Time-Optimal Output Feedback Controller for Toxic Wastewater Treatment in a Fed-Batch Bioreactor

Aerobic processes using sequencing fed-batch bioreactors are an effective technology to treat wastewater with toxic compounds. In order to implement optimal control schemes it is convenient to assess the biodegradation rate on-line. In this work, the dissolved oxygen concentration is used as output variable from the process to estimate this rate using a robust observer based on the generalized supertwisting algorithm. It does not require complete knowledge of the system dynamics or its parameters and is capable of estimating the biodegradation rate despite uncertainties and significant sensor and signal conditioning dynamics. The observer is then used for the implementation of a time-optimal output feedback controller that regulates the feed rate in a sequencing batch bioreactor used to treat toxic wastewater. This is tested using numerical simulations with promising results, while discussing the trade-off between allowed signal noise and convergence speed of the observer and how this affects the controller performance.