Optimization of microwave-assisted carbohydrate extraction from indigenous Scenedesmus sp. grown in brewery effluent using response surface methodology

The use of wastewater as a nutrient source for microalgae cultivation is considered as a cost-effective approach for algal biomass and biofuel production. The microalgal biomass contains carbohydrates that can be processed into bioethanol through different extraction methods. The objective of this study is to optimize the microwave-assisted extraction (MAE) of carbohydrates from the indigenous Scenedesmus sp. grown on brewery effluent. Optimization of independent variables, such as acid concentration (0.1-5 N), microwave power (800-1200 W), temperature (80-180 °C) and extraction time (5-30 min) performed by response surface methodology. It was found that all independent variables had a significant and positive effect on microwave-assisted carbohydrate extraction. The quadratic model developed on the basis of carbohydrate yield had F value of 112.05 with P < 0.05, indicating that the model was significant to predict the carbohydrate yield. The model had a high value of R² (0.9899) and adjusted R² (0.9811), indicating that the fitted model displayed a good agreement between the predicted and actual carbohydrate yield. An optimum carbohydrate yield obtained was 260.54 mg g^-1 under the optimum conditions of acid concentration (2.8 N), microwave power (1075 W), temperature (151 °C) and extraction time (22 min). The validation test showed that the model has adequately described the microwave-assisted extraction (MAE) of carbohydrates from microalgal biomass. This study demonstrated that the indigenous Scenedesmus sp. grown on brewery effluent provides a promising result in carbohydrate production for bioethanol feedstock.