Optimization of ethanol production from spent tea waste by Saccharomyces cerevisiae using statistical experimental designs

The aim of this study was to investigate the prospect for the use of spent tea waste (STW), an important municipal waste, as a potential substrate to generate hydrolysates for fuel ethanol production. Acid pretreated STW was used as substrate for ethanol production. The critical variables that affected ethanol fermentation from STW were identified by Plackett–Burman designs and further optimized by using a five-level-three-factor central composite design of response surface methodology. The optimum conditions for ethanol fermentation were determined to be NH₄Cl concentration of 2.7 g/L, yeast concentration of 11.7 g/L, and temperature of 42.8 °C. Maximum concentration of reducing sugar and ethanol under the optimum conditions were 28.90 g reducing sugar/L and 12.72 g EtOH/L, respectively. Predicted ethanol concentration was obtained using quadratic polynomial equation. The predicted ethanol concentration was 13.38 g EtOH/L in the optimal conditions. Validity of the predicted model was confirmed using verification experiment (12.72 g EtOH/L).