Modeling And Control Problem Studies Of Activated Sludge Wastewater Treatment Processes Based On ASM1

Activated sludge biological wastewater treatment process is one of the most efficient methods that have wide application in the wastewater treatment plants. By introducing the traditional treatment process, which is called A/O process, wastewater treatment plants can purify wastewater to the satisfying extension. The A/O process consists of two anaerobic tanks, three aerobic tanks and a secondary sedimentation tank.First of all, a BSM1 model is established on the Simulink platform. Every chemical in the BSM1 model satisfies its own chemical reaction principle, which is introduced by Monod Equation. According to the principle, a differential equation is proposed for every kind of chemical and then used to establish the BSM1 model on Simulink. Simulation results show that the concentrations of several chemicals at the outlet of the secondary sedimentation tank have reduced significantly compared with those concentrations at the entrance of the first anaerobic tank.Secondly, in order to control the concentration of dissolved oxygen at the out let of the first aerobic tank, a continuous PID controller is proposed and its time constants are tuned by using the traditional PID controller tuning methods. Also, a discrete PID controller is designed by programming a S-function, which realized the function of a satisfying discrete PID controller. The simulation results show that both the continuous and the discrete PID controller satisfy the performance indicators of the Tank 3 system set for the controllers.Then, considering the high nonlinearity and strong coupling of most activated sludge process models, a simplified linear model is proposed in the form of tenth-order state-space model. By deriving the transfer function of the Tank 3 system, a second order state-space model is proposed and a sate feedback controller is designed according to performance requirements. Also, we introduce the output of the new reduced order linear model to the input of Tank 3 system and a corresponding PID controller is established. It is easier to design a state feedback controller for the simplified linear model than the original nonlinear model. The simulation result is presented to demonstrate the effectiveness of the designed state feedback controller.Last but not the least, when concentrations of the chemicals fluctuate at the entrance of Tank 3 system, the whole system is easily affected due to its low robustness. Therefore, a robust controller is needed to attenuate the effect of fluctuations caused by the disturbance variables. A robust control strategy is proposed for maintaining the oxygen concentration in Tank 3. By solving a set of linear matrix inequalities, the state feedback matrix K is obtained.