条件,优化了电极的析氯性能、电化学稳定性和工作寿命,并将其应用在厕所黑臭水的处理中,分析了电极对污水中的COD和氨氮的处理效果,并对电极的制备成本进行了评估。本研究提出了针对厕所黑臭水体处理的涂层电极优化的制备方法,为分散式污水排放存在的富营养化问题提供了可行的解决思路。
用于农村厕所黑水处理的铱钽涂层电极的优化制备及其对析氯性能的影响
Optimized preparation of iridium-tantalum coated electrodes for black water treatment in rural toilets and its effect on chlorine evolution performance
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摘要: 农村厕所黑水通常采用生物法进行处理,存在处理效果不稳定、运行管理复杂等问题。通过对传统钛铱电极进行优化制备,成功构筑了铱钽涂层系列电极 (Tx) 和铱钽锡锑钴涂层系列电极 (Cx) 。利用电化学原位产氯,实现了有机物的氧化降解并同步去除氨氮。优化电极复合氧化物涂层的配方,发现喷涂T3电极 (IrTa氧化物涂层0.6 mg·cm−2,Ti氧化物涂层0.75 mg·cm−2) 在2.4 V的工作电压下表现了最高效的净水效能,60 min内去除了厕所黑臭水生化处理出水50%的COD。系统研究了表面清洁工艺和烧结工艺对电极析氯效能的影响,发现喷砂结合酸洗的表面清洁过程、滚涂的涂层固定过程、500 °C的烧结过程构筑的T3电极具有最高的析氯效能和强化寿命。本研究为分散式污水排放存在的富营养化问题提供了可行的解决思路。Abstract: Black and odorous sewage of rural toilets is commonly treated by biological methods, which suffer from unstable treatment efficiency and complicated operation management. In this study, an iridium-tantalum coated series electrode (Tx) and an iridium-tantalum tin-antimony-cobalt coated series electrode (Cx) were successfully constructed by optimizing the preparation of traditional titanium-iridium electrodes. The oxidative degradation of organic matter and simultaneous removal of ammonia nitrogen were achieved using electrochemical in situ chlorine production. By optimizing the formulation of the electrode composite oxide coating, it was found that the fully sprayed T3 electrode (IrTa oxide coating 0.6 mg·cm−2, Ti oxide coating 0.75 mg·cm−2) exhibited the highest water purification efficiency under a working voltage of 2.4 V, removing 50% of the COD from rural black water within 60 minutes. The surface cleaning process and sintering process were systematically studied on the chlorine production efficiency of the electrode, and it was found that the T3 electrode constructed by sand blasting combined with acid cleaning surface cleaning process, roller coating fixed process, and sintering process at 500 °C had the highest chlorine production efficiency and enhanced service life. This study provides a feasible solution for the eutrophication problem of decentralized sewage discharge.
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表 1 析氯阳极材料成分汇总表
Table 1. Summary of the composition of chlorine-evolving anode materials mg·cm−2
编号 IrTa金属
氧化物Ti金属
氧化物TiCo金属
氧化物SnSb金属
氧化物T1 0.3 0.5 — — T2 0.6 0.5 — — T3 0.6 0.75 — — C1 0.3 — 0.5 1.0 C2 0.6 — 0.5 1.0 C3 0.3 — 0.5 — 表 2 电极成本估算
Table 2. Estimation of electrode cost
序号 类目 极板价格/(元·片−1) 组件价格/ (元·套−1) 备注 1 电极
基底阳极 125.2 876.4 阳极为钛板,阴极为316不锈钢 阴极 45.3 362.4 2 涂覆用化学品 342.5 2 397.5 主要为氯化铱酸 3 耗材 21.4 149.8 喷砂用砂石等 4 连接件 0 409.9 钛螺钉、接线端子、焊条等 5 人工 — 900 — 合计 — 5 096 价格不包括管理费、税费、交通费和利润 -
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