& Publishing. Bioelectrochemical Systems. Biotechnological Application. From Extracellular Electron Transfer to

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1 Bioelectrochemical Systems From Extracellular Electron Transfer to Biotechnological Application Edited by Korneel Rabaey, Largus Angenent, Uwe Schroder and Surg Keller & Publishing London New York TECHNISCHE INFORMATION SBIBLIOTHEK UNIVERSITATSBIBLIOTHEK HANNOVER

2 Contents Foreword List of Contributors xix xxi 1 BIOELECTROCHEMICAL SYSTEMS: A NEW APPROACH TOWARDS ENVIRONMENTAL AND INDUSTRIAL BIOTECHNOLOGY Fuel cells and bio-electricity Underlying principles Microorganisms and current Microbial communities in BESs From microbial metabolism to electrical current Measuring and Defining performance Measuring potentials Rate based performance indicators Efficiency based performance indicators A plethora of applications Acknowledgements 12 References 13 2 MICROBIAL ENERGY PRODUCTION FROM BIOMASS Biomass: solar energy stored in organic material The energy content of biomass Bio-alcohol production from biomass Anaerobic methanogenic digestion: waste stabilization plus renewable energy source Process performance 24

3 vi Bioelectrochemical Systems The microbiology of methanogenesis The importance of extracellular electron transfer in AD Application of anaerobic digestion Anaerobic Digestion (AD) for solid waste AD for wastewater treatment Overall benefits and constraints of anaerobic digestion Bio-hydrogen production from biomass Future perspectives 35 References 36 3 ENZYMATIC FUEL CELLS AND THEIR COMPLEMENTARITIES RELATIVE TO BES/MFC Introduction Similarities between types of microbial and enzymatic biofuel cells Bioreactor design In-situ bioreactor style Catalyst in anolyte solution Immobilized catalyst and/or mediator Direct electron transfer catalysts Catalyst sources for MET and DET systems Comparison of properties of microbial and enzymatic fuel cells Enzymes employed in enzymatic biofuel cells Deep and/or complete oxidation of fuel Conclusions Acknowledgements 53 References 53 4 SHUTTLING VIA SOLUBLE COMPOUNDS Introduction Redox shuttles Early experiments Exogenous redox mediators Artificial mediators Natural redox mediators in the subsurface environment 64

4 Contents vii 4.5 Endogenous redox mediators Known microbially produced redox mediators Phenazines Flavins Quinones Cytochromes and soluble enzymes Melanin Other mediators Unidentified endogenous mediators Methods for identification of soluble redox shuttles Potentiostat-controlled electrochemical cells Environmental conditions Batch experiments Media formulation Electrochemical methods Medium change Chemical structure of the mediator Relevance of soluble redox mediators shuttle to microbial metabolism Soluble redox shuttles in bioelectrochemical devices Microbial fuel cells Biosensors Electrodes modified with redox mediators 75 References 75 5 A SURVEY OF DIRECT ELECTRON TRANSFER FROM MICROBES TO ELECTRONICALLY ACTIVE SURFACES Introduction Extracellular electron transfer microbial connections Localized sites for membrane associated EET Shewanella cytochromes Geobacter cytochromes Bacterial nanowires Geobacter nanowires Shewanella nanowires Nanowires produced by other microorganisms 90

5 viii Bioelectrochemica! Systems Nanowire characterization Composition Regulation Conductivity Function Prevalence Ecological significance of extracellular electron transfer 93 References 95 6 GENETICALLY MODIFIED MICROORGANISMS FOR BIOELECTROCHEMICAL SYSTEMS Introduction Extracellular respiration in Shewanella Oneidensis and Geobacter Sulfurreducens Scientific motivation for heterologous gene expression Methods and challenges for heterologous gene expression in E. coli Biotechnological applications designing the 'super bug' The 'super bug' for BES applications The 'super bug' for bioremediation applications Closing remarks Acknowledgements 113 References ELECTROCHEMICAL LOSSES Introduction Individual electrochemical losses Activation polarization Means to decrease the activation polarization Ohmic polarization Means to decrease the ohmic polarization Concentration polarization (Mass transfer and reaction polarization) 125

6 'internal Contents ix Means to decrease the concentration Reactant crossover - polarization 127 currents' Means to decrease internal current losses The ph splitting between anode and cathode Means to prevent the ph splitting Methods Experimental strategies for the recording of polarization plots Current interrupt technique Conclusions 131 References ELECTROCHEMICAL TECHNIQUES FOR THE ANALYSIS OF BIOELECTROCHEMICAL SYSTEMS Cyclic voltammetry for the study of microbial electron transfer at electrodes Introduction Turnover vs. non-turnover voltammetry experiments General considerations Voltammetry in the presence of substrates Voltammetry in the absence of substrates Concluding remarks 148 References Importance of Tafel plots in the investigation of bioelectrochemical systems Introduction Use of Tafel plots for performance evaluation of microbial fuel cells Tafel plots for monitoring the electrocatalytic activity of anode materials toward microbial consortia Tafel plots for examining charge transfer with microbial pure cultures 162

7 X Bioelectrochemical Systems Estimating the maximum power production from Tafel plots 163 References The use of electrochemical impedance spectroscopy (EIS) for the evaluation of the electrochemical properties of bioelectrochemical systems Introduction Instrumentation and experimental approach Display and analysis of EIS data Determination of key electrochemical parameters from impedance spectra Applications of electrochemical impedance spectroscopy in the study of MFCs Electrochemical characterization of anode and cathode properties Determination and analysis of the internal resistance Rm Conclusions 181 References MATERIALS FOR BES Introduction Electrode specific surface areas and material costs Electrode materials for MFCs Anode Cathode Membranes Other materials Current collectors Wires, resistors and loads Materials for microbial electrolysis cells Conclusions and outlook 200 References TECHNOLOGICAL FACTORS AFFECTING BES PERFORMANCE AND BOTTLENECKS TOWARDS SCALE UP Introduction 205

8 Contents xi 10.2 Design constraints as determined by wastewater application Footprint and energetic efficiency Effect of conductivity Effect of buffer capacity Membrane separator or not Design constraints as determined by scale up Scale up and voltage losses Hydrodynamics and mechanics Costs and choice of materials Material properties and costs Anode Cathode Membranes Overcoming design constraints Constraints and solutions 218 References ORGANICS OXIDATION Introduction Respiratory oxidation to carbon dioxide Fermentation at microbial fuel cell anodes Syntrophy between fermenters and anodophiles Methanogens compete for fermentation products Electrocatalytic oxidation of fermentation products Summary 238 References CONVERSION OF SULFUR SPECIES IN BIOELECTROCHEMICAL SYSTEMS Introduction Properties of sulfur species Elemental sulfur Sulfide and polysulfides Sulfate and other oxyanions Relationship of electrochemical potential and ph for sulfur species in aqueous systems Existing sulfide and sulfate removal technologies Sulfide removal technologies 247

9 Bioelectrochemical Systems Physicochemical processes Biological technologies Sulfate removal technologies Evaluation of existing technologies Abiotic electrochemical removal of aqueous sulfide Introduction Spontaneous sulfide oxidation and electricity generation Final product of sulfide oxidation Properties of electrodeposited sulfur Removal of aqueous sulfide in BES Introduction Sulfide oxidation in a biotic cell Outlook 258 References 259 CHEMICALLY CATALYZED CATHODES IN BIOELECTROCHEMICAL SYSTEMS Introduction Oxygen Reduction Reaction (ORR) Introduction Oxygen reduction catalysts Platinum Transition metal macrocycle based catalysts Metal oxides Enzymes MFC cathode configurations Aqueous cathodes Air cathodes Hydrogen Evolution Reaction (HER) Introduction Hydrogen evolution catalysts Platinum Nickel Tungsten carbide Enzymes MEC cathode configurations 277

10 Contents xiii Aqueous cathodes Gas diffusion cathodes Future possibilities 279 References BIOELECTROCHEMICAL REDUCTIONS IN REACTOR SYSTEMS Introduction Aerobic biocathodes Anoxic and anaerobic biocathodes Electron transfer in biocathodes Limiting factors Outlook Acknowledgements 299 References BIOELECTROCHEMICAL SYSTEMS (BES) FOR SUBSURFACE REMEDIATION Bioremediation of contaminated soils and aquifers Chemical vs. electrochemical strategies of electron delivery Chlorinated hydrocarbons Inorganic pollutants Outlooks, perspectives, and challenges towards field applications 319 References FUNDAMENTALS OF BENTHIC MICROBIAL FUEL CELLS: THEORY, DEVELOPMENT AND APPLICATION Introduction Fundamental principles of sediment reduction-oxidation chemistry Principles of design and approaches to testing Benthic Microbial Fuel Cells (BMFCs) Anode material and design Cathode materials and design Performance and practical considerations of BMFC designs 333

11 xiv Bioelectrochemical Systems 16.7 Microbial ecology of BMFCs Factors governing power output Scaling and environmental variability in BMFCs Commercial viability of BMFCs 341 References MICROBIAL FUEL CELLS AS BIOCHEMICAL OXYGEN DEMAND (BOD) AND TOXICITY SENSORS Introduction Dissolved oxygen probe-based BOD sensors Photometric BOD sensors Titration and respirometric sensors Electrochemical BOD sensors with mediators The mediator-less microbial fuel cell Electrochemically-active bacteria Enrichment of an electrochemically-active bacterial community Microbiology of a mediator-less MFC Optimization of MFC performance Design and performance of an MFC used as BOD sensor MFC to measure BOD values higher than 10 mg/l MFC design Enrichment and operation Performance MFC to measure BOD values lower than 10 mg/l Background Oligotrophic sensor design and performance BOD determination of samples containing oxygen and nitrate Oxygen and nitrate reduce current and coulombic efficiency Use of respiratory inhibitors MFC as a toxicity sensor Conclusions Acknowledgements 361 References 362

12 Contents xv 18 FEEDSTOCKS FOR BES CONVERSIONS Introduction Defined substrates utilized by BES Volatile fatty acids and other fermentation end products Soluble carbohydrates, amino acids and xenobiotics Complex substrates and wastewaters utilized by BES Cellulosic feedstocks Chitin Domestic wastewater Simulated and actual industrial wastewaters Other aspects of feedstock composition Feedstocks and BES integration in wastewater treatment processes Conclusions Acknowledgements 388 References INTEGRATING BES IN THE WASTEWATER AND SLUDGE TREATMENT LINE Introduction BES as the single biological treatment unit (A) or followed by an activated sludge system as a polishing step (B) Preacidification of organic wastewater before BES (C) Anaerobic digesters for sludge stabilization followed by BES (D) Generating caustic in the cathode of BES to control anaerobic digester ph (E) Denitrificaton in the cathode of BES to remove nutrients from water (F) Generating chemical reagents at cathodes for treatment purposes (G) Outlook Acknowledgements 405 References 405

13 SMALL convection, xvi Bioeleclrochemical Systems 20 PERIPHERALS OF BES - SCALE YET FEASIBLE (DEMONSTRATED) APPLICATIONS Introduction Artificial symbiosis Microbial fuel cells and their configurations Definition of peripherals Bridging the power divide Minimal peripheral requirements for continuous and autonomous operation Complexity in stacks Microbial Electrolysis Cells (MECs) that transform organic feedstocks into other types of energy (hydrogen or methane) but require input of electrical power in the process Microbial Electrolysis Cells (MECs) that consume electrical power to drive useful reactions (e.g. denitrification) 420 References TOWARDS A MATHEMATICAL DESCRIPTION OF BIOELECTROCHEMICAL SYSTEMS Introduction Mathematical modelling Model characteristics Mechanistics vs. empirism Dynamic vs. stationary models Level of segregation/aggregation How do model characteristics affect the model user? BESs modelling objectives Key elements for BESs modelling Existing BESs models Current challenges in BESs modelling Bioelectrode kinetics Electron transfer mechanisms Microbial activity: bioenergetics and kinetics Mass transport - diffusion and migration Biofilm and spatial modelling 444

14 focus Contents xvii 21.7 BESs modelling perspectives Acknowledgements 446 References OUTLOOK: RESEARCH DIRECTIONS AND NEW APPLICATIONS FOR BES BES research - on the application Fundamental research directions Understanding bioelectrochemical process fundamentals Practically inspired fundamental research areas Applied research opportunities Contributions and limitations of current research activities BESs for wastewater treatment? Is power the best product from BESs? Potential new BES applications Novel options for cathodic reductions Novel options for anodic oxidations BES Integration into practical applications Concluding thoughts on the future of BES 461 References 462 Index 467