At-line control and fault analysis in an industrial high cell density Escherichia coli fermentation, using NIR spectroscopy

The limited availability of process measurements decreases the efficiency of fermentation development, hinders process control, and can reduce production plant productivity through unidentified bioreactor faults. At-line near-infrared spectroscopy (NIR) provides the opportunity to use rapid, simultaneous measurements of carbon and nitrogen nutrients, byproduct and biomass for improved process control. At-line MR ammonium monitoring was used in an E. coli fermentation to control the accumulation of ammonium by indicating when to switch between NH4OH and NaOH solutions for pH control. In this manner ammonium concentration was successfully controlled between inhibitory and growth limiting concentrations. In this fermentation, as in many industrial fermentations, the carbon nutrient was fed in an open loop, feed-forward control scheme to maintain carbon-limited growth. However, such strategies are not robust and can fail if unplanned process perturbations occur as a result of sensor failures, feed system failures, and accumulation of inhibitory substances. In this fermentation, at-line NIR measurement of carbon nutrient (glycerol) and the inhibitory byproduct (acetate) provided a method for improving such open loop feed forward control by incorporating a feed back component. The improved control of ammonium, acetate and glycerol facilitated a biomass accumulation to 86 gl(-1). This is believed to be the highest biomass concentration reported for a recombinant protein producing E. coli fermentation with a complex medium feed. At-line NIR analysis was also used to determine and identify bioreactor faults by detecting a DO probe failure and a pH controller failure.