Organic Acid Production from Paper Sludge Using SSF Process

초록

Cellulose waste from the pulp and paper industries is a fine resource of biomass, from which valuable products such as ethanol, organic acid, can be fermented. Only a small effort has been made to hydrolyze the cellulose waste in a form of paper sludge, comparing to the researches on the hydrolysis of starch. Mixed cellulase, consisted of endo/exo glucanase and β-glucosidase from Trichoderma reesei Rut C-30 and Aspergillus niger, respectively, was employed to hydrolyze the cellulose portion of the paper sludge. The resulting hydrolysate can be used as a substrate for further fermentation to yield various organic products. For enzyme hydrolysis of paper sludge, the mixed enzyme system was experimentally optimized for maximum production of glucose to be composed of cellulase of 5 U/ml and β-glucosidase of 8 U/ml. The glucose production from 5% paper sludge was 15 g/l at pH 5 and 50 ℃. In fermentation by Lactobacillus rhamnosus, lactic acid production was 90 g/l from model solution of glucose of 100 g/l at optimum pH 6 and 37 ℃. The production rate of lactic acid was not much decreased by temperature increase up to 45 ℃. Production of lactic acid from paper sludge was carried out using simultaneous saccharification and fermentation(SSF) process, based upon the experimental data obtained from the unit process of separate cellulose hydrolysis and fermentation. SSF process was employed to avoid excessively dense solution when the sludge content in the feed is higher than 15 %, for one in several benefits of SSF. In batch SSF, lactic acid of 16 g/l was produced from 5% paper sludge with the yield of 80 %. The content of cellulose in dry paper sludge was between 35 and 40 %. In SSF of paper sludge in fed-batch mode, the lactic acid production was 50 to 55 g/l at 40 ℃, rating a yield of 63 to 70 %. The final product concentration is considered to be limited by the product inhibition effect on fermentation. The mixed enzyme system used in the SSF of fed-batch mo