Fed-batch SSF with pre-saccharification as a strategy to reduce enzyme dosage in cellulosic ethanol production

The pulp and paper industry is a strategic sector to be converted into a forest-based biorefinery, taking advantage of know-how, existing infrastructures and well-established logistic operations to deal with a daily high volume of forest residues. Bioethanol production from Eucalyptus globulus bark previously pretreated by kraft pulping was assessed following two configurations at the bioreactor scale: separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). This last configuration was optimized by using a presaccharification and a fed-batch feeding (FB PS-SSF), allowing for a reduction in the enzyme dosage from 25 to 10 FPU gCH- 1, which is very advantageous from an economic point of view. For 10 FPU gCH-1 enzyme dosage and 20 % (w/v) total solids loading, an ethanol concentration of around 70.6 g L-1 was accomplished, corresponding to overall conversion efficiency and productivity of about 78 % and 1.35 g L-1 h-1, respectively. Increasing solids loading from 20 to 26 % (w/v), using the same enzyme dosage, resulted in the highest ethanol concentration (84.6 g L-1) despite the too-long assay and the decline in productivity. Overall, FB PS-SSF improved bioethanol concentration and allowed decreased enzymatic usage over SHF, maintaining high ethanol concentration.