Ethanol fermentation from food processing waste

Abstract

This study focuses on the use of restaurant waste for production of ethanol. Food wastes (corn, potatoes, and pasta) were converted to ethanol in a two-step process: a two-part enzymatic digestion of starch using alpha-amylase and glucoamylase and then fermentation of the resulting sugars to ethanol using yeast. Because of the low initial composition of starch in the food waste, low ethanol concentrations were achieved: at best 8 mg/ml ethanol (0.8 % by mass). Ethanol concentration increased with increasing enzyme dosage levels. Calculations were conducted to evaluate whether waste heat from restaurant waste could be used to drive flash vaporization to purify ethanol. If the solution produced by fermenting food waste is flashed at a temperature of 99.7°C, 77% of the ethanol is recovered in a vapor stream with 1.14 mole% ethanol (2.87 mass %). Waste heat could provide over a third of the energy for this vaporization process. If 4 mole% ethanol could be produced in the fermentation step by increasing the initial starch content in the waste solution and improving the fermentation process, then a single flash at 98.9°C will recover nearly 99% of the ethanol, giving a mass concentration of ethanol of 10.3%, which is similar to that achieved in industrial grain fermentation.