Increased mining and ore processing of gold (Au) are leading to waters contaminated with Au(III) ions, and a common co-contaminant is nitrate (NO₃⁻). Here, we demonstrate that a hydrogen (H₂)-based membrane biofilm reactor (MBfR) enabled synergistic co-reductions of NO₃⁻ to N₂ and Au(III) to elemental Au° for over 250 days of continuous operation. Au(III) was reduced to Au⁰ nanoparticles (Au⁰NPs) that were retained within the biofilm's extracellular polymeric substances. NO₃⁻ and Au(III) were > 95% reduced at steady state for a wide range of influent conditions: NO₃⁻-N at 1 or 4 mM; Au(III) at 100, 200, or 500 mg/L. Metal-tolerant denitrifiers Azonexus, Pannoibacter, Thermomonas, and Cupriavidus were enriched, as were genes encoding metal reductases. The rate of Au(III) reduction was positively correlated with the abundance of NO₃⁻ and NO₂⁻ reductases, which supports the role of these reductases in Au(III) reduction. Remarkably, the Au(III)-reduction efficiency remained above 90% in the highly acidic condition, despite NO₂⁻ accumulation due to incomplete NO₃⁻ reduction; thus, the microbial community was resilient against environmental perturbation. By providing a mechanistic basis for Au recovery using the MBfR, this study establishes the MBfR as a promising and sustainable technology for treating wastewaters containing valuable metals, such as gold, in coordination with microbial denitrification.

中文翻译：

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在 H2 基膜生物膜反应器中存在 NO3− 的情况下，增强高水平 Au（III） 的长期还原


金 （Au） 的开采和矿石加工的增加导致水被 Au（III） 离子污染，常见的共污染物是硝酸盐 （NO₃⁻）。在这里，我们证明了基于氢 （H₂） 的膜生物膜反应器 （MBfR） 能够在超过 250 天的连续运行中将 NO₃⁻ 协同还原为 N₂，将 Au（III） 协同还原为元素 Au°。Au（III） 被还原为 Au⁰ 纳米颗粒 （Au⁰NPs），这些纳米颗粒保留在生物膜的细胞外聚合物物质中。在多种进水条件下，NO₃⁻ 和 Au（III） 在稳态下降低 > 95%：1 或 4 mM 时 NO₃⁻-N;Au（III） 在 100、200 或 500 mg/L 时富集。金属耐性反氮化剂 Azonexus、Pannoibacter、Thermomonas 和 Cupriavidus 富集，编码金属还原酶的基因也是如此。Au（III） 还原速率与 NO₃⁻ 和 NO₂⁻ 还原酶的丰度呈正相关，这支持这些还原酶在 Au（III） 还原中的作用。值得注意的是，在高酸性条件下，尽管由于 NO₃⁻ 还原不完全导致 NO₂⁻ 积累，但 Au（III） 还原效率保持在 90% 以上;因此，微生物群落对环境扰动具有弹性。通过使用 MBfR 为金回收提供机理基础，本研究将 MBfR 确立为一种有前途且可持续的技术，用于与微生物反氮化协同处理含有有价金属（如金）的废水。