A novel feeding strategy for industrial fed-batch processes based on frequency content analysis

Overflow metabolism, i.e. the production of metabolic by-products at a high glycolytic flux, is a recurring problem in fed-batch processes with many types of microorganisms. In the current study, a novel feeding strategy aimed at avoiding process failures due to overflow by-product formation was designed and implemented in a pilot-scale reactor (0.5 m3). The basic principle behind the strategy was to analyze the effects on the dissolved oxygen concentration by periodic variations in the inlet feed rate. The frequency spectrum of the dissolved oxygen signal was used to estimate the proximity of the system to the region where overflow metabolism occurs by examining the content in the relevant frequency range. A control variable based on the measured frequency content was subsequently used to control the feed rate. The only measurement required for this strategy is the dissolved oxygen level in the broth, for which robust, fast and precise probes are widely available in industrial fermentors today. The strategy was successfully implemented in pilot-scale processes for industrial enzyme production using Bacillus licheniformis. It was shown possible to run the process close to the optimal feed rate, indicated by very low amounts of acetate (the overflow metabolite) in the broth. In comparison to a reference strategy the new control strategy resulted in over 10% higher biomass yields