CONTROL SYSTEM DESIGN FOR ACTIVATED SLUDGE WASTEWATER TREATMENT PLANTS: SOME PRACTICAL EXPERIENCES ABSTRACT

In this paper we present some of our experiences on the design and implementation of control systems for the activated sludge wastewater treatment plants. The following two issues will be particularly addressed: Choosing an appropriate control strategy. Before designing a control system, one usually has on hand an objective function which has to be minimised or maximised by appropriately controlling the process. This, together with the mathematical model of the process, if available, constitutes an optimal control problem which is often difficult to solve due to for instance the complexity of the model, the incomplete on-line information, and so on. Very often one is determined to find a sub-optimal control strategy with which the objective can be approximately achieved. This consists mainly of choosing the controlled and sometimes even the manipulated variables and determining how the controlled variables should be controlled. By presenting a few practical examples[1][2], we show how an appropriate control strategy can be found by means of model-based analysis of the concerned process. Deriving information for feedforward control. A wastewater treatment plant typically suffers large external disturbances. For instance, the peak to minimum ratio of the flow to a smal