Improved bioethanol production from oil palm empty fruit bunch using different fermentation strategies

Abstract

Importance of the work: Bioethanol production from oil palm empty fruit bunch (OPEFB) may be improved by changing the fermentation strategy. Objectives: To investigate different fermentation strategies to achieve the highest bioethanol concentration and the lowest overall process time. Materials & Methods:For the first strategy, OPEFB was pretreated, hydrolyzed and fermented based on separate hydrolysis and fermentation (SHF) with saccharification at 50°C and fermentation at 30°C. The second strategy involved simultaneous saccharification and fermentation (SSF), with both at 37°C. The third strategy applied delayed simultaneous saccharification and fermentation (DSSF), involving hydrolyzation at 50°C that was subsequently reduced to 37°C, after which the yeast was inoculated and the processing continued. The bioethanol concentrations and overall process times of the three strategies were compared. Results: OPEFB consisted of 43.3 ± 0.89% cellulose, 20.3 ± 0.67% hemicellulose and 13.8 ± 0.65% lignin. After NaOH pretreatment, the cellulose content increased to 72.1 ± 0.70%. Different enzyme loadings (Cellic ® CTec2) were used at 5 filter paper units (FPU)/g, 10 FPU/g and 15 FPU/g of substrate. Reducing sugar was produced corresponding to the enzyme loading. However, 10 FPU was chosen as the optimum, with glucose being about 80% of the attained reducing sugar. Hence, it was appropriate for Saccharomyces cerevisiae fermentation. Then, the bioethanol production was compared for the three different fermentation strategies (SHF, SSF, and DSSF). The highest bioethanol production and productivity were from DSSF at 26.1 ± 0.18 g/L and 0.36 g/L/hr, respectively (p < 0.05). In addition, DSSF had the shortest overall process time of 73 hr. Main finding: The DSSF strategy was the best for bioethanol production from OPEFB producing the highest bioethanol concentration of 26.1 ± 0.18 g/L (p < 0.05) and the shortest process time of 73 hr compared to SHF and SSF.