Simultaneous Saccharification and Fermentation of Paper Sludge to Lactic Acid

초록

Simultaneous Saccaharification and Fermentation (SSF) process was employed to produce lactic acid from paper sludge by combining glucose production from cellulose, and lactic acid fermentation from glucose. To increase the final lactic acid concentration, a certain amount of sludges was intermittently added to the SSF process to make up the depleted cellulose in the fed-batch mode. In SSF of paper sludge in fed-batch mode, the lactic acid production was 162g/L, rating a yield of 74% and productivity of 1.4g/L·h. During the fed-batch SSF process, insoluble materials from paper sludge were accumulated. These components, mostly silica, alumina, lignin, affected mass transfer in fermentation broth, such as increasing the viscosity of solution. A bioreactor was designed to remove solid materials in fermentation broth by settling down into stagnant compartment beneath the perforated divider. The modified bioreactor had better performance in lactic acid production by removing waste solid materials from the upper reactor and feeding more paper sludges. A predictive model was studied for SSF by combining the kinetics of saccharification and fermentation. Saccharification kinetics were determined through experiments on enzymatic cellulose hydrolysis. The saccharification kinetics were examined by a Michaelis-Menten type equation, while the growth kinetics of L. rhamnosus, by a Monod expression incorporating lactic acid inhibition. The kinetic model is expected to predict the performance of SSF process.