Opportunities in Enzymatic Conversion of Lignocellulose into Fermentable Sugars

This review article (from the journal, “Biofuels, Biprocessing and Biorefining”)  presents a number of technical and scientific issues related to the conversion of lignocellulosic biomass to ethanol. Pretreatment (to improve digestibility of cellulose fibers), followed by cellulose hydrolysis to liberate the sugars for ethanol fermentation, are seen as important steps. Pretreatment should generally minimize the use of energy, chemicals and capital equipment, and be scalable to industrial size for the process to be economical and practical. Pretreatment technologies include the application of steam, alkali, or solvents. These technologies must be developed with reactor systems capable of operating at high solids concentration with large particles and harsh biomass types.

The presence of lignin in the lignocellulosic material is one of the major obstacles in enzymatic hydrolysis. The optimal enzyme mixture is most likely to be tailor made or adjusted to each different kind of material. Operating hydrolysis with high initial substrate concentrations has been faced by the problem of product inhibition; effect of end product(s) on the enzymes has to be evaluated before selecting the hydrolysis and fermentation strategy. Development of more efficient enzymes is also the subject of extensive research. Significant improvements in yield and cost reduction can therefore be expected, thus making large-scale hydrolysis and fermentation of lignocellulosic substrates possible.