Potential of thermophilic bacteria isolated from cow dung-grass compost for bioethanol production using floral waste

Abstract

In recent years, various efforts have been invested in producing bioethanol from lignocellulosic biomass (LCB) using thermophilic bacteria. Twelve thermophilic ethanologenic bacteria were isolated from cow dung-grass compost using an enrichment technique, and the isolate, CSD6, which produced the highest bioethanol, was studied further. CSD6 utilized both pentose and hexose sugars producing ethanol, lactic acid and acetic acid as major soluble products and was identified through 16S rRNA gene sequencing as a strain of Geobacillus stearothermophilus. The highest ethanol production was found to be 25.05 mM from 5 g/L glucose, equivalent to 55% of the theoretical ethanol yield at 55 °C and initial pH 7.5. The isolate showed average tolerance to ethanol and acetic acid concentration and initial substrate loading. The bioethanol potential of CSD6 was also studied using autoclave-treated mixed floral waste (FW) as a no-cost substrate. CSD6 produced a maximum of 8.9 mM of bioethanol with a 75.47% decrease in reducing sugars using 20 g/L FW as substrate without any enzymatic pretreatment, indicating the ability of CSD6 to produce bioethanol from easily available substrates.