Production of Lactic Acid from Paper Sludge Using Biochemical Process, 2002 Environmental Conference Proceedings

S. M. Lee, J. Lin and Y. M. Koo

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 16g/l was produced from 5% paper sludge with the yield of 80%. In SSF of paper sludge in fed-batch mode, the lactic acid production was 90 g/l at 42°C, rating a yield of 83%. Paper sludge which served as a feed appeared to have a buffering ability during SSF, probably due to inorganic ash components in the sludge. The final product concentration in the SSF was observed to be limited by the cellulose content in the system, which is expected to be solved by intermittent feeding of paper sludge. The mixed enzyme system used in the SSF of fed-batch mode was 10 and 4 U/ml of cellulase and glucosidase, respectively. Cellulase and glucosidase which carry out saccharification reaction of paper sludge were observed not to be degraded by fermenting microorganism, Lactobacillus rhamnosus.