Elucidating acetogenic H2 consumption in dark fermentation using flux balance analysis

In this study, a flux balance analysis (FBA) was adopted to estimate the activity of acetogenic H2-consuming reaction. Experimental data at different substrate concentrations of 10, 20, and 30 g COD/L showing the lowest, medium, and highest H2 yields, respectively, were used in the FBA to calculate the fluxes. It was interesting to note that the hydrogenase activity based on R12 (2Fd+ + 2H+ → 2Fd2+ + H2, ferredoxin (Fd)) flux was most active at 10 g COD/L. The flux of R17 (4H2 + 2CO2 → CH3COOH), a mechanism for reutilizing produced H2, increased in steps of 0.030, 0.119, and 0.467 as the substrate concentration decreased. Contradictory to our general understanding, acetate production found to have a negligible or even negative effect on the final H2 yield in dark fermentation.