Bioethanol production from rice husk using different pretreatments and fermentation conditions

Bioethanol is an environmentally friendly alternative to petroleum energy sources. This study evaluated the effects of H₂O, HCl, NaOH and FeCl₃ pretreated rice husk feedstocks on the production of bioethanol. The pretreatments were carried out using water, 0.1 M HCl, NaOH and FeCl₃ at 121 °C for 15 min, followed by simultaneous saccharification and fermentation (SSF) as well as separate hydrolysis and fermentation (SHF). The raw and pretreated lignocellulosic feedstocks were analyzed using Fourier transform infrared spectroscopy. Saccharification and fermentation were accomplished using Trichoderma reesei cellulase and Saccharomyces cerevisiae, respectively. The products obtained after saccharification and fermentation were collected and analyzed for reducing sugars and ethanol contents using 3,5-dinitrosalicylic acid and high-performance liquid chromatography, respectively. Enzyme hydrolysis of the FeCl₃ and HCl treated samples resulted in hydrolysates containing 3.845 and 3.402 mg/ml glucose equivalent, respectively. In all pretreatments, SSF for each pretreatment produced more ethanol than the SHF method; the FeCl₃ pretreatment gave the highest ethanol yield of 3.011 ± 0.034 and 3.802 ± 0.041% in the SHF and SSF methods, respectively. Utilization of FeCl₃ pretreatment of rice husk is a potential option for bioethanol production in the future.