Licentiate thesis 2001-011

Modelling and control of activated sludge processes with nitrogen removal

Pär Samuelsson

August 2001

Stricter legislations on nitrogen removal together with increasing wastewater loads have successively increased the need for optimization and control of activated sludge processes. The aim of this thesis is primarily to propose and illustrate methods for modelling and control of activated sludge processes, and thus possibly improve process efficiency. The first part of this thesis describes a JAVA based simulator of the activated sludge process. Its features are discussed, and some control strategies are illustrated. The second part of the thesis presents a simple model based feedforward controller for controlling the nitrate level by using an external carbon source. Several simulation examples are used to illustrate the control law. In the third part, a model based strategy for control of the ammonium level by manipulating the aeration volume in the activated sludge process is presented. The strategy is based on exact linearization combined with some logical programming rules in order to deal with discrete volume changes. The control law is also evaluated in simulations.

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