Short communicationCatalytic response of microbial biofilms grown under fixed anode potentials depends on electrochemical cell configuration
Graphical abstract
Introduction
In microbial electrogenesis bacteria oxidize substrates to generate electricity by transferring electrons to a solid electrode, leading to potential for electricity generation in microbial fuel cells (MFC) or to offset the potential required for hydrogen, and other value-added chemical, production at cathodes in bio-electrochemical systems (BES) [1], [2]. BES operating conditions affect growth kinetics and metabolism of the microbial community (Fig. 1). In microbial fuel cells, with current flow between an anode and a cathode across a fixed resistance load, the potential imposed on the anode is difficult to control, because of variations in anode potential as a function of mass transport to, catalytic activity at, and current flow between, anode and cathode. Growth of microbial biofilms can however be induced by precise control of anode potential vs. a reference electrode using a potentiostat. The electron transfer capabilities of microbial films induced to grow by imposition of specific anode potentials can be thus explored in fundamental studies of electroactive biofilms on electrodes. However, results comparing applied anode potentials show a range of response in terms of effect of potential on fuel cell power and/or current density [3], [4], [5], [6], [7], [8], as reviewed recently by Kumar et al. [4].
There are few studies comparing current densities achieved using a fixed resistance load MFC to induce microbial biofilm growth on anodes to those using fixed anode potentials. Wang et al. [9] compare biofilm growth under an applied anode potential of +0.4 V vs. Ag/AgCl to that across a fixed 1000 Ω resistance load between anode and a ferricyanide-reducing cathode, separated by an Ultrex cation exchange membrane. The application of a fixed anode potential produced a reproducible current in fewer cycles, and shorter time, compared to that using the fixed resistance load cell. Other studies on BESs using either individual applied anode potentials (different values), or a single applied potential, show variable results in terms of current or power generation, as reviewed recently [4]. There are however no reports to our knowledge comparing electrocatalytic properties of anode potential-induced biofilms as a function of the electrochemical cell configuration (i.e., in membrane-separated vs. membrane-less electrochemical cells). When MFCs and BESs are operated, anode potentials measured during peak power generation show typical values around −0.40 to −0.48 V vs. Ag/AgCl for mixed cultures oxidizing acetate [4]. Applied anode potentials more positive than this therefore provide a driving force for microbially catalyzed oxidation of acetate in biofilms on anodes. We probe the effect of −0.3 V, −0.2 V and +0.2 V vs. Ag/AgCl applied anode potentials on biofilm performance, as a function of electrochemical cell configuration, using anaerobic sludge as a mixed culture inoculum and acetate as feed.
Section snippets
Reactor configuration and operation
Experiments were conducted in either membrane-less or membrane-separated electrochemical cell configuration. The membrane-less configuration was a single borosilicate glass cell containing a Ag/AgCl (3 M NaCl) reference electrode, and both anode and cathode electrodes. For the membrane-separated configuration, the anodic and cathodic borosilicate glass half-cells were separated by a 12 cm2 Nafion® 117 proton exchange membrane (Sigma, Ireland), with the reference electrode in the anode half-cell.
Results and discussion
Slow scan cyclic voltammetry (CV) of the biofilms, induced to grow on graphite electrodes, Fig. 2, display sigmoidal curves typical of bioelectrocatalytic oxidation of substrate [7], [12], [13], [14], [15], [16] indicative of an electrochemical redox transition coupled to a catalytic oxidation reaction. The observed CV shape and mid-point potential (∼−0.41 V) are the same as those observed for biofilms, oxidizing acetate, induced to grow on anodes from single cultures of Geobacter sulfurreducens
Conclusions, outlook and implications
Linking anode potential to evolution of microbial biofilm current and/or power generation and microbial diversity information has been an issue of debate over the past decade. Our preliminary results indicate that consideration of the electrochemical cell configuration, with or without separating membrane, is required in any attempt to select an applied anode potential or to alter microbial activity in such systems. Among membrane-less bioelectrochemical cells, the electrochemical cell poised
Acknowledgments
Authors acknowledge funding from FP 7 People Programme of European Commission, Marie Curie Intra European Fellowship for Career Development (Grant A/6342 – PIEF-GA-2009-237181) and Science Foundation Ireland (Charles Parsons Energy Research Award – 06/CP/E006).
References (26)
- et al.
Accelerated start-up of two-chambered microbial fuel cells: effect of anodic positive poised potential
Electrochimica Acta
(2009) - et al.
Low-temperature (7 °C) anaerobic treatment of a trichloroethylene-contaminated wastewater: microbial community development
Water Research
(2011) - et al.
Selection of a variant of Geobacter sulfurreducens with enhanced capacity for current production in microbial fuel cells
Biosensors and Bioelectronics
(2009) - et al.
Forming electrochemically active biofilms from garden compost under chronoamperometry
Bioresource Technology
(2008) - et al.
Comparison of microbial electrolysis cells operated with added voltage or by setting anode potential
International Journal of Hydrogen Energy
(2011) - et al.
Effect of anode aeration on the performance and microbial community of an air-cathode microbial fuel cell
Chemical Engineering Journal
(2012) Powering microbes with electricity: direct electron transfer from electrodes to microbes
Environmental Microbiology Reports
(2011)- et al.
A novel approach for spatial analysis of global gene expression within a Geobacter sulfurreducens current-producing biofilm
ISME Journal
(2010) - et al.
The anode potential regulates bacterial activity in microbial fuel cells
Applied Microbial Biotechnology
(2008) - et al.
Does bioelectrochemical cell configuration and anode potential affect biofilm response?
Biochemical Society Transactions
(2012)
Optimal set anode potentials vary in bioelectrochemical systems
Environmental Science Technology
Selecting anode-respiring bacteria based on anode potential: phylogenetic, electrochemical, and microscopic characterization
Environmental Science Technology
Geobacter sulfurreducens biofilms developed under different growth conditions on glassy carbon electrodes: insights using cyclic voltammetry
Chemical Communications
Cited by (35)
Microbial electricity-driven anaerobic phenol degradation in bioelectrochemical systems
2024, Environmental Science and EcotechnologyBio-hydrogen production through microbial electrolysis cell: Structural components and influencing factors
2023, Chemical Engineering JournalAccelerated start-up and improved performance of wastewater microbial fuel cells in four circuit modes: Role of anodic potential
2022, Journal of Power SourcesCitation Excerpt :The electrochemical limitations which result from ohmic, kinetic, and transport resistance can be reduced through cell architecture optimization. Anodic potential is a key factor affecting the start-up process, and is directly related to the microbial catalytic activity [15], community composition [16] and metabolic pattern [17]. Growth of microbial biofilms can be induced by precise control of anode potential vs. a reference electrode using potentiostat or DC power supply to apply external power, but the connection to the external power changes the MFC into MEC.
Anode modification: An approach to improve power generation in microbial fuel cells (MFCs)
2022, Development in Wastewater Treatment Research and Processes: Bioelectrochemical Systems for Wastewater ManagementAnodic-potential-tuned bioanode for efficient gaseous toluene removal in an MFC
2021, Electrochimica ActaElectrons selective uptake of a metal-reducing bacterium Shewanella oneidensis MR-1 from ferrocyanide
2019, Biosensors and BioelectronicsCitation Excerpt :Electrocatalysis promotes an oxidation or a reduction process electrochemically by increasing current or reducing overpotential, giving an asymmetric voltammetry (Lee et al., 2017). Catalytic responses of EAB from substrate (e.g., acetate) were widely studied in BES (Jana et al., 2014; Kumar et al. 2013a, 2013b). In the current case, the electrocatalysis of [Fe(CN)6]4- oxidation manifests a strong anodic peak accomplished with a weak cathodic peak, compared to other microbes and molecules (Fig. 1 middle and Fig. S3).