School of Civil and Environmental Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332-0512, United States.
Environ Sci Technol. 2017 Nov 7;51(21):12956-12964. doi: 10.1021/acs.est.7b02777. Epub 2017 Oct 19.
Methanogenic bioelectrochemical systems (BESs), which convert carbon dioxide (CO) directly to methane (CH), promise to be an innovative technology for anaerobic digester biogas upgrading. Zero-valent iron (ZVI), which has previously been used to improve CH production in anaerobic digesters, has not been explored in methanogenic biocathodes. Thus, the objective of this study was to assess the effect of biocathode ZVI on BES performance at 1 and 2 g/L initial ZVI concentrations and at various cathode potentials (-0.65 to -0.80 V versus SHE). The total CH produced during a 7-day feeding cycle with 1 and 2 g/L initial ZVI was 2.8- and 2.9-fold higher, respectively, than the mean CH production in the four prior cycles without ZVI addition. Furthermore, CH production by the ZVI-amended biocathodes remained elevated throughout three subsequent feeding cycles, despite catholyte replacement and no new ZVI addition. The fourth cycle following a single ZVI addition of 1 g/L and 2 g/L yielded 123% and 231% more total CH than in the non-ZVI cycles, respectively. The higher CH production could not be fully explained by complete anaerobic oxidation of the ZVI and utilization of produced H by hydrogenotrophic methanogens. Microbial community analysis showed that the same phylotype, most closely related to Methanobrevibacter arboriphilus, dominated the archaeal community in the ZVI-free and ZVI-amended biocathodes. However, the bacterial community experienced substantial changes following ZVI exposure, with more Proteobacteria and fewer Bacteroidetes in the ZVI-amended biocathode. Furthermore, it is likely that a redox-active precipitate formed in the ZVI-amended biocathode, which sorbed to the electrode and/or biofilm, acted as a redox mediator, and enhanced electron transfer and CH production. Thus, ZVI may be used to increase biocathode CH production, assist in the start-up of an electromethanogenic biocathode, and/or maintain microbial activity during voltage interruptions.
产甲烷生物电化学系统（BESs）可将二氧化碳（CO）直接转化为甲烷（CH），有望成为一种用于厌氧消化沼气升级的创新技术。零价铁（ZVI）以前曾用于提高厌氧消化器中的 CH 产量，但尚未在产甲烷生物阴极中进行探索。因此，本研究的目的是评估生物阴极 ZVI 在 1 和 2 g/L 初始 ZVI 浓度和各种阴极电位（相对于 SHE 的-0.65 至-0.80 V）下对 BES 性能的影响。在添加 1 和 2 g/L 初始 ZVI 的 7 天进料周期中，总 CH 产量分别比不添加 ZVI 的前四个周期的平均 CH 产量高 2.8 和 2.9 倍。此外，尽管更换了阴极电解液且未添加新的 ZVI，但添加 ZVI 的生物阴极的 CH 产量仍在随后的三个进料周期中保持升高。在添加 1 g/L 和 2 g/L 的 ZVI 后的第四个周期，总 CH 产量分别比不添加 ZVI 的周期高 123%和 231%。更高的 CH 产量不能完全用 ZVI 的完全厌氧氧化和产氢甲烷菌利用产生的 H 来解释。微生物群落分析表明，在没有 ZVI 和添加 ZVI 的生物阴极中，相同的型，与 Methanobrevibacter arboriphilus 最为密切相关，主导了古菌群落。然而，在暴露于 ZVI 后，细菌群落发生了很大变化，添加 ZVI 的生物阴极中的变形菌更多，拟杆菌更少。此外，很可能在添加 ZVI 的生物阴极中形成了一种具有氧化还原活性的沉淀物，该沉淀物吸附在电极和/或生物膜上，充当氧化还原介体，增强了电子转移和 CH 产量。因此，ZVI 可用于提高生物阴极 CH 产量，帮助电甲烷生物阴极启动，以及/或在电压中断期间维持微生物活性。
