On the observability of activated sludge plants

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In this work, the full-state observability properties of a class of biological wastewater treatment plants are analysed. Specifically, the five biological reactors and the secondary settler in the Benchmark Simulation Model no. 1 are studied. For the task, we represented the activated sludge plant as a dynamical system consisting of 145 states, 8 controls, 14 disturbances and 12 outputs and as a complex network to study its observability properties from a structural and a classical point of view. By analysing the topology of the network, we show how the system is not observable in the structural sense and thus how it is also not observable in the classical sense for all possible realisations of its parameters. As this is also true for a linearisation commonly used in the literature, we analysed a reduced-order system that, based on such linearisation, does not consider the state variables corresponding to dissolved oxygen and alkalinity in the upper-layers of the settler. We show how this system configuration is only observable in a structural sense.
Original languageEnglish
Pages (from-to)16802-16807
Number of pages6
Issue number2
Publication statusPublished - 14 Apr 2021
MoE publication typeA4 Conference publication
EventIFAC World Congress - Virtual, Online
Duration: 11 Jul 202017 Jul 2020
Conference number: 21


  • activated sludge process
  • observability
  • structural control
  • complex networks


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