Simultaneous saccharification and co‐fermentation of paper sludge to ethanol by Saccharomyces cerevisiae RWB222—Part I: Kinetic modeling and parameters

Abstract

A kinetic model was developed to predict batch simultaneous saccharification and co-fermentation (SSCF) of paper sludge by the xylose-utilizing yeast Saccharomyces cerevisiae RWB222 and the commercial cellulase preparation Spezyme CP. The model accounts for cellulose and xylan enzymatic hydrolysis and competitive uptake of glucose and xylose. Experimental results show that glucan and xylan enzymatic hydrolysis are highly correlated, and that the low concentrations of xylose encountered during SSCF do not have a significant inhibitory effect on enzymatic hydrolysis. Ethanol is found to not only inhibit the specific growth rate, but also to accelerate cell death. Glucose and xylose uptake rates were found to be competitively inhibitory, but this did not have a large impact during SSCF because the sugar concentrations are low. The model was used to evaluate which constants had the greatest impact on ethanol titer for a fixed substrate loading, enzyme loading, and fermentation time. The cellulose adsorption capacity and cellulose hydrolysis rate constants were found to have the greatest impact among enzymatic hydrolysis related constants, and ethanol yield and maximum ethanol tolerance had the greatest impact among fermentation related constants.

Enzyme inactivation by ethanol and development of a kinetic model for thermophilic simultaneous saccharification and fermentation at 50 °C with Thermoanaerobacterium saccharolyticum ALK2

“…As originally proposed by South et al, and used in several subsequent studies Velkovska et al, 1997;Zhang et al, 2009) the rate of cellulose hydrolysis,…”

“…South et al (1995) incorporated a conversion-dependent cellulose hydrolysis rate constant and Langmuir adsorption capable of describing saturation with respect to either substrate or enzyme. The South et al model has subsequently been elaborated to accommodate intermittent feeding ) and xylan hydrolysis and xylose co-fermentation (Zhang et al, 2009). Hydrolysis models have also been reported at 508C (Fan and Lee 1983;Kadam et al, 2004).…”

KINETIC MODEL DEVELOPMENT ON SOURCE-SEPARATED ORGANIC WASTE FOR ETHANOL PRODUCTION BY S. cerevisiae STRAIN

“…The cell mass was determined by counting colony forming units on agar plates as described in (Zhang et al, 2009). …”

“…The kinetic model adapted in this study uses a semi-mechanistic rate equation for cellulose hydrolysis as proposed by (South et al, 1995) and further modified as in (Zhang et al, 2009). The parameters presented in Zhang's kinetic model were based on cellulose and hemicellulose hydrolysis for pre-treated paper sludge.…”

“…They were unable to obtain glucose concentrations higher than 5.5% using SHF. The SSF approach, featuring enzymatic hydrolysis and fermentation of hexose in one integrated step, considerably increases inhibition to cellulase by cellulose hydrolysis products (Zhang et al, 2009). The SSCF process is similar to SSF except that hexose and pentose fermentations occur in one step.…”