Ethanol production from kitchen waste using the flocculating yeast Saccharomyces cerevisiae strain KF-7

A process for producing ethanol from kitchen waste was developed in this study. The process consists of freshness preservation of the waste, saccharification of the sugars in the waste, continuous ethanol fermentation of the saccharified liquid, and anaerobic treatment of the saccharification residue and the stillage. Spraying lactic acid bacteria (LCB) on the kitchen waste kept the waste fresh for over 1 week. High glucose recovery (85.5%) from LCB-sprayed waste was achieved after saccharification using Nagase N-40 glucoamylase. The resulting saccharified liquid was used directly for ethanol fermentation, without the addition of any nutrients. High ethanol productivity (24.0 g l−1 h−1) was obtained when the flocculating yeast strain KF-7 was used in a continuous ethanol fermentation process at a dilution rate of 0.8 h−1. The saccharification residue was mixed with stillage and treated in a thermophilic anaerobic continuous stirred tank reactor (CSTR); a VTS loading rate of 6 g l−1 d−1 with 72% VTS digestion efficiency was achieved. Using this process, 30.9 g ethanol, and 65.2 l biogas with 50% methane, was produced from 1 kg of kitchen waste containing 118.0 g total sugar. Thus, energy in kitchen waste can be converted to ethanol and methane, which can then be used as fuels, while simultaneously treating kitchen waste.