Evaluating Acid and Alkali Pretreatment Methods for Optimizing Bioethanol Production from Rice Husks

The growing demand for sustainable energy sources has highlighted bioethanol as a promising alternative to fossil fuels due to its renewable nature and lower environmental impact. This study investigates the effectiveness of acid and alkali pretreatment methods in enhancing bioethanol production from rice husks which is a readily available agricultural waste. Saccharomyces cerevisiae, a yeast isolated from palm wine, was employed for the fermentation process. Rice husks were pretreated with dilute sulfuric acid and sodium hydroxide, respectively, to facilitate hydrolysis and the subsequent conversion of cellulose to fermentable sugars. The fermentation parameters, including ethanol yield, glycerol production and inhibitor concentrations, were analysed using gas chromatography-mass spectrometry. Results indicated that alkali pretreatment consistently yielded higher ethanol production compared to acid pretreatment, with maximum ethanol concentrations of 20.13 mg/L and 17.59 mg/L, respectively. Additionally, glucose levels were higher in acid hydrolysates, while xylose and arabinose levels were elevated in alkali hydrolysates. The study also revealed significant variations in inhibitor concentrations, with acetic and formic acids present in both hydrolysates and furfural detected only in acid hydrolysates on the final day of fermentation. However, the findings support the potential of rice husks as a viable substrate for bioethanol production, thus emphasizing the importance of pretreatment methods in optimizing yield. Moreover, the co-inoculation of S. cerevisiae with pentose-metabolizing organisms is suggested to further enhance bioethanol yield and reduce by-product formation. Following this, the research contributes to the sustainable utilization of agricultural waste while advancing the understanding of lignocellulosic biomass conversion for bioethanol production.