Résumé
Aim: In this study, effectiveness of alkali pretreatment of banana pseudostem for the production of biobutanol by fermentation using Clostridium sporogenes under strict anaerobic conditions was studied. Methodology: Banana pseudostem was pretreated by alkali soaking at constant temperature (30, 50 and 70°C) and concentration of 0.25 to 2% (w/v) at solid to liquid ratio of 1:10 for 24 hr to depolymerize the lignocellulosic biomass. Further to increase delignification, the alkali soaked samples were subjected to thermal treatment at 121°C for 15 min. The hydrolysates were subjected to acetone-butanol-ethanol fermentation using Clostridium sporogenes to produce butanol. Results: Maximum delignification of 92% was obtained at 30°C soaking temperature with 2% NaOH (w/v). Increase in temperature led to increase in delignification but also resulted in reduced recovery of cellulose. Maximum glucose yield of 524 mg g-1 glucan was obtained from the pretreated biomass. Fermentation of hydrolysate obtained from alkali soaking pretreatment by C. sporogenes under anaerobic condition resulted in 10.12 g l-1 of butanol with a yield of 0.326 g g-1 of total sugar consumed and it was much higher compared to untreated biomass. Interpretation: Alkali soaking pretreatment at 30°C and alkali concentration of 1.5% (w/v) was effective to depolymerize the biomass to obtain maximum sugar and butanol yield from banana pseudostem. Thermal treatment was not effective in increasing the production of butanol due to pseudo lignin formation and presence of inhibitors.
Résumé
India is amongst the largest banana (Musa acuminata) producing countries and thus banana pseudo stem is commonly available agricultural waste to be used as lignocellulosic substrate. Present study focuses on exploitation of banana pseudo stem as a source for bioethanol production from the sugars released due to different chemical and biological pretreatments. Two fungal strains Aspergillus ellipticus and Aspergillus fumigatus reported to be producing cellulolytic enzymes on sugarcane bagasse were used under co-culture fermentation on banana pseudo stem to degrade holocellulose and facilitate maximum release of reducing sugars. The hydrolysate obtained after alkali and microbial treatments was fermented by Saccharomyces cerevisiae NCIM 3570 to produce ethanol. Fermentation of cellulosic hydrolysate (4.1 g%) gave maximum ethanol (17.1 g/L) with yield (84%) and productivity (0.024 g%/h) after 72 h. Some critical aspects of fungal pretreatment for saccharification of cellulosic substrate using A. ellipticus and A. fumigatus for ethanol production by S. cerevisiae NCIM 3570 have been explored in this study. It was observed that pretreated banana pseudo stem can be economically utilized as a cheaper substrate for ethanol production.