Hyung Joo Kim

OPERATIONAL PARAMETERS AFFECTING THE PERFORMANCE OF A MEDIATOR-LESS MICROBIAL FUEL CELL

A mediator-less microbial fuel cell was optimized in terms of various operating conditions. Current generation was dependent on several factors such as pH, resistance, electrolyte used, and dissolved oxygen concentration in the cathode compartment. The highest current was generated at pH 7. Under the operating conditions, the resistance was the rate-determining factor at over 500 omega. With resistance lower than 500 omega, proton transfer and dissolved oxygen (DO) supply limited the cathode reaction. A high strength buffer reduced the proton limitation to some extent. The DO concentration was around 6 mg l(-1) at the DO limited condition. The fact that oxygen limitation was observed at high DO concentration is believed to be due to the poor oxygen reducing activity of the electrode used, graphite. The current showed linear relationship with the fuel added at low concentration, and the electronic charge was well correlated with substrate concentration from up to 400 mg l(-1) of COD(cr). The microbial fuel cell might be used as a biochemical oxygen demand (BOD) sensor.

A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens

Abstract Direct electron transfer from different Shewanella putrefaciens strains to an electrode was examined using cyclic voltammetry and a fuel cell type electrochemical cell. Both methods determine the electrochemical activity of the bacterium without any electrochemical mediators. In the cyclic voltammetric studies, anaerobically grown cells of Shewanella putrefaciens MR-1, IR-1, and SR-21 showed electrochemical activities, but no activities were observed in aerobically grown Shewanella putrefaciens cells nor in aerobically and anaerobically grown E. coli cell suspensions. The electrochemical activities measured by the cyclic voltammetric method were closely related to the electric potential and current generation capacities in the microbial fuel cell system. Cytochromes localized to the outer membrane are believed to facilitate the direct electron transfer to the electrode from the intact bacterial cells. The concentration of the electron donor in the anode compartment determined the current generation capacity and potential development in the microbial fuel cell. When the high concentration of the bacteria (0.47 g dry cell weight/liter) and an electrode that has large surface area (apparent area: 50 cm2) were used, relatively high Coulombic yield (over 3 C for 12 h) was obtained from the bacteria.

Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor

A mediator-less microbial fuel cell (MFC) was used as a biochemical oxygen demand (BOD) sensor in an amperometric mode for real-time wastewater monitoring. At a hydraulic retention time of 1.05 h, BOD values of up to 100 mg/l were measured based on a linear relationship, while higher BOD values were measured using a lower feeding rate. About 60 min was required to reach a new steady-state current after the MFCs had been fed with different strength artificial wastewaters (Aws). The current generated from the MFCs fed with AW with a BOD of 100 mg/l was compared to determine the repeatability, and the difference was less than 10%. When the MFC was starved, the original current value was regained with a varying recovery time depending on the length of the starvation. During starvation, the MFC generated a background level current, probably due to an endogenous metabolism.

Novel BOD (biological oxygen demand) sensor using mediator-less microbial fuel cell

A microbial fuel cell type of biosensor was used to determine the biochemical oxygen demand (BOD) of wastewater. The biosensor gave a good correlation between the BOD value and the coulomb produced. The BOD sensor has been operated for over 5 years in a stable manner without any servicing. This is much longer that that of previously reported BOD biosensors.

Electrochemical activity of an Fe(III)-reducing bacterium, Shewanella putrefaciens IR-1, in the presence of alternative electron acceptors

Cyclic voltammetry demonstrated that cells of Shewanella putrefaciens grown under anaerobic conditions without nitrate were electrochemically active. The electrochemical activity was inactivated reversibly by exposure to air, but not by nitrate. Lactate and an applied potential at +200 mV against an Ag/AgCl reference electrode restored the electrochemical activity. These findings can be used to improve the performance of a mediator-less microbial fuel cell using electrochemically active bacteria in the presence of nitrate.

Isolation of taxol, an anticancer drug produced by the endophytic fungus, Phoma betae

Phoma betae, an endophytic fungus, was isolated from the healthy leaves of Ginkgo biloba . The fungus was screened for the production of taxol on a modified liquid medium for the first time. The fungal species were identified by their characteristic culture morphology and molecular analysis. The presence of taxol was confirmed by spectroscopic: ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR), liquid chromatography–mass spectrometry (LC-MS); and chromatographic: thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) methods of analysis. The taxol production was quantified by HPLC analysis. The maximum amount of taxol production was recorded as 795 μg/L. The production rate was 15,900-fold more than that found in the culture broth of earlier reported fungus, Taxomyces andreanae . The extracted fungal taxol demonstrate a strong cytotoxic activity in the in vitro culture of tested human cancer cells by apoptotic assay. This indicates that the increase in taxol concentration induced an increased cell death. A polymerase chain reaction (PCR) based screening for taxadiene synthase (ts), a unique gene in the formation of the taxane skeleton was confirmed as a molecular blueprint for taxol biosynthesis. These results designate that the fungus, P. betae is an excellent candidate for taxol supply and can serve as a potential species for genetic engineering to enhance the production of taxol to a higher level. Key words : Taxol production, Phoma betae, analytical methods, cytotoxicity assay, taxadiene synthase.

In Vitro Cytotoxic Evaluation of MgO Nanoparticles and Their Effect on the Expression of ROS Genes

Water-dispersible MgO nanoparticles were tested to investigate their cytotoxic effects on oxidative stress gene expression. In this in vitro study, genes related to reactive oxygen species (ROS), glutathione S-transferase (GST) and catalase, were quantified using real-time polymerase chain reactions (molecular level) and molecular beacon technologies (cellular level). The monodispersed MgO nanoparticles, 20 nm in size, were used to treat human cancer cell lines (liver cancer epithelial cells) at different concentrations (25, 75 and 150 µg/mL) and incubation times (24, 48 and 72 h). Both the genetic and cellular cytotoxic screening methods produced consistent results, showing that GST and catalase ROS gene expression was maximized at 150 µg/mL nanoparticle treatment with 48 h incubation. However, the genotoxic effect of MgO nanoparticles was not significant compared with control experiments, which indicates its significant potential applications in nanomedicine as a diagnostic and therapeutic tool.

Microfluidic Separation of a Soluble Substance Using Transverse Diffusion in a Layered Flow

This paper presents a practical flow-through method to separate anisole and ethyl phenylacetate, respectively, from a polystyrene mixture. The microfluidic separation uses different diffusive dynamics of the substances transverse to the lamination flow formed in a microchannel. The effect of inlet flow rates and ambient temperature on separation is examined. Additionally, the possibility of the separation of the light substance from the mixture with different molecular weight is shown numerically and experimentally. The separation efficiency is explained by the facts that the relaxation time depends on the inlet flow rate and that the diffusivity depends on the ambient temperature. This method can be applied to separate monomers from aggregates.