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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. Source


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. Source


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. Source


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%. Source


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. Source

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