Evaluating biological pretreatment as a feasible methodology for ethanol production from paddy straw

Bioethanol has been recognized as a promising contemporary fuel. One of the most abundant renewable resources for bioethanol production is paddy straw with high carbohydrate content. A pretreatment step disintegrates the recalcitrant lignocellulosic structure in biomass, which facilitates the access of hydrolytic enzymes to the glucan macrostructure. Biological pretreatment is an eco-friendly alternative to harsh thermo-chemical pretreatment methodologies. In this study, paddy straw (rice variety Pusa 2511) was subjected to biological pretreatment with white-rot fungus, Trametes hirsuta and simultaneously with steam pretreatment at 121 °C. Resultant saccharification efficiencies of differentially pretreated paddy straw were compared to evaluate biological pretreatment. After pretreatment cellulose content in steam treated paddy straw was 39.5%, whereas for biological it was 37.6% and respective lignin contents were 14.2% and 4.7%. Lignin removal was substantially higher in biological pretreatment than steam pretreatment. The saccharification yields of biological pretreatment were at par with steam pretreated paddy straw. Highest saccharification efficiency was observed after 24 h, at 2% glucan loading, for both biological (76.5%) and steam pretreatment (74.1%). Maximum production of sugar (52.91 g L−1) was observed in biologically pretreated biomass at 10% glucan loading after 24 h. Fermentation of biomass hydrolysates with Saccharomyces cerevisiae, showed low ethanol production from biologically (0.86 g L−1) as well as steam pretreated biomass (1.13 g L−1) with fermentation efficiency ranging from 26 to 52%, suggesting presence of inhibitory factors necessitating detoxification of hydrolysates. This study, established biological pretreatment as feasible method for pretreatment and higher sugar yields.