Valorization of rice straw biomass for co-production of bioethanol, biopesticide and biofertilizer following an eco-friendly biorefinery process

Abstract

Combustion and depletion of fossil fuels, open burning of agricultural wastes, and use of hazardous chemicals in biofuels production route are some major challenges among scientific community. In the present study these obstacles were mitigated simultaneously. Initially, rice straw biomass was delignified using a combined eco-friendly laccase-assisted sodium chlorite (LASC) pretreatment. The combined pretreatment strategy of rice straw biomass reduced 55.6% lignin and increased the total available carbohydrate by 1.43 fold. Further, enzymatic digestion of LASC pretreated rice straw using a formulated cellulase cocktail from Aspergillus flavus MDU-5 and Trichoderma citrinoviride MDU-1 liberated 526.68 mg/g sugars with high saccharification yield (84.0%). The enzymatic hydrolysates thus obtained were found to contain 7.43–16.78 g/L sugars. The cellulolytic hydrolysates when fermented with Saccharomyces cerevisiae NCIM-3640 produced 3.02–7.28 g/L bioethanol, with high yield (72.96–85.31% of the theoretical value). Parallelly, lignin extracted from waste pretreatment stream showed biopesticidal activity against the larvae of H. armigera; whereas, the evaluation of residual material (after hydrolysis and fermentation) exhibited biofertilizer properties. These findings suggests that the environmentally benign LASC pretreatment, cellulase cocktail, and utilization of waste stream for the production of biopesticide and biofertilizer may provide a promising strategy in the development of holistic lignocellulosic biorefinery process.