Bioethanol Production from Cellulosic Fibers: Comparison between Batch and Fed-batch Saccharification

Unbleached pulp from the pulp and paper industry was used as a cellulosic material source to produce bioethanol in a separate hydrolysis and fermentation process. In the batch enzymatic saccharification, three cellulolytic enzymes and different initial carbohydrate (CH) contents were tested. Cellic CTec2 was shown to be the most efficient enzyme with the lowest dosage used: 35 FPU gCH . Sugar production increased when the initial carbohydrate content increased from 58 to 116 g L, while the hydrolysis efficiency decreased. Enzymatic hydrolyzates from the batch and fed-batch operations were further used in ethanolic fermentation with Saccharomyces cerevisiae ATCC 26602. An ethanol concentration of up to 28 g L was achieved from 80 g L of reducing sugars. A sugar-to-ethanol conversion of up to 69% and an ethanol productivity of 0.39 g L h were obtained with batch hydrolyzates. Nevertheless, the fed-batch mode led to higher bioethanol production per gram of carbohydrate and per enzyme unit.