Control of dilution rate increase in continuous culture

Control of dilution rate increase in continuous culture 

Based on this model, a time-dependent feed flow rate function was derived that should permit an increase in the dilution rate from one value to another without provoking the appearance of reductive metabolism [83]. The idea was to increase the glucose supply in parallel with the dynamic increase of the oxidative capacity of the culture, so that all of the assimilated glucose could always be oxidized. Nevertheless, corresponding feed-profile experiments showed that deviations into the reductive metabolism could not be completely suppressed due to variability in the model parameters. 

A nonlinear proportional controller was used to correct the feed profile. The controlled variable was the heat flow rate because it gives the fastest response to a metabolic switch. As for open-loop feed profile experiments, the profile 

However, it was not expected that the heat flow rate would be higher than the set-point during the first hour after the dilution rate increase. Also, biomass concentration was not supposed to slightly decrease (from 10.5 to 9.5 g dm ) in the absence of significant ethanol production or glucose accumulation. Similarly, the prediction underestimated other on-line measurements (rp, r Q,) at the 

The choice of a controller gain a equal to 0.03 or 0.04 1 h W gave good results. Ethanol concentration varied between 0.10 and 0.55 g dm for a final dilution rate close to 0.20 h . The controller action always resumed towards the end of the experiments. Note that the initial step used to determine experimentally contributes, to a large extent, to the ethanol formation, but is necessary to ensure a fast enough increase in the feed rate. 

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