A comprehensive ligninolytic pre-treatment approach from lignocellulose green biotechnology to produce bio-ethanol

Abstract

In the present study, we developed a novel ligninolytic enzymes based pre-treatment method for lignocellulosic wheat straw to depolymerize lignin and expose the cellulose polymers to produce bio-ethanol. Wheat straw was pre-treated with ligninolytic enzymes extract produced from Ganoderma lucidum under optimum solid state fermentation conditions. The pre-treated biomass was further subjected to the enzymatic hydrolysis by the crude unprocessed cellulases (β-1,4 endoglucanase, 53.5±1.24U/mL; β-1,4 exoglucanase, 41.3±1.31U/mL; β-1,4 glucosidase, 46.8±1.43U/mL; and xylanase 39±2.2U/mL) produced by Trichoderma harzaianum. Under optimal conditions for enzymatic saccharification, 10% (w/v) of pre-treated biomass was hydrolyzed completely and converted to 72.5 and 2.4g/L of glucose and xylose, respectively. Initial time screening Sequential Saccharification and Fermentation (SSF) of the concentrated enzymatic hydrolyzate (10%, w/v) by Saccharomyces cerevisiae produced 22.6g/L ethanol in a fermented medium after 72h of temperature controlled incubation at 37°C. For maximum ethanol production, different physical and nutritional parameters like pH, temperature, substrate level and inoculum sizes were optimized. Under optimal conditions ethanol production of 33.5g/L was obtained from ligninolytic treated residual (wheat straw) biomass.