Regulatory function of divalent cations in controlling the acidogenic biohydrogen production process

The functional role of divalent cations viz., iron (Fe2+), magnesium (Mg2+), nickel (Ni2+), zinc (Zn2+) and manganese (Mn2+) in regulating the biohydrogen (H-2) production potential of a biocatalyst was evaluated under varying concentrations. The optimum conditions were evaluated in detail and compared with the principle conditions for enhanced conversion efficiency. Higher concentration of Fe2+ showed an enhanced H-2 production efficiency of the biocatalyst (61.94 mmol) due to its role as a component of hydrogenase and ferredoxin. On the contrary, a higher concentration of Mg+2 showed a higher substrate utilization capability (76.46%) of the biocatalyst. The optimum metal concentration showed a higher H-2 yield (18.23 mol kg(-1) CODR; 3.5 mol mol(-1) glucose) over principle operation conditions (14.76 mol kg(-1) CODR; 2.84 mol mol(-1) glucose). Higher concentrations of acetate (78 +/- 6%) as the metabolic intermediate over butyrate (12 +/- 2%) supported the observed higher H-2 yields. Higher reductive catalytic current over oxidative current along with the enhanced dehydrogenase activity supported the higher H-2 production efficiency. Shift in the redox Tafel slope was witnessed near zero in the case of Fe2+ and optimum conditions indicating the simultaneous oxidation and reduction reactions facilitating the availability of higher number of protons through metabolite inter-conversions that can make H-2. The presence of divalent cations at an optimum concentration will enhance the H-2 production capability of the biocatalyst. However, elevated levels of metal concentration showed a negative influence on the biocatalyst efficiency.