Bioethanol Production from Citrus limon (Citrus) Peel Substrate Using Aspergillus Niger and Saccharomyces Cerevisae

Abstract

The consumption of petroleum products is marred by the inconveniences of environmental pollution and the emission of greenhouse gases, which are responsible for global warming. Excessive use of fossil fuel has resulted in climate change, the elevation of the greenhouse gas effect, etc., contributing to the search for renewable sources of energy in harmony with the world’s energy needs. Although bioconversion of lignocellulose residue has received much attention, most plant biomass has not been fully exploited to meet human energy needs. Among these alternative energy carriers, ethanol receives great attention. This study aims to determine the optimal conditions for the production of bioethanol from lemon peel using Aspergillus niger and Saccharomyces cerevisiae. Aspergillus niger and Saccharomyces cerevisiae were isolated using the streak plate method and identified macroscopically and microscopically. The cellulose hemicellulose and lignin contents of the substrates were determined, and after that, the substrates were pretreated with 5% sulfuric acid and then subjected to enzymatic hydrolysis using Aspergillus niger. Subsequently, the reducing sugar content of the hydrolysate was determined, followed by fermentation using Saccharomyces cerevisiae. The percentage of bioethanol produced, as well as the fermentation efficiency (%), were calculated. Analysis of Variance was employed to determine statistically significant differences among the determined parameters. The cellulose, hemicellulose, and lignin contents of Citrus limon were found to be 32.00%, 4.99%, and 9.80%. Pretreatment increased the cellulose content from 23.00% to 32.00%. The highest reducing sugar content, 6.63 g/L, was recorded after hydrolysis for 96 hours. Fermentation using Saccharomyces cerevisiae yielded 19.20% of bioethanol from Citrus limon with a fermentation efficiency of 38.42%, respectively. The Optimum fermentation conditions recorded were a time of 96 hrs, pH of 3.5, temperature of 30°C and amount of substrate of 15 g. The combination of these parameters produced a bioethanol yield of 22.90% and a fermentation efficiency of 44.44%, respectively. This research revealed the potential of Citrus limon peel waste as a substrate for bioethanol production and optimized the physicochemical parameters for the fermentation.