Bioethanol production potential of a cellulolytic and thermophilic Geobacillus species from compost sites

Abstract

Screening of cellulolytic thermophilic bacteria from different compost sites in Ibadan for bio-ethanol production using readily available lignocellulosic wastes (corn cobs, cassava peels and saw dust) as substrate was carried out. Eleven out of 25 thermophilic isolates were cellulolytic. Out of these, two isolates (Geobacillus sp. OCO5 and Geobacillus sp. OCO1) with 15% ethanol tolerance were selected for further studies.The lignocellulosic wastes were biologically pretreated with Pleurotus tuberregium for 42 days. Statistical analysis showed that biological pretreatment of substrates with P. tuber-regium had a significant effect (p<0.05) on lignin reduction in the substrates. Percentage reduction of 36.21%, 16.82% and 1.13% was observed in pretreated corn cob, cassava peel and saw dust respectively. Geobacillus sp. OCO5 and Geobacillus sp. OCO1 on pretreated corn cobs respectively gave a reducing sugar yield of 68.5% and 18.75%, while pretreated cassava peels gave a yield of 35% and 25%. Thus, Geobacillus sp. OCO5 was chosen for bio-ethanol production. In single phase fermentation of pretreated corn cobs and cassava peels with this isolate, an ethanol yield of 62.13% and 45% was produced respectively. However, two phase fermentation of the same substrates using Geobacillus sp. OCO5 and Saccharomyces cerevisiae yielded 88.65% and 72.59% ethanol. These results show that the high recalcitrance of lignocellulosic wastes can be overcome by biological pretreatment using Pleurotus tuber-regium and corn cobs was the most suitable raw material for bio-ethanol production. The synergistic effect between the cellulolytic thermophile (Geobacillus sp. OCO5) and baker’s yeast (Saccharomyces cerevisiae) also gave better ethanol yield compared to single phase fermentation. Thus this type of synergy can be employed in probable large scale bio-ethanol production.