Enhanced Productions and Recoveries of Ethanol and Methane from Food Waste by a Three-Stage Process

A three-stage process that consisted of saccharification, ethanol fermentation of the saccharified liquid, and anaerobic treatment of the saccharified residue to convert food waste (FW) to ethanol and CH₄ was developed. Results revealed that high sugar recovery (i.e., 61.7%) from FW could be achieved after saccharification and 15.2% saccharified sugar was retained in saccharified residue after solid-liquid separation. A high ethanol yield was obtained during ethanol fermentation of the saccharified liquid. This high yield indicates the superiority of the system. The ethanol productivity in the ethanol fermentation stage was 0.9 g L^-1 h^-1. A CH₄ yield of 248.4 mL/g of volatile solid (VS) was achieved in the CH₄ fermentation stage, whereas that in the single-stage fermentation system was 252.6 mL/g of VS. A comparison of the two fermentation systems based on material balance and energy outcome demonstrated that the three-stage process achieved a 27.5% increase in the FW decomposition rate, a 51.8% reduction in the energy requirement for system operation, and a 17.6% improvement in the total energy yield. Therefore, the three-stage process is more suitable for practical application in terms of a lower post-treatment cost for the digester residue, a higher organic carbon utilization rate, and a higher bioenergy recovery efficiency compared to the single-stage system.