Estimation of Unmeasured States in a Bioreactor under Unknown Disturbances

The measurement or estimation of bioprocess states is critical for process control and optimization applications. However, certain disturbances or unknown inputs can generate significant model–plant mismatch if not considered by the process models. To better estimate the process states in the presence of these disturbances or unknown inputs, a nonlinear unknown input observer is applied. Experimental studies of batch and fed-batch operations of a bioreactor were performed using a recombinant Saccharomyces cerevisiae to produce β-carotene. Previously developed kinetic models produce model–plant mismatch with changes to the initial conditions or operating mode of the bioreactor. The observer is applied to the bioreactor system to estimate the batch and fed-batch state variables. State estimates from the designed observer are compared to model predictions and experimental measurements. Results show improved state estimation over first-principles model predictions when applying the unknown input observer to the nonlinear dynamic process with unknown disturbances