Taxonomic classification of sulphate-reducing bacteria communities attached to biocathode in hydrogen-producing microbial electrolysis cell

Abstract

Microbial electrolysis cells (MECs) have rapidly evolved as a promising technology to produce hydrogen from organic sources through anodic and cathodic electrochemical reactions. The MEC cathode has a rate-limiting effect on the hydrogen evolution reaction (HER) that necessitated the usage of expensive metal catalysts. Biocathode defined as microorganisms attached to the cathode is a promising alternative to abiotic catalysts for hydrogen production. Sulphate-reducing bacteria (SRB) are a potential source for biocathode enrichment. This study unlike previous literature mainly focused on the detailed characterization of autotrophic SRB-based biocathode MEC which produces hydrogen from a mixed culture source. The HER of MEC was optimized prior to the characterization step by adjusting sodium sulphate concentration, hydrogen feeding step during enrichment and adjusting pH of the media. Hydrogen production rate drastically increased from 0.15 m3/(m3 d) in the mixed culture-catalysed cathode to 1.53 m3/(m3 d) after three months of enrichment, while the cathodic charge transfer resistance decreased substantially from 463 to 1.8 Ω over the same enrichment period. DNA of the microbial communities attached to the biocathodes was then extracted at different enrichment times, and the dominant communities were identified using metagenomic amplicon sequencing. Moreover, Desulfovibrio was detected as the dominant genus in the enriched biocathodes through the enrichment stages. The findings of this study enable development of less-complex system for biocathode-based hydrogen production from any mixed culture sources. This in turn facilitates future commercial-scale implementation of MEC technology.