The snowball effect in fed-batch bioreactions.

The bioreactor will play an important role in future biological manufacturing. For economic profit, important profiles of the feed rate in fed-batch cultures have been discussed. Unfortunately, the optimal feed rate is less robust. In these studies there exists the snowball effect in a substrate-inhibited bioprocess, in which substrate is accumulated due to uncertain parameters in the model or feed-rate error. The snowball effect also exists in multi-substrate-limited processes. In further studies, the interaction between the substrates has been higher in essential substrates than in growth-enhancing substrates. In a typical fed-batch bioreactor, the amount of the product can be reduced to 1% or less when the snowball effect arises. A new control structure, i.e., an off-line optimized feedforward controller added to a gain-scheduling PI(2)D feedback controller, is proposed to eliminate the troublesome snowball effect. The proposed control strategy recovers the yield up to 95%. Moreover, the robustness of the proposed control structure is demonstrated by simulation.