BiotechnologySecond EditionVolume l l a

Environmental Processes I

8WILEY-VCH

BiotechnologySecond EditionFundamentals Special Topics

Volume 1 Biological Fundamentals Volume 2 Genetic Fundamentals and Genetic Engineering Volume 3 Bioprocessing Volume 4 Measuring, Modelling and ControlProducts

Volume 9 Enzymes, Biomass, Food and Feed Volume 10 Special Processes Volumes l l a - c Environmental Processes 1-111 Volume 12 Legal, Economic and Ethical Dimensions

Volume 5a Recombinant Proteins, Monoclonal Antibodies and Therapeutic Genes Volume 5b Genomics Volume 6 Products of Primary Metabolism Volume 7 Products of Secondary Metabolism Volumes 8a and b Biotransformations I and I1

All volumes are also displayed on our Biotech Website: http://www.wiley-vch.de/homelbiotech

A Multi-Volume Comprehensive Treatise

Second, Completely Revised Edition Edited by H.-J. Rehm and G. Reed in cooperation with A. Puhler and F? StadlerVolume l l a

Biotechnology

Environmental Processes IWastewater Treatment

Edited by J. Winter

8 WILEYWCHWeinheim . New York * Chichester Brisbane Singapore .Toronto

Series Editors: Prof. Dr. H.-J. Rehm Institut fur Mikrobiologie Universitat Munster CorrensstraRe 3 D-48149 Miinster FRG Prof. Dr. A. Puhler Biologie VI (Genetik) Universitat Bielefeld P.O. Box 100131 D-33501 Bielefeld FRG

Dr. G. Reed 1029 N. Jackson St. #501-A Milwaukee, WI 53202-3226 USA

Prof. Dr. P.I W. Stadler Artemis Pharmaceuticals Geschaftsfiihrung Pharmazentrum Koln Neurather Ring D-51063 Koln FRG

Volume Editor: Prof. Dr. J. Winter Universitat Karlsruhe (TH) Institut fur Ingenieurbiologie und Biotechnologie des Abwassers Am Fasanengarten Postfach 6980 D-76128 Karlsruhe

This book was carefully produced. Nevertheless, authors, editors 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.

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 Biotechnology: a multi volume comprehensive treatise I ed. by H.-J. Rehm and G. Reed. In cooperationwith A. Piihler and P. Stadler. 2., completely rev. ed. - VCH. ISBN 3-527-28310-2 (Weinheim ...) NE: Rehm, Hans-J. [Hrsg.] Vol. lla: Environmental Processes I ed. by J. Winter ISBN 3-527-28321-80 WILEY-VCH Verlag GmbH, D-69469 Weinheim (Federal Republic of Germany), 1999

Printed on acid-free and chlorine-free 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. Compositionand Printing: Zechnersche Buchdruckerei, D-67330 Speyer. Bookbinding: J. Schaffer, D-67269 Griinstadt. Printed in the Federal Republic of Germany

Preface

In recognition of the enormous advances in biotechnology in recent years, we are pleased to present this Second Edition of Biotechnology relatively soon after the introduction of the First Edition of this multi-volume comprehensive treatise. Since this series was extremely well accepted by the scientific community, we have maintained the overall goal of creating a number of volumes, each devoted to a certain topic, which provide scientists in academia, industry, and public institutions with a well-balanced and comprehensive overview of this growing field. We have fully revised the Second Edition and expanded it from ten to twelve volumes in order to take all recent developments into account. These twelve volumes are organized into three sections. The first four volumes consider the fundamentals of biotechnology from biological, biochemical, molecular biological, and chemical engineering perspectives. The next four volumes are devoted to products of industrial relevance. Special attention is given here to products derived from genetically engineered microorganisms and mammalian cells. The last four volumes are dedicated to the description of special topics. The new Biotechnology is a reference work, a comprehensive description of the state-of-the-art, and a guide to the original literature. It is specifically directed to microbiologists, biochemists, molecular biologists, bioengineers, chemical engineers, and food and pharmaceutical chemists working in industry, at universities or at public institutions. A carefully selected and distinguished Scientific Advisory Board stands behind the

series. Its members come from key institutions representing scientific input from about twenty countries. The volume editors and the authors of the individual chapters have been chosen for their recognized expertise and their contributions to the various fields of biotechnology. Their willingness to impart this knowledge to their colleagues forms the basis of Biotechnology and is gratefully acknowledged. Moreover, this work could not have been brought to fruition without the foresight and the constant and diligent support of the publisher. We are grateful to VCH for publishing Biotechnology with their customary excellence. Special thanks are due to Dr. HansJoachim Kraus and Karin Dembowsky, without whose constant efforts the series could not be published. Finally, the editors wish to thank the members of the Scientific Advisory Board for their encouragement, their helpful suggestions, and their constructive criticism. H.-J. Rehm G. Reed A. Piihler P. Stadler

Scientific Advisory Board

Prof Dr. M.J. Beker

August Kirchenstein Institute of Microbiology Latvian Academy of Sciences Riga, Latvia

Prof Dr. I. Goldberg

Department of Applied Microbiology The Hebrew University Jerusalem, Israel

Department of Chemical Engineering Massachusetts Institute of Technology Cambridge, MA, USA

Prof Dr. C. L.Cooney

DCpartement de GCnie Biochimique et Alimentaire Institut National des Sciences AppliquCes Toulouse, France

Prof Dr. G. Goma

Department of Microbiology University of Queensland St. Lucia, Australia

Prof Dr. H. M? Doelle

Department of Genetics John Innes Institute Nonvich, UK

Sir D. A. Hopwood

F. Hoffmann-La Roche AG Basel. Switzerland

Prof Dr. J. Drews

Prof Dr. E.H. Houwink

Organon International bv Scientific Development Group Oss, The Netherlands

Prof Dr. A.Fiechter

Institut fur Biotechnologie Eidgenossische Technische Hochschule Zurich, Switzerland

Prof Dr. A.E.Humphrey

Center for Molecular Bioscience and Biotechnology Lehigh University Bethlehem, PA, USA

Pro$ Dr. ir: K. Ghose

Biochemical Engineering Research Centre Indian Institute of Technology New Delhi, India

Prof Dr. I. Karube

Research Center for Advanced Science and Technology University of Tokyo Tokyo, Japan

VIII

Scientific Advisory Board

Prof Dr. M. A. LachanceDepartment of Plant Sciences University of Western Ontario London, Ontario, Canada

Prof Dr. K. SchiigerlInstitut fiir Technische Chemie Universitat Hannover Hannover, Germany

Prof Dr. E Liu :

Pro$ Dr. f? Sensi

China National Center for Biotechnology Development Beijing, China

Chair of Fermentation Chemistry and Industrial Microbiology Lepetit Research Center Gerenzano, Italy

Pro$ Dr. J. E Martin

Department of Microbiology University of Ledn Lebn, Spain

Prof Dr. E H. Tan :

Institute of Molecular and Cell Biology National University of Singapore Singapore

Prof Dr. B. MattiassonDepartment of Biotechnology Chemical Center University of Lund Lund, Sweden

Pro$ Dr. D. ThomasLaboratoire de Technologie Enzymatique UniversitC de Compikgne Compibgne,France

Prof Dr. M. RoehrInstitut fur Biochemische Technologie und Mikrobiologie Technische Universitat Wien Wien. Austria

Prof Dr. W Verstraete

Laboratory of Microbial Ecology Rijksuniversiteit Gent Gent, Belgium

Prof Dr. H. SahmInstitut fur Biotechnologie ForschungszentrumJiilich Jiilich, Germany

Pro$ Dr. E.-L. WinnackerInstitut fur Biochemie Universitat Miinchen Miinchen, Germany

Contributors

Dr. Rudolf AmannMPI fur Marine Mikrobiologie CelsiusstraBe 1 D-28359 Bremen Germany Chapter 5

Prof. Dr. Eberhard BockInstitut fur Allgemeine Botanik Abteilung Mikrobiologie Universitat Hamburg OhnhorststraBe 18 D-22609 Hamburg Germany Chapter 3

Dr. Ute Austermann-HaunJnstitut fur Siedlungswassenvirtschaft und Abfalltechnik Universitat Hannover Welfengarten 1 D-30167 Hannover Germany Chapter 10

Prof. Dr. Klaus BuchholzLehrstuhl fur Technologie der Kohlenhydrate Technische Universitat Braunschweig Langer Kamp 5 D-38106 Braunschweig Germany Chapter 24

Dr. Matthias BarjenbruchInstitut fur Kulturtechnik und Siedlungswassenvirtschaft Universitat Rostock Satower Stralje 48 D-18059 Restock Germany Chapter 18

Prof. Dr. Rainer BuchholzInstitut fur Biotechnologie Technische Universitat Berlin AckerstraBe 71-76 D-13355 Berlin Germany Chapter 21

Dr.-Ing. Peter BaumannInstitut fur Siedlungswasserbau,Wassergute und Abfallwirtschaft Abt. Abwassertechnik Bandtale 2 D-70569 Stuttgart Germany Chapter 16

Dr. Gerald BunkeInstitut fur Biotechnologie Technische Universitat Berlin AckerstraBe 71-76 D-13355 Berlin Germany Chapter 21

X

Contributors

Dr.-Ing. Bernd DoriasDrees & Sommer GmbH Obere Waldplatze 13 D-70569 Stuttgart Chapter 16

Prof. Dr. Mogens HenzeDepartment of Environmental Science and Engineering Building 115 Technical University of Denmark DK-2800 Lyngby Denmark Chapter 20

Prof. Dr. Hans-Curt FlemmingInstitut fur Wasserchemie und Wassertechnologie Universitat Duisburg MoritzstraBe 26 D-45476 MulheidRuhr Germany Chapter 4

Dr. Look W. Hulshoff PolDepartment of Environmental Engineering Agricultural University of Wageningen P.O. Box 8129 NL-6700 EV Wageningen The Netherlands Chapter 25

Dr. Claudia GallertInstitut fur Ingenieurbiologie und Biotechnologie des Abwassers Universitat Karlsruhe (TH) Am Fasanengarten Postfach 6980 D-76128 Karlsruhe Germany Chapter 2

Dr. Norbert JardinRuhrverband Essen Kronprinzenstr. 37 D-45128 Essen Germany Chapter 14

Dr. Peter GotzInstitut fur Biotechnologie Technische Universitat Berlin AckerstraBe 71-76 D-13355 Berlin Germany Chapter 21

Dr. Hans-Joachim JordeningLehrstuhl fur Technologie der Kohlenhydrate Technische Universitat Braunschweig Langer Kamp 5 D-38106 Braunschweig Germany Chapter 24

Prof. Dr. Ludwig HartmannAm neuen Berg 10 D-86673 Unterstall Germany Chapter 1

Prof. Dr.-Ing. Rolf KayserAdolf-Bingel-StraBe 2 D-38116 Braunschweig Germany Chapter 13

Prof. Dr.-Ing. Winfried HartmeierLehrstuhl f i r Biotechnologie RWTH Aachen Worringerweg 1 D-52056Aachen Germany Chapter 7

Prof. Dr. Paul KoppeObere Saarlandstralje 3 D-45470 MiilheidRuhr Germany Chapter 9

Contributors

XI

Prof. Dr. Helmut KroissInstitut fur Wassergute und Landschaftswasserbau Technische Universitat Wien Karlsplatz 13/226 A-1040 Wien Austria Chapters 6,23

Dip1.-Ing. Hartmut MeyerInstitut fur Siedlungswassenvirtschaft und Abfalltechnik Universitat Hannover Welfengarten 1 D-30167 Hannover Germany Chapter 10

Dr. Peter KuschkUFZ - Umweltforschungszentrum Leipzig-Halle GmbH Sektion Sanierungsforschung PermoserstraBe 15 D-04318 Leipzig Germany Chapter 12

Dr. Eberhard MorgenrothDepartment of Environmental Science and Engineering Technical University of Denmark Building 115 DK-2800 Lyngby Denmark Chapter 15

Prof. Dr. Gatze LettingaDepartment of Environmental Engineering Agricultural University of Wageningen PO. Box 8129 NL-6700 EV Wageningen The Netherlands Chapter 25

Dr. Volkmar NeitzelRuhrverband KornprinzenstraSe 37 D-45128 Essen Germany Chapter 9

Dr. Judy LibraInstitut fur Verfahrenstechnik Technische Universitat Berlin StraBe des 17. Juni 135 D-10623 Berlin Germany Chapter 19

Dr. Peter NisipeanuRuhrverband KornprinzenstraSe 37 D-45128 Essen Germany Chapter 8

Prof. Dr.-Ing. Herbert Mark1AB BioprozeB- und Bioverfahrenstechnik Technische Universitat Hamburg-Harburg DenickestraBe 15 D-21071 Hamburg Germany Chapter 26

Prof. Dr. Ing. Norbert RabigerInstitut fur Umweltverfahrenstechnik Universitat Bremen Postfach 330440 D-28334 Bremen Germany Chapter 27

Dr. Michael J. McInerneyDepartment of Botany and Microbiology University of Oklahoma 770 Van Vleet Oval Norman, OK 73019-0245 USA Chapter 22

Dr. Monika ReissLehrstuhl fur Biotechnologie RWTH Aachen Worringenveg 1 D-52056 Aachen Germany Chapter 7

XI1

Contributors

Prof. Dr.-Ing.Karl-Heinz Rosenwinkel Prof. Dr. Ulrich StottmeisterInstitut fur Siedlungswassenvirtschaftund Abfalltechnik Universitat Hannover Welfengarten 1 D-30167 Hannover Germany Chapter 10

UFZ - Umweltforschungszentrum Leipzig-Halle GmbH Sektion Sanierungsforschung PermoserstraBe 15 D-04318 Leipzig Germany Chapter 12

Prof. Dr. Georg SchonInsitut fur Biologie I1 Universitat Freiburg SchanzlestraBe D-79104 Freiburg Germany Chapter 14

Chem.-Ing.Alfred StozekAuf dem Loh 7 D-45289 Essen Chapter 9

Dr. Andreas SchrammMPI fiir Marine Mikrobiologie CelsiusstraBe 1 D-28359 Bremen Germany Chapter 5

Dr. Ralf StiivenInstitut fur Allgemeine Botanik Abteilung Mikrobiologie Universitat Hamburg Ohnhorststraae 18 D-22609 Hamburg Germany Chapter 3

Dr. Judith M. Schulz genannt MenningmannENVICON Klaranlagen Postfach 100637 D-46526 Dinslaken Germany Chapter 17

Dr. Karl SvardalInstitut fur Wassergute und Landschaftswasserbau Technische Universitat Wien Karlsplatz 131226 A-1040 Wien Austria Chapters 6,23

Dr. Carin SiekerBerliner Wasserbetriebe Neue JudenstraBe 1 Postfach 02 1098 D-10122 Berlin Germany Chapter 18

Dr. Jules B. van LierDepartment of Environmental Engineering Agricultural University of Wageningen P.O. Box 8129 NL-6700 EV Wageningen The Netherlands Chapter 25

Contributors

XI11

Prof. Dr.-Ing. Peter WeilandBundesforschungsanstalt fur Landwirtschaft Braunschweig-Volkenrode (FAL) Institut fur Technologie Bundesallee 50 D-38116 Braunschweig Germany Chapter 11

Dr. Jost WingenderInstitut fur Wasserchemie und Wassertechnologie Universitat Duisburg MoritzstraBe 26 D-45476 Mulheim/Ruhr Germany Chapter 4

Prof. Dr.-Ing. Udo WiesmannInstitut fur Verfahrenstechnik Technische Universitat Berlin StraBe des 17. Juni 135 D-10623 Berlin Germany Chapter 19

Prof. Dr. Josef WinterInstitut fur Ingenieurbiologie und Biotechnologie des Abwassers Universitat Karlsruhe (TH) Am Fasanengarten Postfach 6980 D-76128 Karlsruhe Germany Chapter 2

Dr. Arndt WieBnerUFZ - Umweltforschungszentrum Leipzig-Halle GmbH Sektion Sanierungsforschung PermoserstraSe 15 D-04318 Leipzig Germany Chapter 12

Dr. Dirk ZartInstitut fur Allgemeine Botanik Abteilung Mikrobiologie Universitat Hamburg OhnhorststraSe 18 D-22609 Hamburg Germany Chapter 3

Prof. Dr.-Ing. Peter A. WildererLehrstuhl fur Wassergute und Abfallwirtschaft Technische Universitat Munchen Am Coulombwall D-85748 Garching Germany Chapter 15

Dr. Grietje ZeemannDepartment of Environmental Engineering Agricultural University of Wageningen P.O. Box 8129 NL-6700 EV Wageningen The Netherlands Chapter 25

Contents

Introduction 1J. Winter

I1 Processes of Wastewater Treatment Waste Water Sources and Composition9 Municipal Wastewater and Sewage Sludge 161 l? Koppe, A . Stozek, l? Neitzel 10 Industrial Wastewater Sources and Treatment Strategies 191 K,-H. Rosenwinkel, U. Austermann-Haun, H. Meyer 11 Agricultural Waste and Wastewater Sources and Management 217 l? Weiland

I General Aspects1 Historical Development of Wastewater Treatment Processes 5 L. Hartmann 2 Bacterial Metabolism in Wastewater Treatment Systems 17 C. Gallert, J. Winter 3 Nitrification and Denitrification Microbial Fundamentals and Consequences for Application 55 D. Zart, R. Stiiven, E. Bock 4 Autoaggregation of Microorganisms: Flocs and Biofilms 65 J. Wingender,H,-C.Flemming 5 Nucleic Acid-Based Techniques for Analyzing the Diversity, Structure, and Dynamics of Microbial Communities in Wastewater Treatment 85 A. Schramm, R. Amann 6 Analytical Parameters for Monitoring of Wastewater Treatment Processes 109 H. Kroiss, K. Svardal 7 Monitoring of Environmental Processes with Biosensors 125 M . Reiss, W Hartmeier 8 Laws, Statutory Orders and Directives on Waste and Wastewater Treatment 141 I! Nisipeanu

Aerobic Carbon, Nitrogen, and Phosphate Removal12 Biological Processes in Wetland Systems for Wastewater Treatment 241 l? Kuschk, A. Wiepner, U.Stottmeister 13 Activated Sludge Process 253 R. Kayser 14 Biological and Chemical Phosphorus Removal 285 G. Schon, N Jardin 15 Continuous Flow and Sequential Processes in Municipal Wastewater Treatment 321 E. Morgenroth, l? A . Wilderer

XVI

Contents

16 Trickling Filter Systems 335 P Baumann, B. Dorias 17 Submerged Fixed-Bed Reactors 349 J. Schulz genannt Menningmann 18 Experience with Biofilters in Wastewater Treatment 365 C. Sieker, M . Barjenbruch 19 Special Aerobic Wastewater and Sludge Treatment Processes 373 U.Wiesmann, J. Libra 20 Modeling of Aerobic Wastewater Treatment Processes 417 M. Henze

Anaerobic Processes22 Anaerobic Metabolism and its Regulation 455 M. Mclnerney 23 CSTR-Reactors and Contact Processes in Industrial Wastewater Treatment 479 H. Kroiss, K. Svardal 24 Fixed Film Stationary Bed and Fluidized Bed Reactors 493 H.-J.Jordening, K . Buchholz 25 Possibilities and Potential of Anaerobic Wastewater Treatment Using Anaerobic Sludge Bed (ASB) Reactors 517 G. Lettinga, L.W Hulshoff Pol, J.B. van Lier, G. Zeemann 26 Modeling of Biogas Reactors 527 H. Mark1 27 Future Aspects Cleaner Production 561 i Rabiger V

Metal Ion Removal21 Metal Removal by Biomass: Physico-Chemical Elimination Methods 431 G. Bunke, P Gotz, R. Buchholz

Index 579

Biotechnology Second, Completely Revised EditionH.-J. Rehm and G. Reed copyright OWILEY-VCH Verlag GmbH, 1999

JOSEFWINTERKarlsruhe, Germany

Except for soil sanitation environmental biotechnology, including air pollution, waste and wastewater treatment processes, surface and ground water pollution and many other topics was subsumed under the title Microbial Degradations in Volume 8 of the First Edition of Biotechnology ,Urbanization and industrialization, especially in developing countries, is still in progress with all negative effects on the environment. Resulting from the accumulation of huge masses of polluted water in human settlements or in industry the limits of self-purification of surface waters are often exceeded, leading to anaerobiosis with all its deteriorating consequences for life. In industrialized countries central wastewater treatment plants have been developed to reduce the pollution freight before disposing the wastewater into the next surface water. In the First Edition of Biotechnology different wastewater treatment processes contribute a major part to Volume 8. Furthermore, the volume is devoted to different processes of solid waste composting, drinking water biofiltration, exhaust gas purification, removal of pathogens and several other environmental processes.

Now, some ten years later, the biological background of aerobic or anaerobic wastewater treatment processes and of most of the other processes in environmental biotechnology (e.g., soil sanitation, waste gas purification, compost preparation, drinking water purification, etc.) has increased tremendeously and various new and differing processes are available to protect the environment. So it is the time to decribe the present state of the art of environmental biotechnological processes in a comprehensive survey. After bringing together the most important issues that had to be covered in the Second Edition of Biotechnology, the editors immediately realized that wastewater treatment, solid waste management (also including the broad field of municipal solids composting or anaerobic fermentation), off-gas purification, biological soil remediation processes, potable water denitrification and purification and many other selected environmental processes were too broad a field to be summarized with significance in a single book. For this reason Volume 11 Environmental Processes of the Second Edition of Biotechnology is divided into three volumes, the first of which, Volume l l a , is devoted to Wastewater

2

Introduction

Treatment Processes.This first volume on environmental biotechnology summarizes the biological principles and the technical limits of all those wastewater treatment processes that are operated by municipalities and industry up to the present state to meet the legal limits for carbon, nitrogen, and phosphorus disposal into surface waters. In the first part of the book the present status of general biological and engineering aspects of wastewater purification procedures is summarized.What does environmental legislation require for wastewater disposal of municipalities or industry into surface waters? What can biology contribute together with chemistry, physics and engineering to wastewater purification from its organic and inorganic pollutants? How can the purification efficiency be measured analytically, either off-line or - even more important for monitoring of continuous processes - on-line? In the second part of the book the different processes for wastewater treatment are described in more detail and under the aspect of full-scale application. At first wastewater sources and variations of wastewater composition are outlined, followed by specific aerobic carbon, nitrogen and phosphate removal processes, metal ion removal and, last but not least, anaerobic wastewater treatment processes. The volume includes well-known and practiced technologies, as well as new and only recently developed processes. Especially in

the field of improved wastewater purification (N and P removal processes), which is a relatively young requirement within environmental legislation, new processes or process combinations had to be developed and applied. It is hoped that the whole range of insights into biology and technology of wastewater treatment processes have been covered by the contributions of expert authors from Europe and America. The editors are well aware on the other hand, that not every individual system offered on the market could be described. Especially in the field of carrier-supported fixed or fluidized bed technologies not every single system could be mentioned, although carrier-supported processes may be a matter of choice for future high-rate wastewater treatment, e.g., in industry. Membrane technologies were not included, since the average lifetime of membranes is generally still too short due to membrane corrosion or biofouling. This first volume on Environmental Processes should give the reader basic information on the biology of the degradation of pollutants, different processes for wastewater purification and process parameters for an optimal purification. It should be regarded as a source of overview information on frequently applied full-scale wastewater treatment processes with some more details presented for certain specific applications. Karlsruhe, March 1999J. Winter

I General Aspects

Biotechnology Second, Completely Revised EditionH.-J. Rehm and G. Reed copyright OWILEY-VCH Verlag GmbH, 1999

1 Historical Development of Wastewater Treatment Processes

LUDWIG HARTMANNUnterstall, Germany

1 General Background 6 2 The Beginnings of Waste and Wastewater Treatment 7 3 Necessity for Further Purification of Wastewater - Development of Trickling Filters 8 4 Land Application of Wastewater and Fish Ponds 9 5 Widening the Theoretical Basis 10 6 The Activated Sludge Process 10 7 Detergents: An Interplay of High Significance 12 8 Treatment of Secondary Pollutants 12 9 A Second Step Forward in Anaerobic Digestion 13 10 Gaps, Lacks, and Outlook 13 11 References 14

6

1 Historical Development of Wastewater Treatment Processes

1 General BackgroundTreatment of all kinds of human wastes has a long history. Procedures depend on the lifestyle of the population and on legislation. Even today in some developing countries solid waste is dumped on little heaps in the backyard and burned once in a while.Wastewater is either generated directly in lakes or rivers by washing clothes or dishes or, if water is available in the houses, e.g., by single deep wells or by a public water supply system, the wastewater is disposed off untreated into the next surface water. This situation is often found in rural areas, but even today it can be observed in megacities of developing countries such as Calcutta, Bangkok, Manila, or Jakarta. Under conditions of rural life with a low population density and a rather elemental lifestyle the direct feedback of organic wastes (e.g., cattle manure) as a fertilizer on the fields and of wastewater into natural surface waters may be acceptable as long as overfertilization of soil is prevented or the capacity for self-purification of the surface water sources is not exceeded. Due to an ongoing urbanization, not only in developing countries and due to the urban lifestyle more and more waste and wastewater are generated locally in a concentrated form. Handling of huge amounts of waste or wastewater under urban conditions excludes recycling into nature for irrigation or fertilization. Instead it requires the application of highly sophisticated techniques for mechanical, chemical, and biological treatment to protect nature from permanent damage. These technically controlled instruments had to be invented as artifical ecosystems and were fitted in between the generation of huge amounts of wastes and wastewater by humans and the natural selfpurification capacity. Many different technical procedures for wastewater treatment have been developed over the past 10 decades, all including biological treatment technologies at some stage, with the task of mitigating the destructive effect of mans wastes and wastewater on nature. Concerning human and industrial wastes and wastewaters an aspect of general importance was that waste or wastewater treatment, although it was considered to be a must to

protect the environment, costs a lot of money and reduces profit. For this reason it was always minimized to the lowest standard enforced by legislation.The philosophy was literally that of the fire police. Only if there was a fire (pressure from state authorities), counteraction was necessary. Major efforts to improve the situation came mostly as a result of irreparable and no longer negligible severe environmental damage. At this stage it should also be mentioned that the debate always started at the definition of what is waste and the state of the art for its treatment. Of general importance were the accepted analytical methods for measuring pollutants or pollution, either by using socalled sum parameters, such as biological oxygen demand (BOD), chemical oxygen demand (COD), or total organic carbon (TOC), or by analyzing single substances, if they were known. Many new chemicals are still synthesized and find their way into wastes or wastewaters and finally into nature. However, their impact on the environment can often only be seen decades after their use, e.g., as wood preservatives, insecticides,pesticides, or detergents. Therefore, counteractions of course are always one step behind. The definition of chemicals in terms of BOD is uncertain and depends on the ability of microorganisms upon exposure to the xenobiotics to acquire the potential for biotransformation or - better - biodegradation. Biotransformation or biodegradation of a single chemical brings us to the general problem of waste or wastewater treatment. Disappearance of a single substance from wastewater, as measured by, e.g., gas chromatography or HPLC, does not necessarily mean complete degradation or detoxification. It may mean nothing but transformation of one substance into another, which may even be of higher environmental significance because of higher toxicity. Finally, it has to be mentioned that progress in wastewater treatment systems was and is only slowly moving. This is mainly due to the fact that huge, central wastewater treatment plants designed for at least one generation in advance have been built and are operated by the municipalities. For this reason, it often takes almost 20-30 years until new developments will be applied.

2 The Beginnings of Waste and Wastewater Treatment

7

neers and scientists. Since most of the bigger cities were located at big rivers, it seemed to be a good solution for the time being. As a result of waste transportation out of the cities by Waste and wastewater treatment reaches sewer channels outbreaks of cholera and tyback to the Egyptian and Roman high cul- phoid fever could be reduced and finally altures. In ancient Rome part of the city had a most completely prevented. The first compresewer channel system for collection of night hensive sewer network was built in the city of soil and urine, whereas in other parts the toi- Hamburg, starting in 1842. Only 25 years later lets were connected to pits. The collected hu- other cities followed. Today the wastewater of man excrement was sold as fertilizer for horti- more than 92% of population equivalents in Germany is connected to underground sewer culture (IMHOFF, 1998). The real history of wastewater treatment systems for wastewater and rainwater drain1998). started in the second half of the previous cen- age (SICKERT, People and industry accepted the new techtury by the invention of the term wastewater. The background were cholera and ty- nology and began to use the sewers to export phoid fever epidemics in some large cities in everything that was not needed anymore. Central Europe. Pioneers of bacteriology and Therefore, in due time, the self-purification cahygiene, such as PETTENKOFER (1890, 1891), pacity of the wastewater-receiving natural waworked out the scientific background for these ters was exceeded, and the water quality of epidemics as diseases caused by infection via rivers decreased more and more. Since river contact with wastes or waste products. PET- water (as a bank filtrate) was increasingly required to serve the needs for potable water TENKOFER demanded that the wastes should be transported out of the cities. He thought supply, new actions of wastewater disposal that waste products were transferred into the were required. The first pollution problem recognized in air-filled pores of soil. From there they evaporated into the atmosphere and finally came surface waters was only of optical nature. It into the houses making people ill. He calculat- was solved by installation of screens and sieves ed that men inhale daily about 9000 L of air, at the wastewater outlet into rivers (FRUH1910; DUNBAR, 1907). Except for satisfybut only take in about 3 L of water, so the risk LING, of an infection by air would be much higher. ing the psychological impression this was necPETTENKOFER proposed a separation of pota- essary to protect pumps for wastewater transble water and wastewater, but his explanation fer into rivers or for land application. A real of infectious diseases was wrong. Only when improvement of the situation was only ROBERT KOCH 1876,1882,and 1983 isolated achieved by the development of settling tanks in the bacteria causing anthrax, tuberculosis, and to remove the settleable solids before the cholera infectious diseases were recognized as wastewater was released into the rivers or bacterial infections for the first time (IMHOFF, eventually treated further. About one third of organic pollution could be retained by this 1998). DUNBAR (1907) found the technical answer method, thus reducing the pollution freight of to the problem by proposing and constructing rivers considerably. Until the 1950s many sewpublic sewer systems for wastewater collection age treatment plants in Germany used only and transportation. By a sewer system wastes mechanical treatment for removal of organic 1998).As a side and wastewater were transported out of the and inorganic solids (SICKERT, cities to the next river or lake where self-pu- effect huge amounts of sludge were prorification could take place and solve the prob- duced and had to be handled. It was found that, in analogy to aerobic selflem. For the first time a problem was solved just by exporting it from one location to an- purification, an anaerobic process existed reother. The problem of environmental health in ducing the amount of organic solids in the the settlements was transformed into an ongo- sludge by formation of biogas. In addition, by ing problem of river pollution, which, as will be anaerobic treatment the water holding capacshown, still today occupies the interest of engi- ity of the sludge was reduced and, if the resi-

2 The Beginnings of Waste and Wastewater Treatment

8

1 Historical Development of Wastewater Treatment Processes

dence time in the digester was long enough, eggs of intestinal worms were destroyed and pathogenic bacteria were inactivated. In other words, the sludge that was removed from the settling tanks periodically could easily be dewatered, dried, and after composting be used as an agricultural fertilizer.The biogas was collected and could be integrated into the municipal gas supply systems. This was a real step forward in wastewater handling. Since in the early days of wastewater treatment sewers and settling tanks were invented by engineers, waste handling in any form has become the domain of civil engineers. Other occupational groups were not interested. Research at that time (before and shortly after the World War I) was, therefore, concentrated on the improvement of technical installations of settling tanks with sludge fermentation. Real progress was made in the densely populated and highly industrialized regions of Germany, especially in the Ruhr and Emscher region. An outstanding pioneer of this time was KARL IMHOFF. technologies developed at The that time, the so-called Imhoff tank or the Emscher-Brunnen (Emscher well) and their variations were still in use until the 1940s and and 1993). 1950s (IMHOFF, IMHOFF IMHOFF, 1979; Other fields of research dealt with the survival of intestinal worms or pathogenic bacteria in sludge, depending on fermentation times and conditions. Basic knowledge on the influence of fermentation time and temperature on gas production and detention time was collected. An optimal temperature for the technical process would be about 33C to satisfy the physiological needs of mesophilic bacteria in sludge.However, this knowledge was not practically applied since heated digestion tanks were not available. Later it was found that anaerobic digestion could also be performed at thermophilic temperatures, e.g., at 55C,the optimum of thermophilic bacteria in sewage sludge. However, except for an application in the sewage treatment plants of Moscow and Los Angeles (GARBER al., et 1975) thermophilic digesters were only operated on a laboratory or pilot plant scale and (KANDLER al., 1981;GALLERT WINTER, et 1997, PFEFFER,1974). Today, thermophilic digestion is used in agricultural co-fermentation plants for biowaste because it kills pathogens.

3 Necessity for Further Purification of Wastewater Development of Trickling FiltersThe screens and settling tanks of the early times of wastewater treatment as the only means for wastewater purification soon turned out to be insufficientfor the protection of natural water resources. This was demonstrated by a new, biological control method for pollution: the system of saprobes, introduced by KOLKWITZ MARSSON and (1902, 1908, 1909). They observed a change in the composition of the biosystem along a river upon wastewater introduction (KOLKWITZ, 1907).Many biological indicator organisms, protozoa among others - especiallyciliates - and insects give information on the pollution and the progress of self-purification of rivers (FAIRet al., 1941; KOLKWITZ, ODUM, 1950; 1971).The system of saprobes was finally revised by LIEBMANN (1960) and made more practicable by inclusion of chemical parameters. The saprobe index showed that pollution of rivers exceeded the capacity of self-purification, especially in densely populated areas.The distances between the different sewer inlets were too short for a full degradation of the organic pollutants. So the question was raised of how to reduce the pollution of degradable organics. The answer at that time was the installation of trickling filters, which started in England. Trickling filters have their technical origin in soil filters that served for wastewater irrigation (Royal Commission of Sewage Disposal, 1908).Instead of using soil and large areas, gravel or small rocks were piled up to a tower of 2-3 m height and the wastewater was sprinkled over the surface.After a short while a biofilm had developed on the surface of the stones. To prevent clogging, the wastewater had to pass a settling tank.A sprinkling system had already been used by CORE~ETT 1893 in who developed the first trickling filter (STANBRIDGE, 1976). According to DUNBARS theory, purification was a two-step process with (1) adsorption of organic matter to the surface of the carrier ma-

4 Land Application of Wastewater and Fish Ponds

9

-

terial and (2) subsequent mineralization. The adsorption theory was a result of a more physical thinking of engineers, who were not aware of the biological background. This adsorption theory for wastewater components was for quite some time the basis of treatment techniques and was even thought to explain the activated sludge process. According to the theory, the trickling filter had to be given time after a period of adsorption for degradation. In other words, the technology required an intermittent operation. A period of a few minutes of wastewater application was followed by a period for biological degradation. This operation mode required rather huge filters and allowed only a low throughput of wastewater. Due to the low-rate operation, the organic pollutants were fully oxidized. Not only bacteria developed on the rocks, but also protozoa, earth worms, insects, etc. belonged to the population of a trickling filter. Psychodu, the socalled trickling filter fly, was a nuisance of this artifical ecosystem and attracted much scientific attention. For a permanent operation the surplus biofilm had to be washed out twice a year to avoid clogging. According to theoretical considerations and practical observations with low-rate trickling filters no final clarifiers were required. Stabilized, clear wastewater left the treatment unit. In Germany low-rate trickling filters were still in operation after World War 11, although a new understanding of the biology of purification has been gained.This resulted in the more effective technique of activated sludge systems which competed with the trickling filters. To catch up with the new development of the activated sludge technology (ARDERN LOCKand EIT, 1914, 1915; LOCKEIT, 1954), high-rate trickling filters with final clarifiers were constructed (HALVORSON, 1936). Much research was carried out to replace the rocks by artifical media, the height was increased, and the relationship between film formation and film removal was studied. The time of trickling filters as the sole aerobic treatment technology, however, ended in the late 1950s. Although trickling filters could not compete with the activated sludge technology in general, they were still applied for special wastewater types or at special locations where the activated sludge technology could

not be installed. Up to the present time their use as a second stage of aerobic treatment to remove the residual, more recalcitrant BOD in effluents of activated sludge treatment systems and for nitrification is of special importance. This is possible since fixed-film treatment systems can successfully host bacteria with long generation times, which would be washed out from an activated sludge system due to the limited sludge age at a short hydraulic retention time. A special form of trickling filters are rotating disc reactors. Developed originally in the United States in the late 1920s by BUSWELL et al. (1928), many of them were built until the 1950s (FAIRet al., 1948) and were introduced in Central Europe in the late 1950s. Due to simple operation, absence of clogging,little energy consumption, and biofilm formation with a good sedimentation behavior they were the method of choice for small communities with a small amount of wastewater or for industry with special types of pollution.

4 Land Application of Wastewater and Fish PondsWastewater was not only understood as a waste but also as a raw material for agricultural or aquatic production. Apart from the fertilizing effect of sewage sludge the wastewater itself could also serve as a fertilizer for agricultural soil. Especially at times of food shortages after World War I these methods were proposed and treatment plants were built. However, due to many problems, e.g., shortage of land areas in the neighborhood of big cities, integration of sewage application into agricultural practice, disinfection pretreatment to avoid epidemics,integration of wastewater application into the climatic situation, distribution of toxic substances, etc. they did not persist until the time after World War 11.Only when wastewater irrigation was the major goal such methods were used for a longer time. A different situation is prevalent in the food industry, e.g., for starch production. In some parts of Germany the wastewater from potato processing is

10

1 Historical Development of Wastewater TreatmentProcesses

still applied by irrigation on agricultural land by use of an underground pipe distribution system. Except for land application (e.g., USEPA, 1981),wastewater was also used as a source of nutrients in fish ponds up to World War 11, e.g., in the city of Munich. However, precautions for several problems had to be taken:

5 Widening the Theoretical Basis

cially in the United States all types of organic materials were tested for their biodegradability in wastewater treatment plants using the BOD test. However, a real biotechnological approach was hindered at that time by the strict orientation of civil engineers to the purely physicochemical approach of the adsorption theory.To change this thinking took more than 30 years. It was only in the 1950s and 1960s that the BOD reactions were really understood. In (1) Pre-sedimentation of the solids to America the research of HOOVER and BUSH avoid sludge sedimentation in the fish (e.g., HOOVER, 1911) led to a change. In Gerpond, many improvements were made by the author (2) dilution with non-polluted water was and his students (HARTMANN, 1992). Bacterial required to avoid oxygen deficiencies, proliferation was recognized as the basis for and last but not least the BOD reaction. Although the bacteriologi(3) an efficient monitoring system had to cal background was never really denied, the exist to prevent toxic effects. The main first-order reaction to describe the process was restraint for practical application was, comfortable to handle for engineers. BUSH dehowever, its low efficiency during winfined the plateau BOD and found that it charter months. In tropical countries under acterized the end of those reactions that were constant climatic conditions fish ponds responsible for degradation of the dissolved might be the method of choice to clean organic material. The plateau BOD could be wastewater from small settlements. reached in the BOD test in less than 24 h and followed the rules of enzyme kinetics (HARTMA, 1992). This gave a sound basis for the analysis of degradability of wastewater components of unknown composition and of new organics that were developed by the chemical industry. The results can be expressed and In the peak time of trickling filters in the handled mathematically to again permit a mid-twenties a very important observation sound design and operation of technologies. was made by STREETER PHELPS and (1925) in Oxygen consumption after the plateau BOD the United States. Studying self-purification of was reached resulted from endogenous respithe Ohio river by monitoring the biological ration of bacteria and from ciliate activity,later oxygen demand, they found that the degrada- on from nitrification. Thus, the technical limit tion of organic material closely followed the for removal of organics from wastewater was characteristics of a first-order reaction. From reached when the biological oxygen consumpthis time on the BOD was used as the method tion reached the plateau phase. to measure wastewater pollution as well as treatment efficiencies and the self-purification of rivers. In addition, the temperature dependence of the biological degradation was observed, leading to a standardization of the BOD analytic method. The test had to be made at 20C. At this temperature each day roughly 20% of the remaining pollutants were oxidized. After 5 d the oxidation of organics The activated sludge process had already was completed and ammonia oxidation startbeen invented by ARDERNand LOCKETT ed. The first-order theory for biological degra- (1915) at the beginning of this century and was dation greatly enhanced basic research. Espe- understood as a technique for larger cities as it

6 The Activated Sludge Process

6 The Activated Sludge Process

11

required a more sophisticated mode of operation. The theory for purification was taken from trickling filter systems. Purification was thought to proceed in two steps; adsorption followed by biological oxidation. The activated sludge flocs were considered as a freely floating biofilm comprised of bacteria and protozoa that did the purification job. Contrary to the early theory it was believed later on that special physicochemical conditions were necessary to create and stabilize the flocs. Biological research concentrated on the composition of the ciliate fauna at different loading rates. The ciliates were believed to contribute greatly to the removal of colloids, thus doing the polishing job. A great problem of activated sludge systems was sludge bulking for which different theories were developed, but technical answers were seldom found. More important questions concerned aeration and aeration techniques, since these caused the major costs in operating activated sludge plants. Much research was done, and numerous aeration devices were invented and competed with each other. The optimal oxygen concentration to satisfy the demand of the bacteria had to be considered. It was understood that about 0.5 ppm were sufficient for degraders of carbohydrates, but about 4 ppm were required for nitrifiers. PASVEER one of the pioneers to define was the oxygenation capacity (OC value) of aeration systems (PASVEER, 1958a), thus providing an analytical method for comparison of different aeration systems. According to the current theory, the organics were primarily adsorbed at the surface of the flocs in the activated sludge basins. After separation of the sludge it had to be cleaned from adsorbed material in re-aeration chambers before it was brought back into the plant and exposed to new pollutants for adsorption. The adsorption theory, although scientifically wrong, was still in the mind of engineers and technicians up to the 1970s: Adsorption activated sludge plants were designed and built, but re-aeration of return sludge was given up in the 1960s. In this context it was of importance how and where to recyle the return s1u dge. Activated sludge plants were in operation under different load rates. At a high space

loading rate the oxidation was incomplete, whereas at a low load rate the oxidation was complete (DOHMANN, 1998).The aeration time ranged from less than 6 h to about 12 h, which was favored in the USA. It was already understood very early that different loading rates led to different biological systems with different ciliate communities. Low loading rates (FM ~ 0 . 2 resulted in a ) complete oxidation, even of ammonia, whereas high loading rates (F/M=2) removed only the plateau BOD. An important side effect of the activated sludge technology was the need to also improve the technologies of sludge digestion to cope with the huge amounts of surplus sludge. A faster treatment was required, which could only be obtained in heated digesters. The retention times of heated digesters ranged from 30 d to less than 10 d. To improve dewatering of sludge which had been stabilized at a short retention time the addition of chemical flocculation agents was required. Biogas formation during anaerobic sludge stabilization served for heat and electricity generation to reduce the costs of aerobic treatment. It was still not understood that bacterial reactions under optimal conditions are not a matter of hours, but of minutes under the conditions given in municipal wastewater, with a low concentration of pollutants and a high concentration of bacteria. Research for a better understanding was performed in Switzerland by HORLER (1969) and by WUHRMANN and VON BEUST(1958) as soon as in the late 1950s. They revealed a sound, almost mathematically exact relationship between the technical conditions of operation and the treatment efficiencies. Only the biological catalyzator still had to be added. In the engineering practice, however, although understanding the activated sludge process as a biotechnological process, its theoretical background was not accepted. All this resulted from the fact that biologists, especially microbiologists, still had not found their way into this field, although some progress for a better understanding had been made by HARTMANN his students. They and bridged the gap between the BOD process and the activated sludge technology. It could be shown that the different stages of the BOD

12

1 Historical Development of Wastewater Treatment Processes

process find their technical realization at different stages of the activated sludge treatment process.The load rate is mainly responsible for different biological systems to develop. A special form of activated sludge process, the oxidation pond, was developed in the Netherlands by PASVEER(1958b, 1964) and found wide acceptance by small communities and by industry due to its simple construction and mode of operation.

7 Detergents: An Interplay of High SignificanceAt the end of the 1950s a problem arose which influenced the philosophy and wastewater treatment policy more than any technical invention: surface-active substances, washing powder. This problem had to be solved rather quickly, and it found a quick answer. The replacement of soaps by washing detergents transformed waste treatment plants, especially activated sludge plants, into lakes of foam every morning. Most of the detergents used at that time were biologically undegradable or only of low degradability and left the plants as they came in. They polluted rivers and led to foam formation everywhere. As there was no technical way to prevent foam formation, a political answer had to be found. It came from legislation demanding biodegradable detergents and outlawing others. Degradability of all newly applied chemicals in washing powder was required and degradation tests had to be performed to prove biodegradability. This first event of successfully outlawing certain chemicals opened the way for other steps to follow. In the years to come other laws were put into operation to limit the heavy metal ion content in sludges that were used as fertilizers in order to avoid heavy metal accumulation in plants. The so-called undegradable rest pollution and the chlorinated hydrocarbons were also critically considered and new standards for treatment efficiencies were set (see also Chapter 8, this volume). Violating these standards led to financial fines by state authorities.

The consequences of a generally more sensitive awareness of pollution were a reduction of wastewater quantities especially in industry by changes of production techniques. Wastes and wastewater could no longer be exported into public sewers free of cost. Disposal and purification in municipal wastewater treatment was charged according to the wastewater volume or the pollution freight. It was less expensive to reduce the waste and wastewater streams in the factory and to pretreat the residual amount within the factory than to hand it over to the public treatment plant as it was. In some cases waste was no longer waste but could be recycled as a secondary raw material either in the factory itself or within other industrial branches.This was especially enforced in Germany by the waste recycling law (KrWAbG, 1996: Kreislaufwirtschaftsgesetz, for details see Chapter 8, this volume). New markets had to develop selling the secondary raw material, including metals,glass, and paper, for which recycling in the past had already been enforced and hence the cycles were almost closed.

8 Treatment of Secondary PollutantsIn the early 1970s the scientific background for wastewater treatment was understood and optimized technologies were developed. The ideal plant for treatment of municipal wastewater was a sequence of a high-rate activated sludge basin for removal of the carbon compounds (detention time around 1 h) followed by a trickling filter for the purpose of ammonia oxidation to nitrate, degradation of organics with low biodegradability and polishing of the bacterial turbidity by ciliates. If a higher quality of treatment was required, a final carbon absorption unit could be added. The aeration basin could be split up into several smaller units to be brought into operation or taken out as required by the wastewater flow. To improve the economy of the plant. A primary sedimentation tank was sometimes considered unnecessary as most of the primary sludge consisted of bacteria, which stabilized the op-

10 Gaps, Lacks, and Outlook

13

eration of the aeration chamber. The surplus sludge was subjected to anaerobic digestion to produce biogas to power the aerators for oxygen introduction. This development was stopped by new requirements, arising from new (or already known, but not taken seriously) environmental problems. In the 1950s,phosphate removal was already required for wastewater treatment plants that fed their effluents into natural still waters in order to avoid eutrophication. In most cases chemical precipitation was applied. In the 1980s the eutrophication problem became more serious. The Baltic Sea and the North Sea, receiving most of the wastewater from England, the Netherlands, Germany, and Denmark developed dangerous algal blooms, caused by an oversupply of nitrogen and phosphate. The new problem had to be fought by improved technologies of wastewater treatment (e.g., ATV, 1998). The theoretical background for biological elimination of nitrogen compounds was well known. Nitrogen removal was based on oxidation followed by denitrification, using the nitrates as oxygen source for respiration. Elimination of phosphate was originally performed by chemical precipitation, but can also be obtained by accumulation of polyphosphates in bacteria (VANLOOSDRECHT al., et 1997). The combination of N and P removal from wastewater within the normal treatment plant led to difficulties. Both processes required carbon sources which were not available in the required amounts. Discussions on the optimal technical solution are still in progress.

complexity of the sludge population followed the early work of BUSWELL SOLLO and (1948) and revealed a better understanding of the ecological requirements, the physiology and biochemistry of the three mutualistically or syntrophically interacting groups (BRYANT, 1979; WOLINand MILLER,1982). With an understanding of the regulatory mechanisms of interaction it was possible to develop special technologies not only for sludge treatment, but also for treatment of highly concentrated liquid wastes. Up to that time these were fed either into activated sludge plants and caused bulking sludge formation or into trickling filter systems and caused clogging. Whereas sludge treatment was performed in completely stirred tank reactors (CSTR), sometimes with sludge recycling in the contact process (SCHROEPFER al., 1955), fixed-bed et and fluidized-bed anaerobic digesters were invented and used for treatment of highly polluted wastewater in the laboratory and in practice (for reviews, see SPEECE, 1983;SAHM, 1984; SWITZENBAUM, WINTER, 1984). Some 1983; types of wastewater could be stabilized by upflow anaerobic sludge blanket (UASB) reactors, which were developed in the Netherlands (LEZTINGA al., 1980) and which, due to the et pellet or granule formation, supplied optimal conditions for syntrophic growth of all members of the anaerobic population. In principle, a similar reactor was the Clarigester of Mc CARTY (1982).

10 Gaps, Lacks, and OutlookSumming up the history of wastewater treatment to date, it is characterized by a few simple facts. For more than half of the time scientific understanding lagged behind practical knowledge. The plants worked successfully, although the operators did not know what was the basis of their success. Civil engineers had taken over the task of wastewater treatment, they developed techniques, gained experience, and the results for most of the time satisfied the needs. Wastewater treatment for all this

9 A Second Step Forward in Anaerobic DigestionFor quite a few years no progress was achieved in anaerobic sludge treatment systems. After the installation of heated reactors, anaerobic sludge digestion seemed to be without further potential for improvement. Impulses for a change started in the 1970s and are still in progress. Detailed studies on the

14

1 Historical Development of Wastewater TreatmentProcesses

time was more a matter of art and personal skills of the plant operator than a result of scientific understanding. Engineers also successfully developed their own ideas and basic theories on biological processes, much to the advantage of their profession. However, increased demands on purification efficiencies required a better and more detailed understanding of the biological processes that were the basis of wastewater treatment. This was developed scientifically in the last 20-30 years by chemical engineers and biologists, and the development is still in et al., progress (e.g., VAN LIMBERGEN 1998).Todays situation is characterized by the fact that practice lags behind scientific knowledge. Not everything which is understood can be realized technologically - and even if it could be realized, there might be economic handicaps, because the costs would be too high. The main reason for insufficient treatment lies in the object itself. In most cases wastewater and its reactions are not defined like the chemicals and their reactions in a production process. For biological treatment wastewater is a sort of nutrition broth for the organisms and they work best under constant and steady conditions. Bacteria would, therefore, need an optimal physically and chemically defined environment and nutrients of known composition. None of these requirements are fully given in wastewater. Municipal wastewater, e.g., at every moment of the day is an integral of unknowns with respect to amount, nutrients, and even toxicants or inhibitors. The main problem of wastewater treatment arises from the quality of its nutrient composition. A good nutrition broth for bacteria should have a C/N ratio of about 12. In reality, the C/N ratio of municipal sewage is about 4, indicating a surplus amount of nitrogen. The same holds true for phosphate. Even for the simple task of biodegradation of carbohydrates conditions are not optimal. Under the new, very recent requirement of nitrogen and phosphorus removal during wastewater treatment, an appropriate carbon supply is even more deficient. No other field of biotechnology has to cope with such problems, arising from the wastewater itself which cannot easily be corrected due to the huge amounts that have to be treated.

Wastewater purification cannot be solved in treatment plants merely as an end-of-pipe technology. One has to look for solutions at an earlier stage of production. Substances that cause severe problems during wastewater treatment have to be kept out of the wastewater or must be separated and recovered at a stage where the concentration is still high enough for recovery. Only unavoidable pollutants should be released into the wastewater.

11 ReferencesARDERN, LOCKEIT, T. (1914), Experiments on E., W. the oxidation of sewage without the aid of filters, J. SOC.Chem. Ind. 33,523-539,1122-1124 (part I and part 11). ARDERN, LOCKEIT, T. (1915), Experiments on E., W. the oxidation of sewage sludge without the aid of filters,J. SOC. Chem. Ind. 34,937-943. ATV (1998), Biologische und weitergehende Abwasserreinigung,4th Edn. Berlin: Ernst & Sohn. BRYANT, F (1979), Microbialmethane production M. ! theoretical aspects,J. Anim. Sci. 48,193-202. BUSWELL, A., et al. (1928), Removal of colloids R. from sewage, The Illinois Engineer (April and May 1928). M., F. BUSWELL,A. SOLLO, W. (1948),The mechanism of methane formation, J. Am. Chem. SOC. 70, 1778-1780. DOHMANN, (1998), Weitergehende AbwasserreiM. nigung, Korrespondenz Abwasser 45,1240-1251. DUNBAR, PH.(1970), Leitfaden f i r die AbwasserW. reinigungsfiage. Munchen: Oldenbourg. FAIR, M., MOORE,E. G. W.,THOMA~,H.A., (1941), Jr. The natural purification of river muds and pullutional sediments, Sewage Works J. 13, 270-307, 756779,1209-1228. FAIR,G. M. et al. (1948), Sewage treatment at military installations,Sewage Works J. 20,52-95. FROHLING, (1910), Handbuch der IngenieunuisA. senschafien. Die Entwasserung der Stadte, Flu& verunreinigung und Behandlung stadtischer Abwusser. Leipzig: Verlag W. Engelsmann. J. GALLERT, WINTER, (1997),Mesophilic and therC., mophilic anaerobic digestion of source-sorted organic wastes: effect of ammonia on glucose degradation and methane formation, Appl. Microbiol. Biotechnol. 48,405-410. G.T., COLBAUGH, RAKJ. E., GARBER, F., OHARA, W. SIT, K. (1975),Thermophilicdigestion at the HyS. perion treatment plant,J. Water Pollut. Contr. Fed. 47,950-961.

11 ReferencesHALVORSON,0. (1936),Aero-filtration of sewage H. and industrial wastes, Water Works Sewage 9, 307-3 15. HARTMANN, (1992), Biologische AbwasserreiniL. gung. Berlin, Heidelberg, New York: SpringerVerlag. HOOVER, B. (1911),A method for determining the C. parts per million of dissolved oxygen consumed by sewage and sewage effluents, Columbus Sewage Works - Engineering News 65,311-312. HORLER, (1969), Entwurf Absetzbecken. Wiener A. Mitteilungen Wasser,Abwasser, Gewasser 4, C1. IMHOFF, R. (1979), Die Entwicklung der AbwasK. serreinigung und des Gewasserschutzes seit 1868, GWF WasserAbwasser 120,563-576. IMHOFF, R. (1998), Geschichte der AbwasserentK. sorgung, Korrespondenz Abwasser 45,32-38. IMHOFF, IMHOFF, R. (1993), Taschenbuch der K., K. Stadtentwasserung. 28th Edn. Munchen, Wien: Oldenbourg. KANDLER, WINTER, O., J.,TEMPER, (1981), MethU. ane fermentation in the thermophilic range, in: Energy from Biomass, 1st E.C. Conf. (PALZ, W., CHARTIER, HALL,D. O., Eds.), pp. 472477. P., London: Appl. Sci. Publ. KOLKWITZ, (1907),Uber die biologische SelbstreiR. nigung und Beurteilung der Gewasser, Hyg. Rundsch. 17,143-150. KOLKWITZ, (1950), Die Okologie der Saprobien, R. Schriftenr. Ver. Wasser-, Boden- und Lufthyg. 4, 1-64. KOLKWITZ, MARSSON, (1902), Grundsatze fur R., M. die biologische Beurteilung des Wassers nach seiner Flora und Fauna, Mitteilungen der koniglichen Priifungsanstalt fur Wasserversorgung und Abwasserbeseitigung zu Berlin 1,33-72. KOLKWITZ, MARSSON, (1908), Okologie der R., M. pflanzlichen Saprobien, Ber. Dtsch. Bot. Ges. %a, 505-519. KOLKWITZ, MARSSON, (1909), Okologie der R., M. tierischen Saprobien, Int. Rev. Ges. Hydrobiol. 2, 126-152. KrWAbG (1996), Kreislaufwirtschaftsgesetz: Gesetz zur Forderung der Kreislaufwirtschaft und Sicherung der umweltvertraglichen Beseitigung von Abfallen. Bundestagsdrucksache 1218084, Bundesratsdrucksache 654194,zuletzt geandert am 25. 08.1998, Bundesgesetzblatt I, p. 2455. A. S. LETTINGA, VAN FELSON, F. M., HOBMA, W., G., DE ZEEUM, W., KLAPWUK, (1980), Use of the A. upflow sludge blanket (UASB) reactor concept for the biological wastewater treatment, especially for anaerobic treatment, Biotech. Bioeng. 22, 299-334. LIEBMANN, (1960), Handbuch der FrischwasserH. und Abwasserbiologie, Vol. 1. Munchen: Oldenbourg.

15

LOCKETT, (1954),The evolution of the activated W.T. sludge process, J. Proc. Ind. Sewage Purit 19, 19-23. Mc CARTY, L. (1982), One hundred years of anP. aerobic treatment, in: Proc. 2nd Int. Symp. Anaerobic Digestion (HUGHES al., Eds.), pp. 3-22. et Amsterdam: Elsevier Biomedical. ODUM, P (1971), Fundamentals of Ecology. PhilaE. . delphia: Sauders. PASVEER, (1958a), Uber den Begriff OClLoad, A. Miinchener Beitrage zur Abwasser-, Fisch- und FluJ3biologie5,240ff. PASVEER, (1958b),Abwasserreinigung im OxydaA. tionsgraben, Bauamt und Gemeindebau 31,78ff. PASVEER, (1964), Uber den Oxydationsgraben, A. Schweiz. Z. Hydrol. 26,466ff. PEPENKOFER, (1890), Uber Verunreinigung und M. Selbstreinigung der Flusse, Schillings Journal f i r Gasbeleuchtung und Wasserversorgung 33, 415421. PEITENKOFER, (1891), Die Untersuchung der Isar M. auf FluBverunreinigung von Munchen bis Ismaning und uber die Selbstreinigung der Flusse, Deutsche Bauzeitung 25,109-112. PFEFFER, T. (1974), Temperature effects on anJ. aerobic digestion of domestic refuse, Biotechnol. Bioeng. 16,771-787. Royal Commission of Sewage Disposal (1908), First Report, Part III: Purification of sewage by treatment on land, pp. 137-158. SAHM, (1984), Anaerobic wastewater treatment, H. in: Advances in Biochemical EngineeringlBiotechnology 29 (FIECHTER,A., pp. 83-115. Berlin, Ed.), Heidelberg, New York Springer-Verlag. SCHROEPFER, J., FULLEN, J., JOHNSON, S., G. W. A. ZIEMKE, R., ANDERSON, J. (1955), The anN. J. aerobic contact process as applied to packing house wastes, Sewage Ind. Wastes 27,46&496. SICKERT, (1998), Kanalisationen im Wandel der E. Zeit, Korrespondenz Abwasser 45,22&246. SPEECE, E. (1983), Anaerobic biotechnology for R. industrial wastewater treatment, Environ. Sci. Technol.17,416A427A. STANBRIDGE,H. (1976), History of Sewage TreatH. ment in Britain. 5. Land Treatment.The Institute of Water Pollution Control, Maidstone. STREETER, W., PHELPS, B. (1925),A study of the H. E. pollution and natural purification of the Ohio river. 111. Factors concerned in the phenomena of oxidation and reaeration. Public Health Service Bull. 146,Washington, DC. SWITZENBAUM, S. (1983), Anaerobic fixed-film M. wastewater treatment, Enzyme Microb. Technol. 5,242-250. USEPA (1981), Process Design Manual for Land Treatment of Municipal Wastewater. Environmental Protection Agency,Washington, DC.

16

1 Historical Development of WastewaterTreatment Processes

VAN LIMEJERGEN, TOP, H.,

E. M., VERSTRAETE, W. (1998), Bioaugmentation in activated sludge: Current features and future aspects,Appl. Microbiol. Biotechnol. 50,1623. VAN LOOSDRECHT, C. M., HOOIJMANS, M., BRDM. C. JANOVIC, HEUNEN, J. (1997), Biological phosD., J. phate removal processes, Appl. Microbiol. Biotechnol. 48,289-296. WINTER, (1984), Anaerobic waste stabilization, J. Biotechnol.Adv. 2,75-99.

MILLER, L. (1982), Interspecies hyT. drogen transfer - 15 years later, ASM-News 48, 561-565. WUHRMANN, VON BEUST, .(1958), Zur Theorie K., F des Belebtschlammverfahrens. 11. Uber den Mechanismus der Elimination geloster organischer Stoffe aus dem Abwasser bei der biologischen fur Reinigung, Schweiz. 2. Hydrol. 20,311-330.WOLIN, J., M.

Biotechnology Second, Completely Revised EditionH.-J. Rehm and G. Reed copyright OWILEY-VCH Verlag GmbH, 1999

2 Bacterial Metabolism in Wastewater Treatment Systems

CLAUDIA GALLERT JOSEF WINTERKarlsruhe, Germany

1 Introduction 19 2 Decomposition of Organic Carbon Compounds in Natural and Man-Made Ecosystems 19 2.1 Basic Biology, Mass and Energy Balance of Aerobic Biopolymer Degradation 20 2.1.1 Mass and Energy Balance for Aerobic Glucose Respiration and Sewage Sludge Stabilization 21 2.1.2 Mass and Energy Balance for Anaerobic Glucose Degradation and Sewage Sludge Stabilization 23 2.2 General Considerations for the Choice of Aerobic or Anaerobic Wastewater Treatment Systems 24 2.3 Aerobic or Anaerobic Hydrolysis of Biopolymers - Kinetic Aspects 25 2.4 Hydrolysis of Cellulose by Aerobic and Anaerobic Microorganisms Biological Aspects 25 2.5 Biomass Degradation in the Presence of Inorganic Electron Acceptors and by an Anaerobic Food Chain 27 2.6 The Role of Molecular Hydrogen and of Acetate During Anaerobic Biopolymer Degradation 29 2.7 Anaerobic Conversion of Biopolymers to Methane and CO, 30 2.7.1 The Anaerobic Degradation of Carbohydrates in Wastewater 30 2.7.2 The Anaerobic Degradation of Protein 32 2.7.3 The Anaerobic Degradation of Neutral Fat and Lipids 34 2.8 Competition of Sulfate Reducers with Methanogens in Methane Reactors 35 2.9 Biogas Amounts and Composition of Biogas During Fermentation of Carbohydrates, Protein, and Fat 36 3 Nitrogen Removal During Wastewater Treatment 37 3.1 Ammonification 37 3.2 Nitrification of Ammonia 38 3.2.1 Autotrophic Nitrification 38 3.2.2 Heterotrophic Nitrification 38

18

2 Bacterial Metabolism in Wastewater Treatment Systems

4 5

6 7 8

3.3 Denitrification - Nitrate Removal from Wastewater 39 3.4 Combined Nitrification and Denitrification 39 3.5 Anaerobic Ammonia Oxidation (AnammoxB) 40 Biological Phosphate Removal 41 Biological Removal, Biotransformation, and Biosorption of Metal Ions from Contaminated Wastewater 42 5.1 Sulfate Reduction under the Aspect of Metal Ion Precipitation 44 Aerobic and Anaerobic Degradation of Xenobiotic Substances 44 Bioaugmentation in Wastewater Treatment Plants for the Degradation of Xenobiotics 46 References 48

List of AbbreviationsMW BOD COD TOC TCA HRT NADH2 FdH, atm molecular weight biological oxygen demand chemical oxygen demand total organic carbon tricarboxylic acid hydraulic retention (residence) time reduced nicotinamide adenosine dinucleotide reduced ferredoxin atmospheres half saturation constant

K s

2 Decomposition of Organic Carbon Compounds in Natural and Man-Made Ecosystems

19

1 IntroductionWater that has been used by man and is disposed into a receiving water body with altered physical and/or chemical parameters is per definition referred to as wastewater. If only the physical parameters of the water were changed, e.g., resulting in an elevated temperature after use as a coolant, treatment before final disposal into a surface water may require only cooling close to its initial temperature. If the water, however, has been contaminated with soluble or insoluble organic or inorganic material, a combination of mechanical, chemical, and/or biological purification procedures may be required to protect the environment from periodic or permanent pollution or damage. For this reason legislation in industrialized and in many developing countries has reinforced environmental laws that regulate the maximum of allowed residual concentrations of carbon, nitrogen, and phosphorous compounds in the purified wastewater, before it is disposed into a river or into any other receiving water body (for details, see Chapter 3,10, 13, 14, this volume). However, the reinforcement of these laws is not always very strict. It seems to be related to the economy of the respective country and thus differs significantly between wealthy industrialized and poor developing countries. In this chapter basic processes for biological treatment of waste or wastewater to eliminate organic and inorganic pollutants are summarized.

2 Decomposition of Organic Carbon Compounds in Natural and Man-Made EcosystemsCatabolic processes of microorganisms, algae, yeasts, and lower fungi are the main pathways for a total or at least a partial mineralization/decomposition of bioorganic and organic compounds in natural or man-made environments. Most of this material is derived directly or indirectly from recent plant or animal bio-

mass. It originates from carbon dioxide fixation via photosynthesis (+plant biomass), from plants that served as animal feed (+detritus, feces, urine, etc.) or from fossil, biologically or geochemically transformed biomass (+peat, coal, oil, natural gas). Even the carbon portion of some xenobiotics may be tracked back to a biological origin, namely if these substances were produced from oil, natural gas, or coal. Only due to the fact that the mineralization process for carbonaceous material of decaying plant and animal biomass in nature under anaerobic conditions with a shortage of water was incomplete, the formation of fossil oil, natural gas, and coal deposits from biomass through biological and/or geochemical transformation occurred. The fossil carbon of natural gas, coal, and oil enters the atmospheric CO, cycle again, as soon as these compounds are incinerated as fuels or for energy generation in industry and private households. The biological degradation of recent biomass and of organic chemicals during solid waste or wastewater treatment proceeds either in the presence of molecular oxygen by respiration, under anoxic conditions by denitrification, or under anaerobic conditions by methanogenesis or sulfidogenesis. Respiration of soluble organic compounds or of extracellularly solubilized biopolymers such as carbohydrates, proteins, fats or lipids in activated sludge systems leads to the formation of carbon dioxide, water, and a significant amount of surplus sludge. Some ammonia and H,S may be formed during degradation of sulfur-containing amino acids or heterocyclic compounds. Oxygen must either be supplied by aeration or by injection of pure oxygen. The two process variants differ mainly in their capacity for oxygen transfer and the stripping efficiency for carbon dioxide from respiration. Stripping of carbon dioxide is necessary to prevent a drop of pH and to carry out heat energy. Respiration with chemically bound oxygen supplied in the form of nitrate or nitrite in the denitrification process abundantly yields dinitrogen. However, some nitrate escapes the reduction to dinitrogen in wastewater treatment plants and contributes about 2% of the total N,O emission in Germany (SCHON al., 1994; et Chapter 14,this volume). Denitrifiers are aerob-

20

2 Bacterial Metabolism in Wastewater TreatmentSystems

ic organisms that switch their respiratory metabolism to the utilization of nitrate or nitrite as terminal electron acceptors, if grown under anoxic conditions. Only if the nitrate in the bulk mass has been used completely the redox potential will be low enough for growth of strictly anaerobic organsims,such as methanogens or sulfate reducers. If in sludge flocs of an activated sludge system anaerobic zones were allowed to form, e.g., by limitation of the oxygen supply, methanogens and sulfate reducers may develop in the center of sludge flocs and form the traces of methane and hydrogen sulfide found in the off-gas. Under strictly anaerobic conditions soluble carbon compounds of wastes and wastewater are degraded step by step to methane, CO,, NH3, and H,S via a syntrophic interaction of fermentative and acetogenic bacteria with methanogens or sulfate reducers. The complete methanogenic degradation of biopolymers or of monomers via hydrolydfermentation, acetogenesis, and methanogenesis can proceed only at a low H, partial pressure, which is maintained mainly by interspecies hydrogen transfer. Interspecies hydrogen transfer is facilitated, if acetogens and hydrogenolytic methanogenic bacteria are arranged in a close spatial neigborhood in flocs or in a biofilm at short diffusion distances. The reducing equivalents for carbon dioxide reduction to methane or sulfate reduction to sulfide are derived from the fermentative metabolism, e.g., of clostridia or Eubacterium sp., from p-oxidation of fatty acids, or the oxidation of alcohols. Methane and CO, are the main products in anaerobic environments where sulfate is absent, whereas sulfide and CO, are the main products if sulfate is present.

2.1 Basic Biology, Mass and Energy Balance of Aerobic Biopolymer DegradationIn order to make soluble and insoluble biopolymers - mainly carbohydrates, proteins, or lipids - accessible for respiration by bacteria, the macromolecules must be hydrolyzed by exoenzymes, which often are only produced and excreted after contact with respective in-

ductors. The exoenzymes adsorb to the biopolymers and hydrolyze them to monomers or at least to oligomers. Only soluble, low molecular-weight compounds (e.g., sugars, disaccharides, amino acids, oligopeptides, glycerol, fatty acids) can be taken up by microorganisms and are metabolized to serve for energy production and cell multiplication. Once taken up, degradation via glycolysis (sugars, disaccharides, glycerol), hydrolysis and deamination (amino acids, oligopeptides), or hydrolysis and p-oxidation (phospholipids, long-chain fatty acids) proceeds in the cells. Metabolism of almost all organic compounds leads to the formation of acetyl-CoA as the central intermediate, which is either used for biosyntheses, excreted as acetate, or oxidized to CO, and reducing equivalents in the tricarboxylic acid (TCA) cycle. The reducing equivalents are respired with molecular oxygen in the respiration chain. Only the energy of a maximum of 2 mol of anhydridic phosphate bonds of ATP is conserved during glycolysis of 1mol of glucose through substrate chain phosphorylation. Further 2 mol of ATP are formed during oxidation of 2 mol of acetate in the TCA cycle, whereas 34 mol ATP are formed by electron transport chain phosphorylation in the respiration chain with oxygen as the terminal electron acceptor. During oxygen respiration reducing equivalents react with molecular oxygen in a controlled Knallgas reaction. When carbohydrates are respired by aerobic bacteria overall about one third of the initial energy content is lost as heat, and two thirds are conserved biochemically in 38 phosphoanhydride bonds of AT? In activated sludge reactors or in wastewater treatment ponds, which are not loaded with highly concentrated wastewater, wall irradiation and heat losses with the off-gas stream of aeration into the atmosphere prevent self-heating. In activated sludge reactors for treatment of highly concentrated wastewater, however, self-heating up to the thermophilic temperature range may occur if the wastewater is warm in the beginning, the hydraulic retention time for biological treatment is short (short aeration time), and the air or oxygen stream for aeration is restricted to just supply sufficient oxygen for a complete oxidation of the pollutants (small aeration volume).

2 Decomposition of Organic Carbon Compounds in Natural and Man-Made Ecosystems

21

The conserved energy in the terminal phospho-anhydride bond of ATE formed during substrate chain and oxidative phosphorylation of proliferating bacteria is partially used for maintenance metabolism of the existing cells and partially serves for cell multiplication. Partitioning between both is not constant, but depends on the nutritional state. In highly loaded activated sludge reactors with a surplus or at least a non-growth-limiting substrate supply approximately 50% of the substrate are respired in the energy metabolism of the cells and 50% serve as a carbon source for cell growth (Tab. 1). The biochemically conserved energy must be dissipated to serve for the maintenance metabolism of existing cells and for cell growth. If the substrate supply is growth limiting, e.g., in a low-loaded aerobic treatment system a higher proportion of ATP is consumed for maintenance, representing the energy proportion that bacteria must spend for non-growthassociated cell survival metabolism, and less energy is available for growth. Overall, more of the substrate carbon is respired and the proportion of respiration products to surplus sludge formation is higher, e.g., around 70: 30% (Tab. 1). In a trickling filter system apparently an even higher proportion of the substrate seems to be respired. This might be due to protozoa grazing off part of the biofilm. For comparison, Tab. 1 also summarizes the carbon dissipation for anaerobic methanogenic degradation. Only about 5% of the fermentable substrate are used for cell growth (surplus sludge formation) in anaerobic reactors, whereas 95% are converted to methane and CO,, and most of the energy of the substrates is conserved in the fermentation products.

2.1.1 Mass and Energy Balance for Aerobic Glucose Respiration and Sewage Sludge StabilizationIn most textbooks of microbiology respiration of organic matter is described exemplarily by Eq. 1, with glucose used as a model substance. Except for an exact reaction stoichiometry of the oxidative metabolism, mass and energy dissipation, if mentioned at all, is not quantified. Both parameters are, however, very important for activated sludge treatment plants. The surplus sludge formed during wastewater stabilization requires further treatment, causes disposal costs, and - in the long run - may be an environmental risk, whereas heat evolution during unevenly high-loaded aerobic treatment may shift the population towards more thermotolerant or thermophilic species and thus, at least for some time, may decrease the process efficiency.1 Mol C,5H,,O, 6 M0102 + 6 Mol CO, 6 Mol H,O Heat Energy

+

+

+

(1)

If 1 mol of glucose (MW = 180 g) is degraded in an activated sludge system at a high BOD loading rate (e.g., >0.6 kg m-3 d- BOD), approximately 0.5 mol (90g) are respired to CO, and water by consumption of 3 mol of 0, (96 g), releasing 19 mol of ATP (Fig. 1). The other 0.5 mol of glucose (90 g) are converted to pyruvate via one of three glycolytic pathways, accompanied by the formation of 0.5-1 mol ATP. Pyruvate or its subsequent metabolic products, e.g., acetate or dicarboxylic acids, are directly taken as carbon substrates for cell multiplication and surplus biomass formation.

Tab. 1. Carbon Flow during Aerobic Degradation in an Activated Sludge System under a) Saturating or b) Limiting Substrate Supply and during Anaerobic Degradation

(A) Aerobic degradation: (a) Saturating substrate supply = high-load condition 1 Unit Substrate Carbon + 0.5 Units COPCarbon + 0.5 Units Cell Carbon (b) Limiting substrate supply = low-load condition 1 Unit Substrate Carbon + 0.7 Units CO, Carbon + 0.3 Units Cell Carbon (B) Anaerobic degradation: 1 Unit Substrate Carbon 0.95 Units (C02+ CH,) Carbon + 0.05 Units Cell Carbon+

a

Estimated from surplus sludge formation in different wastewater treatment plants

22

2 Bacterial Metabolism in Wastewater Treatment Systems

= 96 g1 Mol Glucose

hI\50 % = 1435 kJ Glycolysis

I3 Mol CO:, + 3 Mol HZ0 = 186 g total 19MOlATP\

I

I = 2870 kJ

- 1 Mol ATP144kJ

Biochemical Heat energy conservation 890 kJ I Mol Glucose 1 4 4 k ; IATP l+ 880 kJ 20 M o A T P ]=31%

I

I

kJ in substrates

IGrowth

\

\

,

I

90 g Biomass 22 kJ ig 1980 kJ I Mol Glucose = 69%

Fig. 1. Mass and energy dissipation during glucose respiration at pH 7.

A maximum amount of 20 mol ATP is thus available for growth and maintenance (Fig. 1). At a pH of 7 about 44 kJ of energy are available for growth per mol of ATP hydrolyzed to et ADP and inorganic phosphate (THAUER al., 1977). For an average molar growth yield of aerobes of 4.5 g per mol ATP (LuI, 1998) 90 g biomass can be generated from 180 g glucose. If the incineration energy per g of cell dry mass was 22 kJ, about 890 kJ (2,870 - 980 kJ) are lost as heat during respiration (Fig. 1). The energy loss is the sum of heat losses during respiration and cell growth. At a low BOD loading rate the proportion of glucose respired in relation to the proportion of glucose fixed as surplus biomass may be shifted. Up to 0.7 mol (126 g) of glucose may be oxidized to COz, requiring 4.2 mol of oxygen (134.4 g Oz).Thus, for respiration of 1mol of glucose different amounts of oxygen may be consumed, depending on the loading rate of the wastewater treatment system and different amounts of carbon dioxide and of surplus sludge formed (Fig. 1,Tab. 1). The energy and carbon balance deduced above can be analogously transferred to aerobic stabilization of raw sewage sludge. If the initial dry matter content is around 36 g L-' (average organic dry matter content of sewage sludge) and if a biodegradability of 50% within the residence time in the sludge reactor is

obtained, about 9 g L-l of new biomass are formed and thus 27 g L-l(36 - 18 9) remain in the effluent. The released heat energy is approximately 89 kJ per L reactor content. For an estimation of the theoretical temperature rise this amount of heat energy must be divided by 4,185 kJ (specific energy requirement for heating 1L of H,O from 14.5-15.5 "C). Thus, by respiration of 1 8 g L-' organic dry matter the reactor temperature would increase by 21.3 "C within the residence time required for degradation (I 16 h), provided that no heat energy is lost. A great proportion of the heat energy is, however, transferred via the liquid phase to the aeration gas and stripped out, whereas a smaller proportion is lost via irradiation from the reactor walls. Since air with almost 80% "ballast nitrogen" is normally used as a source of oxygen in aeration ponds or activated sludge reactors, the heat transfer capacity of the offgas is high enough to prevent a significant increase of the wastewater temperature. Thus, ambient or at least mesophilic temperatures can be maintained. An increasing temperature of several "C would lead to a shift of the population in the reactor and - at least temporarily - would result in reduced process stability, whereas an only slightly increased temperature of a few "C might simply stimulate the metabolic activity of the prevalent mesophilic

+

2 Decomposition of Organic Carbon Compounds in Natural and Man-Made Ecosystems

23

population. In practice in activated sewage sludge systems no self-heating is observed due to only about 50% degradability and a complete heat transfer with the off-gas into the atmosphere at a retention time of more than 0.5 d. If, however, wastewater from a dairy plant or from a brewery with a similar COD concentration, but with almost 100% biodegradable constituents would be stabilized with pure oxygen twice as much heat would evolve, leading to a theoretical temperature rise of 57 "C. Self-heating is observed, since the heat loss via much less off-gas is significantly lower and, due to higher reaction rates than with sewage sludge, the heat is generated during a shorter time span (shorter retention time).

2.1.2 Mass and Energy Balance for Anaerobic Glucose Degradation and Sewage Sludge StabilizationFor anaerobic wastewater or sludge treatment oxygen must be excluded to maintain the low redox potential that is required for survival and metabolic activity of the acetogenic, sulfidogenic, and methanogenic population. Hydrolysis of polymers, uptake of soluble or solubilized carbon sources and the primary metabolic reactions of glycolysis up to pyru-

vate and acetate formation seem to proceed identically or are at least analogous in aerobic and anaerobic bacteria. Whereas aerobes oxidize acetate in the TCA cycle and respire the reducing equivalents with oxygen, anaerobes, such as Ruminococcus sp., Clostridium sp., or Eubacterium sp., either release molecular hydrogen or transform pyruvate or acetate to highly reduced metabolites, such as lactate, succinate, ethanol, propionate, n-butyrate, etc. For further degradation within the anaerobic food chain these reduced metabolites must be oxidized anaerobically by acetogenic bacteria. Since the anaerobic oxidation of propionate or n-butyrate by acetogenic bacteria is obligately accompanied by hydrogen production, but is only slightly exergonic under conditions of a low H2 partial pressure (BRYANT, 1979), acetogens can only grow when the hydrogen is consumed by hydrogen-scavenging organisms, such as methanogens or sulfate reducers. During anaerobic degradation of 1 mol glucose approximately 95% of the glucose carbon is used for biogas formation (171 g A 127.7 L CH,+CO,) and only about 5% of the substrate carbon (9g) converted to biomass (Tab. 1). Much less heat energy is released during the anaerobic metabolism as compared to aerobic respiration (131 kJ mol-' versus 890 kJ mol-' during respiration) and the biogas contains almost 90% of the energy of the

Fermentatio