High Power Density from a Miniature Microbial Fuel Cell Using \u3ci\u3eShewanella oneidensis\u3c/i\u3e DSP10

A miniature microbial fuel cell (mini-MFC) is described that demonstrates high output power per device crosssection (2.0 cm2) and volume (1.2 cm3). Shewanella oneidensis DSP10 in growth medium with lactate and buffered ferricyanide solutions were used as the anolyte and catholyte, respectively. Maximum power densities of 24 and 10 mW/m2 were measured using the true surface areas of reticulated vitreous carbon (RVC) and graphite felt (GF) electrodes without the addition of exogenous mediators in the anolyte. Current densities at maximum power were measured as 44 and 20 mA/m2 for RVC and GF, while short circuit current densities reached 32 mA/m2 for GF anodes and 100 mA/m2 for RVC. When the power density for GF was calculated using the cross sectional area of the device or the volume of the anode chamber, we found values (3 W/m2, 500 W/m3) similar to the maxima reported in the literature. The addition of electron mediators resulted in current and power increases of 30-100%. These power densities were surprisingly high considering a pure S. oneidensis culture was used. We found that the short diffusion lengths and high surface-area-to-chamber volume ratio utilized in the mini-MFC enhanced power density when compared to output from similar macroscopic MFCs

High Power Density from a Miniature Microbial Fuel Cell Using \u3ci\u3eShewanella oneidensis\u3c/i\u3e DSP10

A miniature microbial fuel cell (mini-MFC) is described that demonstrates high output power per device crosssection (2.0 cm2) and volume (1.2 cm3). Shewanella oneidensis DSP10 in growth medium with lactate and buffered ferricyanide solutions were used as the anolyte and catholyte, respectively. Maximum power densities of 24 and 10 mW/m2 were measured using the true surface areas of reticulated vitreous carbon (RVC) and graphite felt (GF) electrodes without the addition of exogenous mediators in the anolyte. Current densities at maximum power were measured as 44 and 20 mA/m2 for RVC and GF, while short circuit current densities reached 32 mA/m2 for GF anodes and 100 mA/m2 for RVC. When the power density for GF was calculated using the cross sectional area of the device or the volume of the anode chamber, we found values (3 W/m2, 500 W/m3) similar to the maxima reported in the literature. The addition of electron mediators resulted in current and power increases of 30-100%. These power densities were surprisingly high considering a pure S. oneidensis culture was used. We found that the short diffusion lengths and high surface-area-to-chamber volume ratio utilized in the mini-MFC enhanced power density when compared to output from similar macroscopic MFCs

Probing Single- to Multi-Cell Level Charge Transport in Geobacter Sulfurreducens DL-1

Microbial fuel cells, in which living microorganisms convert chemical energy into electricity, represent a potentially sustainable energy technology for the future. Here we report the single-bacterium level current measurements of Geobacter sulfurreducens DL-1 to elucidate the fundamental limits and factors determining maximum power output from a microbial fuel cell. Quantized stepwise current outputs of 92(±33) and 196(±20) fA are generated from microelectrode arrays confined in isolated wells. Simultaneous cell imaging/tracking and current recording reveals that the current steps are directly correlated with the contact of one or two cells with the electrodes. This work establishes the amount of current generated by an individual Geobacter cell in the absence of a biofilm and highlights the potential upper limit of microbial fuel cell performance for Geobacter in thin biofilms.Chemistry and Chemical Biolog

Laboratory growth of denitrifying water column microbial consortia from deep-sea shipwrecks in the northern Gulf of Mexico [version 2; referees: 2 approved]

Background: Shipwrecks serve as a rich source for novel microbial populations that have largely remained undiscovered. Low temperatures, lack of sunlight, and the availability of substrates derived from the shipwreck’s hull and cargo may provide an environment in which microbes can develop unique metabolic adaptations.   Methods: To test our hypothesis that shipwrecks could influence the microbial population involved in denitrification when a consortium is grown in the laboratory, we collected samples proximate to two steel shipwrecks in the northern Gulf of Mexico. Then under laboratory conditions, we grew two independent denitrifying microbial consortia. Each consortium was grown by using the BART assay system and analyzed based on growth kinetics, ion chromatography and 16S amplicon sequencing. Results: Both denitrifying consortia were different from each other based on varied growth profiles, rates of nitrate utilization and 16S amplicon sequencing. Conclusions: Our observations conclude that the laboratory grown water column microbial consortia from deep-sea shipwrecks in the Gulf of Mexico are able to undergo aggressive denitrification

Laboratory growth of denitrifying water column microbial consortia from deep-sea shipwrecks in the northern Gulf of Mexico [version 3; referees: 2 approved]

Background: Shipwrecks serve as a rich source for novel microbial populations that have largely remained undiscovered. Low temperatures, lack of sunlight, and the availability of substrates derived from the shipwreck’s hull and cargo may provide an environment in which microbes can develop unique metabolic adaptations.   Methods: To test our hypothesis that shipwrecks could influence the microbial population involved in denitrification when a consortium is grown in the laboratory, we collected samples proximate to two steel shipwrecks in the northern Gulf of Mexico. Then under laboratory conditions, we grew two independent denitrifying microbial consortia. Each consortium was grown by using the BART assay system and analyzed based on growth kinetics, ion chromatography and 16S amplicon sequencing. Results: Both denitrifying consortia were different from each other based on varied growth profiles, rates of nitrate utilization and 16S amplicon sequencing. Conclusions: Our observations conclude that the laboratory grown water column microbial consortia from deep-sea shipwrecks in the Gulf of Mexico are able to undergo aggressive denitrification

Air-exposed microbial fuel cells and screening techniques

Microbial fuel cells (MFCs) harvest energy from a wide variety of natural carbon sources to produce electricity at neutral pH and ambient temperatures. To date, standard H2/O2 PEMFC technology has yet to generate significant power under those conditions. Because most environments on earth are exposed to significant levels of oxygen, we believe the transition from sediment based MFCs to oxygen-tolerant MFCs is necessary. This transition would require both a way to simultaneously sequester the metal-reducing microbes and reduce the overall concentration of oxygen in the anode chamber. Recent work suggests that power can be generated with significant oxygen in the anolyte when using three dimensional (3D) electrodes in a miniature MFC design; potentially expanding the role of MFCs to function in more diverse regions (i.e., water column, air/water interface). Exposing the anode to air will also create unique growing conditions for the microbes themselves compared to the standard anaerobic anode conditions used in MFCs

Engineering Microbial Fuels Cells: Recent Patents and New Directions

Fundamental research into how microbes generate electricity within microbial fuel cells (MFCs) has far outweighed the practical application and large scale development of microbial energy harvesting devices. MFCs are considered alternatives to standard commercial polymer electrolyte membrane (PEM) fuel cell technology because the fuel supply does not need to be purified, ambient operating temperatures are maintained with biologically compatible materials, and the biological catalyst is self-regenerating. The generation of electricity during wastewater treatment using MFCs may profoundly affect the approach to anaerobic treatment technologies used in wastewater treatment as a result of developing this energy harvesting technology. However, the materials and engineering designs for MFCs were identical to commercial fuel cells until 2003. Compared to commercial fuel cells, MFCs will remain underdeveloped as long as low power densities are generated from the best systems. The variety of designs for MFCs has expanded rapidly in the last five years in the literature, but the patent protection has lagged behind. This review will cover recent and important patents relating to MFC designs and progress

Late transition metal organometallic porphyrin complexes as catalysts for the activation of organic and biological substrates

The porphyrin ligand provides a stable, adjustable environment for a wide variety of metal ions. Two distinct porphyrin systems were studied; core-modified rhodium and iridium porphyrins (Chapter 1-2) and water-soluble β-fluorinated rhodium porphyrins (Chapters 3-5). Both porphyrin systems were used in the development of tunable complexes for catalytic transition metal mediated organic and biological reactions. Our initial hypothesis was that this weakly basic ligand environment could be used to access new pathways for catalytic oxidation reactions of alkanes, oxidants for biological substrates, and as catalysts to generate or purify gases for use in fuel cells. Rhodium(III) and iridum(III) derivatives of 5,10,15,20-tetraphenyl-21-thiaporphrin [STPP] and 5,10,15,20-tetramesityl-21-thiaporphyrin [STMP] were synthesized for use as alkane functionalization catalysts (Chapter 1). Rhodium complexes of 5,10,15,20-tetraphenyl-21-oxaporphrin [OTPP] and 5,10,15,20-tetramesityl-21-oxaporphyrin [OTMP] were synthesized to provide a more porphyrin-like coordination geometry, as described in Chapter 2. The syntheses and characterization data for water-soluble β-fluorinated porphyrins is reported in Chapter 3. The oxidation of nicotinamide cofactors catalyzed by rhodium derivatives of water soluble porphyrins under aerobic conditions is discussed in Chapter 4. The water-soluble β-fluorinated metalloporphyrins described in Chapter 4 were used to catalyze the oxidation of formic acid or its by-product (carbon monoxide) to generate pure hydrogen fuel cell streams (Chapter 5). Up to 18,000 turnovers were calculated for the decomposition of formic acid at ninety degrees Celsius with rhodium(III) 5,10,15,20-tetrakis(3-sulfonato-2,b-difluorophenyl)2,3,7,8,12,13,17,18-octafluoroporphyrin (RhTSF16TPP). The oxidation of carbon monoxide catalyzed by these water-soluble complexes showed the greatest rate with RhTSF16TPP (140 M-1s-1) in 100 mM sodium hydroxide solution at room temperature. With the addition of redox mediators (phosphomolybdic acid or indigo carmine) this reaction was catalytic under anaerobic conditions. Addition of halides (Cl-, Br-, I-) increased the rate of reduction of RhTSF16TPP at neutral pH to rates competitive with the reaction in 100 mM NaOH. These complexes apparent lack of reactivity with hydrogen makes them good candidates as catalysts for the selective oxidation of carbon monoxide in hydrogen fuel streams

Diversifying Biological Fuel Cell Designs by Use of Nanoporous Filters

The use of proton exchange membranes (PEMs) in biological fuel cells limits the diversity of novel designs for increasing output power or enabling autonomous function in unique environments. Here we show that selected nanoporous polymer filters (nylon, cellulose, or polycarbonate) can be used effectively in place of PEMs in a miniature microbial fuel cell (mini-MFC, device cross-section 2 cm2), generating a power density of 16 W/m3 with an uncoated graphite felt oxygen reduction reaction (ORR) cathode. The incorporation of polycarbonate or nylon membranes into biological fuel cell designs produced comparable power and durability to Nafion-117 membranes. Also, high power densities for novel larger (5 cm3 anode volume, 0.6 W/m3) and smaller (0.025 cm3 projected geometric volume, average power density 10 W/m3) chamberless and pumpless microbial fuel cells were observed. As an additional benefit, the nanoporous membranes isolated the anode from invading natural bacteria, increasing the potential applications for MFCs beyond aquatic sediment environments. This work is a practical solution for decreasing the cost of biological fuel cells while incorporating new features for powering long-term autonomous devices