Continuous solid-state fermentation as affected by substrate flow pattern

The performance of continuous solid state bioreactors having two different solid substrate flow patterns, namely plug flow and completely mixed flow, is quantified for both steady-state and transient operation using a simple mathematical model. The core assumption is that each substrate particle acts as an infinitesimal bioreactor. The residence time distribution of the particles is considered in the formulation of the equations for the mixed-flow bioreactor and the error that results from neglecting it is investigated by comparing the simulation results with those of a completely mixed, continuous bioreactor for submerged liquid fermentation (a chemostat). The model is extended to include autolysis, inter-particle inoculation and contamination. Plug flow is shown to have superior performance when high product concentration is needed, if autolysis or other undesirable late emerging phenomena occur, and when non-sterile fermentation using slow-growing microorganisms is undertaken.