Statistical optimization of biohydrogen and ethanol production from crude glycerol by microbial mixed culture

Design of Experiments (DoE) was applied to improve the ability of enriched activity sludge to efficiently convert crude glycerol from biodiesel industry into hydrogen and ethanol, using a very simple synthetic medium. Based on Plackett–Burman screening design, glycerol concentration, temperature and initial pH were identified as significant variables. Box–Behnken design and Response Surface Method (RSM) were then used for optimization. The maximum hydrogen yield of 0.96 mol H2/mol glycerol was estimated at the temperature of 37.0 °C, initial pH of 7.9 and glycerol concentration of 15.0 g/L. Maximum hydrogen production rate of 2191 mL/L/d was estimated at the temperature of 37.3 °C, initial pH of 8.0 and glycerol concentration of 15.2 g/L. Finally maximum ethanol production of 7.92 g/L was estimated at an initial pH of 8.0 and glycerol concentration of 15.0 g/L (temperature had no significant effect). These results show that it is possible to obtain both, high yield and production of hydrogen and ethanol together, using a very simple synthetic medium, without trace element- and vitamin solution, tryptone or yeast extract.