Interactions between arsenic migration and CH4 emission in a soil bioelectrochemical system under the effect of zero-valent iron

Dissimilatory soil arsenic (As) reduction and release are driven by microbial extracellular electron transfer (EET), while reverse EET mediates soil methane (CH4) emission. Nevertheless, the detailed biogeochemical mechanisms underlying the tight links between soil As migration and methanogenesis are unclear. This study used a bioelectrochemical-based system (BES) to explore the potential effects of zero-valent iron (ZVI) addition on As migration-CH4 emission interactions from chemical and microbiological perspectives. Voltage and ZVI amendment experiments showed that dissolved As was efficiently immobilized with increased CH4 production in the soil BES, As release and CH4 production exhibited a high negative exponential correlation, and reductive As dissolution could be entirely inhibited in the methanogenic stage. Gene quantification and bacterial community analysis showed that in contrast to applied voltage, ZVI changed the spatial heterogeneity of the distribution of electroactive microorganisms in the BES, significantly decreasing the relative abundance of arrA and dissimilatory As/Fe-reducing bacteria (e.g., Geobacter) while increasing the abundance of aceticlastic methanogens (Methanosaeta), which then dominated CH4 production and As immobilization after ZVI incorporation. In addition to biogeochemical activities, coprecipitation with ferric (iron) contributed 77-93% dissolved As

Automated summary

This study investigated the potential effects of zero-valent iron (ZVI) on the interactions between soil arsenic migration and methane emission using a bioelectrochemical system. The results showed that ZVI efficiently immobilized dissolved arsenic and increased methane production. Gene quantification and bacterial community analysis revealed that ZVI changed the spatial distribution of electroactive microorganisms, leading to a decrease in dissimilatory As/Fe-reducing bacteria and an increase in aceticlastic methanogens, which dominated methane production and arsenic immobilization. Additionally, coprecipitation with ferric iron contributed a significant portion of the dissolved arsenic.