Sun Jingyi, Garg Shikha, Waite T David
UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia.
UNSW Centre for Transformational Environmental Technologies, Yixing, Jiangsu Province 214206, P. R. China.
Environ Sci Technol. 2023 Oct 3;57(39):14726-14736. doi: 10.1021/acs.est.3c03922. Epub 2023 Sep 18.
Electrochemical reduction of nitrate is a promising method for the removal of nitrate from contaminated groundwater. However, the presence of hardness cations (Ca and Mg) in groundwaters hampers the electroreduction of nitrate as a result of the precipitation of carbonate-containing solids of these elements on the cathode surface. Thus, some pretreatment process is required to remove unwanted hardness cations. Herein, we present a proof-of-concept of a novel three-chambered flow electrode unit, constituting a flow electrode capacitive deionization (FCDI) unit and a flow cathode (FC) unit, which achieves cation removal, nitrate capture and reduction, and ammonia generation in a single cell without the need for any additional chemicals/electrolyte. The addition of the FCDI unit not only achieves removal of hardness cations but also concentrates the nitrate ions and other anions, which facilitates nitrate reduction in the subsequent FC unit. Results show that the FCDI cell voltage influences electrode stability but has a minimal impact on the overall nitrate removal performance. The concentration of coexisting anions influences the nitrate removal due to competitive sorption of anions on the electrode surface. Our results further show that stable electrochemical performance was obtained over 26 h of operation. Overall, this study provides a scalable strategy for continuous nitrate electroreduction and ammonia generation from nitrate contaminated groundwaters containing hardness ions.
电化学还原硝酸盐是一种从受污染地下水中去除硝酸盐的很有前景的方法。然而，由于这些元素的含碳酸盐固体在阴极表面沉淀，地下水中硬度阳离子（钙和镁）的存在阻碍了硝酸盐的电还原。因此，需要一些预处理过程来去除不需要的硬度阳离子。在此，我们展示了一种新型三室流动电极单元的概念验证，该单元由流动电极电容去离子化（FCDI）单元和流动阴极（FC）单元组成，可在单个电池中实现阳离子去除、硝酸盐捕获与还原以及氨生成，无需任何额外的化学物质/电解质。FCDI单元的加入不仅实现了硬度阳离子的去除，还浓缩了硝酸根离子和其他阴离子，这有利于后续FC单元中的硝酸盐还原。结果表明，FCDI电池电压影响电极稳定性，但对整体硝酸盐去除性能影响最小。共存阴离子的浓度由于阴离子在电极表面的竞争吸附而影响硝酸盐去除。我们的结果进一步表明，在26小时的运行过程中获得了稳定的电化学性能。总体而言，本研究为从含有硬度离子的硝酸盐污染地下水中连续进行硝酸盐电还原和氨生成提供了一种可扩展的策略。
