Modelling of end-product inhibition in fermentation

Microbial conversions are generally inhibited by their products. This product inhibition is particularly dependent on the product's hydrophobicity and on its acid dissociation behaviour, hence on pH. Dependence on the microbial strain is relatively modest according to many published data. Since product inhibition has various mechanistic backgrounds, one requires an empirical model for simulation of fermentation processes. For obtaining a modelling framework that is consistent for various bioreactor operation modes, literature data for the glucose to ethanol fermentation were used to elaborate a relatively simple case. The Pirt equation and hyperbolic substrate uptake equation were used with three parameters that depend linearly on the inhibiting product concentration. This model type should facilitate model-based optimization of bioreactor operation.