Biological pretreatment of lignocellulosics: potential, progress and challenges

The feasibility of producing biofuels and biochemicals from lignocellulosic biomass via the biochemical platform depends largely on advances in pretreatment and hydrolysis technologies to obtain sugars from the cellulose and hemicelluloses of plant cell walls. This paper provides an overview of the merits and challenges related to developing biological pretreatment processes to modify lignin for facilitating subsequent enzymatic extraction of sugars. Although it has so far attracted little attention due to many inherent limitations, biological pretreatment has multiple benefits. Compared with extensively studied thermochemical processes, biological pretreatment is more environmentally benign, requires less energy, results in fewer inhibiting compounds and has potential to produce more co-products. Increasing understanding of termites and fungal systems has provided insights for developing more effective pretreatment technologies to realize these benefits. Specifically, this paper reviews the knowledge on microorganisms and their enzymes for biodegradation of lignin in plant cell walls, summarizes the progress in biopulping as well as in biological pretreatment for obtaining sugars, and provides future perspectives on biological pretreatment development.