Jonathan B. Snape, Irving J. Dunn John Ingham, Jiii E. Pfenosil

Dynamics of Environmental Bioprocesses Modelling and Simulation

VCH + Weinheim . New York Base1 - Cambridge Tokyo

This Page Intentionally Left Blank

J. B. Snape, I. J. Dunn, J. Ingham, J. E.Pfenosi1

Dynamics of Environmental Bioprocesses

VCH 4b

The included diskette contains the ISIM simulation language as well as simulation examples. It can be run on all DOS-PC’s.

OVCH Verlagsgesellschaft mbH, D-69451 Weinheim (Federal Republic of Germany), 1995

Distribution:

VCH, P. 0. Box 101161, D-69451 Weinheim (Federal Republic of Germany)

Switzerland: VCH, P. 0. Box, CH-4020 Basel (Switzerland)

United Kingdom and Ireland: VCH, 8 Wellington Court, Cambridge CBl lHZ (United Kingdom)

USA and Canada: VCH, 220 East 23rd Street, New York, NY 10010-4606 (USA)

Japan: VCH, Eikow Building, 10-9 Hongo 1-chome, Bunkyo-ku, Tokyo 113 (Japan)

ISBN 3-527-28705-1

Jonathan B. Snape, Irving J. Dunn John Ingham, Jiii E. Pfenosil

Dynamics of Environmental Bioprocesses Modelling and Simulation

VCH + Weinheim . New York Base1 - Cambridge Tokyo

Dr. J. B. Snape Nippon Lever Shibuya Tokyo 105 Japan

Dr. J. Ingham Department of Chemical Engineering University of Bradford Bradford BD7 1DP United Kingdom

Dr. I. J. Dunn, Dr. J. E. Pfenosil Department of Chemical Engineering ETH Zurich

Switzerland CH-8092 Ziirich

This book and the diskette were carefully produced. Nevertheless, authors and publisher do not warrant the information contained therein to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Published jointly by VCH Verlagsgesellschaft mbH, Weinheim (Federal Republic of Germany) VCH Publishers, Inc., New York, NY (USA)

Editorial Directors: Karin Sora, James Gardiner Production Manager: Claudia Gross1

Library of Congress Card No. applied for

British Library Cataloguing-in-Publication Data: A catalogue record for this book is available from the British Library

Die Deutsche Bibliothek - CIP-Einheitsaufnahme Dynamics of environmental bioprocesses : modelling and simulation / Jonathan B. Snape . . . - Weinheim ; New York ; Basel ; Cambridge ; Tokyo : VCH.

Medienkombination

NE: Snape, Jonathan B.

Diskette. - 1995

ISBN 3-527-28705-1

Buch. - 1995

OVCH Verlagsgesellschaft mbH, D-69451 Weinheim (Federal Republic of Germany), 1995

Printed on acid-free and low-chlorine paper

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form -by photoprinting, microfilm, or any other means -nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Data conversion: Hagedornsatz, D-68519 Viernheim Printing: strauss offsetdruck GmbH, D-69509 MBrlenbach Bookbinding: GroBbuchbinderei J. Schafer, D-67269 Griinstadt Printed in the Federal Republic of Germany

Preface

The aim of this text is to utilise the twin tools of modelling and computer simulation in developing a better understanding of environmental bioprocesses and their dynamics. This is achieved via a combination of basic theory and bioprocess description, combined with sixty-five simulation examples. This latter feature is probably the most important feature of the book in providing the opportunity for direct on-line computer experimentation and computer- aided self learning. The book follows from our series of post-experience short courses, held annually in the Swiss mountain resort of Braunwald, and the two resulting sister volumes "Biological Reaction Engineering" and "Chemical Engineering Dynamics", both of which are also published by VCH.

Modelling is often an unfamiliar technique for many persons active in the field of environmental science as life scientists may sometimes lack the formal training needed to analyse laboratory kinetic data in its most meaningful way. An additional aim of this book is therefore to provide the mathematical tools required for a quantitative analysis of biological and chemical rate phenomena, based on the techniques of mathematical modelling and digital simulation. More generally, mathematical modelling methods should also lead to a better understanding of bioprocess environmental system behaviour. In formulating models of chemical and bioprocess operations, one of the most important tools is the material balance. Mass balances are simply representations of the first law of conservation, namely that matter can neither be created nor destroyed. The mass balance is thus fundamental to all science and, when combined with other forms of defining relationship, can be used with very great effect in forming mathematical process models, which may be quite simple in form but which nevertheless can be very powerful in describing quite complex process phenomena.

Having formulated a mathematical model, the model must be solved. This is nowadays very easily effected by the computer and the modern approach of using desktop computers with easy-to-program software helps considerably in making modelling far more attractive than in the past. Modern simulation languages are now available that provide the possibility of carrying out an interactive simulation at one's own desktop. The ISIM simulation language, provided with this book, is the language we have used during the last five years of our continuing education short courses. ISIM is especially suitable owing to its sophisticated computing power, interactive ability and ease of programm- ing. We have found that the ISIM based simulation examples enforce the learning process in a very effective manner. Readers can program their own examples, by formulating their own models and programs or by modifying an existing program to a new set of circumstances. A true degree of interaction is possible because, at the stroke of a key, any simulation run can be stopped,

VI Preface

parameters changed, and the run restarted from the point of interruption. The programs also provide a very convenient graphical output of the computed results. Runs can be repeated with new parameters, and the combined results from multiple runs easily plotted. In our experience, digital simulation has proven itself to be absolutely the most effective way of introducing and reinforcing new concepts involving multiple interactions. We hope you will enjoy working on the simulation examples and agree with us that simulation is both useful and enjoyable.

Organisation of the Book

This book is divided into three chapters covering, respectively, principles of modelling, environmental bioprocess descriptions and simulation examples.

The aim of the first chapter is to introduce the basic theory necessary to understand the simulation examples presented in Chapter 3. The chapter opens with a discussion of the need for models in environmental technology and highlights their usefulness and limitations. This is followed by a brief overview of model classification and modelling procedure, including a comparison of available simulation programs. The software provided with this book, ISIM, is discussed in detail and its use is illustrated via the step-by-step development of a simple programming example. The formulation of mass and energy balances is a central theme of this book and a rigorous presentation of the necessary procedures is included. The physical meaning and significance of each term in the model equations are explained and the text is amplified by several examples of relevance to environmental bioprocesses. Our aim here is to present the material in a way that can be understood by biologists who rarely receive any formal training in modelling, and to demonstrate to engineers that they can apply their knowledge to systems outside their normal field of study. In addition to mass and energy balances, other relationships and balances are required in any model formulation. Transport phenomena often need to be modelled and diffusion and interface transport are included. Reactor process technology is discussed, and it is shown how this can be applied both to wastewater treatment plants and to natural water bodies. An understanding of microbial kinetics is essential to environmental bioprocess modelling and an introduction to microbial kinetics is presented in the following section. Monod kinetics are introduced, and then more complex kinetics involving different types of inhibition and interactions, as are more frequently encountered in real life situations, are discussed.

The second chapter provides background information on various environmental bioprocesses. It is not our aim to give a comprehensive review of this large and ever-expanding field, but to give the reader a feel for the types of process that can be modelled and how one can set about a modelling problem. Inevitably the areas covered are biased towards our own research

Preface VII

interests and experiences, but we hope the material presented will be of interest to the majority of readers. This chapter first covers wastewater, its character- istics, analyses and treatment. The section on the treatment-of-wastewater gives an overview of the major primary, secondary and tertiary processes used to treat wastewater. The secondary processes are divided into aerobic and anaerobic processes and also biofilm and floc processes. The modelling of biofilms and flocs is also covered.

The next section is concerned with water pollution modelling. The eutrophi- cation of lakes and reservoirs is discussed, including the major factors causing eutrophication, its consequences and how it can be reversed or prevented. An overview of types of eutrophication model is given. Next the discharge of pollutants into rivers and streams, based on the Streeter-Phelps oxygen sag model, is discussed. Modifications to the basic theory and the ways in which these can be modelled are dealt with. Following on from this the topical area of modelling groundwater pollution is discussed with reference to leaching of landfill sites. Some basic hydrology necessary for modelling ground water pollution is introduced, as well as the fundamental transport and adsorption relationships. The final section deals with the treatment and disposal of solid waste and covers composting, landfill sites and anaerobic digestion.

The third and final chapter comprises 65 simulation examples, all of which are on the diskette and which can be run with the included ISIM software. Each employs the theory covered in Chapter 1 to model the processes describ-ed in Chapter 2. Each simulation example is self contained and includes a model description, the model equations, nomenclature, references and suggest-ed exercises. The exercises vary in complexity from very simple parameter changing to quite complex suggestions for new programs, and are intended to stimulate the reader to gain a greater understanding of the system under study. Due to limitations of space, it has not been possible to reproduce all the program listings, but these can be viewed very easily on the PC. However, when some new program technique is used for the first time, this is mentioned in the program text and the relevant listing is shown. It was not our aim to present very large unwieldy programs that may not easily be understood by the novice programmer, but to present simple, easy to understand models that perhaps cover one or two of the most important processes. This is perhaps best exemplified by the section on activated sludge processes. Here we have presented models that simulate the complex ecological interactions, the sludge settler, processes within an individual floc, temperature effects and different reactor configurations and process strategies. A complete model of an activat- ed sludge process would take into account all these processes (as well as others not considered here), but the size and speed of execution of the program would make it useless as a teaching aid. By splitting the process into these sub- processes it becomes manageable. We hope that after reading this book, the readers will feel motivated to apply what they have learnt in their own specialist field.

VIII Preface

In researching the literature for suitable examples to include in this text, it became obvious that some models presented in the literature are incomplete, in that values of parameters are not given or even equations are missing, so that the process could not be simulated. We would like to thank, therefore, the authors of the work we have cited in the text for publishing their comprehen-sive models, and apologise to them for occasionally simplifying and modifying their models to meet the requirements of this text. The source reference is always given at the end of each example, and the reader is referred to the original papers for more complete explanations and the detailed models.

ISIM Simulation Software

The ISIM software is made available only for the purposes described in this book, and its features are restricted to these examples. An advanced simulation language, ESL, is highly recommended and is also available. Users wishing to purchase the latest menu-driven version of ISIM or ESL should contact ISIM International Simulation directly. User manuals for ISIM may also be purchased for &40 from ISIM International Simulation.

ISIM International Simulation Limited, Technology House, Salford University Business Park, Lissadel Street, Salford M6 6AP, England, (Tel: +44-(0)61-745 7444; Fax: +44-(0)61-737 7700).

Acknowledgements

A major acknowledgement should be made to the pioneering texts of Franks (1967, 1972) for inspiring our interest in digital simulation. Interest in environmental engineering came from our research, and with it an awareness of the important contribution chemical engineering can make to this field.

We are especially grateful to all the participants and course collaborators of our post-experience courses, for their assistance in the development of the material presented in this book. Continual stimulus and assistance has also been given by a sequence of students, at the ETH-Zurich.

One of us (J. B. S . ) is grateful to the ETH for a postdoctoral fellowship which allowed course material on which this book is based to be developed and also to Dr. M. Nakajima of the National Food Research Institute, Japan for providing word processing facilities and support for this project.

Our special thanks are again due to Professor John L. Hay of ISIM International Simulation Limited for his agreement to release the ISIM digital simulation programming language, for use with this book. We hope that the

Preface IX

book will be useful in drawing attention to his advanced simulation language, ESL, for which we are happy to include a programmed example and an advertisement.

This book was written on an Apple Macintosh, using Microsoft Word and Claris MacDraw Pro. Scans of the computer outputs were done with Adobe Photoshop. The Linotype film was made from the Word and Photoshop files. Special thanks are due to Albert Ochsner for his able work on the text and drawings. Marc Deshusses read the entire text and suggested many improvements. We are grateful to VCH for giving financial assistance for the word processing and especially wish to thank Louise Elsam, James Gardiner, Claudia Gross1 and Karin Sora of VCH for correcting the text so carefully and for their many useful discussions and cooperation.

This Page Intentionally Left Blank

Table of Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . V

Organisation of the Book . . . . . . . . . . . . . . . . . . . VI ISIM Simulation Software . . . . . . . . . . . . . . . . . . . VIII Acknowledgements . . . . . . . . . . . . . . . . . . . . . VIII

Nomenclature for Chapters 1 and 2 . . . . . . . . . . . . . . . . XIX

1 Modelling Principles . . . . . . . . . . . . . . . . . . 1

1.1 The Role of Modelling in Environmental Technology 1.2 General Aspects of the Modelling Approach . . . 1.3 Model Classification . . . . . . . . . . . . . 1.3.1 Deterministic Models . . . . . . . . . . . . . 1.3.2 Stochastic Models . . . . . . . . . . . . . . 1.3.3 Steady-State Models . . . . . . . . . . . . .

1.4 General Modelling Procedure . . . . . . . . . 1.5 Simulation Tools . . . . . . . . . . . . . . . 1.6 ISIM . . . . . . . . . . . . . . . . . . . 1.7 Introductory ISIM Example: WASTE . . . . . . 1.8 Formulation of Dynamic Balance Equations . . . 1.8.1 Mass Balance Procedures . . . . . . . . . . . 1.8.1.1 Case A . Continuous Stirred-Tank Reactor . . . . 1.8.1.2 Case B . Tubular Reactor . . . . . . . . . . . 1.8.1.3 Case C . River with Eddy Current . . . . . . . . 1.8.1.4 Rate of Accumulation Term . . . . . . . . . . 1.8.1.5 Convective Flow Terms . . . . . . . . . . . . 1.8.1.6 Production Rate . . . . . . . . . . . . . . . 1.8.1.7 Diffusion of Components . . . . . . . . . . . 1.8.1.8 Interphase Transport . . . . . . . . . . . . .

1.3.4 Dynamic Models . . . . . . . . . . . . . . .

1.8.1.9 Case A . Waste Holding Tank: Total and Component Mass Balance Example . . . . . . . . . . . .

1.8.1.10 Case B . The Plug-Flow Tubular Reactor . . . . . 1.8.1.11 Case C . Biological Hazard Room . . . . . . . . 1.8.1.12 Case D . Lake Pollution Problem . . . . . . . . 1.8.2 Energy Balancing . . . . . . . . . . . . . .

. . . . . 1

. . . . . 3

. . . . . 4

. . . . . 4

. . . . . 5

. . . . . 5

. . . . . 6

. . . . . 6

. . . . . 7

. . . . . 10

. . . . . 11

. . . . . 14

. . . . . 15

. . . . . 17

. . . . . 18

. . . . . 18

. . . . . 21

. . . . . 22

. . . . . 23

. . . . . 24

. . . . . 25

. . . . . 26

. . . . . 28

. . . . . 30

. . . . . 35

. . . . . 40

XI1 Table of Contents

1.8.2.1 Case A . Determining Heat Transfer Area or Cooling Water Temperature . . . . . . . . . . . . . . . . . . .

1.8.2.2 Case B . Heating of a Filling Tank . . . . . . . . . . . . 1.9 Chemical and Biological Reaction Systems . . . . . . . . . 1.9.1 Modes of Reactor Operation . . . . . . . . . . . . . . 1.9.1.1 Batch Reactors . . . . . . . . . . . . . . . . . . . . 1.9.1.2 Semi-Continuous or Fed-Batch Operation . . . . . . . . . 1.9.1.3 Continuous Operation . . . . . . . . . . . . . . . . . 1.9.2 Reaction Kinetics . . . . . . . . . . . . . . . . . . . 1.9.2.1 Chemical Kinetics . . . . . . . . . . . . . . . . . . . 1.9.2.2 Biological Reaction Kinetics . . . . . . . . . . . . . . . 1.9.2.3 Simple Microbial Growth Kinetics . . . . . . . . . . . . 1.9.2.4 Substrate Uptake Kinetics . . . . . . . . . . . . . . . . 1.9.2.5 Substrate Inhibition of Growth . . . . . . . . . . . . . . 1.9.2.6 Additional Forms of Inhibition . . . . . . . . . . . . . . 1.9.2.7 Other Expressions for Specific Growth Rate . . . . . . . . 1.9.2.8 Multiple-Substrate Kinetics . . . . . . . . . . . . . . . 1.9.2.9 Structured Kinetic Models . . . . . . . . . . . . . . . . 1.9.2.10 Interacting Micro-Organisms . . . . . . . . . . . . . . . 1.10 Modelling of Bioreactor Systems . . . . . . . . . . . . .

1.10.2 Modelling Tubular Plug-Flow Reactor Behaviour . . . . . . 1.10.2.1 Steady-State Balancing . . . . . . . . . . . . . . . . . 1.10.2.2 Unsteady-State Balancing . . . . . . . . . . . . . . . . 1.11 Mass Transfer Theory . . . . . . . . . . . . . . . . . . 1.11.1 Phase Equilibria . . . . . . . . . . . . . . . . . . . . 1.11.2 Interphase Mass Transfer . . . . . . . . . . . . . . . . 1.11.2.1 Case A . Steady-State Tubular and Column Modelling . . . . 1.11.3 Case Studies . . . : . . . . . . . . . . . . . . . . . 1.11.3.1 Case A . Aeration of a Tank of Water 1.11.3.2 Case B . Biological Oxidation in an Aerated Tank 1.11.3.3 Case C . Determination of Biological Oxygen Uptake

Rates by a Dynamic Method . . . . . . . . . . . . . . . 1.11.4 Gas-Liquid Phase Transfer Across a Free Surface . . . . . . 1.12 Diffusion and Biological Reaction in Solid Phase Biosystems . 1.12.1 External Mass Transfer . . . . . . . . . . . . . . . . . 1.12.2 Finite Difference Model for Internal Transfer . . . . . . . 1.12.3 Case Studies for Diffusion with Biological Reaction . . . . . 1.12.3.1 Case A . Estimation of Oxygen Diffusion Effects in a

Biofilm . . . . . . . . . . . . . . . . . . . . . . . 1.12.3.2 Case B . Biofilm Nitrification 1.13 Process Control . . . . . . . . . . . . . . . . . . . . 1.14 Optimisation. Parameter Estimation and Sensitivity Analysis . 1.14.1 Case A . Estimation of Bioreaction Kinetic Parameters

for Batch Degradation Using ESL and SIMUSOLV . . . . .

1.10.1 Stirred Tank Reactors . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

43 44 45 45 45 47 48 50 50 52 53 56 57 59 59 61 62 62 65 65 67 67 68 70 70 70 72 73 73 75

77 78 79 82 83 86

86 87 90 94

96

Table of Contents XI11

2 Environmental Bioprocess Descriptions . . . . . . . . . . 103

2.1 2.1.1 2.1.2 2.1.2.1 2.1.2.2 2.1.2.3 2.1.2.4 2.1.3 2.1.3.1 2.1.3.2 2.1.3.3 2.1.3.4 2.1.3.5 2.1.3.6 2.1.4 2.1.4.1 2.1.4.2 2.1.4.3 2.2 2.2.1 2.2.2 2.2.3 2.2.3.1 2.2.3.2 2.2.3.3 2.2.3.4 2.2.4 2.3 2.3.1 2.3.1.1 2.3.1.2 2.3.1.3 2.3.2 2.3.2.1 2.3.2.2 2.3.2.3 2.3.3 2.3.3.1 2.3.3.2 2.3.3.3 2.3.3.4 2.3.3.5

Wastewater Treatment Processes . . . . . . . . . . . . . 103 Wastewater Characteristics . . . . . . . . . . . . . . . 103 Physical Characteristics and Analyses of Wastewater . . . . . 106 Total Suspended Solids . . . . . . . . . . . . . . . . . 106 Volatile Suspended Solids . . . . . . . . . . . . . . . . 106 Temperature . . . . . . . . . . . . . . . . . . . . . 107 Other Physical Parameters . . . . . . . . . . . . . . . 107

Biochemical Oxygen Demand . . . . . . . . . . . . . . 108 Chemical Oxygen Demand . . . . . . . . . . . . . . . 109 Total Organic Carbon . . . . . . . . . . . . . . . . . . 110 Nitrogen Analyses . . . . . . . . . . . . . . . . . . . 111 Kjeldahl Total Nitrogen Test . . . . . . . . . . . . . . 111 Phosphorus . . . . . . . . . . . . . . . . . . . . . . 112

Pathogenic Micro-Organisms . . . . . . . . . . . . . . 113 Pollution Indicator Organisms . . . . . . . . . . . . . . 113 Micro-Organisms Responsible for Biological Treatment . . . 113 Primary Treatment Processes . . . . . . . . . . . . . . 114 Equalisation . . . . . . . . . . . . . . . . . . . . . 114 Neutralisation . . . . . . . . . . . . . . . . . . . . . 115 Sedimentation . . . . . . . . . . . . . . . . . . . . . 115 Discrete Settling . . . . . . . . . . . . . . . . . . . . 115 Flocculent Settling . . . . . . . . . . . . . . . . . . . 116 Zone Settling . . . . . . . . . . . . . . . . . . . . . 117 Coagulating Agents . . . . . . . . . . . . . . . . . . . 117 Flotation . . . . . . . . . . . . . . . . . . . . . . . 117 Secondary Treatment Processes . . . . . . . . . . . . . . 118 The Activated Sludge Process . . . . . . . . . . . . . . 118 Biology of the Activated Sludge Process . . . . . . . . . . 119 Process Analysis . . . . . . . . . . . . . . . . . . . . 119 Modifications of the Activated Sludge Process . . . . . . . . 120 Aerobic Fixed Film Processes . . . . . . . . . . . . . . 121 Trickling Filters . . . . . . . . . . . . . . . . . . . . 122 Fluidised Sand Beds . . . . . . . . . . . . . . . . . . 122 Rotating Biological Contactors . . . . . . . . . . . . . . 124 Anaerobic Treatment Processes . . . . . . . . . . . . . . 124 Reactions and Stoichiometry in Anaerobic Digestion . . . . . 125 Modelling Anaerobic Reactors . . . . . . . . . . . . . . 125 Response Dynamics of Anaerobic Reactors . . . . . . . . 129 Control of Anaerobic Reactors . . . . . . . . . . . . . . 130 Anaerobic Reactor Design . . . . . . . . . . . . . . . . 134

Chemical Characteristics and Analyses of Wastewater . . . . 108

Biological Characteristics and Analyses of Wastewater . . . . 112

XIV Table of Contents

2.3.4 Biofilms and Flocs . . . . . . . . . . . . . . . . . . . 135 2.3.4.1 Formation of Biofilms . . . . . . . . . . . . . . . . . 136 2.3.4.2 Modelling Biofilms . . . . . . . . . . . . . . . . . . . 138 2.3.4.3 Bioflocs . . . . . . . . . . . . . . . . . . . . . . . 139 2.4 Tertiary Treatment Processes . . . . . . . . . . . . . . . 140 2.4.1 Grass Plots . . . . . . . . . . . . . . . . . . . . . . 140

2.4.4 Microstrainers . . . . . . . . . . . . . . . . . . . . . 142 2.4.5 Membrane Technology . . . . . . . . . . . . . . . . . 142 2.5 Water Pollution Modelling . . . . . . . . . . . . . . . . 146 2.5.1 Eutrophication of Lakes and Reservoirs . . . . . . . . . . 146 2.5.1.1 Factors Influencing Lake Productivity . . . . . . . . . . . 147 2.5.1.2 Consequences of Eutrophication . . . . . . . . . . . . . 151 2.5.1.3 Eutrophication Models . . . . . . . . . . . . . . . . . 153 2.5.1.4 Prevention and Reversal of Eutrophication . . . . . . . . . 155 2.5.2 Discharge of Pollutants into Rivers and Streams . . . . . . . 157 2.5.2.1 Modifications to the Streeter-Phelps Theory . . . . . . . . 158 2.5.2.2 Surface Reaeration . . . . . . . . . . . . . . . . . . . 159 2.5.2.3 River Parameters . . . . . . . . . . . . . . . . . . . 160

2.5.3 Groundwater Pollution . . . . . . . . . . . . . . . . . 161 2.5.3.1 Sources of Groundwater Pollution . . . . . . . . . . . . . 163 2.5.3.2 Modelling Groundwater Pollution . . . . . . . . . . . . . 165 2.5.3.3 Nitrates in Groundwater . . . . . . . . . . . . . . . . . 168 2.6 Solid Waste Treatment and Disposal . . . . . . . . . . . 169 2.6.1 Sources of Solid Wastes . . . . . . . . . . . . . . . . . 169 2.6.1.1 Municipal Solid Waste . . . . . . . . . . . . . . . . . 169 2.6.1.2 Waste Sludge . . . . . . . . . . . . . . . . . . . . . 170 2.6.2 Sludge Processing and Disposal . . . . . . . . . . . . . 171 2.6.2.1 Summary of Disposal Methods . . . . . . . . . . . . . 171 2.6.2.2 Sludge Thickening and Dewatering . . . . . . . . . . . . 172 2.6.2.3 Use of Sludge on Agricultural Land . . . . . . . . . . . . 172 2.6.2.4 Dumping at Sea and Pipeline Discharges . . . . . . . . . . 172 2.6.3 Composting . . . . . . . . . . . . . . . . . . . . . . 173 2.6.3.1 Composting Processes . . . . . . . . . . . . . . . . . 173 2.6.3.2 Compost Ecology . . . . . . . . . . . . . . . . . . . 174 2.6.3.3 Process Factors . . . . . . . . . . . . . . . . . . . . 175 2.6.4 Disposal of Municipal Solid Waste . . . . . . . . . . . . 177 2.6.4.1 Microbiology of Landfill Gas Production . . . . . . . . . 177 2.6.4.2 Landfill Gas Production . . . . . . . . . . . . . . . . . 179 2.6.5 Anaerobic Digestion . . . . . . . . . . . . . . . . . . 181 2.6.5.1 Reactor Conditions . . . . . . . . . . . . . . . . . . 181 2.6.5.2 Comparison with Landfill Sites . . . . . . . . . . . . . . 181

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.4.2 Lagoons 141 2.4.3 Filters 141

2.5.2.4 Photosynthesis and Respiration of Green Plants and Algae . . 161

Table of Contents xv

2.7 References for Chapters 1 and 2 . . . . . . . . . . . . . 182

Reading . . . . . . . . . . . . . . . . . . . . . . . 187 2.9 Glossary . . . . . . . . . . . . . . . . . . . . . . . 192

2.8 Recommended Textbooks and References for Further

3 Simulation Examples of Environmental Bioprocesses . . . . . 201

3.1 Introductory Examples . . . . . . . . . . . . . . . . . 201 3.1.1 BASIN - Dynamics of an Equalisation Basin . . . . . . . . 201 3.1.2 OXSAG - Classic Streeter-Phelps Oxygen Sag Curves . . . . 206

3.2 3.2.1 3.2.2

3.2.3 3.2.4 3.2.5 3.2.6

3.2.7 3.2.8 3.2.9

3.2.10

3.3 3.3.1 3.3.2

3.3.3 3.3.4 3.3.5 3.3.6

3.3.7

3.3.8

Basic Biological Reactor Examples . . . . . . . . . . . . 210 BATREACT . Batch Growth and Substrate Uptake . . . . . 210 CONTANK . Continuous Tank Reactor Startup and

SEMIBAT . Semi-Batch Reactor with Batch Startup . . . . 218 UPTAKE . Substrate Uptake with Monod Kinetics . . . . . 221 OXIBAT . Oxidation of Substrate in an Aerated Tank . . . . 223 RESPMET . Oxygen Uptake Experiment with Respirometer . . . . . . . . . . . . . . . . . . . . . 226 REPEAT . Repeated Fed-Batch Culture . . . . . . . . . . 229 CONTI . Continuous Reactor with Substrate Uptake . . . . 233 FEEDINH . Control of Inhibitory Substrate Feed Rate ' to a Continuous Reactor . . . . . . . . . . . . . . . . 235 CONINHIB . Continuous Bioreactor with Inhibitory Substrate . . . . . . . . . . . . . . . . . . . . . . . 239

Operation . . . . . . . . . . . . . . . . . . . . . . 214

Activated Sludge Wastewater lleatment Processes . . . . . ANDREWS . Model of a Batch Activated Sludge Process . . ASCSTR . Continuous Stirred Tank Reactor Model of

ASPLUG . Plug-Flow Model of an Activated Sludge Process CURDS . Curds' Model of Sludge Ecology . . . . . . . FLOCl and FLOC2 Diffusion and Reaction in a Sludge Floc ASTEMP -Temperature Gains and Losses in an Activated

STEPFEED . Step Feed Activated Sludge Process with Structured Kinetics . . . . . . . . . . . . . . . . . SETTLER . Solids-Liquid Separation in a Continuous Settler

Activated Sludge . . . . . . . . . . . . . . . . . .

Sludge Process . . . . . . . . . . . . . . . . . . .

. 244

. 244

. 247

. 250

. 254

. 260

. 264

. 270

. 275

XVI Table of Contents

3.4 Fixed Film Reactors for Wastewater Tkeatment . . . . . . . . 280 3.4.1 ROTATE - Model of a Rotating Biological Disc Reactor . . . 280 3.4.2 TRICKLE - Model of a Trickle Filter . . . . . . . . . . . 284 3.4.3 BIOFILM - Biofilm Tank Reactor . . . . . . . . . . . . 288

3.5 Nitrification of Wastewater , , . . . . . . . . . . . . . . 292 3.5.1 ACIlVITR - Nitrification in a Single-Stage Activated

Sludge System . . . . . . . . . . . . . . . . . . . . . 292 3.5.2 AMMONOX - Continuous Nitrification with

Immobilised Biomass . . . . . . . . . . . . . . . . . . 296 3.5.3 AMMONFED - Fed-Batch Nitrification with

Immobilised Biomass . . . . . . . . . , . . . . . . . . 300 3.5.4 NITBED - Nitrification in a Fluidised Bed Reactor . , . . . 302

3.6 Primary Watment of Wastewater . . . . . . . . . . . . . 307 3.6.1 SEDIMENT - Removal of Solids in a Sedimentation Tank . . 307 3.6.2 LAGOON - Aerated Lagoon for the Treatment of

Industrial Wastewaters . . . . . . . . . . . . . . . . . 311

3.7 Tertiary Water 'keatment Processes . . . . , . . . . . . , 315 3.7.1 FILTER -Tertiary Water Treatment by Filtration . . , . . . 315

3.8 Sludge Disposal and Processing . . . . . . . . . . . . . . 319 3.8.1 COMPOST - Microbial Kinetics in a Continuous

Compost Reactor . . . . . . . , . . , . . . . . . . . 319 3.8.2 WINDROW -Batch Windrow Compost Process . . . . . . 329

3.9 Biodegradation Processes . . . . . . . . . . . . . . . . 332 3.9.1 PCPDEG and PCPDEGCF - Batch and Continuous

Biodegradation of Pentachlorophenol by Mixed Cultures . . . 332 3.9.2 BIOFILTl and BIOFILT2 - Biofiltration Column for

Removing Ketones from Air . . . . . . . . . . . . . . . 335 3.9.3 DCMl and DCM2 - Airlift Biofilm Sandbed for

Dichloromethane-Waste Air Treatment . . . . . . . . . . . 341 3.9.4 FBR - Biofilm Fluidised Bed with External Oxygen Supply . . 347

3.10 Anaerobic Digestion Processes . . . . . . . . . . . . . . 350 3.10.1 ANAEROBE - Andrew's Model of Anaerobic Digestion , . . 350 3.10.2 WHEY - Model for the Anaerobic Degradation of Whey . . . 357

Table of Contents XVII

3.11 Anaerobic Fixed Film Processes . . . . . . . . . . . . . 363

Fluidised Bed Reactor . . . . . . . . . . . . . . . . . 363

Packed Bed Reactor . . . . . . . . . . . . . . . . . . 366

3.11.1

3.11.2

DENITRIF - Denitrification of Drinking Water in a

MOLASSES - Anaerobic Degradation of Molasses in a

3.12 Microbial Interaction Kinetics . . . . . . . . . . . . . . 373 3.12.1 MIXPOP - Predator-Prey Population Dynamics . . . . . . 373 3.12.2 TWOONE -Competition Between Organisms . . . . . . . 376 3.12.3 COMPETE - Lotka-Volterra Model of Competition . . . . . 378

3.13 Ecological Population Studies . . . . . . . . . . . . . . 380 3.13.1 BLOWFLY - Cycling Populations of the Australian Blowfly . . 380 3.13.2 BUDWORM - Dynamics of the Growth of the Spruce

Budworm in Canada . . . . . . . . . . . . . . . . . . 382

3.14 River and Stream Modelling . . . . . . . . . . . . . . . 387

along a River . . . . . . . . . . . . . . . . . . . . . 387

Aeration and Degradation in a Stream . . . . . . . . . . . 391

Profiles along a River . . . . . . . . . . . . . . . . . 396

3.14.1

3.14.2

3.14.3

RIVER - Dissolved Oxygen and BOD Dynamic Profiles

STREAM - One-Dimensional Steady-State Model of

DISCHARG - Dissolved Oxygen and BOD Steady-State

3.15 Lake and Reservoir Modelling . . . . . . . . . . . . . . 400

3.15.2 PCYCLE - Phosphorus Cycles in a Lake . . . . . . . . . 408 3.15.1 NCYCLE - Nitrogen Cycles in a Reservoir in Slovakia . . . . 400

3.15.3 ALGAE -Algal Growth in a Deep Lake in Canada . . . . . 414 3.15.4 EUTROPH - Eutrophication in a Shallow Lake in Hungary . . 421 3.15.5 METAL -Transport of Heavy Metals in Water Column

and Sediments . . . . . . . . . . . . . . . . . . . . . 429

3.16 Land Pollution Modelling . . . . . . . . . . . . . . . . 433 3.16.1

from a Landfill Site . . . . . . . . . . . . . . . . . . 433 3.16.2 LEACH - One-Dimensional Transport of Solute Through Soil . 437 3.16.3 SOIL - Bioremediation of Soil Particles . . . . . . . . . . 443

LANDFILL - One-Dimensional Transport of Pollutant

3.17 Miscellaneous Examples . . . . . . . . . . . . . . . . . 449

3.17.2 GAIA - The Parable of Daisyworld . . . . . . . . . . . 452

3.17.1 DEADFISH - Distribution of an Insecticide in an Aquatic Ecosystem . . . . . . . . . . . . . . . . . . . . . . 449

3.17.3 CABBAGE - Structured Growth of the White Cabbage . . . 456

XVIII Table of Contents

Appendix: Instructions for Using ISIM . . . . . . . . . . . . . . .

1 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 3 3.1 3.2 3.3 4 4.1 4.2 4.3 5

ISIM Installation Procedure . . . . . . . . . . . . . . . Programming with ISIM . . . . . . . . . . . . . . . . . Getting Started . . . . . . . . . . . . . . . . . . . . Reading Files From Disk . . . . . . . . . . . . . . . . Running Simulations . . . . . . . . . . . . . . . . . . Interacting with ISIM Simulations . . . . . . . . . . . . . Editing ISIM Files . . . . . . . . . . . . . . . . . . . Writing ISIM Models . . . . . . . . . . . . . . . . . . ISIM Statements and Functions . . . . . . . . . . . . . output . . . . . . . . . . . . . . . . . . . . . . . . Useful Sequences of Statements . . . . . . . . . . . . . Further Information . . . . . . . . . . . . . . . . . . Summary of ISIM Commands . . . . . . . . . . . . . . COMMAND and INPUT modes . . . . . . . . . . . . . ISIM Commands . . . . . . . . . . . . . . . . . . . . ISIM Program Statements . . . . . . . . . . . . . . . . ISIM Error Messages . . . . . . . . . . . . . . . . . . Monitor and Syntax Failures . . . . . . . . . . . . . . . Compilation Failures . . . . . . . . . . . . . . . . . . Execution Phase Errors . . . . . . . . . . . . . . . . . Quick Reference to Common ISIM Commands . . . . . .

461

461 462 462 462 462 463 463 464 466 467 469 470 470 470 470 474 477 478 479 480 481

. . . . . . . . . . . . . . . . . . . . . . . . . . . . Index 483

Nomenclature for Chapters 1 and 2

Symbol

a a A A, b

cP CD CA CC CL*

CG*

C d D D Dhd

DS E ED g grad G h h H H AH

I j J JS k k

1

Description

Specific interfacial or surface area Constant in Logistic equation Surface or cross-sectional area Cross-sectional area Constant in Logistic equation Molar heat capacity Drag coefficient Anion concentration Cation concentration Equilibrium concentration in liquid phase Equilibrium concentration in gas phase Concentration Particle diameter Depth Diffusion coefficient Hydrodynamic dispersion coefficient Dispersion coefficient Activation energy Eddy diffusivity Gravitational constant Gradient Volumetric gas flow rate Hydraulic head Partial molar enthalpy Henry's coefficient Depth of river, lake etc. Enthalpy change Hydraulic gradient Concentration of inhibitor Flux Total mass flux; Mass transfer rate Dispersion flux Rate constant Hydraulic constant

Units

m2 m-3 h-I m2 mL m3 kg-' h-1 kJ kg-I K-I

mole L-1 mole ~ - 1

-

mg ml-1; mmole L-1

mg ml-1; mmole L-1

mg ml-I; mmole L-1 m m m2 s-1

m2 s-1 m2 s-1 J mole-I m2 s-1 m s-2 m- 1

m3 h-I m kJ kg-1 bar m3 kg-' m kJ mole-I; kJ kg-I

mg ml-1; mmole L-1 kg m-2 h-l; mole m-2 h-1 kg S - I ; mole h-1 kg m-2 h-l; mole m-2 h-' various

-

xx ~

kC kC kCL kd kF kSL K K Ka KI KLa KM KP KS L L

m m m M n n N N P P P P

q02 Q r

rQ '02 R R R Re Ra S Sh t

Nomenclature for Chapters 1 and 2

Reaction rate constant Concentration parameter Saturation kinetics constant Death rate coefficient Flow parameter Mass transfer coefficient Constant in Monod equation Mass transfer coefficient Atmospheric reaeration coefficient Inhibition coefficient Mass transfer coefficient Constant in Darcy's Law Proportional gain Saturation constant Volumetric liquid flow rate Length; Eddy length; Biofilm thickness Equilibrium constant Maintenance coefficient Constant in Freundlich equation Mass Hydraulic constant Number of moles Total number of segments Molar flow rate Partial pressure Surface oxygen production Total pressure Product concentration Specific oxygen uptake rate Volumetric flow rate Reaction rate Rate of heat production Rate of oxygen uptake Universal gas constant Surface respiratory demand Total reaction rate or rate Reynolds number Rate of oxygen transfer (reaeration) Substrate concentration Sherwood number Time

h- kg m-3 kg m-3 h- m3 h-' m s-1 kg m-3; mole m-3 m h-l h- kg m-2 h-l h-1 m s-1

mg ml-1; mmole L-' m3 h-'

m various h-

mole h- 1 bar g 0 2 m-2 h-1 bar mg ml-1; mmole ~ - 1

g 0 2 g biomass - l h-l

kg m-3 h-l; kmole m-3 h- J s-l g s-1; mmole s-1 J mole-l K-' g 0 2 m-2 h-l kg h-l; kmole h-'

g m-3 h-l mg m1-1; mmole ~ - 1

various

m3 h-1. m3 s-1

-

-

Nomenclature for Chapters 1 and 2 XXI

T TI12 Urms U v, v Vmax

VS

V Vm VM W

X A X Y Y Y Z Z Z

X

Greek

a P A 6 E E

77 h P P Pmax

@C

@m P c

V

z z

Temperature Radioactive half life Root mean square eddy velocity Heat transfer coefficient Velocity Maximum rate of substrate consumption Sedimentation velocity Volume Groundwater microscopic flow rate Groundwater macroscopic flow rate Width of river, lake, etc. Mole fraction Fractional conversion of A Cell concentration Mole fraction in gas phase Variable name Yield coefficients Axial distance Frequency factor Ionic charge

Reaction order, constant Reaction order, constant Difference operator Partial differential operator Control error Fractional gas holdup Efficiency Constant in Moser equation Dynamic viscosity Specific growth rate Maximum specific growth rate Stoichiometric coefficient Sludge age Sludge residence time Density Summation operator Controller time constant Residence time

OC or K h m s-1

m s-1

J ,-1 m-2 OC-I

g m-3 h-' m s-1 m3 m h-l m h-l m

kg m-3

XXII Nomenclature for Chapters 1 and 2

z ZE TG

Indices

* 0 1 2 , 3 ,...., n a, b, ..., f a amb air agit aPP A Ac B Bu d d D f G hY d i, j in I lim L max n out P P phot Pr 4 / 0 2 Q/S r resp R

set S

Tortuosity (hydrology) -

Gas dynamics time constant S

Electrode time constant S

Equilibrium concentration Initial; Inlet; External values Component 1; Outlet conditions Components 2, 3, ...., n Constants Adsorption Ambient conditions Air conditions Agitation Apparent value Component A Acetic acid Bulk conditions; Component B Butyric acid Death Desorption Derivative control Final; Outlet conditions Gas phase Hydrodynamic Components i, j Inlet conditions Inhibition; Integral control Limiting value Liquid Maximum value Segment; Reaction order Outlet conditions Particle; Pollutant Product; Proportional control Photosynthesis Propionic acid Heat yield per unit oxygen uptake Heat yield per unit substrate uptake Reaction Respiration Recycle Surface value Set point

Nomenclature for Chapters 1 and 2 XXIII

S tot Total value W Wall conditions X Biomass XL Biomass loss a9 P Orders of reaction

Solid; Steam; Total number of components

This Page Intentionally Left Blank

1 Modelling Principles

1.1 The Role of Modelling in Environmental Technology

Understanding the environment we live in and man's interaction with the environment, protecting the environment from damage and rectifying the damage already caused are essential to the long term survival of the planet. The range of environmental problems is immense and covers all aspects of our daily lives, and their study embraces many traditional subject areas, in which the environmental engineer plays a very positive role. In this chapter, the basic engineering modelling concepts relevant to environmental issues are introduced and their applications are illustrated via the use of simplified case examples.

Engineers have had a direct influence on many of the environmental problems we face today; for instance, the pollution caused by chemical industries, car exhaust fumes, mining and smelting and ecological damage caused by the construction of reservoirs and roads. The engineer nowadays has an important role to play in designing processes that help to improve the environment - for instance, better wastewater treatment plants, air filters, the production of biodegradable or reusable products - and in minimising the environmental impact for any new project. The modern concept of waste minimisation in process design is an important tool in this area. Engineering principles can also be applied to the study of natural processes such as the flow of water in rivers and lakes, the transport of solutes through soil and the mixing of water bodies by wind, etc.

Environmental bioprocesses consist of complex interactions between physical, chemical and biological processes. The most important of these can be expressed in engineering terms using the scientific and engineering techniques of mass and energy balances, microbial and population kinetics, thermodynamics, transport processes, chemical and biochemical reactions, mass and heat transfer and stoichiometry. These aspects of the basic modelling process constitute the major part of this chapter. In addition many other factors may influence the process such as climate, human intervention, geography, natural disaster, etc. It is difficult to synthesise this large volume of material mentally and almost impossible to predict how even the simplest process will behave under different conditions. Mathematical models can be used to tie together this material into a more unified and understandable package which can be used for the purposes of prediction, process control, design, education and management.

2 1 Modelling Principles

A good mathematical model is a compromise between accuracy, applicability and clarity. It is often desirable to be able to predict future events with a high degree of accuracy which consequently requires a rather complex model. The greater the complexity of the model, however, the greater will be the difficulty in determining appropriate values for the model parameters and the less generally applicable the model will be. For instance, a model may be developed to predict the influence of an industrial effluent discharge on the dissolved oxygen concentrations in a river. An accurate prediction may be obtained by one particular model for the river in question, but this might give unsatisfactory results when applied to another river under different conditions. An alternative model could give more generally applicable results but at the cost of a loss of accuracy. In addition, an increase in complexity can lead to a reduction in understandibility. If the model is to be used by others, then it needs to be presented in a clear and understandable way if it is not to remain a mathematical curiosity. When developing a model it is therefore essential that the proposed use of the model is clearly understood and kept in mind during the model development. One final point: mathematical modelling can not replace sound experimental techniques and data, but it can prove to be an excellent way of presenting complex ideas in an efficient form.

The approach in this book is to concentrate on a simplified treatment of the dynamic modelling and simulation of environmental engineering applications. Nevertheless, quite realistic process phenomena can often be described by relatively simple models, as exemplified by this text. Often a simplified approach can be very useful in clarifying preliminary ideas before tackling the full real life problem in all its complexity. No attempt is made here to deal with large-scale environmental problems, such as climatological, meteorological or geographical effects. Complex modelling software packages to solve large- scale problems, such as chemical spills into rivers, estuaries or at sea, gaseous discharges from stacks, the effects of automobile emissions in urban centres or discharges into multimedia environments, are very much the concern of specialist agencies and are generally not suitable for teaching purposes - the main concern of this book.

The four basic tenets of mathematical modelling, shown in Fig. 1.1, are very much a matter of common sense (Kapur 1988) and can be summarised as follows:

1. The mathematical model can only be an approximation of real-life processes which are often extremely complex and often only partially understood. Thus models are themselves neither good nor bad but should satisfy some previously well defined aim.

2. Modelling is a process of continuous development in which it is generally advisable to start off with the simplest conceptual representation of the process and to build in more and more complexities as the model develops.

1.1 The Role of Modelling in Environmental Technology 3

Starting off with the process in its most complex form often leads to confusion.

3. Modelling is an art but also a very important learning process. In addition to a mastery of the relevant theory, considerable insight into the actual functioning of the process is required. One of the most important factors in modelling is to understand the basic cause and effect sequence of individual processes.

4. Models must be both realistic and robust. A model which predicts effects which are quite contrary to common sense or to normal experience is unlikely to be received with confidence.

I Start simple I Build In comDlexlties later

. I Use the model to learn

~~

I Models are there to be applled I Figure 1.1. The basic principles of model building.

1.2 General Aspects of the Modelling Approach

An essential stage in the development of any model is the formulation of appropriate mass and energy balance equations. To these may be added additional relationships representing: rates of chemical reaction, rates of heat and mass transfer, system property changes, phase equilibria and control. The combination of these relationships provides a basis for the quantitative description of the process and comprises the basic mathematical model. The resulting model can range from a simple case of relatively few equations to models of great complexity. The greater the complexity of the model, however, the greater is then the difficulty in identifying the increased number of

4 1 Modelling Principles

parameter values. One of the skills of modelling is thus to derive the simplest possible model, capable of a realistic representation of the process.

The application of a combined modelling and simulation approach leads to the following advantages:

1. Modelling improves understanding.

2. Models help in experimental design.

3. Models may be used predictively.

4. Models can be used in training.

5. Models can be used to improve processes.

1.3 Model Classification

Many different approaches to the modelling of environmental bioprocesses have been adopted. A distinction can be drawn between deterministic models and stochastic models, and between steady-state and dynamic models.

1.3.1 Deterministic Models

Models in which all the parameters have defined values are termed deterministic. The majority of models presented in this course are deterministic in that they do not take into account random environmental fluctuations and assign constant values to the model parameters such as growth rates, flow rates, volumes, concentrations and temperatures. In many processes this is a reasonable assumption and deterministic models can often give such good prediction that extra complexity introduced by assigning statistically variable parameter values is often not worthwhile. This applies especially to wastewater treatment process modelling applications where certain operating parameters usually are maintained constant.