Abstract
The article investigates the operability of a nonideal unstructured kinetic model of continuous bioreactors. The study of operability (interactions between design and control) can help in identifying control problems that could be overcome during the design stage. The issue of operability has been studied extensively in the literature for chemically reactive systems but has not received the same attention for bioreactive systems. The bioreactor model investigated here allows for general dependence of growth rate and yield coefficient on the substrate. The nonideality of the bioreactor is described by the fraction of reactor total volume that is perfectly mixed and by the fraction of the feed entering the perfectly mixed zone. The static and dynamic analyses of the model enable the delineation of regions of input and output multiplicity, as well as the conditions for the existence of oscillatory behavior in the bioreactor. This allows the determination of boundaries between safe and washout regions and the delineation of regions of undesired oscillations. The general analysis is illustrated through a specific example for substrate-inhibited growth rate and linear dependence of the yield on the substrate. The analysis illustrates how modeling decisions and ultimately the design and operating parameters influence the operating characteristics of the bioreactor.