Microbe assisted valorization of lignin rich residues

Abstract

Increasing urbanization and industrialization causing depletion of fossil fuel resources combined with the escalating focus towards scientific battle against the climate change as well as to meet the sustainability goals has led researchers towards biofuels development using biomass, especially agricultural residues, as feedstock. Lignocellulosic biomass is considered as the renewable biomass to replace fossil fuels and their derived products with the bio-based compounds. Though, many ways have been identified for the conversion of cellulose and hemicellulose fractions of biomass into bioenergy/biofuels, still effective utilization of residual lignin remains a major challenge for the economic viability and commercial success of biomass based biofuel technologies. Lignin is considered as dominant aromatic polymer in nature and is found in most terrestrial plants, which provides the structural integrity. Approximately, it constitutes in a range of 15 to 40% dry weight. Several studies reported utilization of the lignin containing biomass as feedstock for ethanol production. However, the major limitation of the established process is disposal of residual lignin enriched stream, which contains recalcitrant complex carbon moieties that has calorific value but unable to tap it sustainably. Various physico-chemical and thermal processes were attempted to break down the lignin rich residual waste, obtained from biomass derived fuels, but were not energy efficient as well as not eco-friendly making the whole process unsustainable. At this juncture, researchers across the globe are in search of alternate biological routes to valorize the lignin rich waste along with the other components of the biomass. The three potential possible biological routes for the depolymerization of lignin containing waste include enzymatic, fungal and bacterial routes which are cost effective, energy efficient and also eco-friendly. Among the three biological routes, fungal and enzymatic routes are well studied but both of them have their own li