Optimisation of dilute acid hydrolysis for bioethanol production from selected agricultural wastes

Abstract

Firstly, yeasts were isolated from rotting orange and subjected to ethanol tolerance screening. Next, the substrates were subjected to dilute acid hydrolysis using different concentrations of HNO₃ (3 %, 4 % and 5 %) at 20 % solid loading and then autoclaved at 121 ^oC for 30 minutes. Dilute acid optimisation yielded varying amounts of reducing sugars. The 3 %, 4 % and 5 % HNO₃ solutions produced hydrolysates with the highest amounts of reducing sugars of 19.28 g/L, 16.36 g/L and 7.59 g/L from cassava peels, corn bran, and millet bran, respectively. Hydrolysate fermentation resulted in bioethanol concentrations of 7.73 g/L from cassava peels hydrolysate, 8.98 g/L from corn bran hydrolysate and 1.69 g/L from millet bran hydrolysate.