Alternate charging and discharging of capacitor to enhance the electron production of bioelectrochemical systems.
ABSTRACT A bioelectrochemical system (BES) can be operated in both "microbial fuel cell" (MFC) and "microbial electrolysis cell" (MEC) modes, in which power is delivered and invested respectively. To enhance the electric current production, a BES was operated in MFC mode first and a capacitor was used to collect power from the system. Then the charged capacitor discharged electrons to the system itself, switching into MEC mode. This alternate charging and discharging (ACD) mode helped the system produce 22-32% higher average current compared to an intermittent charging (IC) mode, in which the capacitor was first charged from an MFC and then discharged to a resistor, at 21.6 Ω external resistance, 3.3 F capacitance and 300 mV charging voltage. The effects of external resistance, capacitance and charging voltage on average current were studied. The average current reduced as the external resistance and charging voltage increased and was slightly affected by the capacitance. Acquisition of higher average current in the ACD mode was attributed to the shorter discharging time compared to the charging time, as well as a higher anode potential caused by discharging the capacitor. Results from circuit analysis and quantitatively calculation were consistent with the experimental observations.
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ABSTRACT: Microbial fuel cell (MFC) technology offers a sustainable approach to harvest electricity from biodegradable materials. Energy production from MFCs has been demonstrated using external resistors or charge pumps, but such methods can only dissipate energy through heat or receive electrons passively from the MFC without any controllability. This study developed a new approach and system that can actively extract energy from MFC reactors at any operating point without using any resistors, especially at the peak power point to maximize energy production. Results show that power harvesting from a recirculating-flow MFC can be well maintained by the maximum power point circuit (MPPC) at its peak power point, while a charge pump was not able to change operating point due to current limitation. Within 18-h test, the energy gained from the MPPC was 76.8 J, 76 times higher than the charge pump (1.0 J) that was commonly used in MFC studies. Both conditions resulted in similar organic removal, but the Coulombic efficiency obtained from the MPPC was 21 times higher than that of the charge pump. Different numbers of capacitors could be used in the MPPC for various energy storage requirements and power supply, and the energy conversion efficiency of the MPPC was further characterized to identify key factors for system improvement. This active energy harvesting approach provides a new perspective for energy harvesting that can maximize MFC energy generation and system controllability.Environmental Science & Technology 04/2012; 46(9):5247-52. · 5.48 Impact Factor
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ABSTRACT: Capacitor is a storage device to harvest charge produced from microbial fuel cells (MFCs). In intermittent charging mode, the capacitor is charged by an MFC first, and then discharged through an external resistance. The charge harvested by capacitor is affected by the charging and discharging frequency. In the present study, the effect of the charging and discharging frequency on charge harvest was investigated. At the switching time (ts) of 100s, the average current over each time segment reached its maximum value (1.59mA) the earliest, higher than the other tested conditions, and the highest COD removal (63%) was also obtained, while the coulombic efficiency reached the highest of 67% at the ts of 400s. Results suggested that lower ts led to higher current output and COD removal, but appropriate ts should be selected in consideration of charge recovery efficiency.Bioresource Technology 08/2013; · 5.04 Impact Factor
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ABSTRACT: To enhance the MFC's denitrification performance, this study investigated three different external circuits/operation modes of the MFC: alternative charging and discharging (ACD), intermittent charging (IC) and constant external resistance (R). Results showed that the ACD and IC modes offered larger output currents as well as higher nitrate and COD removal rates than the steady R mode. The best performance was achieved with the ACD mode. At the initial [COD]=∼1200mg/L and [NO3(-)]=∼140mg/L, the ACD mode delivered an average power density of 0.91W/m(3), an average nitrate removal rate of 15.5mg/(Ld) and an average COD removal rate of 137mg/(Ld), 268%, 207% and 168% respectively greater than those by the R mode. The enhancement by the ACD and IC modes was more pronounced at lower nitrate and COD concentrations and/or with the lack of stirring of electrolyte solutions.Bioresource Technology 08/2013; 147C:228-233. · 5.04 Impact Factor