The compound pollution of nitrate and hexavalent chromium (Cr(VI)) in groundwater poses a serious hazard to human health and ecology. The use of H₂-connected graphene oxide loaded nano zero-valent iron (rGO/nZVI) chemical reduction coupled with hydrogen autotrophic bioreduction system is expected to reduce the economic cost and alleviate the problem of gas blockage. In this study, we investigated the process and mechanism of the removal of NO₃^–/Cr(VI) compound pollution by rGO/nZVI coupled HAM under weak magnetic field (WMF). The results showed that rGO/nZVI coupled HAM system had the highest removal of NO₃^– (93.8 %), and the allocation ratio of chemical reduction to biological reduction of nitrate was about 4:1. Under the compound pollution conditions, the removal of Cr(VI) in the coupled system could reach 100 %. The abiotic reaction mechanism should be the main pathway for Cr(VI) removal, and the ratio of chemical reduction to biological reduction was 99:1 within 24 h. The results showed that the chemical reduction and biological reduction of Cr(VI) in the coupled system was the most effective way to remove Cr(VI). High N₂ conversion of rGO/nZVI coupled with HAM system at 30 mT was obtained (66.98 % and 43.17 %) at NO₃^– and NO₃^–/Cr(VI) composite contamination systems, respectively. The presence of WMF corroded rGO/nZVI towards lepidocrocite moving the denitrification process towards harmlessness (high N₂ selectivity). This finding provides a theoretical basis of the coupled system of rGO/nZVI and HAM for the groundwater compound pollution removal.

中文翻译：

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在弱磁场下使用 rGO/nZVI 耦合氢自养生物增强 Cr（VI） 和硝酸盐还原：性能和机制


地下水中硝酸盐和六价铬 （Cr（VI）） 的复合污染对人类健康和生态构成严重危害。使用 H₂ 连接的负载氧化石墨烯的纳米零价铁 （rGO/nZVI） 化学还原与氢自养生物还原系统相结合，有望降低经济成本并缓解气体堵塞问题。在本研究中，我们研究了弱磁场 （WMF） 下 rGO/nZVI 耦合 HAM 去除 NO₃^–/Cr（VI） 化合物污染的过程和机制。结果表明，rGO/nZVI 偶联 HAM 系统对 NO₃^– 的去除率最高 （93.8 %），硝酸盐化学还原与生物还原的分配比例约为 4：1。在化合物污染条件下，耦合体系中 Cr（VI） 的去除率可达 100 %。非生物反应机理应是去除 Cr（VI） 的主要途径，24 h 内化学还原与生物还原的比例为 99：1。结果表明，耦合体系中 Cr（VI） 的化学还原和生物还原是去除 Cr（VI） 的最有效方法。在 NO₃^– 和 NO₃^–/Cr（VI） 复合污染系统中，rGO/nZVI 与 HAM 系统耦合在 30 mT 下的高 N₂ 转化率分别为 （66.98 % 和 43.17 %）。WMF 的存在腐蚀了 rGO/nZVI 向锂云母方向发展，使反硝化过程走向无害（高 N₂ 选择性）。这一发现为 rGO/nZVI 和 HAM 耦合系统去除地下水化合物污染提供了理论依据。