Bioethanol (Bio-Fuel) Production From Agro-Waste Using Yeast Isolates From Nigeria

ABSTRACT

Bio-fuels are fuels derived from biological materials or their by-products such as agricultural waste. A study was carried out to assess the production of bio-fuel (bioethanol) from some hydrolyzed agricultural wastes using yeast species isolated from Cola acuminata, Ipomoea batatas, Manihot esculenta, Pennisetum glaucum, Sorghum bicolor, Solanum tuberosum, Zea mays and palmwine (from Elaeis guineensis). Eight yeast species including Candida krusei, Candida tropicalis strain A, Candida tropicalis strain B, Kluyveromyces marxianus, Pichia caribbica, Saccharomyces cerevisiae strain A, Saccharomyces cerevisiae strain B and Schizosaccharomyces pombe were used. The agrowastes and starchy substrates were pretreated through milling, saccharification with mineral acid (H2SO4/HCl) and Anacardium occidentale (cashew) Nut Shell Extract (CNSE). Substrates were distilled after 72 h of fermentation. The quantity of bioethanol produced varied with substrates and organisms used. The analysis of the CNSE revealed the presence of hydrolytic enzymes such as endoglucanase, exoglucanase and xylanase in varying concentrations. Biochemical analysis and DNA sequencing revealed that some of the fungal species are probably new strains. Using 100 g hydrolyzed substrates, the highest amount (33.34 ± 2.81 g/L) of bioethanol was obtained from sweet potato tuber hydrolyzed with 50 ml of 50% HCl and fermented with S. pombe. Plantain peel hydrolyzed with CNSE and fermented with S. pombe produced 28.12±1.61 g/L of bioethanol. The quantity of reducing sugar in the agro-waste hydrolyzed with CNSE was maximum of 491 mg/g in sugarcane chaff and minimum of 46 mg/g in rice husk. Sugar fermentation test of the yeasts showed that they can ferment sugars such as glucose, lactose, maltose, fructose and xylose. Lactose and xylose were fermented.