Conversion of pentose sugars from lignocellulosic hydrolysate to isopropyl alcohol via integrated Chlorella vulgaris cultivation and yeast fermentation: An alternative fuel to diesel engines

Abstract

Lignocellulosic biomass counts 50 % of the total biomass in the biosphere, making it one of the hemisphere's most abundant organic resources. However, pentose sugars comprise most of hemicellulose, and fermentation presents a significant problem in turning it into alcohol for biofuel applications. The efficient use of pentose sugar which is the second most common sugar in the hemicellulosic hydrolysate, is one of the main issues facing the bioethanol industry. In this context, efforts have been made to utilize lignocellulosic hydrolysate containing both C6 and C5 sugars for the growth of Chlorella vulgaris through a mixotrophic approach, yielding 9.2 mg/mL/d biomass with 38.56 % total lipid content concerning dry cell weight. Further, Isopropyl alcohol was prepared from hydrolysate obtained through acid hydrolysis of spent biomass of Chlorella vulgaris through yeast fermentation of Saccharomyces cerevisiae under oxygen stress conditions. It was observed that the microalgae Chlorella vulgaris could utilize non-fermentable sugars, arabinose, and xylose present in the hemicellulosic hydrolysate for its growth through a mixotrophic approach and isopropyl alcohol can be produced from hydrolysate prepared from deoiled microalgal biomass through yeast fermentation.