[Biocathode denitrification in a two-columnar microbial fuel cell].

The biocathode of the two-columnar microbial fuel cell was used to denitrify. Factors influencing denitrification performance and power production were studied. When the external resistance decreased from 50 omega to 5 omega, the nitrate removal rate increased from 0.26 mg/(L x h) to 0.76 mg/(L x h). The nitrite accumulated to 55 mg/L with the external resistance decreasing to 5 omega. The nitrate degradation followed the zero order reaction model when the initial nitrate concentration was 20-120 mg/L. The power generation was not affected by the nitrate concentration distinctly. The nitrite concentration increased with the initial nitrate concentration. The nitrite removal could be enhanced by adding organic matter, without significant influence on the power generation.

Electricity generation from glucose by a Klebsiella sp. in microbial fuel cells.

As electrochemically active bacteria play an important role in microbial fuel cells (MFCs), it is necessary to get a comprehensive understanding of their electrogenesis mechanisms. In this study, a new electrochemically active bacterium, Klebsiella sp. ME17, was employed into an "H" typed MFC for electrogenesis, with glucose as the electron donor. The maximum power density was 1,209 mW/m2 at a resistance of 340 Omega and the maximum current was 1.47 mA. Given the original anode medium, fresh medium, and the supernatant of the anode medium in the same MFC, respectively, the polarization curves illustrated that the strain produced mediators to promote extracellular electron transfer. The anode medium supernatant was electrochemically active, based on cyclic voltammogram, and the supernatant was very likely to contain quinone-like substances, as indicated by spectrophotometric and excitation-emission matrix fluorescence spectroscopy analysis. Further investigation on the color and ultraviolet absorbance at 254 nm of the filtered anode medium showed that the redox states of mediators strongly associated with the electricity generation states in MFCs.

[Influence of environmental factors on electricity production by microbial fuel cell inoculation Shewanella baltica].

The influences of the anodic substance, concentration, pH and temperature on the electricity production by MFCs were discussed. The lactic sodium was better than acetic sodium or glucose. The power density of MFC and the concentration of lactic sodium were well filled with Monod model. The power density was 1236 mW/m2 when the pH of anodic chamber was 8. The power density of MFC increased with the pH increasing from 6 to 8, which was due to the anodic internal resistance. The power density was 1 197 mW/m2 when the temperature was 50 degrees C. The power density of MFC changed with temperature because the anodic resistance decreased with the temperature increasing. While the temperature changed from 20 degrees C to 50 degrees C, the current density and the temperature were well filled in Arrhenius equation.

[Characteristic in electricity-generation and wastewater-treatment by the two-cylinder microbial fuel cells].

A two-cylinder MFC, which is of new configuration, was constructed to study its power generation and waste water treatment performance. When the graphite granule was used in anode as packing material, the internal resistance was 38.9 Omega. The anodic resistance, ohmic resistance and the cathodic resistance were 5.1, 14.1 and 18.7 Omega respectively. The maximal power density was 6,253 mW/m3. When the concentration of COD was higher than 1,000 mg/L, the removal load was 1.6 kg/(m3 x d) and the columbic efficient was 10%-12%. When the graphite granule with the diameter of 6 mm, the graphite granule with the diameter of 3 mm, carbon felt and the improved carbon felt were used as anode packing materials, the MFCs' resistances were 47, 39, 28 and 33 Omega and the stabilization cycles were 20, 18, 11 and 18 d, respectively. Considering steadily performance, the improved carbon felt and the graphite granule with diameter of 3 mm are more suitable as anode packing material.

[Electricity generation by the microbial fuel cells using carbon nanotube as the anode].

The characteristic of anode plays an important role in the performance of the microbial fuel cell (MFC). Thus, carbon nanotube (CN), flexible graphite (FG) and activated carbon (AC) were used as anode material in this study, and the performances of three MFCs (CN-MFC, FG-MFC and AC-MFC) were studied. The results show that CN is a kind of suitable material to be used as anode in the MFC. The maximal power densities of CN-MFC, FG-MFC and AC-MFC are 402,354 and 274 mW/m2, respectively. The CN-MFC shows a higher power density and coulombic efficiency compared with FG-MFC and AC-MFC. The CN-anode can reduce the internal resistance obviously. The internal resistances of CN-MFC, AC-MFC and FG-MFC are 263, 301 and 381 omega, respectively. The protein contents on the CN-anode, AC-anode and FG-anode are 149, 132 and 92 microg/cm2 after stable operation, and there is a positive relation between the protein content and internal resistance. The conductivity of the three types of MFCs from high to low was FG-MFC, CN-MFC and AC-MFC, which was accordant with the ohmic resistance. The stable times of CN-MFC, FG-MFC and AC-MFC, which were needed to measure the internal resistances, were 1800, 1200 and 300 s respectively.

[Electricity generation using the packing-type microbial fuel cells].

The packing-type microbial fuel cells (MFCs) were constructed using the granular graphite and the carbon felt as packing materials. The start-up time of the packing-type MFC was about 1 d, which was lower than that of the flat-type MFC. The maximal power density (Pm) of the MFC with carbon felt as packing material was 1502 mW/m2 (37.6 W/m3), which was higher than that with granular graphite as packing material. The carbon felt and carbon paper were sintered together to enhance the electric conductivity. Compared with the flat-type MFC, the area-specific resistance of the packing-type MFC decreased from 0.071 omega x m2 to 0.051 omega x m2, the maximal current density increased from 3000 mA to 8000 mA, the Pm increased from 1100 mW/m2 (27.5 W/m3) to 2426 mW/m2 (60.7 W/m3) and the potentials of anode decreased about 100 mV. The flow rate affected the power generation of the MFC. When the flow rate was lower than 1 mL/min, the Pm dropped with the flux decreasing. The packing-type MFC was operated for over 30 and the coulomb efficiency was about 10.6%.

[Effect of the initial anode potential on electricity generation in microbial fuel cell].

The initial anode potential of the microbial fuel cell (MFC) was changed by additional circuit in the anode chamber, and the influence of the initial anode potential on the electricigens was studied. When the initial anode potential was 350 mV (vs Hg/Hg2 Cl2), the growth of microorganisms was much slower than that of the microorganisms which grew on the anode with an initial potential of -200 mV or 200 mV (vs Hg/Hg2 Cl2). After stable electricity generation, the anode resistances of the three MFCs, which had initial anode potentials of 350 mV, 200 mV and -200 mV respectively, were 71 Omega, 43 Omega and 80 Omega. The community structures in MFCs, before and after the electricity generation, were also studied by denaturing gradient gel electrophoresis (DGGE). Clostridium sticklandii, Pseudomonas mendocina and Paenibacillus taejonensis were the three most enriched strains on the anode.

[Composition and measurement of the apparent internal resistance in microbial fuel cell].

The electrochemical limitations on the performance of microbial fuel cells (MFCs) are mainly due to the internal resistance. The total resistance in the MFC was expressed as the apparent internal resistance (R(i)) which was partitioned into ohmic resistance (R(omega)) and non-ohmic resistance (R(n)), referring to the equivalent circuit of the MFC. In the one-chamber MFC, R(i) and R(omega) were measured using the steady discharging method and the current interrupt method, and they were 289 omega and 99 omega, respectively. The maximal power density was 241 mW/m2 when the external resistance equaled to the apparent internal resistance. The stabilization time of 60 s was enough to remove the influence of the capacitors in the steady discharging method. When the MFC was in the activation overpotential area, the ohmic overpotential area and the concentration overpotential area respectively, R(n) accounted for 93%, 66% and 75% in R(i). The ratio of R(n) to R(i) was the lowest when power output of the one-chamber MFC reached its highest value. Decreasing R(n) and R(omega) is the key to one-chamber MFC's output increasing.

Composition and distribution of internal resistance in three types of microbial fuel cells.

High internal resistance is a key problem limiting the power output of the microbial fuel cell (MFC). Therefore, more knowledge about the internal resistance is essential to enhance the performance of the MFC. However, different methods are used to determine the internal resistance, which makes the comparison difficult. In this study, three different types of MFCs were constructed to study the composition and distribution of internal resistance. The internal resistance (R(i)) is partitioned into anodic resistance (R(a)), cathodic resistance (R(c)), and ohmic resistance (R(Omega)) according to their origin and the design of the MFCs. These three resistances were then evaluated by the "current interrupt" method and the "steady discharging" method based on the proposed equivalent circuits for MFCs. In MFC-A, MFC-B, and MFC-C, the R(i) values were 3.17, 0.35, and 0.076 Omega m(2), the R(Omega) values were 2.65, 0.085, and 0.008 Omega m(2), the R(a) values were 0.055, 0.115, and 0.034 Omega m(2), and the R(c) values were 0.466, 0.15, and 0.033 Omega m(2), respectively. For MFC-B and MFC-C, the remarkable decrease in R(i) compared with the two-chamber MFC was mainly ascribed to the decline in R(Omega) and R(c). In MFC-C, the membrane electrodes' assembly lowered the ohmic resistance and facilitated the mass transport through the anode and cathode electrodes, resulting in the lowest R(i) among the three types.