Pretreatment and optimization of reducing sugar extraction from indigenous microalgae grown on brewery wastewater for bioethanol production

The aim of this study was to select a suitable pretreatment method and optimize total reducing sugar extraction from indigenous Scenedesmus sp. grown on brewery wastewater for bioethanol production. Microalgal biomass was pretreated using a microwave, autoclave, water bath, and oven with HCl, H2SO4, NaOH, and KOH, followed by the optimization of the best pretreatment method and hydrolytic agent using response surface methodology for reducing sugar extraction. Four independent variables (acid concentration, microwave power, temperature, and extraction time) were then considered in the optimization and model development process; results showed that the maximum reducing sugar content was achieved in a microwave with HCl. Analysis of variance (ANOVA) and regression coefficient (0.983) also showed that the developed model was significant (P < 0.05) and fitted to the experimental data, respectively. The optimum conditions of an acid concentration of 1.68 N, microwave power of 1200 W, the temperature of 145 degrees C, and extraction time of 19 min were predicted a maximum total reducing sugar production of 175.5 mg/g. The experimental result of total reducing sugar obtained at optimum conditions was 172.5 mg/g, which was well close to the predicted value, verifying the appropriateness of the model. The highest bioethanol yield of 0.08 g ethanol/g microalgal biomass was obtained at 24-h fermentation time with a fermentation efficiency of 88.15%. This study demonstrates the possibility of bioethanol production from indigenous microalgae grown on brewery wastewater through microwave-assisted acid extraction of reducing sugar.