Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley, CA, USA.
Department of Civil Engineering, Jadavpur University, Kolkata, India.
Water Res. 2020 May 15;175:115668. doi: 10.1016/j.watres.2020.115668. Epub 2020 Feb 29.
Iron electrocoagulation (Fe-EC) is an effective technology to remove arsenic (As) from groundwater used for drinking. A commonly noted limitation of Fe-EC is fouling or passivation of electrode surfaces via rust accumulation over long-term use. In this study, we examined the effect of removing electrode surface layers on the performance of a large-scale (10,000 L/d capacity) Fe-EC plant in West Bengal, India. We also characterized the layers formed on the electrodes in active use for over 2 years at this plant. The electrode surfaces developed three distinct horizontal sections of layers that consisted of different minerals: calcite, Fe(III) precipitates and magnetite near the top, magnetite in the middle, and Fe(III) precipitates and magnetite near the bottom. The interior of all surface layers adjacent to the Fe(0) metal was dominated by magnetite. We determined the impact of surface layer removal by mechanical abrasion on Fe-EC performance by measuring solution composition (As, Fe, P, Si, Mn, Ca, pH, DO) and electrochemical parameters (total cell voltage and electrode interface potentials) during electrolysis. After electrode cleaning, the Fe concentration in the bulk solution increased substantially from 15.2 to 41.5 mg/L. This higher Fe concentration led to increased removal of a number of solutes. For As, the concentration reached below the 10 μg/L WHO MCL more rapidly and with less total Fe consumed (i.e. less electrical energy) after cleaning (128.4 μg/L As removed per kWh) compared to before cleaning (72.9 μg/L As removed per kWh). Similarly, the removal of P and Si improved after cleaning by 0.3 mg/L/kWh and 1.1 mg/L/kWh, respectively. Our results show that mechanically removing the surface layers that accumulate on electrodes over extended periods of Fe-EC operation can restore Fe-EC system efficiency (concentration of solute removed/kWh delivered). Since Fe release into the bulk solution substantially increased upon electrode cleaning, our results also suggest that routine electrode maintenance can ensure robust and reliable Fe-EC performance over year-long timescales.
铁电凝聚（Fe-EC）是一种从饮用水中去除砷（As）的有效技术。Fe-EC 的一个常见局限性是，在长期使用过程中，电极表面会因铁锈积累而结垢或钝化。在这项研究中，我们研究了去除电极表面层对印度西孟加拉邦一个大型（10000 L/d 容量）Fe-EC 工厂性能的影响。我们还对该工厂使用超过 2 年的活性电极上形成的层进行了特征描述。电极表面形成了三个不同的水平层，由不同的矿物质组成：靠近顶部的方解石、Fe(III)沉淀物和磁铁矿，中间是磁铁矿，靠近底部的是 Fe(III)沉淀物和磁铁矿。所有靠近 Fe(0)金属的表面层的内部都以磁铁矿为主。我们通过测量电解过程中的溶液成分（As、Fe、P、Si、Mn、Ca、pH、DO）和电化学参数（总电池电压和电极界面电位）来确定通过机械研磨去除表面层对 Fe-EC 性能的影响。在电极清洗后，大量的 Fe 浓度从 15.2 增加到 41.5 mg/L。更高的 Fe 浓度导致许多溶质的去除量增加。对于 As，在清洗后（每千瓦时去除 128.4μg/L As），其浓度更快地达到低于 10μg/L 的世界卫生组织 MCL，且消耗的总 Fe 更少（即每千瓦时消耗的电能更少），而在清洗前（每千瓦时去除 72.9μg/L As）则不然。同样，在清洗后，P 和 Si 的去除率分别提高了 0.3mg/L/kWh 和 1.1mg/L/kWh。我们的结果表明，通过机械去除在 Fe-EC 操作过程中长时间积累在电极上的表面层，可以恢复 Fe-EC 系统的效率（去除的溶质浓度/kWh 输送）。由于在电极清洗后，Fe 大量释放到溶液中，我们的结果还表明，常规的电极维护可以确保 Fe-EC 在长达一年的时间内具有稳健可靠的性能。
