Enzymatic lignocellulose hydrolysis: Improved cellulase productivity by insoluble solids recycling

One of the challenges to making an economical process for lignocellusoe hydrolysis is the high cost of cellulase enzymes.  It has been proposed that one method for decreasing the amount of enzyme needed is to recycle the enzymes.  Many studies have explored cellulase recycle, however they have relied primarily on low lignin substrates, high enzyme dosages, and low solids concentrations.  In this study, the recycle of enzymes associated with the insoluble solid fraction that remained after enzymatic hydrolysis was investigated for pretreated corn stover at 10-15% total solids concentrations by recycling the solids over several batch hydrolysis reactions.  The goal of this study was to determine whether recycling the insoluble solid fraction could significantly increase glucose yields while lowering enzyme dosage, and to investigate the impact of the variation in process parameters that might result from solids recycle on enzyme hydrolysis performance. 

It was found that a significant amount of cellulase activity could be recovered by recycling the insoluble biomass fraction, and the enzyme dosage could be decreased by 30% to achieve the same glucose yields under the most favorable conditions. Enzyme productivity (g glucose produced/g enzyme applied) increased between 30 and 50% by the recycling, depending on the reaction conditions. While increasing the amount of solids recycled improved process performance, the methods applicability was limited by its positive correlation with increasing total solids concentrations, reaction volumes, and lignin content of the insoluble residue. However, increasing amounts of lignin rich residue during the recycle did not negatively impact glucose yields.