Moon Sik Hyun

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.

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.

Practical field application of a novel BOD monitoring system.

A biochemical oxygen demand (BOD) monitoring system, based on electrochemically-active bacteria in combination with a microbial fuel cell, has been developed for the purpose of on-site, on-line and real-time monitoring of practical wastewater. A microbial fuel cell that had been enriched with electrochemically-active bacteria was used as the basis of the measurement system. When synthetic wastewater was fed to the system, the current generation pattern and its Coulombic yield were found to be dependent on the BOD5 of the synthetic wastewater. A linear correlation between the Coulombic yields and the BOD5 of the synthetic wastewater were established. Real wastewater obtained from a sewage treatment plant also produced a highly linear correlation between the Coulombic yield and BOD5 in the system. To examine on-site, on-line and real-time monitoring capability, the BOD monitoring system was installed at a sewage treatment plant. Over 60 days, the measurement system was successfully operated with high accuracy and good stability with the measuring period for a sample being 45 min. This application showed that the application of the measurement system was a rapid and practical way for the determination of BOD5 in water industries.

Membrane‐electrode assembly enhances performance of a microbial fuel cell type biological oxygen demand sensor

A membrane‐electrode assembly (MEA) was applied to a microbial fuel cell (MFC) type biological oxygen demand (BOD) sensor and the performance of the sensor was assessed. To establish the optimal conditions for MEA fabrication, platinum‐catalysed carbon cloth cathodic electrodes were assembled with cation exchange membranes under various temperatures and pressures. By analysing coulombs from the MFCs, it could be determined that the optimal hot‐pressing conditions were 120 °C and 150 kg cm−2 for 30 s. When the MEA fabricated under optimal conditions and an air cathode were utilized for the construction of the MFC type BOD sensor, coulombs increased to 4.65 C from 0.52 C and power increased to 69,080 mW m−3 from 880 mW m−3 (at a BOD concentration of 200 mg L−1), respectively, compared with the conventional MFC lacking a MEA. The increased power improved the performance of the MFC type BOD sensor: sensitivity increased from 1.2 × 10−3 to 1.8 × 10−2 C per mg L−1 of BOD, with good linearity (r2 = 0.97) and over 97% repeatability. We conclude that the MEA can be successfully applied to MFCs to make them highly sensitive BOD sensors.

A Novel Combined Biomonitoring System for BOD Measurement and Toxicity Detection using Microbial Fuel Cells

Microbial fuel cell enriched with electrochemically-active bacteria using sludge was successfully applied as BOD and toxicity detection biosensors. The current from the microbial fuel cells was proportional to concentration up to 200 mg/L of BOD5 with high linearity. A microbial fuel cell could be also applied to a toxicity detection biosensor. An electric current signal change was observed in the presence of toxic substances (singular/complex) such as cadmium, lead, chromium(VI), mercury, cyanide, arsenic, PCB, organophosphorus and surfactant. By combining the principles of BOD measurement and toxicity detection, a novel biomonitoring system that could simultaneously monitor BOD concentration and the presence of toxic substances in aqueous system could be developed.