Environmental and Energy Engineering

Stacking of microbial fuel cells (MFC) by connecting multiple small-sized units in a series is used for generating higher power from the MFCs. However, voltage reversal is a critical problem in a serially connected MFC unit. The voltage reversal often occurs when substrate concentration is relatively low in the anodic compartment. Two rectangular individual cells were stacked together in series: MFC1 was fed with 1 g glucose L -1 throughout the experiment while MFC2 was fed with various concentrations of glucose (0.1, 0.2, 0.3, 0.5 and 0.8 g L -1 ). Voltage reversal occurred when the stack configuration was performed using (1 ? 0.1) g glucose L -1 . The stacked configurations with (1 ? 0.2, 1 ? 0.3, 1 ? 0.5 and 1 ? 0.8) g glucose L -1 were operated successfully without the voltage reversal. The maximum powers of 1.88, 2.04, 3.6, 2.5 and 2.18 mW were obtained with the stacked configurations of (1 ? 0.2), (1 ? 0.3), (1 ? 0.5), (1 ? 0.8) and (1 ? 1) g glucose L -1 , respectively. Except in the stacked configuration with (1 ? 0.1) g glucose L -1 , the stacked voltages obtained were similar.

Pore-filled anion-exchange membranes (PFAEMs) with a thickness of about 25 μm have been prepared using porous polyethylene substrates and tested for diffusion dialysis (DD) application. The membranes possess strong mechanical properties (tensile strength and elongation at break of 125.8 MPa and 76.2%, respectively) as well as excellent electrochemical characteristics such as low electrical resistance ( o0.4 Ω cm 2 ), high anion transport number (4 0.97), and high fraction of conductive region on the membrane surface etc. Moreover, in order to further improve the diffusion dialysis performance of the PFAEMs, the surface of PFAEMs was modified by introducing a thin polypyrrole layer with good affinity to anions. As a result, the PFAEMs exhibited excellent DD performances (high acid permeability and selectivity) superior to that of commercial membrane (i.e. Neosepta-AFX, Astom Corp., Japan) by the surface-modification.

ABSTRACT Understanding exoelectrogenic reactions of the bioanode is limited due to its complexity and the absence of analytics. Impedance and thermodynamics of bioanode, abiotic anode, and riboflavin-amended anode were evaluated. Activation overpotential of the bioanode was negligible compared with that of the abiotic anode. Impedance spectroscopy shows that the bioanode had much lower charge transfer resistance and higher capacitance than the abiotic anode in low frequency reaction. In high frequency reaction, the impedance parameters, however, were relatively similar between the bioanode and the abiotic anode. At open-circuit impedance spectroscopy, a high frequency arc was not detected in the abiotic anode in Nyquist plot. Addition of riboflavin induced a phase angle shift and created curvature in high-frequency arc of the abiotic anode, and it also drastically changed impedance spectra of the bioanode.

For monitoring environmental conditions of remote places, sustainable power generators are necessary to power telemetry sensor systems. A sediment microbial fuel cell (SMFC) is a device that produces electricity biologically from organic matters in sediment. Because a SMFC utilizes sediment organic materials and microbial catalysts in river or oceanic sediment, a SMFC can be a feasible solution for sustainable power generation in remote places. However, oligotrophic sediment conditions often limit energy source supply, resulting in insufficient power output for operating electronic devices. The objective of this study is to investigate power generation and anode bacterial communities of SMFCs with different anode materials and carbon sources for enhancement of power output and longevity of SMFCs. Four kinds of anode electrodes were tested in SMFCs; a magnesium electrode (M), a magnesium electrode supplied with chitin particles (M+C), a graphite electrode (G), and a graphite electrode supplied with chitin particles (G+C). Average maximum power density was highest in Mg+C (1878 ± 982 mW m -2 ), followed by M (848 ± 348 mW m -2 ), G+C (1.9 ± 0.6 mW m -2 ) and G (0.7 ± 0.6 mW m -2 ). Maximum power densities of the magnesium electrodes were ~1,000 times larger than those of the graphite electrodes. The chitin supplement increased maximum power densities by 121% in the magnesium anodes and 164% in the graphite anodes on average. A magnesium electrode in M+C degraded more slowly than that of M. Anode bacterial communities of the magnesium anodes were diverse than the graphite anodes, and the supplemented chitin greatly influenced anode bacterial community compositions. Although magnesium corrosion was a main process of power production in the magnesium-anode SMFCs, species-level anode bacterial communities were very different between M and M+C. Anode bacterial communities of the chitin-absent anodes had larger richness estimates and diversity estimates than those of the chitin-supplemented anodes, suggesting that the saturated carbon source greatly simplified anode bacterial communities.