KEYWORDS: Microsoft Foundation Class Library, Solar cells, Electrodes, Solar energy, Sulfur, Photovoltaics, Copper indium gallium selenide, Metals, Thin films, Oxidation
Combined photovoltaic module-microbial fuel cell construction shows prospect of advanced autonomous functioning effective energy-production system with the possibility of round-the-clock power generation. Application of Desulfuromonas sp. as anode biocatalyst in photovoltaic (PV) - microbial fuel cell (MFC) could support highly effective eco-friendly energy derivation with simultaneous reduction of organic and inorganic wastes in water environment. D. acetoxidans is exoelectrogenic bacterium that supports S0-reduction with H2S formation and S0-oxidation while an electrode serves as the electron acceptor. Simultaneous sulfur redox processes enhance electron transfer to the electrode surface that may increase the effectiveness of microbial fuel cell performance. It was shown that D. acetoxidans IMV B-7384 possesses selective resistance to 0.5-2.5 mM of copper, iron, nickel, manganese and lead ions. Metal-resistant strains of this bacterium may help overcome H2S toxicity, which is produced because of dissimilative S0-reduction, since divalent cations will interact with sulfide ions, forming insoluble precipitates. Thus D. acetoxidans IMV B-7384 may be applied for remediation of toxic metal ions from water environments because of metal fixation in form of insoluble complexes of metal sulfides. D. acetoxidans IMV B-7384 is presumed to have the capability to convert organic compounds, such as malate, pyruvate, succinate and fumarate via reductive stage of tricarboxylic acid cycle. Thus application of effluents as anolyte in MFC, based on D. acetoxidans IMV B-7384, may cause decrease of its organic content with formation of simple benign constituents, such as CO2 and H2O. Hence the advanced system for eco-friendly energy generation with simultaneous water pollution control is proposed.
Desulfuromonas acetoxidans IMV B-7384 is exoelectrogenic obligate anaerobic sulfur-reducing bacterium. Its one of the first described electrogenic bacterium that performs complete oxidation of an organic substrate with electron transfer directly to the electrode in microbial fuel cell (MFC). This bacterium is very promising for MFC development because of inexpensive cultivation medium, high survival rate and selective resistance to various heavy metal ions. The size of D. acetoxidans IMV B-7384 cells is comparatively small (0.4-0.8×1-2 μm) that is highly beneficial while application of porous anode material because of complete bacterial cover of an electrode area with further significant improvement of the effectiveness of its usage. The interconnection between functioning of reductive stage of tricarboxylic acid (TCA) cycle under anaerobic conditions, and MFC performance was established. Malic, pyruvic, fumaric and succinic acids in concentration 42 mM were separately added into the anode chamber of MFC as the redox agents. Application of malic acid caused the most stabile and the highest power generation in comparison with other investigated organic acids. Its maximum equaled 10.07±0.17mW/m2 on 136 hour of bacterial cultivation. Under addition of pyruvic, succinic and fumaric acids into the anode chamber of MFC the maximal power values equaled 5.80±0.25 mW/m2; 3.2±0.11 mW/m2, and 2.14±0.19 mW/m2 respectively on 40, 56 and 32 hour of bacterial cultivation. Hence the malic acid conversion via reductive stage of TCA cycle is shown to be the most efficient process in terms of electricity generation by D. acetoxidans IMV B-7384 in MFC under anaerobic conditions.
Microbial fuel cells (MFCs) are devices that use bacteria as the catalysts to oxidize organic and inorganic matter and generate current. Up to now, several classes of extracellular electron transfer mechanisms have been elucidated for various microorganisms. Shewanellaceae and Geobacteraceae families include the most of model exoelectrogenic microorganisms. Desulfuromonas acetoxidans bacterium inhabits aquatic sedimental sulfur-containing environments and is philogenetically close to representatives of Geobacteraceae family. Two chamber microbial fuel cell (0.3 l volume) was constructed with application of D. acetoxidans IMV B-7384 as anode biocatalyst. Acetic, lactic and fumaric acids were separately applied as organic electron donors for bacterial growth in constructed MFC. Bacterial cultivation in MFC was held during twenty days. Lactate oxidation caused electric power production with the highest value up to 0.071 mW on 64 hour of D. acetoxidans IMV B-7384 growth. Addition of acetic and fumaric acids into bacterial growth medium caused maximal power production up to 0.075 and 0.074 mW respectively on the 40 hour of their growth. Increasing of incubation time up to twentieth day caused decrease of generated electric power till 0.018 mW, 0.042 mW and 0.047 mW under usage of lactic, acetic and fumaric acids respectively by investigated bacteria. Power generation by D. acetoxidans IMV B-7384 was more stabile and durable under application of acetic and fumaric acids as electron donors in constructed MFC, than under addition of lactic acid in the same concentration into the growth medium.
Sulfur - reducing bacteria are a part of normal microflora of natural environment. Their main function is supporting
of reductive stage of sulfur cycle by hydrogen sulfide production in the process of dissimilative sulfur-reduction. At the
same time these bacteria completely oxidize organic compounds with CO2 and H2O formation. It was shown that they are able to generate electric current in the two chamber microbial-anode fuel cell (MAFC) by interaction between these two processes. Microbial-anode fuel cell on the basis of sulfur- and ferric iron-reducing Desulfuromonas acetoxidans bacteria has been constructed. It has been shown that the amount of electricity generation by investigated bacteria is influenced by the concentrations of carbon source (lactate) and ferric iron chloride. The maximal obtained electric current and potential difference between electrodes equaled respectively 0.28-0.29 mA and 0.19-0.2 V per 0.3 l of bacterial suspension with 0.4 g/l of initial biomass that was grown under the influence of 0.45 mM of FeCl3 and 3 g/l of sodium lactate as primal carbon source. It has also been shown that these bacteria are resistant to different concentrations of silver ions.
Desulfuromonas acetoxidans are uncoloured gram-negative sulfur bacteria that inhabit sulfur containing aquatic
environments. These are gram-negative obligatory anaerobes that have an ability to reduce S0 to H2S and Fe3+ to Fe2+ in
the processes of dissimilation Sulfur- and Fe (III)-reduction. Existence of Sulfur and Ferric ions in the anaerobic
sediments causes binding of hydrogen sulfide which diffuses from the zone of sulfur reducing. As a result hydrogen
sulfide is detoxificated. The ability of these bacteria to use Sulfur or Ferric ions as acceptors of electrons during organic
carbon oxidation causes their special adaptation to the changes of surrounding environment. Interaction between
bacterial Desulfuromonas acetoxidans cells and different concentrations of ferrous Fe2+ and ferric Fe3+ ions possibly
could cause the changes of cells' light scattering characteristics. The changes of cells relative content and their size
distribution during five days of cultivation under the influence of FeSO4 and FeCl3×6H2O in concentration from 0.01 to
10 mM was investigated by the new method of measurement. It includes sounding of flow suspended bacterial cells by
monochromatic coherent light, registration of signals of co-operation of sounding radiation with the explored
microbiological objects by detects of the changes of amplitudes and durations of scattered light impulses. Under the
influence from 0.01 to 10 mM of FeSO4 the maximum of cells' size distribution changed from 0.55 to 0.62 μm and effect
of investigated range of FeCl3×6H2O concentrations caused it changes from 0.43 to 0.49 μm during five days of sulfurreducing
Desulfuromonas acetoxidans bacteria growth.
Desulfuromonas acetoxidans, which is regarded to the oldest microorganisms that exist in the Earth, are uncoloured
gram-negative obligatory anaerobic bacteria that have an ability to reduce S0 to H2S. This process supports bacteria with
sufficient amount of energy which they need for growth. At the same time high concentrations of hydrogen sulfide are
very toxic towards all living organisms. Different metal ions that exist in surrounding environment in small
concentrations are essential for microorganisms because they support normal functionality of them. But in high
concentrations they have a detrimental influence on cell structure and it functions. Srains of D. acetoxidans bacteria that
have high toxic metals resistance can neutralize the toxicity of hydrogen sulfide, which is the final product of
dissimilative sulfurreduction, and these metals as the result of their particular binding and forming the insoluble
precipitations. Light scattering changes and metals accumulation ability of D. acetoxidans bacterial cells under the
influence of CuSO4, PbNO3, ZnSO4 and CdSO4 have been investigated. The changes of light scattering characteristics of
bacterial D. acetoxidans cells on the base of their size distribution and relative content under the influence of
investigated metal salts have been observed by the new method of measurement.
Microbial fuel cell (MFC) technologies represent the newest approach for generating electricity - bioelectricity
generation from biomass using bacteria. Desulfuromonas acetoxidans are aquatic obligatory anaerobic sulfur-reducing
bacteria that possess an ability to produce electric current in the processes of organic matter oxidation and Fe3+- or Mn4+-
reduction. These are pattern objects for MFC systems. They could be applied as a highly effective and self-sustaining
model of wastewater treatment which contains energy in the form of biodegradable organic matter. But wastewaters
contain high concentrations of xenobiotics, such as different heavy metals that have a detrimental effect towards all
living organisms. The influence of different concentrations of MnCl2×4H2O, FeSO4 CuSO4, CdSO4, ZnSO4 and PbNO3
on light scattering properties of aquatic D. acetoxidans bacteria on the base of their cells' size distribution and relative
content has been investigated by the new method of measurement. The cell distribution curve was in the range of 0.4 -
1.4 μm. The most crucial changes of cell concentration dependences, compared with other investigated metal ions, have
been observed under the influence of copper ions. The ability of D. acetoxidans bacteria to produce electric current upon
the specific cultivation conditions and the influence of Fe2+ and Mn2+ has been verified.
Light scattering properties of bacterial cells mostly depend on their sizes, refractive indexes of their components and
surrounding environment. Interaction between bacterial cells and 3d3 type transition metals causes their optical
characteristics' changes. Desulfuromonas acetoxidans are uncolored gram-negative obligatory anaerobic sulfur reducing
bacteria that can be used as microbial fuel cells with high electron recovery from different organic compounds oxidation
to electric current as a result of electrons transfer in the processes of sulfur and some 3d3 type transition metals reduction,
such as Ferrum and Manganese. In this study size distribution and relative content in the chosen interval of sizes (0.2 -
2.0 μm) of sulfur reducing D. acetoxidans bacterial cells under the influence of different concentrations of manganese
chloride (II) hexahydrate, ferrous chloride (III) hexahydrate and ferrous sulfate (II) have been investigated by the new
method of measuring. A method includes sounding of flow suspended bacterial cells by monochromatic coherent light,
registration of signals of co-operation of sounding radiation with the explored microbiological objects by detects
amplitudes and durations of scattered light impulses. Correlation between changes of light-scattering properties and
growth of Desulfuromonas acetoxidans cells under these conditions has been shown.
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