Recovery of silver metal and electric power generation using a microbial fuel cell

The purpose of this study was to model recovering silver metal from wastewater using a two-chambered silver (I) microbial fuel cell (Ag(I)-MFC) with carbon felt electrodes. Both anode and cathode chambers held a volume of about 900 mL. The anode and cathode were graphite felts with a surface area of 122.3 and 34.6 cm2. The chambers were separated by an anion exchange membrane with a surface area of about 78.3 cm2. The MFC was discharged by connecting a 1,000 Ω load resistor. The anode chamber contained 10mM sodium acetate with 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid buffer medium as electron donors, and the cathode chamber contained synthetic wastewater with silver nitrate. It was verified that the Ag(I)-MFC system in the present study could successfully be operated. The effluent silver concentration was in the range of 0.003–0.153 ppm, representing that the recovery efficiencies for silver ion were in the range of 98.2–92.3% for the Ag(I) concentration range from 50 to 4000 ppm after operating the reaction for 10 h. Initial Ag(I) concentration affected the power generation by both increasing the cathode potential and decreasing the internal resistance of the MFC. The highest maximum power density and current density was 1.93 W/m2 and 4.25 A/m2 (for 2,000 ppm Ag(I)), respectively. Shinny silver metals on the graphite felt cathode were visible and they were verified to be very pure silver by scanning electron microscope and energy dispersive spectroscopy. A charge transfer resistance of 1,687 Ω was obtained for 1,000 ppm Ag(I) by electrochemical impedance spectroscopy.