Dark fermentative biohydrogen production from rice mill wastewater

Summary Hydrogen (H2) is one of the most promising fuels for sustainable energy production. Microbial bio‐H2 fermentation is considered to be one of the environment friendly alternatives for satisfying the demand for fossil fuels. The study has aimed to isolate the effective bio‐H2 producing microbes from rice mill wastewater (RMWW) using various pre‐treatment enrichment methods. Among the 27 enriched isolates, three isolates produced higher H2 utilizing rice mill wastewater as the substrate. Molecular level identification revealed that the three bacterial strains were Bacillus thuringiensis‐RH1, Bacillus aerophilus‐RH2, and Bacillus beringensis‐AARAT1. Optimization studies revealed that B. thuringiensis‐RH1 would be a promising bio‐H2 producing bacterium with a yield of 0.96 ± 0.06 mol H2/ mol glucose utilizing 50% of rice mill wastewater at pH 5.5. Furthermore, the obtained optimized substrate concentration (50%) and pH (5.5) from batch fermentation were used in the 3 L batch bioreactor experiment using B. thuringiensis‐RH1. A higher hydrogen yield (HY) of 1.63 ± 0.14 mol H2/mol glucose using B. thuringiensis‐RH1 at 72 hours was obtained in the extensive scale up process.