Fermentation Process Optimization for Bioethanol Production from Hydrothermally Pretreated Leftover Food Waste

The increasing global challenge of food waste management, coupled with the growing demand for renewable energy, has spurred research into converting food waste into biofuels. The Woldia University student cafeteria generates approximately 18.25 kilograms of leftover food waste per person each year. This study aimed to produce bioethanol from hydrothermally pretreated mixed food waste by optimizing the fermentation process to maximize yield. The production process involved sample collection, preparation, hydrolysis, fermentation, and separation. Specifically, 60 g of food waste underwent hydrothermal hydrolysis at 121 ℃ for 1 hour. The Central Composite Design tool was utilized to design the fermentation process parameters, specifically targeting temperature (30–45 ° C), fermentation time (1–7 days), and agitation speed (150–200 rpm). The results show that the proximate analysis of food waste revealed moisture content of 11. 6%, volatile matter of 31. 3%, ash content of 11%, fat content of 2.05%, protein content of 2.1%, and carbohydrates of 43. 42%. According to Central Composite Design analysis, the three independent factors have a significant effect on yield, and the fermentation time and its interaction with agitation speed positively influence yield, while other factors have a negative relationship. The optimum ethanol yield of 23.83% was achieved under fermentation conditions of 37. 5 ℃, 4 days, and 175 rpm. The bioethanol produced exhibited promising physicochemical properties, including a density of 0.79 g/cm³, viscosity of 1.23 cP, boiling point of 79.3 °C, acid number of 0.561 mg KOH/g, pH of 5.97, flash point of 13.35 °C, heating value of 27.2 MJ/kg, and an alcohol content of 76%. Generally, this study highlights that bioethanol production from mixed food waste serves as a promising renewable energy source. It also provides insights into the suitability of mixed food waste as a feedstock, the efficiency of hydrothermal hydrolysis for biomass breakdown, and the optimal conditions required for effective microbial fermentation.