A model-based investigation of the potential advantages of multi-layer packed beds in solid-state fermentation

We use a mathematical model, based on the N-tanks-in-series approach, to evaluate the potential advantages that can be obtained in solid-state fermentation processes by operating packed-bed bioreactors as multi-layer beds. We explore classical operation, in which air is blown unidirectionally through a substrate bed that remains immobile, with two strategies that involve movement of the layers. The first strategy involves batch operation, in which the positions of the layers are changed at 1 h intervals, in a cycling motion. The second strategy involves continuous plug-flow of the layers, with the regular addition of new layers at the air outlet and removal of spent layers at the air inlet. Under the conditions of the simulation, the rate of metabolic heat generation during the steady state of the continuous plug-flow process is only 60% of the peak value predicted for classical operation. As a result, the maximum bed temperature in the continuous plug-flow process is 4.5 °C lower than that predicted for classical operation. We conclude that the operation of multi-layer packed beds in the continuous plug-flow mode can improve bioreactor performance significantly.