OPTIMIZATION OF PARAMETERS FOR BIO-ETHANOL PRODUCTION FROM SWEET POTATO (Ipomoea batatas) PEELS USING TAGUCHI METHOD

Abstract

Over the years, the demand for chemical energy has increased due to the growing population’s rising energy needs. Today’s demand for energy for heating, transportation, and industrial processing increases spontaneously; thus, environmental issues attributed to unclean energy sources are a point of concern. Renewable energy sources have been employed as the best alternative to meet energy needs and sustain a healthy environment. Bio-ethanol is a potential renewable energy source produced through a microbiological process known as fermentation. This research focused on the optimization of production parameters for bioethanol production from sweet potato (Ipomoea batatas) peels using the Taguchi method. The specific objectives were to determine the effect of HCl concentration on reducing sugars and pH after hydrolysis and fermentation; optimize production conditions for bioethanol from sweet potato peels-pH, time, yeast-substrate ratio, and temperature; and evaluate the suitability of the bioethanol produced as a potential fuel by determining its caloric value, flashpoint, specific density, and viscosity. Sweet potatoes were purchased from farmers in Kirinyaga County and transported to Murang’a University of Technology laboratory for analysis. The species was identified as the Bungoma sweet potato variety. The peels were washed to remove dirt, sun-dried for 10 days, and mechanically crushed into fine flour. Acid hydrolysis was done using hydrochloric acid at 0.2M, 0.5M, 1.0M, 1.5M, and 2.0M concentrations at 98°C to break down starches into fermentable sugars, followed by filtration and pH adjustment. Fermentation of hydrolysates was conducted using Saccharomyces cerevisiae for 72 hours under optimized conditions of pH, temperature, yeast concentration, and time. Carbon dioxide collection using balloon setups indicated active fermentation. The fermented mixture was then distilled to collect bioethanol for further analysis. Results showed that 0.5 M HCl was the most effective, producing 28.77 g/L of reducing sugar after hydrolysis and 21.83 g/L of reducing sugar consumed. The pH after fermentation was highest at 1.0 M and 2.0 M (3.70), indicating reduced acidity. One-way ANOVA results showed that pH (p=0.030) and yeast amount (p=0.032) had significant independent effects on bioethanol yield, while temperature (p=0.086) and time (p=0.086) were not independently significant but influenced yield through interactions. Significant interaction effects were observed for temperature–pH, temperature–yeast amount, and pH–time (p<0.05), indicating that these combinations play a crucial optimizing role in bioethanol production. The bioethanol produced had an average density of 0.803 g/cm³, sulfur content of 0.0131%, ash content of 2%, flashpoint of 14.6°C, viscosity of 1.747 mPa•s, calorific value of 25,080 kJ/kg, and electrical conductivity of 2.53 µS/cm. Despite slight deviations from pure ethanol, the fuel properties met acceptable standards, making it a viable renewable energy source. The study recommends avoiding excessively high HCl concentrations during hydrolysis, as this may reduce sugar availability and negatively affect fermentation efficiency. Regular monitoring and adjustment of optimization parameters should be done to maximize yield. Future research should focus on expanding to the production of bio-butanol and other fuels from sweet potato peels and exploring advanced fermentation techniques such as fed-batch systems. The findings are significant to policymakers and bioenergy stakeholders since they confirm that bioethanol produced from sweet potato peels is suitable for use as fuel.