Biological pretreatment of lignocellulosic biomass: An environment-benign and sustainable approach for conversion of solid waste into value-added products

Agricultural residue is produced in large quantities during crop harvesting, and open burning of this waste causes environmental pollution and health risks. Due to the structural complexity of the lignocellulose and problems associated with physical and chemical methods of its pretreatments, there is an utmost need for an eco-friendly pretreatment strategy. Biological pretreatment involving microorganisms and their enzymes is an environment-benign and economic process due to lack of release or requirement of toxic chemicals during the process. Among microorganisms, filamentous fungi (mainly Basidiomycetes) with efficient enzymatic machinery have been used in efficient delignification and bioconversion of lignocellulosic biomass. Enzyme-mediated pretreatment has further improved the saccharification of plant biomass with no sugar loss as in case of microbial pretreatment. Composting, ensiling, solid state fermentation, and biogas production are based on biological pretreatment, which are used for the generation of value-added products. Biological pretreatment does not require/release toxic chemicals but, is highly useful in detoxification of such toxic compounds. Biological pretreatment is significantly affected by biotic and abiotic factors. Pretreated biomass is hydrolyzed by cellulases and xylanases into sugars that are fermented into biofuels, organic acids, enzymes, and other products. The slow and long incubation nature of biological pretreatment has been overcome by combining with milder physico-chemical methods. Furthermore, the consolidated bioprocessing-based biorefinery approach has enhanced the potential of biological pretreatment by involving microbial consortium for the production of biofuels and other value-added products in a single step. Therefore, biological pretreatment-based biorefinery approach would be quite beneficial for the large-scale production of value-added products from lignocellulose with concomitant reduction in environmental pollution and solid waste management.