Dissolved oxygen control for activated sludge processes

Abstract

Controllers for dissolved oxygen reference trajectory tracking for activated sludge processes are proposed and investigated. A nonlinear model predictive controller and a direct reference adaptive controller are investigated. Both the nutrient and the phosphorous removal from a wastewater by its biological treatment using an activated sludge technology are considered. An approach to the controller design utilises a structure of the dissolved oxygen dynamics and its two time scales: fast and slow. The predictive controllers offer good tracking performance and robustness. The direct model reference adaptive controller is much simpler to implement. However, it is more difficult to compromise between tracking accuracy and rate of change and magnitudes of the control actions. The controllers are validated by simulation using real data sets and an ASM2d model of the biological reactor.

Keywords:

• Biotechnological processes
• Process control
• Nonlinear predictive control
• DMRAC
• Trajectory tracking in non-linear systems

Acknowledgements

This work was supported by the Polish State Committee for Scientific Research under grant No. 8T11A-021-18 and grant No. 4 T11A 019 25 and by the European Commission under contract No. EVK1-CT-2000-00056 SMAC. The authors wish to express their thanks for this support.

Wiktor Chotkowski received the M.Sc. degree in Automatic Control from the Department of Electronic Engineering at Gdansk University of Technology in 1963 and the Ph.D. in Control Systems from the Department of Electrical and Control Engineering at Gdansk University of Technology in 1972. Since 2000 he has been with the Intelligent Decision Support and Control System Group at GUT working on modelling, monitoring and control of wastewater systems. He has widely served as Consultant for drinking water and wastewater industry in Poland. He is author and co-author of about 30 refereed papers.

Mietek A. Brdys received the M.Sc. degree in Electronic Engineering and the Ph.D. and the D.Sc. degrees in Control Systems from the Institute of Automatic Control at the Warsaw University of Technology in 1970, 1974 and 1980, respectively. From 1974 to 1983, he held the posts of Assistant Professor and Associate Professor at the Warsaw University of Technology. In 1992 he became Full Professor of Control Systems in Poland. Between 1978 and 1995, he held various visiting faculty positions at the University of Minnesota, City University, De Montfort University and University Polytechnic of Catalunya. Since January 1989, he has held the post of Senior Lecturer in the School of Electronic, Electrical and Computer Engineering at The University of Birmingham. Since February 2001 he has held the post of Full Professor of Control Systems in the Department of Automatic Control at Gdansk University of Technology. He has served as Consultant for Honeywell Systems and Research Center in Minneapolis, GEC Marconi and Water Authorities in UK, France, Spain, Germany and Poland. He is Head of Interdisciplinary Research Network on Decision Support and Control Systems at The University of Birmingham and Head of Intelligent Decision Support and Control System Group at Gdansk University of Technology. His research is supported by the UK and Polish Research Councils, and industry and European Commission. He is author and co-author of about 200 refereed papers and six books. His current research includes intelligent decision support and control of complex uncertain systems, robust monitoring and control. The applications include environmental systems, technological processes and defence systems. He is a Chartered Engineer, a Member of the IEE, a Senior Member of IEEE, a Fellow of IMA and a Vice-Chair of the IFAC Technical Committee on Large Scale Complex Systems.

Kamil Konarczak received the M.Sc. degree in Automatic Control from Department of Control Engineering at Gdansk University of Technology in 2001. Since then he has been with Intelligent Decision Support and Control System Group at GUT working on modelling and control of wastewater systems and he has just completed his Ph.D. dissertation. He is author and co-author of 11 refereed papers.