| Summary: | Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 === 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.
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