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The effects of electrode surface modifications on biofilm formation and electron transfer in bioelectrochemical systems

Kun Guo (UGent)
(2014)
Author
Promoter
(UGent) and Stefano Freguia
Organization
Abstract
Bioelectrochemical systems (BESs) are bioreactors that use bacteria as catalysts to drive oxidation and/or reduction reactions at solid-state electrodes. They are considered as a promising technology for energy efficient wastewater treatment, power production, bioremediation, and the production of valuable chemicals. Currently, the practical application of this technology is limited by low current and power densities. Electrode surface modification has been proved an efficient way to enhance of the performance of BESs. However, there is still limited knowledge on the effects of surface chemistry on the biofilm formation and electron transfer. Moreover, most of the reported electrode modification methods are either complex, expensive or unscalable. There is a need to fill in some of these knowledge gaps and to develop simple, effective, and scalable surface modification methods to enhance the bioanode current output of BESs. Therefore, the objectives of this work were: (i) to clarify the effects of surface chemistry of carbon electrode on anodic biofilm formation and current generation in BESs; (ii) to develop a quick approach to achieve desirable surface chemical properties on carbon electrode for faster anodic biofilm formation; (iii) to invent a novel strategy to graft electron transfer mediator to carbon electrode surface to enhance extracellular electron transfer (EET); (iv) to establish a simple method to make stainless steel (SS) surface biocompatible for scalable electrodes of BESs. To investigate the effects of surface charge and surface hydrophobicity on anodic biofilm formation and current generation in BESs, glassy carbon electrodes were modified with –OH, –CH3, –SO3-, or –N+(CH3)3 functional groups and then tested as anode in BESs. The results demonstrated that: (i) positively charged and hydrophilic surfaces were more selective to electroactive microbes (e.g. Geobacter) and more conducive for electroactive biofilm formation; (ii) The effects of the surface hydrophilicity were more pronounced than surface charge; (iii) differences in the maximum current output between surface modifications were correlated with biomass quantity; and (iv) all biofilms were dominated by Geobacter populations, but the composition of –CH3-associated biofilms differed from those formed on surfaces with different chemical modification. Now that the mode of action of the surface charge was established with expensive aryl diazonium salts, the next step was to perform the modification in a more cost effective, realistic manner. To convert carbon the felt surface into hydrophilic and positively-charged surface, a cationic surfactant, cetyltrimethylammonium bromide (CTAB) based treatment method was developed. In an acetate-fed bioanode, the start-up time of current production and the time to reach stable current output at the CTAB-treated felt anodes were 36.1% and 49.4% shorter than the untreated anodes, respectively. Moreover, the maximum current output with these treated electrodes was 23.8% higher than the untreated counterparts. Comparing to the routinely used electrode pretreatment methods such as high temperature ammonia, HNO3/H2SO4 oxidation, NaOH/HCl soaking, and plasma treatment, surfactant treatment is quick, simple, cheap, and environmentally friendly way to make carbon felt surfaces hydrophilic and positively-charged. The use of this method will help researchers to save both time and chemicals involved in the electrode pretreatment procedure. To accelerate EET, immobilization of neutral red onto carbon electrodes was achieved via spontaneous reduction of in situ generated NR diazonium salts. The current output of NR-modified graphite felt electrodes when used as bioanodes in BESs were 3.63 ± 0.36 times higher than the unmodified electrodes, which demonstrated the effectiveness of covalently bound NR as insoluble redox mediator during the microbial anodic oxidation of acetate. Comparing to the existing NR modification methods, no nitric/sulfuric acids and organic solvents were involved, and no expensive equipment were required in the new method. Most importantly, the whole procedure of this method only takes a couple of hours. Hence, spontaneous reduction of in situ generated NR diazonium salts is a simple, effective, and environmentally friendly method to graft NR molecules on carbon surface. To enhance the biocompatibility of stainless steel felt (SS felt), iron oxide nanoparticles (IONPs) were in situ generated on SS felt by flame oxidation. Consequently, a robust anodic biofilm formation was achieved on SS felt surface in BESs. The current density of IONPs-coated SS felt electrodes were 14 times higher current than the untreated electrodes. The maximum current density achieved on the IONPs-coated SS felt (1.92 mA/cm2) was one of the highest current densities reported. The flame oxidized SS felt reported here meets all requirements of the ideal anode materials for BESs:(1) high conductivity; (2) good biocompatibility; (3) strong chemical stability; (4) large specific surface area; (5) excellent mechanical strength; and (6) low cost. Attributed to these advantages, flame oxidized SS felt holds exciting opportunities for scaling-up of anode and for achieving high current densities in BESs.
Keywords
bioelectrochemical systems, aryl diazonium salts, neutral red, surfactant, stainless steel felt, biofilm formation, microbial fuel cells, surface modification, extracellular electron transfer, surface chemistry

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Citation

Please use this url to cite or link to this publication:

MLA
Guo, Kun. “The Effects of Electrode Surface Modifications on Biofilm Formation and Electron Transfer in Bioelectrochemical Systems.” 2014 : n. pag. Print.
APA
Guo, K. (2014). The effects of electrode surface modifications on biofilm formation and electron transfer in bioelectrochemical systems. University of Queensland. School of Chemical Engineering ; Ghent University. Faculty of Bioscience Engineering, Brisbane St Lucia, QLD, Australia ; Ghent, Belgium.
Chicago author-date
Guo, Kun. 2014. “The Effects of Electrode Surface Modifications on Biofilm Formation and Electron Transfer in Bioelectrochemical Systems”. Brisbane St Lucia, QLD, Australia ; Ghent, Belgium: University of Queensland. School of Chemical Engineering ; Ghent University. Faculty of Bioscience Engineering.
Chicago author-date (all authors)
Guo, Kun. 2014. “The Effects of Electrode Surface Modifications on Biofilm Formation and Electron Transfer in Bioelectrochemical Systems”. Brisbane St Lucia, QLD, Australia ; Ghent, Belgium: University of Queensland. School of Chemical Engineering ; Ghent University. Faculty of Bioscience Engineering.
Vancouver
1.
Guo K. The effects of electrode surface modifications on biofilm formation and electron transfer in bioelectrochemical systems. [Brisbane St Lucia, QLD, Australia ; Ghent, Belgium]: University of Queensland. School of Chemical Engineering ; Ghent University. Faculty of Bioscience Engineering; 2014.
IEEE
[1]
K. Guo, “The effects of electrode surface modifications on biofilm formation and electron transfer in bioelectrochemical systems,” University of Queensland. School of Chemical Engineering ; Ghent University. Faculty of Bioscience Engineering, Brisbane St Lucia, QLD, Australia ; Ghent, Belgium, 2014.
@phdthesis{4392628,
  abstract     = {Bioelectrochemical systems (BESs) are bioreactors that use bacteria as catalysts to drive oxidation and/or reduction reactions at solid-state electrodes. They are considered as a promising technology for energy efficient wastewater treatment, power production, bioremediation, and the production of valuable chemicals. Currently, the practical application of this technology is limited by low current and power densities. Electrode surface modification has been proved an efficient way to enhance of the performance of BESs. However, there is still limited knowledge on the effects of surface chemistry on the biofilm formation and electron transfer. Moreover, most of the reported electrode modification methods are either complex, expensive or unscalable.
There is a need to fill in some of these knowledge gaps and to develop simple, effective, and scalable surface modification methods to enhance the bioanode current output of BESs. Therefore, the objectives of this work were: (i) to clarify the effects of surface chemistry of carbon electrode on anodic biofilm formation and current generation in BESs; (ii) to develop a quick approach to achieve desirable surface chemical properties on carbon electrode for faster anodic biofilm formation; (iii) to invent a novel strategy to graft electron transfer mediator to carbon electrode surface to enhance extracellular electron transfer (EET); (iv) to establish a simple method to make stainless steel (SS) surface biocompatible for scalable electrodes of BESs. 
To investigate the effects of surface charge and surface hydrophobicity on anodic biofilm formation and current generation in BESs, glassy carbon electrodes were modified with –OH, –CH3, –SO3-, or –N+(CH3)3 functional groups and then tested as anode in BESs. The results demonstrated that: (i) positively charged and hydrophilic surfaces were more selective to electroactive microbes (e.g. Geobacter) and more conducive for electroactive biofilm formation; (ii) The effects of the surface hydrophilicity were more pronounced than surface charge; (iii) differences in the maximum current output between surface modifications were correlated with biomass quantity; and (iv) all biofilms were dominated by Geobacter populations, but the composition of –CH3-associated biofilms differed from those formed on surfaces with different chemical modification.
Now that the mode of action of the surface charge was established with expensive aryl diazonium salts, the next step was to perform the modification in a more cost effective, realistic manner. To convert carbon the felt surface into hydrophilic and positively-charged surface, a cationic surfactant, cetyltrimethylammonium bromide (CTAB) based treatment method was developed. In an acetate-fed bioanode, the start-up time of current production and the time to reach stable current output at the CTAB-treated felt anodes were 36.1% and 49.4% shorter than the untreated anodes, respectively. Moreover, the maximum current output with these treated electrodes was 23.8% higher than the untreated counterparts. Comparing to the routinely used electrode pretreatment methods such as high temperature ammonia, HNO3/H2SO4 oxidation, NaOH/HCl soaking, and plasma treatment, surfactant treatment is quick, simple, cheap, and environmentally friendly way to make carbon felt surfaces hydrophilic and positively-charged. The use of this method will help researchers to save both time and chemicals involved in the electrode pretreatment procedure.
To accelerate EET, immobilization of neutral red onto carbon electrodes was achieved via spontaneous reduction of in situ generated NR diazonium salts. The current output of NR-modified graphite felt electrodes when used as bioanodes in BESs were 3.63 ± 0.36 times higher than the unmodified electrodes, which demonstrated the effectiveness of covalently bound NR as insoluble redox mediator during the microbial anodic oxidation of acetate. Comparing to the existing NR modification methods, no nitric/sulfuric acids and organic solvents were involved, and no expensive equipment were required in the new method. Most importantly, the whole procedure of this method only takes a couple of hours. Hence, spontaneous reduction of in situ generated NR diazonium salts is a simple, effective, and environmentally friendly method to graft NR molecules on carbon surface.
To enhance the biocompatibility of stainless steel felt (SS felt), iron oxide nanoparticles (IONPs) were in situ generated on SS felt by flame oxidation. Consequently, a robust anodic biofilm formation was achieved on SS felt surface in BESs. The current density of IONPs-coated SS felt electrodes were 14 times higher current than the untreated electrodes. The maximum current density achieved on the IONPs-coated SS felt (1.92 mA/cm2) was one of the highest current densities reported. The flame oxidized SS felt reported here meets all requirements of the ideal anode materials for BESs:(1) high conductivity; (2) good biocompatibility; (3) strong chemical stability; (4) large specific surface area; (5) excellent mechanical strength; and (6) low cost. Attributed to these advantages, flame oxidized SS felt holds exciting opportunities for scaling-up of anode and for achieving high current densities in BESs.},
  author       = {Guo, Kun},
  isbn         = {9789059897045},
  keywords     = {bioelectrochemical systems,aryl diazonium salts,neutral red,surfactant,stainless steel felt,biofilm formation,microbial fuel cells,surface modification,extracellular electron transfer,surface chemistry},
  language     = {eng},
  pages        = {XIX, 156},
  publisher    = {University of Queensland. School of Chemical Engineering ; Ghent University. Faculty of Bioscience Engineering},
  school       = {Ghent University},
  title        = {The effects of electrode surface modifications on biofilm formation and electron transfer in bioelectrochemical systems},
  year         = {2014},
}