| Summary: | Abstract Background The combination of nutrient removal using microalgae from wastewater with carbohydrate production has been considered as a promising approach for sustainable wastewater treatment and production of valuable products such as biofuels. In Ethiopia, urbanization and industrial development are not in tandem with wastewater treatment system The objective of this study was to evaluate nutrient removal and carbohydrate production potential of the indigenous microalgae Scenedesmus sp. grown in anaerobically digested brewery wastewater. The indigenous Scenedesmus sp. was grown in an anaerobically digested brewery effluent in different seasons of the year. The biomass was converted into carbohydrate using microwave, autoclave, and oven as pretreatment, followed by optimization for acid concentrations and hydrolysis time. Result The overall removal efficiencies for the indigenous Scenedesmus sp. based wastewater treatment system were over 99%, 92%, 63%, 65% and 75% for NH4 +-N, TN, PO4 3− -P, TP and COD, respectively. The concentrations of final effluent quality of these parameters except for phosphorus nutrient were below the permissible discharge limit for brewery effluent standard set by Ethiopian Environmental Protection Authority. With regard to carbohydrate production, microwave-assisted acid hydrolysis with HCl produced a higher total sugar than that of autoclave and oven pretreatments. Among acid concentrations, HCl with 3 N produced a higher total sugar, which is significantly different (P < 0.05) to the other acid concentrations. The highest total sugar (233.89 mg g−1) was obtained from microalgal biomass during the 20 min hydrolysis time with 3 N HCl and 5% (w/v) biomass at 1000 watts and 1200C. Conclusions This study showed that there is an opportunity for using the indigenous microalgae for sustainable wastewater treatment and for carbohydrate production that uses as bioethanol source in Ethiopia.
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