Characterization and bioethanol production from agricultural residues of rice and sweet sorghum in Kenya

Agro-processing residues are often undervalued and improperly disposed of in many developing countries, which contribute to environmental pollution and resource loss. This study evaluated the compositional characteristics and bioethanol production potential of underutilized postharvest residues from Basmati rice and sweet sorghum grown in Kenya. Proximate composition was determined using standard AOAC methods, while FT-IR and HPLC were used to characterize structural carbohydrates and fermentable sugars, respectively. The substrates were pretreated with dilute sulfuric acids (1.2 and 2.25%, w/w), detoxified with 2 M Ca(OH)2, pH 9, saccharified using cellulase enzymes, and fermented with Saccharomyces cerevisiae. Proximate analysis revealed moisture (4.3–9.1%) Protein (3.5–7.4%), fat (0.35–1.2%), ash (8.6–20.2%), and fiber (21.9–34.9%) contents. The substrates contained 32.1–39.7% cellulose, 26.0–29.4% hemicellulose, and 7.5–18.8% lignin. Glucose was the predominant fermentable sugar across all the substrates, with Basmati and Nerica husks containing the highest levels and yielding the greatest ethanol outputs of 8.9% and 8.43%, respectively, under 2.25% acid pretreatment. This study provides baseline data on postharvest residues from Basmati rice and sweet sorghum grown in Kenya and demonstrate their viability as promising feedstock for the production of second-generation bioethanol.