Bioconversion of secondary fiber fines to ethanol using counter-current enzymatic saccharification and co-fermentation

This research examined several enzymatic and microbial process for the conv ersion of waste cellulosic fibers into ethanol. The first was a one-stage p rocess in which pulp fines were contacted with commercial enzyme solutions. The second process used sequential, multistage saccharification. The third used sequential enzyme addition in a countercurrent mode. Experiments comp ared the results with various feedstocks, different commercial enzymes, sup plementation with beta-glucosidase, and saccharification combined with ferm entation. The highest saccharification (65%) from a 4% consistency pulp and the highest sugar concentration (5.4%) from an 8% consistency pulp were at tained when 5 FPU/g plus 10 IU/g of beta-glucosidase were used. Sequential addition of enzyme to the pulp in small aliquots produced a higher overall sugar yield/U enzyme than the addition of the same total amount of enzyme i n a single dose. In the saccharification and fermentation experiments, we p roduced 2.12% ethanol from a 5.4% sugar solution. This represents 78% of th e theoretical maximum. This yield could probably be increased through optim ization of the fermentation step. Even when little saccharification occurre d, the enzyme facilitated separation of water, fiber, and ash, so cellulase treatment could be an effective means for dewatering pulp sludges.