bioelectrochemical systems : from extracellular electron
TRANSCRIPT
Bioelectrochemical SystemsFrom Extracellular Electron Transfer to
Biotechnological Application
Edited byKorneel Rabaey, Largus Angenent,Uwe Schroder and Surg Keller
&PublishingLondon • New York
TECHNISCHE
INFORMATION SBIBLIOTHEK
UNIVERSITATSBIBLIOTHEK
HANNOVER
Contents
Foreword xix
List of Contributors xxi
1 BIOELECTROCHEMICAL SYSTEMS: A NEW
APPROACH TOWARDS ENVIRONMENTAL AND
INDUSTRIAL BIOTECHNOLOGY 1
1.1 Fuel cells and bio-electricity 1
1.2 Underlying principles 5
1.2.1 Microorganisms and current 5
1.2.2 Microbial communities in BESs 6
1.2.3 From microbial metabolism to electrical current 7
1.3 Measuring and Defining performance 8
1.3.1 Measuring potentials 9
1.3.2 Rate based performance indicators 10
1.3.3 Efficiency based performance indicators 10
1.4 A plethora of applications 11
1.5 Acknowledgements 12
References 13
2 MICROBIAL ENERGY PRODUCTION FROM BIOMASS 17
2.1 Biomass: solar energy stored in organic material 17
2.2 The energy content of biomass 20
2.3 Bio-alcohol production from biomass 22
2.4 Anaerobic methanogenic digestion:waste stabilization plus renewable energy source 24
2.4.1 Process performance 24
vi Bioelectrochemical Systems
2.4.2 The microbiology of methanogenesis 26
2.4.3 The importance of extracellular electron
transfer in AD 27
2.4.4 Application of anaerobic digestion 29
2.4.4.1 Anaerobic Digestion (AD) for
solid waste 29
2.4.4.2 AD for wastewater treatment 30
2.4.4.3 Overall benefits and constraints of
anaerobic digestion 32
2.5 Bio-hydrogen production from biomass 34
2.6 Future perspectives 35
References 36
3 ENZYMATIC FUEL CELLS AND THEIR
COMPLEMENTARITIES RELATIVE TO BES/MFC 39
3.1 Introduction 39
3.2 Similarities between types of microbial and
enzymatic biofuel cells 43
3.2.1 Bioreactor design 44
3.2.2 In-situ bioreactor style 44
3.2.3 Catalyst in anolyte solution 45
3.2.4 Immobilized catalyst and/or mediator 46
3.2.5 Direct electron transfer catalysts 46
3.3 Catalyst sources for MET and DET systems 47
3.4 Comparison of properties of microbial and
enzymatic fuel cells 48
3.5 Enzymes employed in enzymatic biofuel cells 49
3.6 Deep and/or complete oxidation of fuel 52
3.7 Conclusions 52
3.8 Acknowledgements 53
References 53
4 SHUTTLING VIA SOLUBLE COMPOUNDS 59
4.1 Introduction 59
4.2 Redox shuttles 61
4.3 Early experiments 62
4.4 Exogenous redox mediators 63
4.4.1 Artificial mediators 63
4.4.2 Natural redox mediators in the subsurface
environment 64
Contents vii
4.5 Endogenous redox mediators 65
4.5.1 Known microbially produced redox mediators 67
4.5.1.1 Phenazines 67
4.5.1.2 Flavins 67
4.5.1.3 Quinones 68
4.5.1.4 Cytochromes and soluble enzymes 69
4.5.1.5 Melanin 69
4.5.1.6 Other mediators 69
4.5.2 Unidentified endogenous mediators 70
4.6 Methods for identification of soluble redox shuttles....
70
4.6.1 Potentiostat-controlled electrochemical cells 71
4.6.2 Environmental conditions 71
4.6.3 Batch experiments 71
4.6.4 Media formulation 71
4.6.5 Electrochemical methods 71
4.6.6 Medium change 72
4.6.7 Chemical structure of the mediator 72
4.7 Relevance of soluble redox mediators shuttle to
microbial metabolism 72
4.8 Soluble redox shuttles in bioelectrochemical
devices 74
4.8.1 Microbial fuel cells 74
4.8.1.1 Biosensors 74
4.8.1.2 Electrodes modified with redox
mediators 75
References 75
5 A SURVEY OF DIRECT ELECTRON TRANSFER FROM
MICROBES TO ELECTRONICALLY ACTIVE SURFACES 81
5.1 Introduction 81
5.2 Extracellular electron transfer - microbial
connections 82
5.2.1 Localized sites for membrane associated EET 83
5.2.1.1 Shewanella cytochromes 83
5.2.1.2 Geobacter cytochromes 85
5.2.2 Bacterial nanowires 87
5.2.2.1 Geobacter nanowires 88
5.2.2.2 Shewanella nanowires 88
5.2.2.3 Nanowires produced by other
microorganisms 90
viii Bioelectrochemica! Systems
5.2.3 Nanowire characterization 90
5.2.3.1 Composition 91
5.2.3.2 Regulation 91
5.2.3.3 Conductivity 92
5.2.3.4 Function 93
5.2.3.5 Prevalence 93
5.3 Ecological significance of extracellular electron
transfer 93
References 95
6 GENETICALLY MODIFIED MICROORGANISMS FOR
BIOELECTROCHEMICAL SYSTEMS 101
6.1 Introduction 101
6.2 Extracellular respiration in Shewanella Oneidensis
and Geobacter Sulfurreducens 102
6.3 Scientific motivation for heterologous
gene expression 105
6.4 Methods and challenges for heterologous
gene expression in E. coli 107
6.5 Biotechnological applications - designing the
'super bug' 110
6.5.1 The 'super bug' for BES applications 110
6.5.2 The 'super bug' for bioremediation
applications 112
6.6 Closing remarks 113
6.7 Acknowledgements 113
References 113
7 ELECTROCHEMICAL LOSSES 119
7.1 Introduction 119
7.2 Individual electrochemical losses 120
7.2.1 Activation polarization 121
7.2.1.1 Means to decrease the activation
polarization 122
7.2.2 Ohmic polarization 122
7.2.2.1 Means to decrease the ohmic
polarization 124
7.2.3 Concentration polarization (Mass transfer and
reaction polarization) 125
Contents ix
7.2.3.1 Means to decrease the concentration
polarization 127
7.2.4 Reactant crossover - 'internal currents' 127
7.2.4.1 Means to decrease internal current
losses 128
7.2.5 The pH splitting between anode and cathode 129
7.2.5.1 Means to prevent the pH splitting 129
7.3 Methods 129
7.3.1 Experimental strategies for the recording of
polarization plots 129
7.3.1.1 Current interrupt technique 130
7.4 Conclusions 131
References 132
8 ELECTROCHEMICAL TECHNIQUES FOR THE ANALYSIS
OF BIOELECTROCHEMICAL SYSTEMS 135
8.1 Cyclic voltammetry for the study of microbial
electron transfer at electrodes 137
8.1.1 Introduction 137
8.1.2 Turnover vs. non-turnover voltammetryexperiments 140
8.1.2.1 General considerations 140
8.1.2.2 Voltammetry in the presence of
substrates 141
8.1.2.3 Voltammetry in the absence of
substrates 145
8.1.2.4 Concluding remarks 148
References 148
8.2 Importance of Tafel plots in the investigationof bioelectrochemical systems 153
8.2.1 Introduction 153
8.2.2 Use of Tafel plots for performance evaluation
of microbial fuel cells 156
8.2.2.1 Tafel plots for monitoring the
electrocatalytic activity of anode
materials toward microbial consortia 157
8.2.2.2 Tafel plots for examining chargetransfer with microbial pure cultures 162
X Bioelectrochemical Systems
8.2.2.3 Estimating the maximum power
production from Tafel plots 163
References 165
8.3 The use of electrochemical impedance spectroscopy
(EIS) for the evaluation of the electrochemical
properties of bioelectrochemical systems 169
8.3.1 Introduction 169
8.3.2 Instrumentation and experimental approach 170
8.3.3 Display and analysis of EIS data 172
8.3.4 Determination of key electrochemical
parameters from impedance spectra 175
8.3.5 Applications of electrochemical impedance
spectroscopy in the study of MFCs 176
8.3.5.1 Electrochemical characterization of
anode and cathode properties 176
8.3.5.2 Determination and analysis of the
internal resistance Rm 179
8.3.6 Conclusions 181
References 181
9 MATERIALS FOR BES 185
9.1 Introduction 185
9.1.1 Electrode specific surface areas and
material costs 187
9.2 Electrode materials for MFCs 187
9.2.1 Anode 187
9.2.2 Cathode 189
9.2.3 Membranes 193
9.3 Other materials 197
9.3.1 Current collectors 197
9.3.2 Wires, resistors and loads 197
9.4 Materials for microbial electrolysis cells 198
9.5 Conclusions and outlook 200
References 201
10 TECHNOLOGICAL FACTORS AFFECTING BES
PERFORMANCE AND BOTTLENECKS TOWARDS
SCALE UP 205
10.1 Introduction 205
Contents xi
10.2 Design constraints as determined bywastewater application 207
10.2.1 Footprint and energetic efficiency 207
10.2.2 Effect of conductivity 210
10.2.3 Effect of buffer capacity 212
10.2.4 Membrane separator or not 212
10.3 Design constraints as determined by scale up 213
10.3.1 Scale up and voltage losses 213
10.3.2 Hydrodynamics and mechanics 215
10.4 Costs and choice of materials 215
10.4.1 Material properties and costs 215
10.4.2 Anode 216
10.4.3 Cathode 217
10.4.4 Membranes 217
10.5 Overcoming design constraints 218
10.5.1 Constraints and solutions 218
References 220
11 ORGANICS OXIDATION 225
11.1 Introduction 225
11.2 Respiratory oxidation to carbon dioxide 228
11.3 Fermentation at microbial fuel cell anodes 231
11.4 Syntrophy between fermenters and anodophiles 234
11.5 Methanogens compete for fermentation products 236
11.6 Electrocatalytic oxidation of fermentation products ...237
11.7 Summary 238
References 239
12 CONVERSION OF SULFUR SPECIES IN
BIOELECTROCHEMICAL SYSTEMS 243
12.1 Introduction 243
12.2 Properties of sulfur species 244
12.2.1 Elemental sulfur 244
12.2.2 Sulfide and polysulfides 244
12.2.3 Sulfate and other oxyanions 245
12.2.4 Relationship of electrochemical potentialand pH for sulfur species in aqueous systems ...
245
12.3 Existing sulfide and sulfate removal technologies 247
12.3.1 Sulfide removal technologies 247
Bioelectrochemical Systems
12.3.1.1 Physicochemical processes 248
12.3.1.2 Biological technologies 248
12.3.2 Sulfate removal technologies 249
12.3.3 Evaluation of existing technologies 249
12.4 Abiotic electrochemical removal of aqueous
sulfide 250
12.4.1 Introduction 250
12.4.2 Spontaneous sulfide oxidation and electricity
generation 252
12.4.3 Final product of sulfide oxidation 252
12.4.4 Properties of electrodeposited sulfur 254
12.5 Removal of aqueous sulfide in BES 256
12.5.1 Introduction 256
12.5.2 Sulfide oxidation in a biotic cell 257
12.6 Outlook 258
References 259
CHEMICALLY CATALYZED CATHODES IN
BIOELECTROCHEMICAL SYSTEMS 263
13.1 Introduction 263
13.2 Oxygen Reduction Reaction (ORR) 265
13.2.1 Introduction 265
13.2.2 Oxygen reduction catalysts 267
13.2.2.1 Platinum 267
13.2.2.2 Transition metal macrocycle based
catalysts 268
13.2.2.3 Metal oxides 268
13.2.2.4 Enzymes 269
13.2.3 MFC cathode configurations 269
13.2.3.1 Aqueous cathodes 269
13.2.3.2 Air cathodes 269
13.3 Hydrogen Evolution Reaction (HER) 270
13.3.1 Introduction 270
13.3.2 Hydrogen evolution catalysts 274
13.3.2.1 Platinum 274
13.3.2.2 Nickel 276
13.3.2.3 Tungsten carbide 276
13.3.2.4 Enzymes 277
13.3.3 MEC cathode configurations 277
Contents xiii
13.3.3.1 Aqueous cathodes 277
13.3.3.2 Gas diffusion cathodes 278
13.4 Future possibilities 279
References 280
14 BIOELECTROCHEMICAL REDUCTIONS IN REACTOR
SYSTEMS 285
14.1 Introduction 285
14.2 Aerobic biocathodes 286
14.3 Anoxic and anaerobic biocathodes 289
14.4 Electron transfer in biocathodes 294
14.5 Limiting factors 297
14.6 Outlook 298
14.7 Acknowledgements 299
References 299
15 BIOELECTROCHEMICAL SYSTEMS (BES) FOR
SUBSURFACE REMEDIATION 305
15.1 Bioremediation of contaminated soils
and aquifers 305
15.2 Chemical vs. electrochemical strategies of
electron delivery 306
15.2.1 Chlorinated hydrocarbons 309
15.2.2 Inorganic pollutants 315
15.3 Outlooks, perspectives, and challenges towards
field applications 319
References 322
16 FUNDAMENTALS OF BENTHIC MICROBIAL FUEL CELLS:
THEORY, DEVELOPMENT AND APPLICATION 327
16.1 Introduction 327
16.2 Fundamental principles of sediment
reduction-oxidation chemistry 328
16.3 Principles of design and approaches to testingBenthic Microbial Fuel Cells (BMFCs) 329
16.4 Anode material and design 330
16.5 Cathode materials and design 332
16.6 Performance and practical considerations of
BMFC designs 333
xiv Bioelectrochemical Systems
16.7 Microbial ecology of BMFCs 335
16.8 Factors governing power output 338
16.9 Scaling and environmental variability in BMFCs 340
16.10 Commercial viability of BMFCs 341
References 343
17 MICROBIAL FUEL CELLS AS BIOCHEMICAL OXYGEN
DEMAND (BOD) AND TOXICITY SENSORS 347
17.1 Introduction 347
17.1.1 Dissolved oxygen probe-based BOD sensors 348
17.1.2 Photometric BOD sensors 348
17.1.3 Titration and respirometric sensors 349
17.1.4 Electrochemical BOD sensors with mediators 349
17.2 The mediator-less microbial fuel cell 351
17.2.1 Electrochemically-active bacteria 351
17.2.2 Enrichment of an electrochemically-activebacterial community 352
17.2.3 Microbiology of a mediator-less MFC 353
17.2.4 Optimization of MFC performance 353
17.3 Design and performance of an MFC used as
BOD sensor 355
17.3.1 MFC to measure BOD values higher than
10 mg/L 356
17.3.1.1 MFC design 356
17.3.1.2 Enrichment and operation 357
17.3.1.3 Performance 358
17.3.2 MFC to measure BOD values lower than
10 mg/l 359
17.3.2.1 Background 359
17.3.2.2 Oligotrophic sensor design and
performance 359
17.3.3 BOD determination of samples containingoxygen and nitrate 360
17.3.3.1 Oxygen and nitrate reduce current
and coulombic efficiency 360
17.3.3.2 Use of respiratory inhibitors 360
17.4 MFC as a toxicity sensor 361
17.5 Conclusions 361
17.6 Acknowledgements 361
References 362
Contents xv
18 FEEDSTOCKS FOR BES CONVERSIONS 369
18.1 Introduction 369
18.2 Defined substrates utilized by BES 372
18.2.1 Volatile fatty acids and other fermentation
end products 372
18.2.2 Soluble carbohydrates, amino acids
and xenobiotics 376
18.3 Complex substrates and wastewaters utilized
by BES 377
18.3.1 Cellulosic feedstocks 378
18.3.2 Chitin 379
18.3.3 Domestic wastewater 379
18.3.4 Simulated and actual industrial wastewaters 379
18.4 Other aspects of feedstock composition 381
18.5 Feedstocks and BES integration in wastewater
treatment processes 383
18.6 Conclusions 387
18.7 Acknowledgements 388
References 388
19 INTEGRATING BES IN THE WASTEWATER AND SLUDGE
TREATMENT LINE 393
19.1 Introduction 393
19.2 BES as the single biological treatment unit (A)or followed by an activated sludge system as a
polishing step (B) 396
19.3 Preacidification of organic wastewater before
BES (C) 398
19.4 Anaerobic digesters for sludge stabilization
followed by BES (D) 399
19.5 Generating caustic in the cathode of BES to
control anaerobic digester pH (E) 401
19.6 Denitrificaton in the cathode of BES to remove
nutrients from water (F) 402
19.7 Generating chemical reagents at cathodes
for treatment purposes (G) 403
19.8 Outlook 404
19.9 Acknowledgements 405
References 405
xvi Bioeleclrochemical Systems
20 PERIPHERALS OF BES - SMALL SCALE YET FEASIBLE
(DEMONSTRATED) APPLICATIONS 409
20.1 Introduction 409
20.2 Artificial symbiosis 410
20.3 Microbial fuel cells and their configurations 411
20.3.1 Definition of peripherals 411
20.3.2 Bridging the power divide 412
20.3.3 Minimal peripheral requirements for continuous
and autonomous operation 415
20.3.4 Complexity in stacks 416
20.3.5 Microbial Electrolysis Cells (MECs) that
transform organic feedstocks into other typesof energy (hydrogen or methane) but require
input of electrical power in the process 419
20.3.6 Microbial Electrolysis Cells (MECs) that consume
electrical power to drive useful reactions
(e.g. denitrification) 420
References 420
21 TOWARDS A MATHEMATICAL DESCRIPTION OF
BIOELECTROCHEMICAL SYSTEMS 423
21.1 Introduction 423
21.2 Mathematical modelling 424
21.2.1 Model characteristics 425
21.2.1.1 Mechanistics vs. empirism 425
21.2.1.2 Dynamic vs. stationary models 426
21.2.1.3 Level of segregation/aggregation 426
21.2.2 How do model characteristics affect the
model user? 427
21.3 BESs modelling objectives 427
21.4 Key elements for BESs modelling 429
21.5 Existing BESs models 429
21.6 Current challenges in BESs modelling 436
21.6.1 Bioelectrode kinetics 437
21.6.2 Electron transfer mechanisms 439
21.6.3 Microbial activity: bioenergetics and kinetics 440
21.6.4 Mass transport - convection, diffusion and
migration 443
21.6.5 Biofilm and spatial modelling 444
Contents xvii
21.7 BESs modelling perspectives 445
21.8 Acknowledgements 446
References 446
22 OUTLOOK: RESEARCH DIRECTIONS AND
NEW APPLICATIONS FOR BES 449
22.1 BES research - focus on the application 449
22.2 Fundamental research directions 450
22.2.1 Understanding bioelectrochemical processfundamentals 450
22.2.2 Practically inspired fundamental research
areas 452
22.3 Applied research opportunities 453
22.3.1 Contributions and limitations of current
research activities 453
22.3.2 BESs for wastewater treatment? 455
22.3.3 Is power the best product from BESs? 456
22.4 Potential new BES applications 457
22.4.1 Novel options for cathodic reductions 457
22.4.2 Novel options for anodic oxidations 459
22.5 BES Integration into practical applications 459
22.6 Concluding thoughts on the future of BES 461
References 462
Index 467