Co-factors applicability in hydrogen production from rice straw hydrolysate in a bioelectrochemical system

Abstract

The hydrogen production efficiency of sulfate-reducing bacteria (SRB) is governed by complex hydrogenase metabolism functions depending on the metal co-factors concentrations. The potential of SRB rich in hydrogenase enzyme activity for hydrogen production is rarely explored. Therefore, in this study, the hydrogenase enzyme cofactors of Fe2+ (0.67–0.85 mM), Ni2+ (0.01–0.02 mM), and Se4+ (0.1 mM) were tested for hydrogen production from rice straw hydrolysate using response surface methodology optimized conditions. The Fe2+ and Se4+ ions are essentially required to express hydrogenases in SRB. The positive contribution of [FeFe] hydrogenase and negative impact of [NiFe] at a higher level of Ni2+ (p = 0.061) in Phase I (cofactor added in SO42− free Postage media), whereas, in Phase II (SO42− free Postage media added to residual of Phase I), Ni2+ dependent hydrogenase contributed more (p = 0.005) is a good indicator for higher hydrogen production. The hydrogenase enzyme expression is more positively correlated with Se4+ ions (Vector angle <5°), whereas lesser correlated with Ni2+ (Vector angle ∼30°). The higher Acetate/Butyrate ratio shows the existence of the acetate type of pathway correlated with high hydrogen production. The applied potential to the hydrolysates further improves the hydrogen production to 782.69% and 172.61% in ammonia and NaOH reactors, respectively.