Fermentative hydrogen production using sorghum husk as a biomass feedstock and process optimization

The potential of isolated actinomycetes and fungi were evaluated for the cellulase and xylanase production under solid state fermentation conditions. Maximal secretion of enzymes was observed with Phanerochaete chrysosporium using soybean straw. The potential of the produced crude enzyme complex was demonstrated by two-step enzymatic hydrolysis of untreated and mild acidpretreated sorghum husk (SH). A cellulase dose of 10 filter paper units (FPU) released 563.21 mg of reducing sugar (RS) per gram of SH with 84.45% hydrolysis and 53.64% glucose yields, respectively. Finally, enzymatic hydrolysates of SH were utilized for hydrogen production by Clostridium beijerinckii. Effects of temperature, pH of media, and substrate concentration on the biohydrogen production from SH hydrolysates were investigated. The optimal conditions for maximal hydrogen production using SH hydrolysate were determined to be a loading of 5.0 g RS/L, at 35°C, and controlled pH at 5.5. Under these optimal conditions, the cumulative H₂ production, H₂ production rate, and H₂ yield were 1,117 mL/L, 46.54 mL/L/h, and 1.051 mol/mol RS, respectively. These results demonstrated a cost-effective hydrogen production is possible with sorghum husk as a lignocellulosic feedstock.