Experimental investigation on effect of season on the production of bioethanol from wheat-stalk (WS) using simultaneous saccharification and fermentation (SSF) method

Abstract

Global dependency on conventional fuel, its limited stock, and their adverse effects on the environment have driven researchers into alternative fuel. Wheat-stalk (WS), which is a residue of the harvested wheat crop, is considered a potential feedstock for bioethanol production as an alternative fuel due to its high cellulose and hemicellulose content and abundant availability. The objective of this work is to optimize the environment condition for fermentation in the different seasons to get the maximum bioethanol production yield from wheat-stalk straw (WSS) by using minimal laboratory resources. In this study, field collected WS was taken for physical treatment to get size less than 1 mm. Steam explosion pretreatment of WSS was performed to increase its accessible surface area and to reduce degree of polymerization. Next, to remove lignin, it was pretreated with alkali (1 M NaOH) with a solid-loading of 1:15 (w/v) at pH 10. After that, an acidic pretreatment was performed with 0.1 N diluted H2SO4 at pH 4.8 to increase anaerobic digestibility and for quicker hydrolysis. The pretreated WSS slurry was further enzymatically hydrolysed for 48 h to have monomeric sugar from cellulose and hemicellulose by adding cocktail of three enzymes amylase, cellulase, and hemicellulase with amount of 0.1% w/v of each. After that simultaneous saccharification and fermentation (SSF) were performed to convert monomeric sugar into bioethanol in the presence of microbial yeast media containing yeast (1% w/v), and peptone (2% w/v) under anaerobic conditions at pH 5.0. It has been found that the minimum time required during SSF for bioethanol production is different for different seasons. In addition, the fermentation period is shorter in monsoon as compared to spring and summer. As the fermentation period increases, the production of bioethanol yield increases up to a certain limit. The maximum bioethanol yields from the WSS were obtained as 0.183, 0.19, and 0.21 ml/g of dry WSS biomass in the spring, summer, and monsoon seasons for the fermentation period of 15, 9, and 11 days respectively. Consequently, it has been found that the enhancement in maximum bioethanol yield in the monsoon season is 8.42% and 12.57% as compared to the summer and spring seasons, respectively.