Control Techniques for Fed-Batch Fermentation
A control system is required in the fed-batch fermentation to manage concentrations and volume during the fermentation process. This set-up is generally known as the adaptive control, in which the controller learns about the process by acquiring data from a certain process and keeps on updating according to a control model. A schematic diagram of the control system used in a fed-batch fermentation set-up is shown in Figure 9.1.
In adaptive control, the controller compares the estimates from a mathematical model applied to the system to the readings obtained from the fermentation process. The controller then sends the signal to the device controlling the fermentation, for example, by increasing or decreasing a flow rate by adjusting control valves. The
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Figure 9.1 A schematic diagram of the control system used in a fed-batch fermentation set-up. |
optimal strategy for the fed-batch fermentation of most organisms is to feed the growth-limiting substrate at the same rate that the organism utilizes the substrate; this is to match the feed rate with demand for the substrate. Four basic approaches have been used in an attempt to balance substrate feed with demand:
1. Open-loop control schemes in which feed is added according to historical data or predicted data.
2. Indirect control of substrate feed based on non-feed source parameters such as pH, off-gas analysis, dissolved O2 or concentrations of products.
3. Indirect control schemes based on mass balance equations, the values of which are calculated from data obtained by sensors.
4. Direct control schemes based on direct on-line measurements of substrates.