Modelling, Simulation and Control of Urban Wastewater Systems

Springer-Verlag London Ltd.

Manfred Schiitze, David Butler and M. Bruce Beck

Modelling, Simulation and Control of Urban Wastewater Systems With 81 Figures

, Springer

Manfred R. Schiitze, Dr Dipl-Math, PhD, DIC ifak e. V. Magdeburg, Institute for Automation and Communication, D-39179 Barleben, Germany

David Butler, PhD, DIC Department of Civil and Environmental Engineering, Imperial College of Science, Technology and Medicine, London, SW7 2BU, UK

M. Bruce Beck, PhD Warnell School of Forest Resources, The University of Georgia, Athens, Georgia, 30602-2152, USA

British Library Cataloguing in Publication Data Schutze, Manfred R

Modelling, simulation and control of urban wastewater systems 1.Urban runoff - Mathematical models 2. Sewage disposal­Mathematical models I.Titie II.Butler,David, 1959- III.Beck, M. B. 363.7'284 ISBN 978-1-4471-1105-4

Library of Congress Cataloging-in-Publication Data Schiitze, Manfred R., 1966-

Modelling, simulation and control of urban wastewater systems / Manfred R. Schiitze, David Butler, and M. Bruce Beck.

p.cm. Includes bibliographical references and index. ISBN 978-1-4471-1105-4 (alk. paper) 1. Sewage--Purification--Mathematical models. 2. Sewage disposal

plants--Mathematical models. 3. Sewerage--Mathematical models. I. Butler, David 1959- II. Beck, M. Bruce, 1948- III. Title. TD745 .S37 2002 628.3'09173'2--dc21 2001055108

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers.

ISBN 978-1-4471-1105-4 ISBN 978-1-4471-0157-4 (eBook) DOI 10.1007/978-1-4471-0157-4 http://www.springer.co.uk

© Springer-Verlag London 2002 Originally published by Springer-Verlag London Berlin Heidelberg in 2002 Softcover reprint of the hardcover Ist edition 2002

The use of registered names, trademarks etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore free for general use.

The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.

Typesetting: Electronic text fIles prepared by editors 69/3830-543210 Printed on acid-free paper SPIN 10830782

llciv"ta pei

Heraclitus

(c. 544 - 483 BC)

Foreword by Professor Poul Harremoes

Environmental engineering has been a discipline dominated by empirical approaches

to engineering. Historically speaking, the development of urban drainage structures

was very successful on the basis of pure empiricism. Just think of the impressive

structures built by the Romans long before the discipline of hydraulics came into

being. The fact is that the Romans did not know much about the theories of

hydraulics, which were discovered as late as the mid-1800s. However, with the

Renaissance came a new era. Astronomy (Galileos) and basic physics (Newton)

started the scientific revolution and in the mid-1800s Navier and Stokes developed

the application of Newtons laws to hydrodynamics, and later, St. Venant the first

basic physics description of the motion of water in open channels. The combination

of basic physical understanding of the phenomena involved in the flow of water in

pipes and the experience gained by "trial and error", the engineering approach to

urban drainage improved the design and performance of the engineering drainage

infrastructure. However, due to the mathematical complications of the basic

equations, solutions were available only to quite simple cases of practical

significance until the introduction of new principles of calculation made possible by

computers and their ability to crunch numbers. Now even intricate hydraulic

phenomena can be simulated with a reasonable degree of confidence that the

simulations are in agreement with performance in practice, if the models are

adequately calibrated with sample performance data. This development started in the

1970s and has the potential to significantly improve the design of urban drainage

systems and structures.

On top of this development of the combination of theory and practice came the

potential of optimising the performance in operation based on on-line data on the

status of the system at any particular point of time. For this development to become

effective the on-line provision of adequate performance data at selected points in the

sewer system and tools for optimising performance on the basis of on-line data.

Vlll Foreword

Since the mid-1800s European cities have been provided with infrastructures for

water supply and sewerage, consistently separating the clean and dirty water. This is

the basis for the fact that modem cities of the developed world are virtually without

waterborne diseases. This infrastructure is a huge investment that is hidden under

ground, more often than not taken for granted and ignored by the public and

politicians. That investment has to be upgraded to modem demands for better

environmental performance, on top of the ongoing demand for flood control. These

indispensable infrastructures have to be maintained (refurbished when ignored for

too long) and operated to get the most out of the investment. That problem will be

with us for as far as we can look ahead. The challenge is to make the system and the

investments sustainable. Advanced tolls for mathematical simulation of the systems,

adequate data on performance and on-line measurements, in combination with

advanced procedures for optimisation will be indispensable in the approach to

drainage of urban cities with an established water infrastructure.

As an after-thought, it is important to realise that most cities, in fact almost all of

the megatropolises of the world, are not in a similar position. The route for

sustainable development may take a completely different direction. Copying the

European approach does not provide the basis for development, due to lack of funds

required for the huge investments. While appreciating, maintaining and optimising

the drainage of cities in the developed world, the provision of alternatives for the

growing megacities of the developing world has to be kept in sight.

Lyngby, July 2001

Poul Harremoes

Professor at Technical University of Denmark, Lyngby, Denmark

Foreword by Professor Peter Vanrolleghem

This book, which originated from the comprehensive PhD work of Dr Manfred

Schlitze combined with the many years of related investigations of the co-authors Dr

David Butler and Dr Bruce Beck, deals with the modelling and control of the entire

urban wastewater system. I very much welcome its publication since it is an

important step forward towards making the quantitative analysis and optimisation of

the urban wastewater system an objective process in which design/optimisation

options can be evaluated in a step-wise fashion. This does not mean, however, that

the creativity, skill and challenging fun of designing/optimisation is to be lost. It does

mean that engineers making choices can be inspired by the examples and procedures

provided in this book and can be more confident that their solutions are thoroughly

evaluated with respect to the needs and constraints which represent the ambitions of

their potential customers and, indeed, anyone that will come into contact with that

(implemented) solution.

This book is all about integration. Foremost, it deals with the integration of the

urban wastewater system. No longer can the sewer system be considered separate

from the treatment plant, let alone the river system. The same holds for the treatment

plant that needs to be regarded as an integral part of the urban wastewater system.

The work reported here can be seen as an anticipation of what, for instance, the

recently adopted European Water Framework Directive is imposing. From now on it

is not the separate emissions from the subsystems that need to be looked after, but

rather the integrated input of the different pollution sources must be looked at in

terms of the effect on river quality (in all its aspects). The urban system is clearly one

of the main pollutant sources into the river and should be tackled as a whole. The

important contribution of the work reported in this book is that it is shown to be

possible to make comprehensive models of the whole system that can be used within

optimisation studies that focus on river water quality objectives. A number of hurdles

that had to be taken were jumped, such as the problem of linking existing

mathematical descriptions that use different state variables, the problem of model

complexity and the necessity of having bi-directional information flow between the

x Foreword

subsystems for real-time control. This has led to what is probably the first simulator

that can simultaneously solve a truly integrated urban wastewater system model.

The next aspect of integration pertinent to this book is the integration of

disciplines. Going through the book the reader will be confronted with such widely

varying disciplines as civil engineering, software engineering, (micro )biology,

numerical analysis, control engineering, mathematical modelling, statistics,

environmental and chemical engineering, and probably some more. It is remarkable

that the authors have been able to master all of these disciplines and have brought

them to synergy. This is quite an accomplishment and should set an example for any

future work (not only in environmental issues!) that will increasingly rely on the

multi-disciplinarity of individuals and teams.

Finally, an integration of backgrounds (schools of thought) was established in

this work. In this era of globalisation, it is good to realise that this book is the result

of a collaboration of a German PhD student with an English and an American

supervisor. However, the effective supervision of this book is probably much wider.

Dr Schutze started his research within MA TECH, the European Centre for

MAthematics and TECHnology of Urban Water Pollution, financed by the EC

Human Capital and Mobility project. It links different research groups in Europe

active in the field of Urban Water Pollution, concentrating on the modelling aspects.

It goes without saying that tapping into such a network allows the efficient

absorption of the necessary multi-disciplinary expertise to move forward quickly. In

addition, it provides the necessary peer review options to (re)direct research.

Consequently, through this comprehensive network, this book can also be seen as a

result of an integrative effort within the profession.

At the time when I started my own research in the field of modelling and

simulation, my then supervisor Dr Jan Spriet, introduced me to the methodological

thinking of Dr Beck. Much of the fundamentals of my modelling work can still be

traced back to his key publications. I feel fortunate to have the luck to discuss many

of the methodological aspects with him, and to be able together, within the IW A

Specialist Group on Systems Analysis and Computing in Water Quality

Management, to highlight the methodological angle of quantitative thinking related

to water quality problems. In view of my historical bias towards biological

wastewater treatment, I feel very complementary to Dr Butler's background,

particularly his work on sewer system processes and the characterisation of the

dynamics of inhabitant equivalent inputs into the sewer system. These studies have

had a major impact on my thinking of the sewer system as a part of the whole that

can be manipulated to improve wastewater treatment.

Foreword xi

I have been privileged to know Dr Schlitze from the beginning of his PhD studies

and have had many in-depth discussions with him on the different aspects of his

work, in particular - to name a few - optimisation algorithms, the simultaneous

integrated modelling approach, the real-time control options he proposed and the

way they were evaluated. I have admired his multi-disciplinary knowledge base, his

eagerness to learn and his sense of organisation. Also, having Manfred present in

conferences or in EU COST (European Cooperation in the field of Scientific and

Technical Research) Working Group meetings was always a pleasure. He was

always driven to make progress in the convergence of thinking in the discipline. I

feel that this book - to which he is the main contributor - is a reflection of this focus

on common thinking and the efforts in this book to structure knowledge, work with

clear terminology and methodology are illustrative of this. I am convinced the book

will allow this terminology and methodology to further spread in the profession and

will eliminate one of the main limitations to scientific progress, i.e., the absence of

common language and working procedures.

With this book the three authors share their significant contribution to the field of

urban wastewater system modelling and control. They have much to tell us, and there

is still more to come as they continue their research and apply it across the world.

Gent, July 2001

Peter A. Vanrolleghem

Professor at BIOMATH, Ghent University, Belgium

Acknowledgements

This book essentially presents the results of a PhD project, which I conducted at

Imperial College of Science, Technology and Medicine (University of London)

under the supervision of my coauthors, Professor Bruce Beck and Professor David

Butler. Although the thesis work was carried out in the years 1994 to 1998, this

book also includes some recent developments since then.

My special thanks are expressed to my coauthors for supervising this work.

Without continuous interest and encouragement, numerous fruitful discussions and

support this work would not have been possible.

Furthermore, the stimulating discussions, useful comments on this work and

support of various kinds also of many colleagues and friends are acknowledged with

gratitude and appreciation. Particular mention is made of Hans Aalderink, Maria do

Ceu Almeida, Jenny Blight, Andreas Cassar, Eran Friedler, Chantal Fronteau, Jian

Hua Lei, Jonathan Parkinson, Petr Prax, Wolfgang Rauch, Mohammed Saidam,

John Tyson, Peter Vanrolleghem, Hans-Reinhard Verwom, and Kala Vairaavamoorthy. Important contributions to this project were also made by a

number of MSc and project students, to whom thanks are expressed: Sibel Gwen,

Okan Giiven, Christophe Leclerc, Eva Vazquez-Sanchez, and Wai Meng Wan.

Overall, the discussions I enjoyed at my various working places over the years,

including Hannover, Diibendorf, London, Dundee, Bmo, Gent and Magdeburg,

proved (and continue to prove) to be fruitful sources of inspiration for this and for

further work. Many cups of coffee were emptied whilst the tray of ideas was filled.

Acknowledgements are also made to the University of Hannover and to

Wageningen Agricultural University for the rights to use their software and to the

Environment Agency of the German state of Niedersachsen for the permission to

use the Fuhrberg rainfall data set within this project.

The fmancial support of the European Union's Human Capital and Mobility

programme is greatly appreciated, which funded the thesis work under the

MATECH network.

xiv Acknowledgements

Furthermore, I am deeply indebted to my family and friends for their unreserved

and continuous support throughout the project. Particular mention should be made

here to Jonathan and Luiza, who always reminded me on the existence of life

besides simulation.

Finally, I would like to express my special thanks to Simone Hildebrandt and to

Sabine, my wife, for their assistance in preparation of the final manuscript. I am

particularly grateful to Sabine for her patience on those long evenings and weekends

I spent on the final manuscript rather than with her.

Manfred Schiitze

Magdeburg, July 2001

Table of Contents

1. Introduction ........................................................................................................ 1

1.1 Motivation of this Book ................................................................................. 1 1.1.1 Administrative Responsibilities .......................................................... .4 1.1.2 Standards ............................................................................................ .4 1.1.3 Computer Software .............................................................................. 5 1.1.4 Design and Operation .......................................................................... 5

1.2 Outline of Chapters ........................................................................................ 7

2. The State of the Art ........................................................................................ .. 11

2.1 Components of the Urban Wastewater System: Basic Processes and Modelling Concepts ..................................................................................... 11 2.1.1 Urban Catchment Runoff and Sewer System ..................................... ll

2.1.1.1 Surface Runoff in Urban Areas ............................................ 12 2.1.1.2 Flow in the Sewer System .................................................... 13 2.1.1.3 Pollutant Transport in the Sewer System ............................. 17 2.1.1.4 Biochemical Transformations in the Sewer System ............. 19 2.1.1.5 Storage Tanks ....................................................................... 21

2.1.2 The Wastewater Treatment Plant... .................................................... 24 2.1.2.1 Storm Tank ........................................................................... 25 2.1.2.2 Primary Clarification ............................................................ 27 2.1.2.3 The Activated Sludge Process .............................................. 29 2.1.2.4 Secondary Clarification ....................................................... .37

2.1.3 Rivers ................................................................................................ .43 2.1.3.1 River Flow ........................................................................... .43 2.1.3.2 Pollutant Transport in the River.. ........................................ .44 2.1.3.3 Biochemical Transformations in the River. ......................... .46

2.2 Impact of Storm Events on the Urban Wastewater System .......................... 57 2.2.1 Impacts on Sewer Systems ................................................................. 57 2.2.2 Impacts on Treatment Plant Performance .......................................... 59 2.2.3 Impacts on the Receiving River ......................................................... 62 2.2.4 Criteria for the Assessment of River Water Quality .......................... 68 2.2.5 The Dilemma of Control of the Urban Wastewater System ............... 70

2.3 Integrated Modelling Approaches ................................................................ 70

XVi Table of Contents

2.4 Operational Management of Wastewater Infrastructure .............................. 80 2.4.1 General Concepts ............................................................................... 80 2.4.2 Real-time Control of Sewer Systems ................................................. 83 2.4.3 Development of Control Strategies - Exemplified for Sewer

Systems .............................................................................................. 85 2.4.3.1 Off-line Development ofStrategies ...................................... 85 2.4.3.2 On-line Development of Strategies ...................................... 89

2.4.4 Operation of Wastewater Treatment Plants ....................................... 96 2.4.5 Real-time Control of Receiving Rivers ............................................ 109 2.4.6 Integrated Real-time Control .......................................................... .111 2.4.7 Concluding Remarks ....................................................................... 113

2.5 Mathematical Optimisation Techniques .................................................... 114 2.5.1 Definition of the Optimisation Problem ........................................... 114 2.5.2 A Review of Optimisation Methods ................................................ 118

2.5.2.1 Local Optimisation ............................................................. 120 2.5.2.2 Global Optimisation ........................................................... 122

2.6 Conclusion ................................................................................................. 126

3. Development of the Integrated Simulation and Optimisation Tool SYNOPSIS ...................................................................................................... 129

3.1 Requirements on the Simulation TooL ..................................................... 129 3.2 Modules Simulating the Parts of the Urban Wastewater System ............... 133

3.2.1 Implementation of the Sewer System Module ................................. 133 3.2.2 Implementation of the Treatment Plant Module .............................. 135

3.2.2.1 The Original Implementation of Lessard and Beck's Treatment Plant Model. ...................................................... 135

3.2.2.2 Modifications of the Treatment Plant Model ..................... 143 3.2.3 Implementation of the River Module ............................................... 145

3.3 Assembling the Integrated Simulation Tool... ............................................ 150 3.3.1 Integration of the Simulation Software ............................................ 151 3.3.2 Variables in SYNOPSIS .................................................................. 152 3.3.3 Auxiliary Routines Necessary for Simulation .................................. 157

3.4 Implementation of Control in SYNOPSIS ................................................. 161 3.5 Optimisation Algorithms in SYNOPSIS .................................................... 163

3.5.1 Controlled Random Search .............................................................. 164 3.5.2 A Genetic Algorithm ....................................................................... 166 3.5.3 Powell's Local Optimisation Method ............................................... 170 3.5.4 Interfacing the Simulation Tool with the Optimisation Routines ..... 172

3.6 Summary: Overview of the Integrated Simulation and Optimisation Tool SYNOPSIS ........................................................................................ 176

4. Simulation of the Urban Wastewater System Using SYNOPSIS ............... 179

4.1 Definition of a Case Study Site .................................................................. 179 4.1.1 Existing Data Sets ............................................................................ 180

Table of Contents xvii

4.1.2 Definition of the Sewer System ....................................................... 181 4.1.3 Definition of the Wastewater Treatment Plant... .............................. 189 4.1.4 Definition of the River ..................................................................... 192 4.1.5 Overview of the Case Study Site Defined ........................................ 196

4.2 Simulation of Dry-weather Flow ................................................................ 198 4.3 Simulation of a Rainfall Time Series ......................................................... 203 4.4 Analysis of the Control Devices of the Urban Wastewater System ........... 209 4.5 Potential of Reduction in Simulation Time by Selective Simulation ......... 218

4.5.1 Separation of Rainfall Events .......................................................... 218 4.5.2 Potential Savings in Simulation Time .............................................. 221 4.5.3 Selective Versus Continuous Simulation ......................................... 225 4.5.4 Conclusions ..................................................................................... 227

5. Analysis of Control Scenarios by Simulation and Optimisation .................. 229

5.1 Definitions and Methodology .................................................................... 230 5.2 Analysis of Strategy Parameters - an Example .......................................... 233

5.2.1 Definition of a Strategy Framework ................................................ 233 5.2.2 Exploring the Parameter Space by Gridding ................................... 235 5.2.3 Optimisation of Strategy Parameters ............................................... 238

5.3 A Top-down Approach to the Definition of Control Strategies ................. 243 5.3.1 Definition of Various Frameworks .................................................. 244 5.3.2 Evaluation of the Optimisation Algorithms ..................................... 249 5.3.3 Conclusions ..................................................................................... 251

5.4 A Bottom-up Approach to the Definition of Control Strategies ................ 255 5.4.1 Towards a Systematic Definition ofFrameworks ............................ 255 5.4.2 Analysis of Frameworks Involving Several Controllers .................. 258

5.5 Integrated Versus Local ControL ............................................................. 262 5.6 Further Aspects .......................................................................................... 264

5.6.1 Sensitivity of Solutions .................................................................... 265 5.6.2 Multi-objective Optimisation ........................................................... 268 5.6.3 Simulation Period Required for Optimisation ................................. 270 5.6.4 Control Potential of Various Case Study Sites ................................ 273

6. Conclusions and Further Research ............................................................... 277

6.1 Summary .................................................................................................... 277 6.2 Suggestions for Further Research .............................................................. 280

Appendix A. Overview of Existing Software .................................................... 285

Al Software for Simulation of Sewer Systems ................................................ 285 A2 Software for Simulation of Activated Sludge Wastewater Treatment

Plants ......................................................................................................... 292 A3 Software for Simulation of Rivers ............................................................. 298

xviii Table of Contents

Appendix B. Parameters of the Treatment Plant Model... .............................. 307

Appendix C. Rainfall Data Used in This Study ................................................ 311

Appendix D. Detailed Results of Optimisation Runs Presented in Chapter 5 ....................................................................................... 313

References ............................................................................................ ................ .317

Index ...................................................................................................................... 359