Bioethanol Production from Oryza sativa Husk Combined with Sorghum sp. Bran: Optimization and Yield in the Sudano-Sahelian Zone of Cameroon

Abstract

This article explores the production of bioethanol from a combination of Oryza sativa husk and Sorghum sp. bran, two abundant agricultural biomasses. The main objective of this study is to optimize the ratio between these two materials, test different chemical pretreatments (acidic and alkaline), and compare the efficiency of two fermentation yeasts, Saccharomyces cerevisiae and Pichia stipitis, in order to maximize bioethanol yield. Optimization of the ratio between Oryza sativa husk and sorghum bran showed that a 50:50 ratio produced the highest ethanol yield, with a concentration of 37.5 g/L and a conversion efficiency of 0.42 g ethanol/g dry biomass. This ratio provides an optimal balance between fermentable sugars derived from the starch in Sorghum sp. bran and the cellulose in Oryza sativa husk, thereby facilitating enzymatic hydrolysis and fermentation. Regarding pretreatments, the study compared an acid pretreatment using 1.5% H₂SO₄ and an alkaline pretreatment using 3% NaOH. The alkaline pretreatment was more effective in breaking down lignocellulose and releasing fermentable sugars, leading to a higher ethanol yield (37.5 g/L) compared to the acid pretreatment (33.0 g/L). As for the yeasts, Saccharomyces cerevisiae showed a higher ethanol yield (37.5 g/L) than Pichia stipitis (32.5 g/L), due to its greater ability to ferment hexoses (glucose) present in the substrate. However, Pichia stipitis may be beneficial for substrates rich in pentoses. The results of this study demonstrate the efficiency of combining rice husk and sorghum bran for bioethanol production. Optimization of the substrate ratio, alkaline pretreatment, and the use of Saccharomyces cerevisiae offer a promising approach for more sustainable bioethanol production from local agricultural biomass.

Keywords: Bioethanol, Oryza sativa husk, Sorghum sp. bran, acid pretreatment, alkaline pretreatment, Saccharomyces cerevisiae, Pichia stipitis, optimization, yield