The enhancement on biohydrogen production by the driving forces from extracellular iron oxide respiration.

Biohydrogen productions from xylose and glucose under dark condition were enhanced by the presence of natural Fe3O4. The electron equivalent of H2 fractions accounted for 4.55 % and 5.69 % of the total given xylose and glucose in the experiments without Fe3O4, and that were correspondingly increased to 5.14 % and 6.50 % in the experiments with 100 mg/L of Fe3O4, respectively. Moreover, Fe3O4 increased the total intracellular NAD(H) concentrations by 8.84 % and 8.37 %, and boosted the ratios of NADH/NAD+ by 8.33 % and 17.72 % in xylose and glucose fermentation, respectively, comparing to the corresponding control experiments. The formation of electron couples of Fe(III)/Fe(II) during the iron oxide respiration and more generation of active extracellular polymeric substances components were determined as the important reasons for the improved biohydrogen production performance. Thus, a promotion mechanism of the internal "driving forces" from extracellular iron oxide respiration on the biohydrogen production was proposed.