Methane Production from the Co-digestion of Algal Biomass with Crude Glycerol by Anaerobic Mixed Cultures

The optimization of factors affecting methane production from the co-digestion of algal biomass with crude glycerol was investigated using response surface methodology with a central composite design. The investigated parameters included algal biomass, crude glycerol and inoculum concentration. The inoculum and algal biomass concentration had a significant individual effect on the methane production (p ≤ 0.05). The interactive effect on methane production was found to be between algal biomass and crude glycerol (p ≤ 0.05). The optimal conditions were 20.02 g-VS/L of crude glycerol, 9.76 g-VS/L of inoculum concentration and 5.50 g-VS/L of algal biomass. Under optimum conditions, the maximum methane production of 58.88 mL-CH4/L was obtained. The difference between the observed methane production (58.88 mL-CH4/L) and the predicted methane (68.94 mL-CH4/L) was 14.59%. Under the optimum conditions, the energy production of 92.47 J/g-VSadded was obtained. The polymerase chain reaction-denaturing gradient gel electrophoresis analysis indicated that the methane producers present in the fermentation broth were Methanosarcina sp., Methanoregula sp., Methanospirillum sp. and Methanoculleus sp.