AbstractThis study presents a multifaceted approach combining characterization of microbial communities, extracellular polymeric substances (EPS), reactive oxygen species (ROS), and expression of genes associated with extracellular electron transfer (EET) to shed light on their significance on electro-methanogenic activity in different biocathode materials. Carbon fiber and stainless-steel mesh biocathode were tested in microbial electrolysis cell assisted anaerobic digestion (MEC-AD) systems fed with synthetic glucose medium. Despite the higher specific surface area provided by carbon fiber biocathode, methanogenesis performance was much inferior (100.3 mL CH4) than that obtained from a stainless steel biocathode (179.5 mL CH4) operated under the same operating conditions. Interestingly, biofilms did not entirely cover the surfaces of carbon fibers, while stainless steel biocathode showed evenly denser biofilms with higher biovolume (30.2±4.2 vs. 13.5±2.8 μm3/μm2). Analyses of microbial communities indicated that the key mechanism for electro-methanogenesis in both reactors was hydrogenotrophic methanogenesis by Methanobacterium species. Along with the effective catalysis of hydrogen evolution reaction (HER), a higher abundance of known hydrogenotrophic Methanobacterium sp. and homoacetogenic Acetobacterium appeared to play a major role in superior methanogenesis on stainless steel biocathode. The most considerable secretion of EPS accompanied by the lowest ROS level in stainless steel biocathode indicated that higher EPS possibly protected cells from harsh metabolic conditions (e.g., unfavorable local pH) induced by faster HER. Moreover, the redox activity of EPS derived from biocathode, as well as expressions of EET genes, suggested that electro-methanogenesis via direct electron transfer might have occurred to some extent in both biocathodes. Overall, the results of this study have important significance in the development of effective biocathode for MEC-AD systems.
The Synergistic Effect of Proteins and Reactive Oxygen Species on Electrochemical Behaviour of 316L Stainless Steel for Biomedical Applications
