Comparison of MPC and PI Control Strategies for Activated Sludge Process

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Abstract:
This paper deals with comparison of PI Controller with model predictive control (MPC) applied to benchmark simulation model no.1 (BSM1) of an activated sludge process in order to maintain the effluent quality within the limits. The objective is to compare the control strategies based on better performance with respect to effluent concentration under specified limits and operating costs. In this study, the control strategies such as PI and model predictive control (MPC) are compared and applied to control the dissolve oxygen concentration in the last aerobic reactor of the activated sludge process. Also, the nitrate concentration is controlled in the second anoxic reactor using PI control strategy. Simulations are performed using sewage treatment plant influent data. The influent fractionation is carried out using activated sludge model no.1 (ASM1). The results of the dynamic simulation indicate that model predictive control is more effective than PI control in meeting the effluent limits especially when ammonia concentration is considered significant. By comparing performance evaluation criteria, dissolved oxygen MPC and nitrate PI (MPC-PI) control strategies have achieved almost the same operating costs as with dissolved oxygen PI and nitrate PI (PI-PI) control strategies.
Keywords:Activated sludge process, Benchmark Simulation Model No.1, MPC, Operating cost, PI control

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