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Design and implementation of a nonlinear controller in PLC as a part of an adroit scada system for optimal adaptive control of the activated sludge process
Nketoane, Paseka Augustinus
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More than 70% of the earth's surface is covered by water, only a small part of which is suitable for either human consumption or agricultural use. Due to pollution from agriculture, households and industry reaching rivers, lakes and seas it is Important for wastewater to be properly treated in order to remove harmful substances before it reaches the environment. Strict environmental and health regulations together with a demand for cost effective ways of wastewater treatment have made control technology in wastewater Treatment Plants an important priority. Dissolved oxygen (DO) is the amount of oxygen in the effluent and it plays a vital role of controlling VV\YTP. Oxygen dissolves in water through mixing water surface with the atmosphere, The dissolved oxygen concentration in the aerobic part of an activated sludge process should be sufficiently high to supply enough oxygen to the microorganisms in the sludge. an excessive high DO leads to high energy consumption and may also deteriorate the sludge quality, A high DO concentration in the internally recirculated water also makes the denitrification less efficient Hence, both for economical and process reasons, it is of interest to control the DO. The used controllers are normally linear controllers, proportional integral (PI) or proportional integral derivative (PID) ones. The work of these controllers leads to bad system performance, because, the process of dissolving oxygen into the wastewater is a nonlinear process and requires nonlinear control. The aim of the research project is to develop methods for design of linear and nonlinear controllers of the concentration of the DO in the aeration tank of the WWTP and to implement the designed controllers in the frameworks of PLC. The nonlinear linearizing controller based on a reference model and Lyapunov second method is designed. Additionally a linear controller is developed in a form of PI controller based on pole placement method to improve, the performance of the closed loop system. The resultant controller is to be on a PLC as a part of Adroit SCADA system. The developed programmes are used to control the wastewater treatment process in laboratory scale plant and can be applied as a part of SCADA software for control of the wastewater treatment plants.