Kyu-Seon Yoo

Bioelectrochemical enhancement of direct interspecies electron transfer in upflow anaerobic reactor with effluent recirculation for acidic distillery wastewater

Methane production in the upflow anaerobic bioelectrochemical reactor (UABE) treating acidic distillery wastewater was compared to the upflow anaerobic sludge blanket reactor (UASB), and the electron transfer pathways for methane production were also evaluated in the effluent recirculation. The methane productions from reactors were influenced by the low pH of influent wastewater. However, the methane production rate and yield of the UABE were 2.08L/L.d and 320mL/g CODr, which were higher than the UASB. The effluent recirculation containing alkalinity neutralized the acidic influent and increased the upflow velocity in both reactors, and improved the direct interspecies electron transfer more in the UABE. When the effluent recirculation ratio was 3.0 in the UABE, the methane production rate and yield were reached up to 3.88L/L.d and 501.0mL/g CODr, respectively. The UABE requires electrode installation and electrical energy for operation, but the benefits from increased methane production are much higher.

Performance of Upflow Anaerobic Bioelectrochemical Reactor Compared to the Sludge Blanket Reactor for Acidic Distillery Wastewater Treatment

The performance of upflow anaerobic bioelectrochemical reactor (UABE), equipped with electrodes (anode and cathode) inside the upflow anaerobic reactor, was compared to that of upflow anaerobic sludge blanket (UASB) reactor for the treatment of acidic distillery wastewater. The UASB was stable in pH, alkalinity and VFAs until the organic loading rate (OLR) of 4.0 g COD/L.d, but it became unstable over 4.0 g COD/L.d. As a response to the abrupt doubling in OLR, the perturbation in the state variables for the UABE was smaller, compared to the UASB, and quickly recovered. The UABE stability was better than the UASB at higher OLR of 4.0-8.0 g COD/L.d, and the UABE showed better performance in specific methane production rate (2,076 mL CH4/L.d), methane content in biogas (66.8%), and COD removal efficiency (82.3%) at 8.0 g COD/L.d than the UASB. The maximum methane yield in UABE was about 407 mL/g CODr at 4.0 g COD/L.d, which was considerably higher than about 282 mL/g CODr in UASB. The rate limiting step for the bioelectrochemical reaction in UABE was the oxidation of organic matter on the anode surface, and the electrode reactions were considerably affected by the pH at 8.0 g COD/L.d of high OLR. The maximum energy efficiency of UABE was 99.5%, at 4.0 g COD/L.d of OLR. The UABE can be an advanced high rate anaerobic process for the treatment of acidic distillery wastewater.

Polarized electrode enhances biological direct interspecies electron transfer for methane production in upflow anaerobic bioelectrochemical reactor

The influence of polarized electrodes on the methane production, which depends on the sludge concentration, was investigated in upflow anaerobic bioelectrochemical (UABE) reactor. When the polarized electrode was placed in the bottom zone with a high sludge concentration, the methane production was 5.34 L/L.d, which was 53% higher than upflow anaerobic sludge blanket (UASB) reactor. However, the methane production was reduced to 4.34 L/L.d by placing the electrode in the upper zone of the UABE reactor with lower sludge concentration. In the UABE reactor, the methane production was mainly improved by the enhanced biological direct interspecies electron transfer (bDIET) pathway, and the methane production via the electrode was a minor fraction of less than 4% of total methane production. The polarized electrodes that placed in the bottom zone with a high sludge concentration enhance the bDIET for methane production in the UABE reactor and greatly improve the methane production.

Two-stage Bioprocesses Combining Dark H2 Fermentation: Organic Waste Treatment and Bioenergy Production

This study was performed to investigate the application of dark H2 fermentation to two-stage bioprocesses for organic waste treatment and energy production. We reviewed information about the two-stage bioprocesses combining dark H2 fermentation with CH4 fermentation, photo H2 fermentation, microbial fuel cells (MFCs), or microbial electrolysis cells (MECs) by using academic information databases and university libraries. Dark fermentative bacteria use organic waste as the sole source of electrons and energy, converting it into H2. The reactions related to dark H2 fermentation are rapid and do not require sunlight, making them useful for treating organic waste. However, the degradation is not complete and organic acids remain. Thus, dark H2 fermentation should be combined with a post-treatment process, such as CH4 fermentation, photo H2 fermentation, MFCs, or MECs. So far, dark H2 fermentation followed by CH4 fermentation is a promising two-stage bioprocess among them. However, if the problems of manufacturing expenses, operational cost, scale-up, and practical applications will be solved, the two-stage bioprocesses combining dark H2 fermentation with photo H2 fermentation, MFCs, or MECs have also infinite potential in organic waste treatment and energy production. This paper demonstrated the feasibility of two-stage bioprocesses combining dark H2 fermentation as a novel system for organic waste treatment and energy

Effect of External Resistance on Electrical Properties of Two-Chamber type Microbial Fuel Cells

The Effects of external resistance on electrical properties such as current density, power density and coulombic efficiency were investigated in two-chamber type MFCs using a ferricyanide as reducing agent. A stable electricity was produced when a constant time elapsed after innoculation of mixed cultures into the anode compartment; voltages from 0.13 to 0.16 V was measured at 50 Ω of external resistance. When the external resistance was increased, the current density decreased and the power density rapidly increased and then slowly decreased. Big variation of electrical properties was observed in high-current density region due to the concentration loss related with substrate consumption in repeated experiments changing the external resistance. The maximum power density (175.8 mW/m) and coulombic efficiency (46.1%) were obtained at 100 Ω of the external resistance which is nearest with the internal resistance (134 Ω) of MFC system.

Modification of Anode Surface with Hydrogel and Multiwall Carbon Nanotube for High Performance of Microbial Fuel Cells

The surface of graphite fiber fabric anode was modified with a hydrogel and a mixture of hydrogel and multiwall carbon nanotube, and their effectiveness were compared to the unmodified anodes in a batch microbial fuel cell (microbial fuel cells). The maximum power density of the MFC was determined by both performance of the anode and cathode. The maximum power density for the MFC with the anode modified with the mixture of hydrogel and multiwall carbon nanotube was 1,162 mW/m which was 27.7% higher than that with the unmodified graphite fiber fabric anode. “The mixture of hydrogel and multiwall carbon nanotube is a good surface modifier for anode with high biological affinity and low activation losses.”

Analysis of Influence Factors of Interaction on the Electric Power of Microbial Fuel Cell

Microbial fuel cell (MFC) is a device to produce a electricity from the oxidation of organic materials using microorganism. Recently many researchers have been studying MFC which is focused as regeneration energy source. Previews studies have focused every each factor that influence the production of electric power. However they didn`t study a lot about the correlation among the factors. In order to improve the MFC, we analysed the factors which influencing the generation of electric power of MFC. Also, we made a new compartment to verify the correlations among the factors efficiently. Based on the result obtained from the experiments in the laboratory, we analysed the factors and we suggested a new concept of waste water treatment system to produce electrical energy during the treatment of waste water.