Probing control in B. licheniformis fermentations

In industrial biotechnical processes in fed-batch mode it is desirable to keep a high feed rate in order to achieve a high production rate, while simultaneously avoiding overflow metabolism. This means that the optimum of the process is close to the point where it risks crashing due to the effects of overflow metabolites. Probing control of feed rate is a control strategy for microbial processes which utilises the characteristic saturation in oxidative metabolism at the critical limit for overflow, in order to keep the feed rate as high as possible while not exceeding this limit. In this degree project, probing control has been implemented in an industrially relevant process utilizing B. licheniformis at Novozymes’ fermentation pilot plant in Bagsværd, Denmark. The aim of the project has been to find out if successful implementation of probing control in a B. licheniformis process is possible and whether this can improve the properties of the process. A draft of a probing controller has been created in MATLAB and developed step by step through a series of experiments in pilot scale, into a controller capable of successfully controlling the process from start to end. The outcome shows that the probing controller achieves a process yield similar to when using the existing control strategy for the process, while it is indicated that the probing controller is more capable of avoiding process crashes due to overflow metabolism early in the process. Methods for verifying this outcome experimentally and for optimising the probing controller are described. Furthermore, a design for an improved probing control strategy based on observations in this project is suggested.