Enhanced hydrogen and volatile fatty acid production from sweet sorghum stalks by two-steps dark fermentation with dilute acid treatment in between

This study investigated the potential of hydrogen and volatile fatty acid coproduction from two steps dark fermentation with dilute acid treatments of the residual slurry after 1st step fermentation. Sweet sorghum stalks (SS) was used as substrate along with Clostridium thermosaccharolyticum as production microbe. Residual lignocelluloses after 1st step fermentation were treated for 1 h by sulfuric acid concentration of 0.25, 0.5, 1.0, 1.5, 2.0 and 2.5% (w/v) with different reaction temperature of 120, 90 and 60 °C were studied. The optimum severity conditions for the highest yield of products found from the treatment acid concentration of 1.5% (w/v) at 120 °C for 10 g/L of substrate concentration. Experimental data showed that two-step fermentation increased 76% hydrogen, 84% acetic acid and 113% of butyric acid production from single step. Maximum yields of hydrogen, acetic acid and butyric acid were 5.77 mmol/g-substrate, 2.17 g/L and 2.07 g/L respectively. This two-step fermentation for hydrogen and VFA production using the whole slurry would be a promising approach to SS biorefinery.