On the controllability of continuous fermentation processes

Abstract Different reactor configuration for continuous fermenters are examined in terms of their controllability properties. This is done by examining the control input required for perfect disturbance rejection. It is shown that using an additional inlet stream (which does not contain any growth limiting substrate) as a control input leads to superior control performance than a single stream fermenter. Recycles can improve the controllability if the outlet stream is used as a control input. The controllability analysis is based on linearised process models and is illustrated with simulations of the nonlinear process models using PI controllers.