Interval Type-2 Fuzzy Neural Network Control For Municipal Wastewater Treatment Process

Due to the rapid growth of urban population and the rapid development of industrial production,the water shortage has become a global problem to be solved urgently.Wastewater recycling,as one of the important means to relieve the crisis of water resource,has attracted considerable attention around the world.In recent years,many municiple wastewater treatment plants have been built to purify wastewater around the world,so as to protect the ecological environment and improve the utilization of water resources.Among the various wastewater treatment technologies,the activated sludge method has been widely used in municipal wastewater treatment plants,and it can utilize the biochemical reaction processes of activated sludge to obtain the clean water.However,these biochemical reactions own the complex mechanisms and interfering factors and express the strong nonlinearity,high uncertainty and time-varying dynamics.Meanwhile,the interaction effects exist in these biochemical reactions and the corresponding control variables,and the different operation conditions are complex in wastewater treatment process(WWTP).Therefore,it is a challenge to deal with the nonlinear,uncertainty and time-varying dynamics of WWTP and overcome the interaction effects in different control variables to ensure the stable operation of WWTP under different operation conditions.To accurately control the key variables to achieve the stable operation of WWTP,a control method based on the interval type-2 fuzzy neural network is proposed in this paper.First,a cooperative strategy-based self-constructing interval type-2 fuzzy neural network(SC-IT2FNN)is designed.In this proposed SC-IT2 FNN,the cooperative learning of structure and parameters and the cooperative optimization of nonlinear and linear parameters can be achieved to obtain the good generalization performance and fast convergence rate.Second,an interval type-2 fuzzy neural network-based cooperative controller(IT2FNN-CC)is proposed.In this proposed IT2FNN-CC,the controller structure can be adaptively adjusted and the parameters are cooperatively optimized to improve the adaptivity of IT2FNN-CC and reduce the computational burden to achieve the cooperative control for WWTP.Third,the corresponding hardware and software are combined to achieve the IT2FNN-CC.This IT2FNN-CC is applied in a real municipal wastewater treatment plant and achieve a good control perfoemance.The main works in the paper are as follows:1.The design of the cooperative strategy-based self-constructing interval type-2 fuzzy neural network.In this paper,a cooperative strategy-based self-constructing interval type-2 fuzzy neural network is designed to improve the modeling performance of interval type-2 fuzzy neural network.Fitst,a comprehensive evaluation algorithom is proposed to adjust the structure of SC-IT2 FNN to improve the generalization performance.Second,a hierarchical optimization mechanism is designed to cooperatively optimize the nonlinear and linear parameters of SC-IT2 FNN to accelerate the learning speed.Third,the convergence of SC-IT2 FNN is analyzed in detail to ensure its successful application.Several benchmark nonlinear systems and a practical application are used to test the effectiveness of SC-IT2 FNN.The results demonstrate that this proposed SC-IT2 FNN can obtain the high modeling accuracy and compact structure.2.The design of the interval type-2 fuzzy neural network-based cooperative controller.In this paper,an interval type-2 fuzzy neural network-based cooperative controller is proposed to cooperatively control the dissolved oxygen and nitrate concentrations to improve the operating efficiency of WWTP.First,a structre cooperative strategy is proposed to adjust the number of fuzzy rules in IT2FNN-CC.Then,the structure of IT2FNN-CC can be adaptively adjusted to meet the different operation conditions of WWTP.Second,a parameter cooperative strategy is proposed to coordinate the global and local parameters of IT2FNN-CC.Then,the parameters of IT2FNN-CC can be cooperatively optimized to meet the control requirments.Third,the stability of IT2FNN-CC is proven according to the Lyapunov theorem.Then,the corresponding stability conditions are given to guide the application in practice.The proposed IT2FNN-CC is simulated in Benchmark Simulation Model No.1 and analyzed in detail.The results indicate that IT2FNN-CC can accurately control the dissolved oxygen and nitrate concentrations of WWTP under different operation conditions.3.The study on the application of cooperative controller for municipal wastewater treatment process.In order to verify the effect of IT2FNN-CC in the real municipal WWTP,the corresponding hardware and software are utilized to realize the cooperative controller for the municipal wastewater treatment process.First,the operating environment of the cooperative controller is analyzed to provide support for hardware selection and software design.Second,according to the actual situation,the appropriate hardware equipments are selected and the corresponding software function modules are designed to achieve the control function.Finally,the cooperative controller was tested in a real municipal wastewater treatment plant.The results show that this cooperative controller can achieve the cooperative control of the dissolved oxygen and nitrate concentrations under the different operation conditions.