Continuous and efficient uranium recovery in a bioelectrochemical system

Microbial fuel cell (MFC) is a feasible technology for uranium removal and recovery from uranium-containing wastewater. However, the accumulation of reductive product (UO2) on the cathode surface hindered the continuous removal of uranium due to the increase of over-potential. In this study, we developed a microbial electrolysis cell (MEC) system in a mixed microbial consortium with a low energy input that can continuously remove uranium on the UO2-coated cathode. Thermodynamic calculation results demonstrated that the cathode potential controls U(VI) removal in the MEC system, and U(VI) removal was the contribution of the microbial process and the applied voltage (Eap). Experimental results indicated that the cathode potential for the electrochemical reduction of U(VI) on the UO2-coated cathode was about –0.64 V vs. Ag/AgCl, whereas the microbial species in the anode of MEC can provide an Ecathode of –0.47 V vs. Ag/AgCl. Therefore, only a small Eap (about 150 mV) can trigger the continuous U(VI) removal in the MEC. The continuous removal capacity of the UO2-coated cathode was evaluated over 15,830.86 μmol m−2, and the removal efficiencies were higher than 94.0% after all the 22 cyclic tests. Furthermore, over 98.0% of uranium can be recovered from the cathode by acid or alkali method, and the recovery process does not affect the electrode itself. The excellent continuous removal capacity and reusability of the electrode demonstrate that MEC is a promising technology for U(VI) removal from wastewater.