Design of modified digital PWM controller for aeration in wastewater treatment process

The activated sludge process (ASP) is widely used in many wastewater treatment process (WWTP), which consists of a biological reactor and a sedimentation tank, and also is used to take the contaminant (substrate) away by means of activated sludge (microorganisms). The first part of this paper gets the simplified model of the activated sludge model No.1 (ASM1), which contains the nitrification and denitrification. Because of the nonlinear nature of ASM1, the optimal linearization technique is applied to it for finding a local optimal linear model, which has the same dynamics of the original nonlinear model at the operation point of interest. Then, a discrete-time optimal control law in pulse-amplitude-modulated (PAM) is designed using linear quadratic regulator (LQR) method. For engineering implementation, a modified pulse-width-modulation (PWM) method is proposed. At last, some simulations are made to demonstrate the effectiveness of the proposed control strategy, which can reduce the whole operational energy and spend less reaction time, comparing to Multi-set point on/off control and PWM control techniques.