Study on the ethanol production from hydrolysate derived by ultrasonic pretreated defatted biomass of chlorella sorokiniana NITTS3

•Defatted C. sorokiniana NITTS3 biomass used as a precursor for ethanol production.•Ultrasound pretreatment of biomass improves ethanol yield by 25.83 g/L.•Hydrolysate of microalgal biomass mainly constituted fermentable sugars.•Pretreated microalgal biomass yielded 52.10 ± 0.12 g/L of ethanol.•Defatted microalgal biomass could be a suitable feedstock for ethanol production. Microalgae biomass is considered by many as a most promising renewable source for future generation feedstock for simultaneous production of biodiesel and bioethanol due to the accumulation of considerable amounts of lipids and carbohydrates, respectively. In this work, defatted green microalga, Chlorella sorokiniana NITTS3 biomass was ultrasonic pretreated and effectively used as a culture medium for ethanol production through fermentation using Saccharomyces cerevisiae NITTS1. The ultrasonic pretreatment improved ethanol yield by 25.83 g/L than untreated defatted microalgal biomass. Carbohydrate content of hydrolysate of defatted microalgal biomass after ultrasonic pretreatment was analyzed and found that hydrolysate primarily possessed simple sugars, namely glucose and xylose. Maximally 52.10 ± 0.12 g/L (86.70 ± 0.52 mg bioethanol/g DMB) of ethanol was produced at optimum fermentation conditions of 30 ℃, pH 4 and 200 rpm. This study results show that pretreated microalgal biomass could be used as a cheap, sustainable feedstock for enhanced ethanol production.