PWM digital control of aeration in wastewater treatment process

A pulse-width-modulation (PWM) digital controller design method in aeration control, which can reduce the energy costs of the control procedure, is proposed for wastewater treatment process based on the ASM1 model. First, an optimal linearization technique is applied to the aeration nonlinear system for finding a local optimal linear model, which has the same dynamics of the original nonlinear system at the operating point of interest. Then, a discrete-time optimal control law in pulse-amplitude-modulated (PAM) form is designed using LQR method. The PWM digital control law is then converted, using the digital redesign technique, from the corresponding PAM control law for the purpose of engineering realization. Last, simulation results demonstrate the effectiveness of the proposed method and the whole energy consumption is also computed. It has been shown that compared with the conventional multi-set point on/off control and on/off control method, the proposed method can save more energy than other approaches.