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Watanabe K.,Hashimoto Light Energy Conversion Project | Watanabe K.,Tokyo University of Science | Watanabe K.,Tokyo University of Pharmacy and Life Science | Miyahara M.,Hashimoto Light Energy Conversion Project | And 4 more authors.
Applied Microbiology and Biotechnology | Year: 2011

Cassette-electrode microbial fuel cells (CE-MFCs) have been demonstrated useful to treat biomass wastes and recover electric energy from them. In order to reveal electricity-generation mechanisms in CE-MFCs, the present study operated a bench-scale reactor (1 l in capacity; approximately 1,000 cm 2 in anode and cathode areas) for treating a high-strength model organic wastewater (comprised of starch, peptone, and fish extract). Approximately 1 month was needed for the bench reactor to attain a stable performance, after which volumetric maximum power densities persisted between 120 and 150 mW/l throughout the experiment (for over 2 months). Temporal increases in the external resistance were found to induce subsequent increases in power outputs. After electric output became stable, electrolyte and anode were sampled from the reactor for evaluating their current-generation abilities; it was estimated that most of current (over 80%) was generated by microbes in the electrolyte. Cyclic voltammetry of an electrolyte supernatant detected several electron shuttles with different standard redox potentials at high concentrations (equivalent to or more than 100 μM 5-hydroxy-1,4- naphthoquinone). Denaturing gradient gel electrophoresis and quantitative real-time PCR of 16S ribosomal RNA gene fragments showed that bacteria related to the genus Dysgonomonas occurred abundantly in association with the increases in power outputs. These results suggest that mediated electron transfer was the main mechanism for electricity generation in CE-MFC, where high-concentration electron shuttles and Dysgonomonas bacteria played important roles. © 2011 Springer-Verlag.


Miyahara M.,Hashimoto Light Energy Conversion Project | Miyahara M.,Tokyo University of Pharmacy and Life Science | Hashimoto K.,Hashimoto Light Energy Conversion Project | Hashimoto K.,University of Tokyo | And 2 more authors.
Journal of Bioscience and Bioengineering | Year: 2013

Cassette-electrode microbial fuel cells (CE-MFCs) have been developed for the conversion of biomass wastes into electric energy. The present study modified CE-MFC for its application to wastewater treatment and examined its utility in a long-term (240 days) experiment to treat a synthetic wastewater, containing starch, yeast extract, peptone, plant oil, and a detergent (approximately 500 mg of total chemical oxygen demand [COD] per liter). A test MFC reactor (1 l in capacity) was equipped with 10 cassette electrodes with total anode and cathode projection areas of 1440 cm2, and the operation was initiated by inoculating with rice paddy-field soil. It was demonstrated that CE-MFC achieved COD removal rates of 80% at hydraulic-retention times of 6 h or greater, and electricity was generated at a maximum power density of 150 mW m-2 and Coulombic efficiency of 20%. Microbial communities established on anodes of CEs were analyzed by pyrosequencing of PCR-amplified 16S rRNA gene fragments, showing that Geobacter, Clostridium, and Geothrix were abundantly detected in anode biofilms. These results demonstrate the utility of CE-MFC for wastewater treatment, in which Geobacter and Geothrix would be involved in the electricity generation. © 2012 The Society for Biotechnology, Japan.


Nishio K.,University of Tokyo | Hashimoto K.,University of Tokyo | Hashimoto K.,Tokyo University of Science | Watanabe K.,Hashimoto Light Energy Conversion Project | And 2 more authors.
Bioscience, Biotechnology and Biochemistry | Year: 2013

Algal biomass serves as a fuel for electricity generation in microbial fuel cells. This study constructed a model consortium comprised of an alga-digesting Lactobacillus and an iron-reducing Geobacter for electricity generation from photo-grown Clamydomonas cells Total power-conversion efficiency (from Light to electricity) was estimated to be 0.47%.


Zhang L.,University of Tokyo | Zhang Y.,University of Tokyo | Wei Q.,HASHIMOTO Light Energy Conversion Project | Wei Q.,Japan Science and Technology Agency | And 7 more authors.
Macromolecular Rapid Communications | Year: 2012

Copolymers with an alternating structure of regioregular oligo(3-hexylthiophene) (O3HT) with different lengths and 2,5-dibutyl-3,6- di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) were synthesized through Stille coupling reaction. The light absorption of the copolymers can be rationally tuned to have a broad spectrum across the visible region by adjusting the length of O3HT. Organic solar cells fabricated with the copolymers and PCBM showed a broad photoresponse and a comparable efficiency to that of poly(3-hexylthiophene) (P3HT):PCBM cells. The external quantum efficiency and fluorescence spectra suggested that the intrachain energy transfer from the O3HT block to the vicinity of the DPP unit could limit the photovoltaic performance of the copolymers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nishio K.,University of Tokyo | Hashimoto K.,University of Tokyo | Watanabe K.,Hashimoto Light Energy Conversion Project | Watanabe K.,Tokyo University of Science
Applied Microbiology and Biotechnology | Year: 2010

Biological energy-conversion systems are attractive in terms of their self-sustaining and self-organizing nature and are expected to be applied to low-cost and environmentfriendly processes. Here we show a biofilm-based light/ electricity-conversion system that was self-organized from a natural microbial community. A bioreactor equipped with an air cathode and graphite-felt anode was inoculated with a green hot-spring microbialmat.When the reactor was irradiated with light, electric current was generated between the anode and cathode in accordance with the formation of green biofilm on the anode. Fluorescence microscopy of the green biofilm revealed the presence of chlorophyll-containing microbes of ∼10 μm in size, and these cells were abundant close to the surface of the biofilm. The biofilm community was also analyzed by sequencing of polymerase chain reactionamplified small-subunit rRNA gene fragments, showing that sequence types affiliated with Chlorophyta, Betaproteobacteria, and Bacteroidetes were abundantly detected. These results suggest that green algae and heterotrophic bacteria cooperatively converted light energy into electricity. © 2009 Springer-Verlag.


Shibanuma T.,University of Tokyo | Nakamura R.,University of Tokyo | Hirakawa Y.,University of Tokyo | Hashimoto K.,HASHIMOTO Light Energy Conversion Project | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2011

Morning light: In vivo photodissociation of CO from bacterial c-type cytochromes yields a redox-active Fe 2+ form, which can be oxidized at an electrode surface to the Fe 3+ form. Reduction by electrons from the metabolic pathway regenerates the Fe 2+ form (see picture). Spectroscopic monitoring of this process yields information on the in vivo respiratory electron-transport dynamics. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


PubMed | Hashimoto Light Energy Conversion Project
Type: Journal Article | Journal: Microbes and environments | Year: 2013

Some bacteria utilize (semi)conductive iron-oxide minerals as conduits for extracellular electron transfer (EET) to distant, insoluble electron acceptors. A previous study demonstrated that microbe/mineral conductive networks are constructed in soil ecosystems, in which Geobacter spp. share dominant populations. In order to examine how (semi)conductive iron-oxide minerals affect EET paths of Geobacter spp., the present study grew five representative Geobacter strains on electrodes as the sole electron acceptors in the absence or presence of (semi)conductive iron oxides. It was found that iron-oxide minerals enhanced current generation by three Geobacter strains, while no effect was observed in another strain. Geobacter sulfurreducens was the only strain that generated substantial amounts of currents both in the presence and absence of the iron oxides. Microscopic, electrochemical and transcriptomic analyses of G. sulfurreducens disclosed that this strain constructed two distinct types of EET path; in the absence of iron-oxide minerals, bacterial biofilms rich in extracellular polymeric substances were constructed, while composite networks made of mineral particles and microbial cells (without polymeric substances) were developed in the presence of iron oxides. It was also found that uncharacterized c-type cytochromes were up-regulated in the presence of iron oxides that were different from those found in conductive biofilms. These results suggest the possibility that natural (semi)conductive minerals confer energetic and ecological advantages on Geobacter, facilitating their growth and survival in the natural environment.


PubMed | Hashimoto Light Energy Conversion Project
Type: Journal Article | Journal: Journal of bioscience and bioengineering | Year: 2013

Cassette-electrode microbial fuel cells (CE-MFCs) have been developed for the conversion of biomass wastes into electric energy. The present study modified CE-MFC for its application to wastewater treatment and examined its utility in a long-term (240 days) experiment to treat a synthetic wastewater, containing starch, yeast extract, peptone, plant oil, and a detergent (approximately 500mg of total chemical oxygen demand [COD] per liter). A test MFC reactor (1l in capacity) was equipped with 10 cassette electrodes with total anode and cathode projection areas of 1440cm(2), and the operation was initiated by inoculating with rice paddy-field soil. It was demonstrated that CE-MFC achieved COD removal rates of 80% at hydraulic-retention times of 6h or greater, and electricity was generated at a maximum power density of 150mWm(-2) and Coulombic efficiency of 20%. Microbial communities established on anodes of CEs were analyzed by pyrosequencing of PCR-amplified 16S rRNA gene fragments, showing that Geobacter, Clostridium, and Geothrix were abundantly detected in anode biofilms. These results demonstrate the utility of CE-MFC for wastewater treatment, in which Geobacter and Geothrix would be involved in the electricity generation.


PubMed | Hashimoto Light Energy Conversion Project
Type: Journal Article | Journal: Applied microbiology and biotechnology | Year: 2011

Cassette-electrode microbial fuel cells (CE-MFCs) have been demonstrated useful to treat biomass wastes and recover electric energy from them. In order to reveal electricity-generation mechanisms in CE-MFCs, the present study operated a bench-scale reactor (1 l in capacity; approximately 1,000 cm(2) in anode and cathode areas) for treating a high-strength model organic wastewater (comprised of starch, peptone, and fish extract). Approximately 1 month was needed for the bench reactor to attain a stable performance, after which volumetric maximum power densities persisted between 120 and 150 mW/l throughout the experiment (for over 2 months). Temporal increases in the external resistance were found to induce subsequent increases in power outputs. After electric output became stable, electrolyte and anode were sampled from the reactor for evaluating their current-generation abilities; it was estimated that most of current (over 80%) was generated by microbes in the electrolyte. Cyclic voltammetry of an electrolyte supernatant detected several electron shuttles with different standard redox potentials at high concentrations (equivalent to or more than 100 M 5-hydroxy-1,4-naphthoquinone). Denaturing gradient gel electrophoresis and quantitative real-time PCR of 16S ribosomal RNA gene fragments showed that bacteria related to the genus Dysgonomonas occurred abundantly in association with the increases in power outputs. These results suggest that mediated electron transfer was the main mechanism for electricity generation in CE-MFC, where high-concentration electron shuttles and Dysgonomonas bacteria played important roles.

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