Critical Role of Bicarbonate in Zero-Valent Iron for Hydrogen Generation and Biogas Upgrading in Anaerobic Digestion

This study evaluated the role of stainless steel (SS316) in anaerobic sludge processes, with a focus on its impact on microbial community structures and the potential facilitation of direct interspecies electron transfer (DIET) and CO2 reduction. SS316, known for its high conductivity but inability to generate hydrogen, was tested in environments where glucose and CO2 served as the sole carbon sources.Despite the conductive properties of SS316, the introduction of this material into anaerobic sludge did not significantly enhance methane production, maintaining levels comparable to controls without SS316. This outcome was consistent across experiments with both carbon sources, suggesting limited interaction between SS316 and the microbial mechanisms involved in methane generation.Microbial analysis using 16S rRNA next-generation sequencing revealed that the addition of SS316 did not significantly alter the composition of bacterial and archaeal communities. The microbial profiles in both the presence and absence of SS316 showed a similar dominance of Methanothrix and Methanolinea across all conditions. Notably, Methanobacterium appeared in smaller quantities, indicating its lesser role in the community dynamics under the study conditions.Further detailed microbial profiling showed that the presence of SS316 did not affect the relative abundance of key archaeal populations, which remained consistent even in varied experimental setups. This suggests that the potential for SS316 to facilitate DIET or significantly impact microbial electron transfer processes within these anaerobic systems is limited.Given the stability of microbial communities despite the introduction of a highly conductive material, the findings highlight the resilience and specificity of microbial interactions in anaerobic digestion processes. Future research may explore more targeted interventions or different conductive materials to better understand the conditions under which DIET can be enhanced in such systems.