Activated Carbon for Water and Wastewater Treatment E-Book

Ferhan Cecen

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 722

Veröffentlichungsjahr: 2011

Beschreibung

This monograph provides comprehensive coverage of technologies which integrate adsorption and biological processes in water and wastewater treatment. The authors provide both an introduction to the topic as well as a detailed discussion of theoretical and practical considerations. After a review of the basics involved in the chemistry, biology and technology of integrated adsorption and biological removal, they discuss the setup of pilot- and full-scale treatment facilities, covering powdered as well as granular activated carbon. They elucidate the factors that influence the successful operation of integrated systems. Their discussion on integrated systems expands from the effects of environmental to the removal of various pollutants, to regeneration of activated carbon, and to the analysis of such systems in mathematical terms. The authors conclude with a look at future needs for research and develoment. A truly valuable resource for environmental engineers, environmental and water chemists, as well as professionals working in water and wastewater treatment.

Leseprobe

Contents

Preface

List of Abbreviations

Acknowledgement

CHAPTER 1: Water and Wastewater Treatment: Historical Perspective of Activated Carbon Adsorption and its Integration with Biological Processes

1.1 Historical Appraisal of Activated Carbon

1.2 General Use of Activated Carbon

1.3 Application of Activated Carbon in Environmental Pollution

CHAPTER 2: Fundamentals of Adsorption onto Activated Carbon in Water and Wastewater Treatment

2.1 Activated Carbon

2.2 Adsorption

2.3 Activated Carbon Reactors in Water and Wastewater Treatment

2.4 Activated Carbon Regeneration and Reactivation

CHAPTER 3: Integration of Activated Carbon Adsorption and Biological Processes in Wastewater Treatment

3.1 Secondary and Tertiary Treatment: Progression from Separate Biological Removaland Adsorption to Integrated Systems

3.2 Fundamental Mechanisms in Integrated Adsorption and Biological Removal

3.3 Integration of Granular Activated Carbon (GAC) into Biological Wastewater Treatment

3.4 Integration of Powdered Activated Carbon (PAC) into Biological Wastewater Treatment

3.5 Biomembrane Operation Assisted by PAC and GAC

3.6 Observed Benefits of Integrated Systems

3.7 Regeneration of PACT and BAC Sludges

CHAPTER 4: Effect of Activated Carbon on Biological Treatment of Specific Pollutants and Wastewaters: Laboratory- and Pilot-Scale Studies

4.1 Treatment of Industrial Wastewaters

4.2 Removal of Specific Chemicals

4.3 Landfill Leachate Treatment

CHAPTER 5: Combination of Activated Carbon with Biological Wastewater Treatment at Full-Scale

5.1 Full-Scale PACT Systems

5.2 Biological Activated Carbon (BAC) Filtration at Full Scale

CHAPTER 6: Modeling the Integration of Adsorption with Biological Processes in Wastewater Treatment

6.1 Modeling of GAC Adsorbers with Biological Activity

6.2 Modeling of the PACT Process

CHAPTER 7: Bioregeneration of Activated Carbon in Biological Treatment

7.1 Mechanisms of Bioregeneration

7.2 Offline Bioregeneration

7.3 Concurrent (Simultaneous) Bioregeneration in PACT and BAC Systems

7.4 Dependence of Bioregeneration on the Reversibility of Adsorption

7.5 Other Factors Affecting Bioregeneration

7.6 Determination of Bioregeneration

7.7 Bioregeneration in Anaerobic/Anoxic Systems

7.8 Models Involving Bioregeneration of Activated Carbon

CHAPTER 8: Combination of Activated Carbon Adsorption and Biological Processes in Drinking Water Treatment

8.1 Introduction

8.2 Rationale for Introduction of Biological Processes in Water Treatment

8.3 Significance of Organic Matter in Water Treatment

8.4 Removal of NOM in Conventional Water Treatment

8.5 Use of Activated Carbon in Water Treatment

8.6 Biological Activated Carbon (BAC) Filtration

8.7 Adsorption and Biodegradation Characteristics of Water

CHAPTER 9: Removal of NOM, Nutrients, and Micropollutants in BAC Filtration

9.1 Removal of Organic Matter

9.2 Factors Affecting the Performance of BAC Filtration

9.3 Performance of BAC Filters: Organics Removal

9.4 Performance of BAC Filters: Nutrient Removal

9.5 Removal of Micropollutants from Drinking Water in BAC Systems

9.6 Removal of Ionic Pollutants in BAC Filtration

9.7 Integration of PAC and GAC into Biological Membrane Operations

9.8 Integration of GAC into Groundwater Bioremediation

9.9 Biomass Characteristics in BAC Filtration

CHAPTER 10: BAC Filtration Examples in Full-Scale Drinking Water Treatment Plants

10.1 Limits for BDOC and AOC as Indicators of Re-growth Potential in Water Distribution

10.2 BAC Filtration Experiences in Full-Scale Surface Water Treatment

10.3 New Approaches in the Evaluation of Ozonation and BAC Filtration

10.4 BAC Filtration Experiences in Full-Scale Groundwater Treatment

CHAPTER 11: Review of BAC Filtration Modeling in Drinking Water Treatment

11.1 Substrate Removal and Biofilm Formation

11.2 Modeling of BAC Filtration

CHAPTER 12: Concluding Remarks and Future Outlook

12.1 Overview of Applications in Wastewater and Water Treatment: PACT and BAC Systems

12.2 Further Research on Removal Mechanisms and Micropollutant Elimination

12.3 Further Research on Regeneration of Activated Carbon

Index

Activated Carbon for Water and Wastewater Treatment

Integration of Adsorption and Biological Treatment

Ferhan Çeçen and Özgür Akta

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The Authors

Prof. Ferhan Çeçen

Bogazici University

Inst. of Environmental Sciences

34342 Istanbul

Turkey

Dr. Özgür Akta

TUBITAK-MRC

Environment Institute

41470 Gebze, Kocaeli

Turkey

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Preface

Purpose of the Book

The subject of the book is the ‘integrated application of activated carbon adsorption with biological processes in water and wastewater treatment.’ The enhancement of biological mechanisms by activated carbon adsorption merits serious study since it has been shown to be an effective method for the elimination of various organic and inorganic environmental pollutants.

During my studies over many years on adsorption and biodegradation, alone or together with my students, I realized with some surprise that the existing books on these subjects were either addressing activated carbon adsorption or biological treatment, but not both together in an integrated manner. I also realized that few books contained single chapters that dealt with either PACT or BAC processes. While invaluable work had been published in the form of papers or chapters, all these addressed some specific aspect of integrated treatment, and there was no comprehensive book that gave a detailed account of the different aspects of integrated adsorption and biological treatment. Thus, my idea to write this book originated from my own needs, and the idea was then supported by the book’s co-author, Özgür Akta. Our goal in writing the book is to provide the reader with a document that attempts to present in a unified way most of the material to date on this subject.

The project necessitated an extensive literature survey spanning a period of approximately 40 years, from the beginning of integrated treatment in the 1970s to the present day. As a result, the book was inevitably expanded to include a wide range of topics. It covers the positioning of various integrated adsorption and biological removal treatment systems within the water and wastewater treatment train, describes how various pollutants can be removed, highlights the mechanisms that underlie the improved performance in small- and full-scale integrated systems, and extensively discusses to what extent pollutants can be eliminated from water or wastewater and what other side advantages are to be expected. However, for a full understanding, only to look at the underlying mechanisms and extent of removal would be inadequate. Therefore, we have also attempted to describe and analyze suspended- or attached-growth reactors involving PAC or GAC in mathematical terms. In this context, models pertaining to integrated water and wastewater treatment systems are also discussed. Results from small- and full-scale water and wastewater treatment are best understood if mechanisms and mathematical analyses of integrated adsorption and biological treatment systems are considered jointly.

In preparing this book, the assumption was made that the reader is equipped with basic knowledge of environmental science and technology, particularly the basics of adsorption and biological treatment. Thus, the book is not an elementary textbook, but is intended for people who are already involved with adsorption and/or biological processes. The principal readership of this book will be in the academic community, to whom the book will hopefully be useful. Some parts of the book may also be used for teaching of graduate level courses in environmental and chemical engineering.

The hope is that the book will appeal to people from both science and engineering disciplines. For scientists, who generally deal with fundamentals, it may be of interest to see the true value of integrated processes in practice. To practicing people, such as engineers operating water or wastewater treatment plants, who are mostly concerned with results, the book should provide a fundamental understanding of the main mechanisms in integrated adsorption and biotreatment. It should also serve as a work of reference for all those engaged in institutions relating to water quality, activated carbon production, and activated carbon adsorption.

Organization of the Book

Chapter 1 provides a brief overview of the history of activated carbon and its use in the water and wastewater treatment sector, and also gives a brief introduction to integrated adsorption and biological treatment.

Chapter 2 is an introductory chapter covering the fundamentals of adsorption and adsorption systems used in water and wastewater treatment. Since the basics of adsorption and adsorber systems are well explained in the existing literature, the chapter focuses on the main aspects of adsorbers that are also integrated into biological systems.

Chapters 3–7 are mainly devoted to the integration of activated carbon adsorption with biological processes in wastewater treatment.

Chapter 3 addresses the integration of activated carbon in biological wastewater treatment. It first highlights the progression from adsorption to concurrent adsorption and biological removal in wastewater treatment. The basic idea in this chapter is to give a clear idea of the main mechanisms underlying the observed positive effects in integrated systems. After this, the improvement of organics removal, removal of volatile pollutants, nitrification, denitrification, and anaerobic digestion in integrated systems are discussed. The chapter also includes the impact of activated carbon on biological sludge. Following the basic mechanisms, two basic processes are discussed that currently integrate the merits of activated carbon adsorption and biological removal in a single unit: the suspended-growth PACT process and the attached-growth biological activated carbon (BAC) process. Another specific application, the coupling of membrane bioreactors (MBRs) with activated carbon, is also considered.

Chapter 4 concentrates on the effect of activated carbon in biological removal of pollutants. This chapter focuses on the removal of specific compounds as well as the extent of pollutant reduction in various types of wastewater, such as industrial wastewaters and landfill leachates, which contain many inhibitory, toxic, slowly degradable or nonbiodegradable pollutants.

Complementary to Chapter 4, which discusses the results and experiences from laboratory- and pilot-scale studies, Chapter 5 provides examples of full-scale PACT and BAC applications in wastewater treatment.

Chapter 6 addresses the modeling of combined adsorption and biological wastewater treatment systems. Relevant background information on mass transport, biodegradation, and adsorption processes is discussed in order to throw light on the complex interactions between adsorption and biological removal. The chapter then looks at the basic models that have been developed for attached-growth (BAC) and suspended-growth (PACT) systems.

Chapter 7 deals with bioregeneration of activated carbon, a very important phenomenon in all integrated systems. Bioregeneration is defined as the renewal of the adsorptive capacity of activated carbon by microorganisms in order to provide further adsorption. This chapter provides a comprehensive analysis of various aspects of GAC and PAC bioregeneration and the models describing bioregeneration.

The second part of the book, extending from Chapter 8 to 11, focuses on issues related specifically to drinking water treatment and addresses the integration of activated carbon adsorption with biological removal in this field.

Chapter 8 addresses the rationale for the introduction of biological processes into water treatment in general, highlighting the development and role of Biological Activated Carbon (BAC) Filtration. The significance of Natural Organic Matter (NOM) in drinking water treatment is discussed. This chapter also includes detailed information about the importance of ozonation, a treatment step that often precedes BAC filtration. The adsorption and biodegradation potential of raw and ozonated waters are discussed, as these properties have a strong influence on subsequent BAC filtration.

Chapter 9 deals with the removal of NOM, nutrients, and various organic and inorganic micropollutants in BAC filtration. Both removal mechanisms and the extent of removal are discussed. The chapter also includes a section on the characteristics and determination of biomass in BAC filters and on the safety of finished water.

Chapter 10 addresses the full-scale application of BAC filtration of drinking water. The chapter first discusses the limits set for the re-growth potential of water. It covers experiences from different water treatment plants and exemplifies the extent of the reduction of organic and inorganic pollutants that can be achieved.

Chapter 11 addresses the modeling of BAC filtration in drinking water treatment. Since the fundamentals of mass transport, biodegradation, and adsorption are discussed in Chapter 6, the only issues covered in this chapter are those pertaining specifically to drinking water treatment. The chapter provides an overview of drinking water biofiltration models that have been developed to describe NOM and micropollutant removal.

Chapter 12 provides an overview of some of the issues discussed in the book, and highlights the need for further research on integrated adsorption and biological removal in water and wastewater treatment.

Suggestions for the Reader

In writing this book, the attempt was made to treat each chapter as a stand-alone topic while at the same time not impairing the cohesiveness of the whole subject. Therefore, in almost all chapters, frequent cross-referencing to other chapters is provided.

Bearing in mind that not all chapters are necessary for every reader, the following suggestions are made:

For a reader who wants to acquire a general idea about adsorption and its historical evolution in combination with biological processes in water and wastewater treatment, it may be sufficient to concentrate on Chapter 1.

Chapter 2 presents the fundamentals of adsorption and the use of adsorbers in the water/wastewater field. It can be read independently of other chapters and is perfectly suited to a reader who is interested in adsorption only, and not in biological processes.

Chapter 3 is the key to the comprehension of the chapters that follow, and the reader who wishes to gain a fundamental understanding of the mechanisms and synergism associated with integrated adsorption and biological removal is strongly advised to study it.

The reader who is only interested in wastewater treatment and wants to focus on operational and practical aspects of integrated adsorption and biological removal needs to read Chapters 2, 3, 4 and 5 only.

To acquire further insight into the mechanism and mathematical description of integrated adsorption and biological removal, the reader is advised to refer also to Chapters 6 and 7, which address modeling of integrated systems and bioregeneration of activated carbon, respectively.

In general, the reader who is interested in the combination of activated carbon adsorption with biological processes in drinking water treatment should refer to Chapters 8 to 11. For this reader it would also be helpful to read Chapter 3 first. Chapter 8 provides general information on BAC filtration in drinking water treatment, and detailed information on this subject is provided in Chapter 9. The reader who is interested in practical aspects of BAC filtration and wants to learn about possible full-scale applications of the process should refer to Chapter 10, while the reader who is interested in the mathematical formulation of BAC filtration of drinking water is advised to examine the models presented in Chapter 11, but, before this, it would be most useful to read Chapter 6.

Ferhan Çeçen

List of Abbreviations

16S rDNASmall Sub-Unit (SSU) rDNA16S rRNASmall Sub-Unit (SSU) rRNA2,4-D2,4-Dichlorophenoxyacetate2-FB2-Fluorobenzoate5-Fu5-FluorouracilABSAcrylonitrile Butadiene StyreneACActivated CarbonAFLPAmplified Fragment Length PolymorphismAMOAmmonia MonooxygenaseamoAAmmonia Monooxygenase geneAOBAmmonia Oxidizing BacteriaAOCAssimilable Organic CarbonAOClAdsorbable Organic ChlorineAOPAdvanced Oxidation ProcessAOXAdsorbable Organic Xenobiotics (Halogens)APHAAmerican Public Health AssociationASActivated SludgeASTMAmerican Society for Testing and MaterialsATPAdenosine TriphosphateB(GAC)Biological Granular Activated CarbonBACBiological(ly) Activated Carbon (used primarily for granular activated carbon)BAC-FBRFluidized-Bed Reactor containing biological GAC (BAC)BAFBiological Aerated FilterBASMBiodegradation/Adsorption–Screening ModelBDOCBiodegradable Dissolved Organic CarbonBETBrunauer, Emmett, TellerBFACBioFilm on Activated Carbon (Model)BiBiot NumberBioMACBiological Membrane Assisted Carbon FiltrationBKMEBleached Kraft Pulp Mill EffluentBODBiochemical Oxygen DemandBOMBiodegradable Organic MatterBPBromophenolBPABisphenol ABSFBiological Rapid Sand FiltrationBTEXBenzene, Toluene, Ethylbenzene, XyleneBTXBenzene, Toluene, XyleneBVBed VolumeCAAChloroacetaldehydeCBChlorobenzeneCBZCarbamazepineCFContinuous-FlowCMFContinuous MicrofiltrationCMF-SContinuous Microfiltration-SubmergedCODChemical Oxygen DemandCPChlorophenolCSTRContinuous-flow Stirred Tank ReactorCURCarbon Usage RateCytrCytarabineDaDamköhler NumberDAFDissolved Air FlotationDBPDisinfection By-ProductDCADichloroethaneDCEDichloroetheneDCFDiclofenacDCMDichloromethaneDCPDichlorophenolDgSolute Distribution ParameterDNPDinitrophenolDODissolved OxygenDOCDissolved Organic CarbonDOMDissolved Organic MatterDTPADiethylene Triamine Pentaacetic AcidDZPDiazepamE217 β-EstradiolE3EstriolEBCTEmpty-Bed Contact TimeECExpanded ClayEDCEndocrine Disrupting CompoundEDTAEthylene Diamine Tetraacetic AcidEE217 α-EthinylestradiolEEMExcitation-Emission MatrixEOClExtractable Organic ChlorineEPSExtracellular Polymeric SubstancesESEMEnvironmental Scanning Electron MicroscopyF/MFood to Microorganism (ratio)FAFree AmmoniaFBRFluidized-Bed ReactorFNAFree Nitrous AcidGACGranular Activated CarbonGAC/BACGranular /Biological Activated Carbon (with no clear distinction)GAC-FBRFluidized-Bed Reactor packed with Granular Activated CarbonGAC-MBRGAC added Membrane BioreactorGAC-SBBRGAC Reactor operated as a Sequencing Batch Biofilm ReactorGAC-UASBUpflow Anaerobic Sludge Blanket packed with Granular Activated CarbonGAC-UFBRUpflow Fixed-Bed Reactors packed with GACGC-MSGas Chromatography-Mass SpectrometryHAAHaloacetic AcidHAA5Five Haloacetic AcidsHAAFPHAA Formation PotentialHLRHydraulic Loading RateHMWHigh Molecular WeightHMXHigh Melting eXplosiveHPCHeterotrophic Plate CountHRTHydraulic Retention TimeHSDMHomogeneous Surface Diffusion ModelIASIdeal Adsorbed SolutionIASTIdeal Adsorbed Solution TheoryIBPIbuprofenIBPCTIntegrated Biological-Physicochemical TreatmentIC50Concentration leading to 50% inhibition in biological testsISIASImproved Simplified Ideal Adsorbed SolutionIUPACInternational Union of Pure and Applied ChemistryKATOXA process leading to accelerated oxidation in the presence of activated carbonLC50Concentration leading to lethal effect in 50% of biological speciesLCALife Cycle AssessmentLCCLife Cycle CostLDFLinear Driving ForceLMWLow Molecular WeightMADAMMichigan Adsorption Design and Applications ModelMAPMicrobially Available PhosphorusMBRMembrane BioReactorMDBAMultiple-Component Biofilm Diffusion Biodegradation and Adsorption modelMEPMetabolic End ProductsMFMicrofiltrationMIB2-MethylisoborneolMLSSMixed Liquor Suspended SolidsMLVSSMixed Liquor Volatile Suspended SolidsMNPm-NitrophenolMTBEMethyl-Tert-ButyletherMTZMass Transfer ZoneMWMolecular WeightNBDOCNonbiodegradable Dissolved Organic CarbonNMRNuclear Magnetic ResonanceNOBNitrite Oxidizing BacteriaNOMNatural Organic MatterNPNitrophenolNPDESNational Pollutant Discharge Elimination SystemNPEsNonylphenol EthoxylatesNPXNaproxenOCDOrganic Carbon DetectionOCPSFOrganic Chemicals, Plastics and Synthetic FiberONDOrganic Nitrogen DetectionOUROxygen Uptake RatePACPowdered Activated CarbonPAC-MBRPAC added Membrane BioreactorPACTPowdered Activated Carbon TreatmentPACT®Registered Powdered Activated Carbon TreatmentPAEPhthalate EsterPAHPolycyclic Aromatic HydrocarbonPBRPacked-Bed ReactorPCEPerchloroethylene (Tetrachloroethylene)PCPPentachlorophenolPCPsPersonal Care ProductsPCRPolymerase Chain ReactionPDMPore Diffusion ModelPePeclet numberPFRPlug Flow ReactorPNPp-NitrophenolPOCParticulate Organic CarbonPOPPersistent Organic PollutantPOTWPublicly Owned Treatment WorksPPCPsPharmaceutical and Personal Care ProductsPZGPlane of Zero GradientRBFRiver Bank FiltrationRDXRoyal Demolition eXplosiveRFBRecycle Fluidized-BedRWWRheinisch-Westfälische WasserwerksgesellschaftSATSoil Aquifer TreatmentSBBRSequencing Batch Biofilm ReactorSBRSequencing Batch ReactorSBR-PACTPowdered Activated Carbon Treatment in a Sequencing Batch ReactorSCFBSemi-Continuously Fed Batch (Reactor)SCODSoluble Chemical Oxygen DemandSCRSpecific Cake ResistanceSECSize Exclusion ChromatographySEMScanning Electron MicroscopyShSherwood numberSIASSimplified Ideal Adsorbed SolutionSMPSoluble Microbial ProductsSOCSynthetic Organic CompoundSOURSpecific Oxygen Uptake RateSRFSpecific Resistance to Filtration.SRTSludge Retention TimeSSSuspended SolidsSSFSlow Sand FiltrationStStanton numberSTPSewage Treatment PlantSUVASpecific Ultraviolet AbsorbanceSVISludge Volume IndexSVOCSemi-Volatile Organic CompoundTCATrichloroethaneTCBTrichlorobenzeneTCETrichloroethyleneTCODTotal Chemical Oxygen DemandTDSTotal Dissolved SolidTHMTrihalomethaneTHMFPTrihalomethane Formation PotentialTKNTotal Kjeldahl NitrogenTMPTransmembrane PressureTNTotal NitrogenTOCTotal Organic CarbonT-RFLPTerminal-Restriction Fragment Length PolymorphismTSMSBMTransient-State Multiple-Species Biofilm ModelTSSTotal Suspended SolidsTTHMTotal TrihalomethanesTVHTotal Volatile HydrocarbonsUASBUpflow Anaerobic Sludge BlanketUFUltrafiltrationUSEPAUnited States Environmental Protection AgencyUVUltravioletVOCVolatile Organic Compound (Carbon)WAOWet Air OxidationWARWet Air RegenerationWWTPWastewater Treatment PlantXOCXenobiotic Organic Compound

Acknowledgement

This work would not have been possible without the Bogaziçi University, Istanbul/Turkey, to which I owe much, first for my education and later for its support during my activities as a faculty member. Most of the information presented in this book was accumulated during the last 20 years of my teaching and research at the University, much of it supported through grants from the Research Fund. Similarly, I am indebted to our national research council TÜBTAK for its support of several research projects in these years.

I also owe much to the Institute of Environmental Sciences of Bogaziçi University, which offered me an academic career, and to the direct and indirect support of all members of the Institute. I owe special thanks to Prof. Nadim Copty for his careful examination of some chapters, particularly for his critical reading and invaluable suggestions made for the modeling chapters (Chapters 6 and 11).

I am grateful to all of my former thesis students with whom I had the opportunity to work, who helped me realize my ideas and contributed to many of the concepts and results presented in this book. Of these students, two in particular have done great work that has directly contributed to the book:

Özgür Akta, who is also the co-author of this book, worked mainly on wastewater treatment and produced his MSc thesis, under my supervision, on ‘Powdered activated carbon addition to activated sludge in the treatment of landfill leachate.’ After this, his PhD thesis, also under my supervision, ‘Bioregeneration of activated carbon in the treatment of phenolic compounds,’ contributed much to the literature.

Kozet Yapsakli, a PhD student, wrote her thesis on ‘Application of biological activated carbon (BAC) in drinking water treatment’ under my supervision. This study further extended our understanding of integrated adsorption and biological removal as applied to drinking water treatment. Some examples, described in Chapters 8 and 9 of this book, are derived from these studies. I also thank her for her careful reading of the chapters in this book, particularly those related to drinking water treatment.

Special thanks go to my research assistant Aye Gül Geyik who has worked tirelessly on literature surveys, drawing, and formatting.

Finally, I am indebted to my family members, who supported me throughout my life in all aspects. I dedicate this book to my father, now deceased, who had a great influence on my personality and on my path to becoming an academician.

Ferhan Çeçen

CHAPTER 1

Water and Wastewater Treatment: Historical Perspective of Activated Carbon Adsorption and its Integration with Biological Processes

Ferhan Çeçen

1.1 Historical Appraisal of Activated Carbon

Activated carbon is broadly defined to include a wide range of amorphous carbon-based materials prepared in such a way that they exhibit a high degree of porosity and an extended surface area [1]. Moreover, all non-carbon impurities are removed and the surface is oxidized. Although today the term ‘activated carbon’ is taken for granted, a long time elapsed before it became generally adopted.

The use of activated carbon in its current form has only a short history. On the other hand, according to records, the use of carbon itself dates back to ancient times. The earliest known use of carbon in the form of wood chars (charcoal) by the Egyptians and Sumerians was in 3750 BC [2]. At that time, charcoal was used for various purposes such as reduction of ores in the manufacture of bronze, domestic smokeless fuel, and medicinal applications [3]. In Egyptian papyri dating from 1550 BC we find the first citation of the use of charcoal for the adsorption of odorous vapors – from putrefying wounds and the intestinal tract. The ancient Greeks used charcoal to ease the symptoms of food poisoning [4]. The beneficial effect was due to the adsorption of the toxins emitted by ingested bacteria, thereby reducing their toxic effects.

Hindu documents dating from 450 BC refer to the use of sand and charcoal filters for the purification of drinking water. Recent studies of the wrecks of Phoenician trading ships led to the discovery that drinking water was stored in charred wooden barrels in order to keep the water fresh [4]. In the time of Hippocrates (ca. 460 –370 bc) and Pliny the Elder (ad 23–79) wood chars were employed for medicinal purposes [5]. In about 157 BC carbons of vegetable and animal origin were applied in the treatment of many diseases [2]. A Sanskrit text around 200 ad recommends the use of filtration of water through coal after storing it in copper vessels and exposing it to sunlight, providing probably one of the earliest documents describing the removal of compounds from water in order to disinfect it [6].

In the fifteenth century, during the time of Columbus, sailors used to blacken the insides of wooden water barrels with fire, since they observed that the water would stay fresh much longer. It is likely that people at that time proceeded by intuition only, without having any insight into the mechanisms of the effect; these mechanisms were recognized beginning from the eighteenth century.

In the eighteenth century, carbons made from blood, wood, and animals were used for the purification of liquids. The specific adsorptive properties of charcoal (the forerunner of activated carbon) were first observed by Scheele in 1773 in the treatment of gases. Later, in 1786, Lowitz performed experiments on the decolorizing of solutions. He provided the first systematic account of the adsorptive power of charcoal in the liquid phase [7]. In those days, the sugar refining industry was looking for an effective means of decolorizing raw sugar syrups, but the wood charcoals then available were not particularly effective because of their limited porosity [4]. However, a few years later, in 1794, an English sugar refinery successfully used wood charcoal for decolorization. This application remained a secret until 1812 when the first patent appeared in England [2], although from 1805 wood charcoal was used in a large-scale sugar refining facility in France for decolorizing syrups, and by 1808 all sugar refineries in Europe were using charcoal as a decolorizer [4].

In 1811 it was shown that bone char had an even higher decolorizing ability for sugar syrups than wood char. Consequently, a switch took place from wood charcoal to bone char in the sugar industry. In 1817 Joseph de Cavaillon patented a method of regenerating used bone chars, but the method was not entirely successful. In 1822 Bussy demonstrated that the decolorizing abilities of carbons depended on the source material, the thermal processing, and the particle size of the finished product. His work constitutes the first example of producing an activated carbon by a combination of thermal and chemical processes. Later in the nineteenth century, systematic studies were carried out on the manufacture and regeneration of bone chars by Schatten in Germany and the application of charcoal air filters for removing vapors and gases in London sewers by Stenhouse [4].

In 1862, Lipscombe prepared a carbon material to purify potable water. This development paved the way for the commercial applications of activated carbon, first for potable water and then in the wastewater sector. In 1865 Hunter discovered the excellent gas adsorption properties of carbons derived from coconut shells. It is remarkable that the term ‘adsorption’ was first introduced by Kayser in 1881 to describe the uptake of gases by carbons [4].

Activated carbon was first produced on an industrial scale at the beginning of the twentieth century, and major developments then took place in Europe. However, at the beginning of the twentieth century activated carbon was only available in the form of powdered activated carbon (PAC). The Swedish chemist von Ostreijko obtained two patents, in 1900 and 1901, covering the basic concepts of chemical and thermal (or physical) activation of carbon, with metal chlorides and with carbon dioxide and steam, respectively [7]. In 1909, a plant named ‘Chemische Werke’ was built to manufacture, for the first time on a commercial scale, the powdered activated carbon Eponit® from wood, adopting von Ostrejko’s gasification approach [8]. Other activated carbons known as Norit® and Purit® were produced in this plant by the activation of peat with steam. The NORIT company, a manufacturer in Holland, first appeared in about 1911 and became widely known in the sugar industry [5]. The powdered activated carbons were used at that time mainly for decolorizing solutions in the chemical and food industries.

On an industrial scale, the process of chemical activation of sawdust with zinc chloride was carried out for the first time in an Austrian plant at Aussing in 1914, and also in the dye plant of Bayer in 1915 [9]. This type of activation involved pyrolytical heating of the carbonaceous material in the presence of dehydrating chemicals such as zinc chloride or phosphoric acid [10].

In parallel to the developments in Europe, in the United States the first activated carbon was produced from black ash, a waste product of soda production, after it was accidentally discovered that the ash was effective in decolorizing liquids [5]. The first commercial production of activated carbon in the United States took place in 1913 [11]. Activated carbon in the form of PAC was used for the first time in 1928 by Chicago meat packers for taste and odor control [12].

The use of poisonous gases in the First World War paved the way for the development and large-scale production of granular activated carbon (GAC). These carbons were used in gas masks for the adsorption of poisonous gases. Subsequently, they were used for water treatment, solvent recovery, and air purification. After the First World War, considerable progress was made in Europe in the manufacture of activated carbons using new raw carbonaceous materials such as coconut and almond shells. The treatment with zinc chloride yielded activated carbons with high mechanical strength and high adsorptive capacities for gases and vapors. Later, in 1935–1940, pelletized carbons were produced from sawdust by zinc chloride activation for the recovery of volatile solvents and the removal of benzene from town gas. Nowadays, the zinc chloride process of chemical activation has been largely superseded by the use of phosphoric acid [4].

1.2 General Use of Activated Carbon

Nowadays, activated carbon finds wide application in many areas, but especially in the environmental field. Aside from environmental pollution control, activated carbon is mainly used in industry in various liquid and gas phase adsorptions [1]. Among liquid phase applications one can list food processing, preparation of alcoholic beverages, decolorization of oils and fats, product purification in sugar refining, purification of chemicals (acids, amines, gylcerin, glycol, etc.), enzyme purification, decaffeination of coffee, gold recovery, refining of liquid fuels, purification in electroplating operations, purification in the clothing, textile, personal care, cosmetics, and pharmaceutical industries, and applications in the chemical and petrochemical industries. Gas phase applications include recovery of organic solvents, removal of sulfur-containing toxic components from exhaust gases and recovery of sulfur, biogas purification, use in gas masks, among others. Activated carbon is also used in medical and veterinary applications, soil improvement, removal of pesticide residues, and nuclear and vacuum technologies.

1.3 Application of Activated Carbon in Environmental Pollution

Although the use of carbon-based materials dates back to ancient times, the use of activated carbon in its current form began in the second half of the twentieth century as a consequence of the rising awareness of environmental pollution. Today, activated carbon is very often utilized in the removal of various organic and inorganic species from surface water, groundwater, and wastewater.

1.3.1 Activated Carbon in Drinking Water Treatment

Adsorption by activated carbon is employed today in drinking water treatment for various purposes. An overview of historical development shows that the first application of activated carbon in the form of GAC was in the year 1910 in Reading, England for the purpose of dechlorination of chlorinated water [12]. In the 1930s and 1940s, in particular in Europe, water works used high chlorine doses for the disinfection of water following the growing pollution of surface waters. Often, GAC filtration was used for dechlorination purposes. However, the dechlorination in these filters cannot be regarded as an adsorptive process since the removal of chlorine depends on a catalytic reaction taking place on the carbon surface. However, the use of GAC for dechlorination purposes was abandoned a long time ago because of the formation of additional haloforms and other chlorine compounds within filters [7].

The use of activated carbon in water treatment for removal of substances responsible for taste and odor dates back to the late 1920s [11]. The undesirable taste and odor in drinking water was mainly attributed to the presence of chlorophenols formed in water as a result of the chlorination of phenols at the disinfection stage [7].

PAC was used for the control of taste and odor in drinking water for the first time in the USA in 1929–1931 [7]. The first GAC filters were installed in Germany in 1929 and in the USA in 1930 for taste and odor removal. By 1932 about 400 water treatment works in the USA were adding PAC to their water to improve taste and odor, and this number increased to 1200 by 1943. The first major GAC filter for public water supply was installed in the USA at the Hopewell, VA, water treatment plant in 1961 [12]. By 1970 the number of waterworks which added PAC to their units or used GAC adsorbers was estimated at 10000 worldwide [7]. In later years, PAC adsorption for water treatment was also integrated with Dissolved Air Flotation (DAF), in which PAC served as an adsorbent for various pollutants and was subsequently floated to the surface by DAF [13].

When activated carbon was used in granular or powdered form in the early 1960s in water treatment, the main aim was the removal of taste and odor. In Europe, where surface waters were heavily polluted, early breakthroughs of odor-causing species were observed in GAC filters, necessitating frequent regenerations. Intensive investigations beginning in the early 1960s revealed that pretreatment of water with ozone was an effective solution to this problem since it extended the GAC bed life. The well-known Mülheim process was developed as a result of these efforts [7]. Details of this process can be found in Chapter 8.

Currently, problems in drinking water treatment extend beyond the scope of taste and odor control. Much attention is being paid to the regulation and control of numerous organic and inorganic compounds in water. Concerns about the presence of Synthetic Organic Compounds (SOC) arose in 1960s. Beginning in the 1970s it was recognized that disinfection of water with chlorine gas or chlorine-containing compounds led to the generation of organic compounds, collectively termed Disinfection By-Products (DBPs), which were suspected of having adverse effects on health [7]. In this regard, Natural Organic Matter (NOM) constitutes the key group of organics acting as precursors for DBP formation. It was also shown that pretreatment of water with ozone led to inorganic hazardous by-products such as bromates. For many decades, adsorption onto activated carbon has appeared to be one of the most reliable methods of NOM and DBP control. This type of treatment is usually conducted in GAC filters. These are usually placed after sand filtration and before disinfection, but, depending on the characteristics of the water and the object of the treatment, GAC filters may also be positioned at other locations within the treatment train.

The presence of synthetic organic contaminants in surface and groundwaters is largely attributed to the discharge of municipal and industrial wastewaters into receiving waters in treated or untreated form. The increased use of fertilizers and pesticides in agriculture is another factor contributing to pollution. Further, discharges into surface waters from non-point sources such as urban runoff also add to pollution.

Raw waters taken from surface and groundwater supplies contain many organic compounds such as phenols, pesticides, herbicides, aliphatic and aromatic hydrocarbons and their chlorinated counterparts, dyes, surfactants, organic sulfur compounds, ethers, amines, nitro compounds, and newly emerging substances such as Endocrine Disrupting Compounds (EDCs). More than 800 specific organic and inorganic chemicals have been identified in various drinking waters, and many more are suspected to be present [1]. Therefore, concerns are frequently expressed about the presence of these compounds, which can be present at levels as low as ng L−1 or μg L−1. Because of their proven or suspected health and environmental effects, great efforts are made to control and/or remove them, and one of the major methods of doing this is by adsorption onto activated carbon.

1.3.2 Activated Carbon in Wastewater Treatment

The groups of organics that are generally amenable to adsorption onto activated carbon include pesticides, herbicides, aromatic solvents, polynuclear aromatics, chlorinated aromatics, phenolics, chlorinated solvents, high-molecular-weight (HMW) aliphatic acids and aromatic acids, HMW amines and aromatic amines, fuels, esters, ethers, alcohols, surfactants, and soluble organic dyes. Compounds having low molecular weight (LMW) and high polarity, such as LMW amines, nitrosamines, glycols, and certain ethers, are not amenable to adsorption [11].

Many compounds falling into these categories are encountered in the effluents of various industries and to some extent also in municipal wastewaters and drinking water supplies. Activated carbon has gained importance especially since the mid 1960s as an adsorptive material in the treatment of municipal and industrial wastewaters.

1.3.2.1 Municipal Wastewater Treatment

The first full-scale advanced (tertiary) wastewater treatment plant incorporating GAC was put into operation in 1965 in South Lake Tahoe, California. The use of GAC beds as a unit process became common in the tertiary treatment train [11]. The purpose in employing GAC was to reuse the effluent of municipal wastewater treatment plants for purposes such as industrial cooling water, irrigation of parks, and so on.

Physicochemical treatment options involving PAC adsorption were also tested in lieu of biological treatment. The idea was that primary settling was followed by coagulation and PAC adsorption, settling and perhaps filtration. However, secondary treatment could not be replaced with a merely physicochemical process because of cost [11].

Today, GAC filtration or PAC-assisted membrane operation are mainly conducted as a tertiary treatment step to remove dissolved and refractory organic matter from secondary sewage effluent. The main goal remains to be the reuse of effluent for various purposes.

1.3.2.2 Industrial Wastewater Treatment

Activated carbon adsorption is most commonly applied in industrial wastewater treatment to meet stringent regulations for discharge into receiving waters. In industrial wastewater treatment, activated carbon adsorption can be utilized as a separate unit process. It may be placed after various physicochemical treatment steps such as coagulation/clarification, filtration, and dissolved air flotation. Another alternative is to use activated carbon adsorption prior to biological treatment to remove compounds which might be toxic to a biological system. However, the most widely adopted procedure is to place activated carbon adsorption as a tertiary or advanced treatment step subsequent to biological treatment for removal of refractory organics. To some extent this procedure may also be effective in the removal of inorganics.

Nowadays, activated carbon finds wide application in the treatment of wastewaters generated from industries such as food, textile, chemical, pharmaceutical, pesticides and herbicides production, coke plant, munitions factories, petroleum refineries and storage installations, organic pigments and dyes, mineral processing plants, insecticides, pesticides, resins, detergents, explosives, and dyestuffs. It is also employed in the treatment of sanitary and hazardous landfill leachates.

1.3.3 Applications of Activated Carbon in Other Environmental Media

1.3.3.1 Remediation of Contaminated Groundwater and Soil

Groundwaters are significantly polluted with organic and inorganic substances as a result of industrial spills, accidents, discharges, and so on. Activated carbon adsorption is often employed in remediation of groundwaters for drinking purposes. In groundwater remediation, activated carbon may either directly adsorb contaminants or remove them after their transfer into the gas phase by air sparging or stripping.

Today, activated carbon is also applied in the remediation of contaminated soils. Remediation of soils contaminated with petroleum hydrocarbon and other substances involves the use of thermal desorption methods. The resulting off-gases containing Volatile Organic Compounds (VOCs) are usually treated with PAC or GAC. In contaminated soils, PAC may also be used as a soil additive to immobilize organic contaminants.

1.3.3.2 Treatment of Flue Gases

Activated carbon also finds application in the purification of flue gases such as those emerging from incinerators, and in the removal of gases such as radon, hydrogen sulfide, and other sulfur compounds from gas streams [2].

1.3.3.3 Water Preparation for Industrial Purposes

Activated carbon is utilized in industrial facilities for the production of the water required for various plant items such as steam generators, heat exchangers, cooling towers, and also in the production of ultra pure water.

1.3.4 Integration of Activated Carbon Adsorption with Biological Processes in Wastewater and Water Treatment

Nowadays, adsorption and biological processes for the control of various pollutants generally take place in separate unit, whereas the combination of adsorption and biological processes in the same reactor is relatively less common and more complicated. The main purpose of this book is to provide an insight into this system of integrated application, whose usefulness has been clearly recognized since the 1970s, in both wastewater and water treatment.

1.3.4.1 Wastewater Treatment

1.3.4.1.1 Combined Suspended-Growth Processes

The Powdered Activated Carbon Treatment (PACT) process

The PACT process is essentially a modification of the activated sludge process by the addition of PAC. The application of concurrent adsorption and biodegradation in the same suspended-growth reactor is an effective alternative for the removal of biodegradable and non biodegradable compounds. The PACT system has also been adopted for anaerobic treatment.

Integration of PAC adsorption with membrane processes

In recent years PAC has been integrated into Membrane Bioreactors (MBR) to bring about a positive effect on contaminant removal and to prevent membrane biofouling.

1.3.4.1.2 Combined Attached-Growth Processes

The Biological Activated Carbon (BAC) Process

While PACT is a modification of a suspended-growth process, BAC is essentially a biofilm process that is based on the establishment of biological activity in a GAC adsorber by gradual attachment of microorganisms and development of a biofilm.

Since 1970s, both PAC- and GAC-based biological processes have been applied in the treatment of industrial wastewaters such as organic chemicals, petrochemicals, refineries, textiles/dyes, in joint treatment of municipal and industrial wastewaters for discharge or reuse purposes, and in the treatment of sanitary and hazardous landfill leachates. Detailed discussion of such applications is presented in Chapters 3–7 of this book.

1.3.4.2 Water Treatment

Since the 1970s, a gradual development has taken place in the direction of integrating adsorptive and biological processes in the treatment of surface water or groundwaters. In this regard, BAC filtration is a well-known unit process that combines the merits of adsorption and biological removal in the same reactor. While the majority of GAC adsorption applications target the removal of natural and/or anthropogenic organic compounds, BAC filtration is also suited to some extent for the elimination of inorganics such as ammonia, perchlorate, and bromate. The characteristics of this unit process is extensively addressed throughout Chapters 8–11.

1.3.5 Improved Control of Pollutants through Integrated Adsorption and Biological Treatment

Water and wastewaters are multi component mixtures. As such, it is impossible to measure the presence and removal of a large number of compounds present in treatment or remediation systems. Therefore, in the case of organic compounds, monitoring is commonly carried out by the use of sum (collective) parameters such as TOC, DOC and UV absorbance, and the BOD and COD parameters, in water and wastewater treatment, respectively (Table 1.1).

Table 1.1 Reduction in parameters or pollutant groups achieved by adsorption, biological removal, or integrated means.

Over the years, more specific parameters have been developed. In the characterization of waters and wastewaters one of the widely used parameters is referred to as Adsorbable Organic Xenobiotics (AOX), and represents halogenated organics that have a high affinity towards activated carbon. This parameter is most often used to indicate the chlorinated organic compounds (AOCl).

There are also definitions that are specific to water treatment. In this context, one can list the Disinfection By-Products (DBPs). Specific groups among DBPs are referred to by terms such as Trihalomethanes (THMs) and Haloacetic Acids (HAAs). The respective formation potentials of these groups are abbreviated as THMFP and HAAFP.

In addition to these, in recent decades, a large number of new compounds have been detected in water and wastewater media. Since in raw and finished waters these compounds, referred to as micropollutants, are present at μg L−1 or ng L−1 levels, the sum parameters mentioned above prove to be useless in their monitoring. Due to this fact, efforts are made to monitor them individually by advanced analytical techniques. Within this context, one can list various pharmaceuticals and EDCs that have received a great deal of attention in the last decades.

Various pollutants found in water and wastewater systems are amenable to either adsorption or biological degradation or transformation. Still, a number of them can be removed by both adsorptive and biological means. Combination of activated carbon adsorption and biological processes in the same unit often offers a synergism, in that a higher removal is achieved than expected from adsorption or biodegradation alone. For many pollutants that are considered to be slowly biodegradable or even non biodegradable, integration of adsorption with biological removal may provide the opportunity for biological degradation. This integrated approach can also enable the effective elimination of micropollutants at trace levels.

Various organic and inorganic pollutants are encountered in surface waters, groundwaters, and wastewaters. Table 1.1 provides a brief overview of the relative reduction achieved in parameters or specific groups by means of adsorption, biological activity or integration of both. However, the evaluation presented here is rather general, relative, and qualitative. Comprehensive discussion of the elimination mechanisms, the synergism in integrated adsorption and biological removal, the laboratory-, pilot- and full-scale studies, and the modeling of integrated adsorption and biological removal in wastewater and water treatment is presented throughout Chapters 3–11.

References

1 Bansal, R.P. and Goyal, M. (2005) Activated Carbon Adsorption, CRC Press, Taylor & Francis Group, 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL, USA 33487–2742.

2 Inglezakis, V.J. and Poulopoulos, S.G. (2006) Adsorption, Ion Exchange and Catalysis: Design of Operations and Environmental Applications, Elsevier Science & Technology.

3 Menendez-Diaz, J.A. and Gullon, I.M. (2006) Types of carbon adsorbents and their production, in Activated Carbon Surfaces in Environmental Remediation (eds T.J.Bandosz), Elsevier, Printed in the Netherlands, pp. 1–47.

4www.caer.uky.edu/carbon/history/carbonhistory.shtml. University Of Kentucky, Center for Applied Energy Research, History of Carbon (accessed 29 January 2010).

5 Hassler, J.W. (1963) Activated Carbon, Chemical Publishing Co., Inc., New York, N.Y., USA.

6www.carbonit.com. Carbonit Brochure-Westa Gruppe, CARBONIT Filtertechnik GmbH, Salzwedel, Germany.

7 Sontheimer, H., Crittenden, J., and Summers, R.S. (1988) Activated Carbon for Water Treatment, 2nd edn, Forschungstelle Engler – Bunte- Institute, Universität Karlsruhe, Karlsruhe, Germany.

8 Dabrowski, A. (1998) Adsorption – its development and application for practical purposes, in Adsorption and Its Applications in Industry and Environmental Protection. Studies in Surface Science and Catalysis, vol. 120 (ed. A. Dabrowski), Elsevier Science B. V., pp. 3–68.

9 Dabrowski, A. (2001) Adsorption-from theory to practice. Advances in Colloid and Interface Science, 93, 135–224.

10 Purcell, P.J. (2006) Milestones in the development of municipal water treatment science and technology in the 19th and early 20th centuries: part I. Water and Environment Journal, 19 (3), 230–237.

11 Hendricks, D. (2006) Water Treatment Unit Processes: Physical and Chemical, CRC Press. Printed in the USA.

12 Hung, Y.T., Lo, H.H., Wang, L.K., Taricska, J.R., and Li, K.H. (2005) Granular activated carbon adsorption, in Physicochemical Treatment Processes, Handbook of Environmental Engineering, vol. 3 (eds L. K. Wang, Y.T. Hung and N. Shammas), Humana Press Inc., Totowa, New Jersey, USA pp. 573–633.

13 Wang, L.K. (2007) Emerging flotation technologies, in Advanced Physicochemical Treatment Technologies, Handbook of Environmental Engineering, vol. 5 (eds L.K. Wang, Y. T. Hung and N. Shammas) Humana Press Inc., Totowa, New Jersey, USA pp. 449–489.

CHAPTER 2

Fundamentals of Adsorption onto Activated Carbon in Water and Wastewater Treatment

Özgür Akta Ferhan Çeçen

2.1 Activated Carbon

Activated carbons are porous carbonaceous adsorbents. A large variety of organic solutes (Table 2.1) can be removed from water and wastewater by adsorption onto activated carbon, and some inorganic solutes can also be removed by this means. The porous surface of activated carbon adsorbs and retains solutes and gases, the amount of material adsorbed being potentially very large because of the great internal surface of activated carbon. Activated carbon has a high adsorptive surface area (500–1500 m2g−1), while the pore volume ranges between 0.7 and 1.8 cm3g−1. It is mainly used in the form of powdered activated carbon (PAC) or granular activated carbon (GAC).

Table 2.1 Classes of organic compounds adsorbed on activated carbon (adapted from [5]).

Organic chemical classExamplesAromaticsBenzene, Toluene, Ethylbenzene, XylenePolynuclear AromaticsNaphthalene, Anthracenes, BiphenylsChlorinated AromaticsChlorobenzene, Polychlorinated biphenylsPhenolicsPhenol, Cresol, Chlorophenols, NitrophenolsHigh-molecular-weight hydrocarbonsGasoline, KeroseneChlorinated aliphaticsTrichloroethylene, Carbon tetrachlorideAliphatic and aromatic acidsTar acids, Benzoic acidsKetones, esters, ethers, and alcoholsHydroquinone, Polyethylene glycolSurfactantsAlkyl benzene sulfonatesSoluble organic dyesMethylene blue, Indigo carmine

2.1.1 Preparation of Activated Carbons

Commercially available activated carbons are prepared from materials having a high carbon content such as coal, lignite, wood, peat, nut shell, coconut shell, lignin, petroleum coke, and synthetic high polymers. The manufacturing process comprises two phases, carbonization and activation. The carbonization process includes drying and heating to remove undesirable by-products such as tar and other hydrocarbons. The carbonaceous materials are then pyrolyzed and carbonized within a temperature range of 400–600°C in an oxygen-deficient atmosphere. This removes the volatile low-molecular-weight fraction and causes the material to undergo an activation process. Activation can be achieved thermally by the use of oxidation gases such as steam at above 800°C or carbon dioxide at higher temperatures. Chemical activation, on the other hand, involves impregnation of the raw material with chemicals such as phosphoric acid, potassium hydroxide, and zinc chloride [1–3]. The term activation refers to the development of the adsorption properties of carbon. Micropores are formed during the activation process, the yield of micropore formation being usually below 50% [3].

The raw material has a very large influence on the characteristics and performance of activated carbon obtained. Raw materials such as coal and charcoal have some adsorption capacity, but this is greatly enhanced by the activation process [4]. The common materials used in the production of activated carbon and the basic properties of the activated carbons produced are summarized in Table 2.2.

Table 2.2 Basic properties of common materials used in the manufacture of activated carbon (adapted from [5]).

2.1.2 Characteristics of Activated Carbon

Activated carbon is composed of microcrystallites that consist of fused hexagonal rings of carbon atoms, this structure being quite similar to that of graphite. The spaces between the individual microcrystallites are called pores. Micropores of activated carbon, where most of the adsorption takes place, are in the form of two-dimensional spaces between two parallel crystalline planes with an interlayer distance of 3–35Å. The diameter of the microcrystallites is roughly nine times the width of one carbon hexagon. Functional groups that terminate the microcrystallite planes interconnect the microcrystallites. Adsorption occurs on the planar surfaces of the microcrystallites and at the functional groups on the edges of the planes [3, 6, 7]. Adsorption on the microcrystallite planes predominantly results from van der Waals forces. On the other hand, adsorption at the edges of the microcrystallite occurs because of chemical bonding [7].

Activated carbon surfaces generally contain various oxygen complexes. These complexes arise from raw materials as well as from chemisorption of oxygen during the activation process. Oxygen complexes on the activated carbon surface exist mainly in the form of four different acidic surface oxides, namely strong carboxylic, weak carboxylic, phenolic, and carbonyl groups. Also, there are basic groups such as cyclic ethers. Activation at higher temperatures results in a basic surface. The presence of surface oxides adds a polar nature to activated carbons. Thermal treatment of carbons in an inert atmosphere or a vacuum can remove these surface oxide groups [3].

Surface functional groups play an important role in the adsorption of various organic molecules. For example, aromatic compounds can be adsorbed at the carbonyl oxygens on the carbon surface according to a donor–acceptor complexation mechanism. The carbonyl oxygen acts as the electron donor, while the aromatic ring of the solute acts as the electron acceptor. Adsorption also occurs by hydrogen bonding of the phenolic protons with surface functional groups and by complexation with the rings of the microcrystallite planes [7]. Activated carbon may contain large quantities of minerals, mostly calcium, sulfate, and phosphate ions. These groups as well as the acidic or basic organic surface functional groups influence the activated carbon surface properties [8]. The importance of surface chemistry on adsorption and its reversibility in integrated adsorption and biological processes are discussed in Chapter 7.

Activated carbon also contains some ash derived from the raw material, the amount of ash ranging from 1% to 12%. The ash mainly consists of silica, alumina, iron oxides, and alkaline and alkaline earth metals. The ash in the activated carbon increases its hydrophilicity. This is advantageous when PAC is used for water treatment because PAC does not stick on the reactor walls if the ash content is high [3].

2.1.3 Activated Carbon Types

2.1.3.1 Powdered Activated Carbon (PAC)

PAC is made up of crushed or ground carbon particles such that 95–100% of it will pass through a designated sieve of 0.297 mm according to the American Water Works Association Standard, or 0.177 mm according to ASTM D5158 [5]. PAC is generally produced from wood in the form of sawdust, the average particle size of PAC being in the range of 15–25 μm. PAC finds wide application in the treatment of both drinking water and wastewater. In wastewater treatment, it is either added to activated sludge or is contacted with wastewater in a separate unit. PAC may also act as a coagulant for colloidal fractions in the liquid phase. The regeneration of PAC can be rather difficult, because colloidal particles have to be separated from water before regeneration [3].

2.1.3.2 Granular Activated Carbon (GAC)

GAC is usually in the form of crushed granules of coal or shell. GAC may also be prepared by granulation of pulverized powders using binders such as coal tar pitch [3]. Unlike PAC adsorption from the liquid phase, the rate-limiting step in GAC adsorption from the liquid phase often becomes the intraparticle diffusion (Section 2.2.3). GAC particles have sizes ranging from 0.2 to 5 mm. GAC is designated by mesh sizes such as 8/20, 20/40, or 8/30 for liquid phase applications and 4/6, 4/8, or 4/10 for vapor phase applications [5]. Particle sizes in the range of 12/42 mesh are advantageous for liquid phase adsorption [3].

GAC filters, as shown in Section 2.3.2, are widely used in purification processes for drinking water, groundwater and wastewater as an advanced treatment step, particularly for the removal of toxic organic compounds. In some GAC applications in drinking water and wastewater treatment, a microbiological film can form on the particles. Thereby, biological removal of pollutants is combined with GAC adsorption. The resulting material, called biological activated carbon (BAC), is extensively discussed in later chapters.

2.2 Adsorption

Adsorption is considered to be an important phenomenon in most natural physical, biological, and chemical processes, and activated carbon is the most widely used adsorbent material in water and wastewater treatment.

Adsorption is the accumulation or concentration of substances at a surface or interface. The adsorbing phase is termed the adsorbent, and the material being adsorbed the adsorbate. Adsorption can occur between two phases, namely liquid–liquid, gas–liquid, gas–solid, or liquid–solid interfaces. When activated carbon is used, the adsorbing phase is a solid. In activated carbon adsorption, a hypothetical interfacial layer exists between the solid and fluid phases. This layer consists of two regions: that part of the fluid (gas or liquid) residing in the force field of the solid surface and the surface layer of the activated carbon.

Adsorptive surface reactions occur as a result of the active forces within the phase or surface boundaries. These forces result in characteristic boundary energies. The surface tension developed at the surface of the liquid phase results from the attractive forces between the molecules of liquid. The liquid (solvent) molecules have a smaller attractive force for the solute molecules than for each other. Hence, a solute that decreases surface tension is concentrated at the surface. The phenomenon of increased concentration of the soluble material in a boundary or surface is commonly referred to as adsorption [9]. The term ‘adsorption’ refers to the process in which molecules accumulate in the interfacial layer, whereas desorption denotes the reverse.

2.2.1 Types of Adsorption

In most types of water and wastewater treatment practice, two primary driving forces result in the adsorption of a solute from a solution onto a solid phase. The first driving force is related to the lyophobic (solvent disliking) character of the solute. The most important factor for the intensity of adsorption is the solubility of a dissolved substance. A hydrophilic substance likes the water system and tends to stay there. Hence, it is less adsorbable on a solid phase. Contrarily, a hydrophobic substance tends to be adsorbed rather than staying in water. Complex organic contaminants, such as humic acids have both hydrophobic and hydrophilic groups, so that the hydrophobic part of the molecule is adsorbed, whereas the hydrophilic part tends to stay in the solution.