Modelling and Estimation of the Oxygen Transfer Function in a Bioreactor with Aeration Driven by PWM Signal

The dissolved oxygen concentration is a critical variable to the aerobic biological processes and, hence, the rate of oxygen transfer from gas phase to the liquid phase, where the biological reactions are taking place, is an important issue. The gas-liquid oxygen transfer process is characterized by the volumetric mass transfer coefficient, or oxygen transfer function, which is a parameter that has been used in the design, operation and optimization of such processes. For practical purposes, the oxygen transfer function is considered to depend only on the aerators inlet airflow rate, which is typically nonlinear. In this paper, a linear model of the oxygen transfer function is proposed, where the aerators are driven in a PWM mode rather than in a variable flow rate. Results from experiments with clean water and activated sludge samples show the validity of the proposed linear model.