Glucose Conversion for Biobutanol Production from Fresh Chlorella sorokiniana via Direct Enzymatic Hydrolysis

Microalgae, which accumulate considerable carbohydrates, are a potential source of glucose for biofuel fermentation. In this study, we investigated the enzymatic hydrolysis efficiency of wet microalgal biomass compared with freeze-dried and oven-dried biomasses, both with and without an acidic pretreatment. With the dilute sulfuric acid pretreatment followed by amy (alpha-amylase and amyloglucosidase) and cellulase hydrolysis, approximately 95.4% of the glucose was recovered; however, 88.5% was released by the pretreatment with 2% (w/v) sulfuric acid, which indicates the potential of the acids for direct saccharification process. There were no considerable differences in the glucose yields among the three kinds of materials. In the direct amy hydrolysis without any pretreatment, a 78.7% glucose yield was obtained, and the addition of cellulase had no significant effect on the hydrolysis to glucose. Compared with the oven-dried biomass, the wet biomass produced a substantially higher glucose yield, which is possibly because the cross-linked cells of the oven-dried biomass prevented the accessibility of the enzymes. According to the results, the fresh microalgal biomass without cell disruption can be directly used for enzymatic hydrolysis to produce glucose. The enzymatic hydrolysate of the wet microalgal biomass was successfully used for acetone-butanol-ethanol (ABE) fermentation, which produced 7.2 g/L of ABE, indicating the application potential of wet microalgae in the bioalcohol fuel fermentation process.