Modeling of a still reactor banana peels fermentation: waste to energy approach

Abstract

Limited information on optimal biofuel production conditions leads to non-economical and inefficient process hence uncompetitive low grade biofuels. Fermentation process optimization is very crucial especially while using relatively low fermentable sugars substrates. In this research, banana peels derived from Ngombe cultivar were dried, ground into fine powder to pass through a 1 mm screen, and then hydrolyzed using 60% concentrated H2SO4 at 50oC. Bioethanol was produced by anaerobic fermentation of the hydrolysate using Saccharomyces cerevisiae. Erlenmeyer Flasks fitted with non-return air valves were used as laboratory scale still reactors. Fermentation systems were subjected to various conditions based on half factorial Central Composite Rotatable Design (CCRD). Total Reducing Sugars (TRS) concentrations and bioethanol yield analyses were done by Dubois and Gas Chromatography methods respectively. Optimum bioethanol yield of 13.09 ml/L was obtained at 180 g/L substrate concentration, 35oC fermentation temperature, 5.5 initial medium pH, 2 g/L yeast concentration, and 120 hours incubation corresponding to a TRS degradation of 30.30 g/L. Lowest yield of 1.44 ml/L was obtained at 84.86 g/L substrate concentration, 35oC fermentation temperature, 5.5 initial medium pH, 2 g/L yeast concentration, and 120 hours incubation corresponding to a TRS degradation of 2.85 g/L. Maximum bioethanol yield realized from these wastes manifested viable concentrations which could further be distilled and dried to be used as an energy resource. The mathematical model developed also posed as a predictive tool on bioethanol yield while using banana peels and similar wastes in energy resource generation.