Production of ethanol from kitchen waste by using flocculating Saccharomyces cerevisiae KF-7

Kitchen waste is rich in carbohydrates and can potentially serve as feedstock for ethanol production. Starch was the primary carbohydrate in kitchen waste obtained from the canteen in the Sichuan University, which was used to evaluate long-term ethanol fermentation performance in this study. The optimal conditions for liquefaction and saccharification of the kitchen waste were as follows: adding α-amylase at 0.3 μL/g glucan for liquefaction at 90°C for 30 min, and adding glucoamylase at 4 μL/g glucan for saccharification at 50°C. Glucose yield obtained under the optimal conditions was over 80%. Addition of cellulase did not enhance glucose yield, but decreased the viscosity of the saccharified slurry. Repeated-batch presaccharification followed by simultaneous saccharification and fermentation of 20 batches was successfully carried out at an aeration of 0.1 vvm. Ethanol concentration of 43.9-45.0 g/L was achieved, corresponding to ethanol yield and productivity of 88.9-91.2% and 3.3-3.5 g/L/h, respectively, and the CO₂/ethanol molar ratio was approximately 1. Continuous PSSF was stably carried out at a dilution rate of ≤0.3 h^-1. Productivity was 11.5 g/L/h at a dilution rate of 0.3 h^-1. Ethanol concentration and yield were 42.0 g/L and 82.8% at a dilution rate of 0.2 h^-1, respectively.