The fermentation of lignocellulosic biomass slurries generally produces low ethanol concentrations that are expensive to distil. Lignocellulosic slurries exhibit high viscosities at moderate solids loadings, thus limiting final ethanol concentrations. This study sought to determine the optimum lignocellulosic fermentation operating strategy, by employing previously validated hydrolysis, fermentation and rheological models.

The results of these simulations have shown that increases in temperature, enzyme loading and delignification can increase the amount ethanol produced. However, the maximum concentration that could be produced by a batch simultaneous saccharification and fermentation (SSF) was 7.5% (w/w) from a cellulose loading of 200g/L (27.2% solids loading). However, the yield stress of such a slurry will be a significant constraint early in the batch resulting in poor mass transfer and slower than modelled reaction rates and is thus unlikely to be achievable. Under more realistic conditions the maximum simulated ethanol concentration was 3.15% (w/w) using a cellulose loading of 100g/L (13.6% solids loading).

The potential of fed batch operation was investigated as it requires little extra energy or capital expenditure. Simulation of fed batch SSF, found that it was possible to increase the solids loading and avoid the viscosity constraints that are present in a high solids loading batch fermentation until late in the batch by which time the ethanol concentration had reached 11% (w/v).