Modeling simultaneous saccharification and fermentation of lignocellulose to ethanol in batch and continuous reactors

An adsorption-based kinetic model was sought that accurately predicts simultaneous saccharification and fermentation (SSF) of insoluble lignocellulosic substrates in batch and continuous reactors. With a common set of three heuristic parameters, a hydrolysis rate equation of the form r = {k × (1 − x)n + c} × (ES)(Çs) conjunction with Langmuir adsorption is capable of accurately representing batch SSF data from well-mixed bioreactors for a variety of feed substrate concentrations and cellulase loadings (root mean squared (RMS) difference in predicted and measured conversion = 5.2%). Using a particle population model in conjunction with the batch kinetics, conversion in a CSTR as a function of residence time is also well predicted (4.6% RMS difference). Including both batch and continuous data, the model is successful over a four-fold range of enzyme loadings and a 12.8-fold range of substrate concentrations. Commentary is offered on useful features of kinetic models for processes including cellulose hydrolysis.