Fractional Order Model-Based Design of Controllers for Improved Operation of Wastewater Treatment Plants
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ORIGINAL ARTICLE
Fractional Order Model‑Based Design of Controllers for Improved Operation of Wastewater Treatment Plants Soniya Panjwani1 · E. S. S. Tejaswini1 · A. Seshagiri Rao1 Received: 7 July 2020 / Accepted: 31 August 2020 © Indian National Academy of Engineering 2020
Abstract A non-integer order model is developed for a biological wastewater treatment plant (WWTP) represented in benchmark simulation model (BSM1) scenario. In BSM1 framework, sufficient nitrification is maintained by providing a constant aeration flow rate, by controlling the dissolved oxygen (DO) in the fifth reactor at pre-selected set-point. The nitrates in the anoxic reactor-2 are controlled by manipulating internal recirculation flow. Initially, a state-space model for both the loops is developed by varying both the manipulated variables by ± 10% around the nominal operating point. Then, fractional order models are developed for both the loops around the operating point. After obtaining the fractional order model, fractional IMC-PID-based controllers are designed for controlling the WWTPs. The designed fractional order simple PI controllers provided improved plant as well as controller performance when compared to the traditional integer order PI controllers. Keywords BSM1 model · Fractional controller · Fractional order model · Wastewater treatment
Introduction Biological wastewater treatment plants (WWTPs) are typical non-linear processes with interlacing dynamics besides the sub-processes involved. The treatment methods are spread over a range of time constants. It is subjected to many types of disturbances and variations in the characteristics of the influent with the magnitudes that surpass most other process industries (Copp 2002). Also, process being extremely resourced intensive; it is essential that plant should be functioned in a resource-effective manner. Due to expansion in urban areas, the burden on existing treatment plants is expected to rise. This condition necessitates more adequate wastewater treatment operations. All these factors together pose challenge for control of wastewater treatment plants. An effective control strategy is required to keep all the pollutants in the effluent under the permissible values. A Electronic supplementary material The online version of this article (https://doi.org/10.1007/s41403-020-00169-9) contains supplementary material, which is available to authorized users. * A. Seshagiri Rao [email protected] 1
Department of Chemical Engineering, National Institute of Technology, Warangal 506 004, Telangana, India
range of wastewater treatment plant configurations and scenarios can be used as base to implement control strategy developed making the comparison of controller performance a tough job. This is because the performance differs with respect to objectives to be achieved and it is also affected by number of aspects including influent concentrations and flow rate, complexity of plant itself, geographical region-dependent effluent standards and the evaluation criteria. All th
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