Kinetic modelling of cellulase recycling in paper sludge to ethanol fermentation

Abstract

This study investigated the extent of enzyme savings that could be achieved by recycling enzyme-containing supernatant or whole fermentation broth from simultaneous saccharification and fermentation (SSF) of paper waste sludge (PS). Kinetic models were developed to identify the preferred enzyme recycling method. Kinetic models accounted for the loss of enzyme activity with time and the effect of enzyme supplementation on ethanol concentrations and predicted the performance of PS fermentation with acceptable accuracy. Process performance of SSF cultures was maintained during successive recycling steps by recycling either the enzyme-containing supernatant or whole broth without resorting to enzyme separation methods. Recycling of enzymes in the clarified supernatant during 5 L bioreactor fermentations allowed up to 23% savings on the overall enzyme loading. Recycling enzymes in the supernatant further increased the ethanol concentration in the fermentation broth from 40 to 70 g/L. The combined advantages of high ethanol concentrations and savings on enzyme consumption, opens up the possibility of achieving significant improvements in the economic viability of ethanol production from lignocellulosic substrates.