Bioelectrochemical recovery of ammonia–copper(II) complexes from wastewater using a dual chamber microbial fuel cell

The cathodic reduction of complex-state copper(II) was investigated in a dual chamber microbial fuel cell (MFC). The inner resistance of MFC system could be reduced in the presence of ionizing NH4+, however, mass transfer was hindered at higher ammonia concentration. Thermodynamic and electrochemical analyses indicated that the processes of complex dissociation and copper reduction were governed by the ratio of T[Cu]:T[NH3] and the pH of solution. The reduction of Cu(NH3)42+ could be achieved via two possible pathways: (1) releasing Cu2+ from Cu(NH3)42+, then reducing Cu2+ to Cu or Cu2O and (2) Cu(NH3)42+ accepting an electron and forming Cu(NH3)2+, and depositing as Cu or Cu2O consequently. At initial concentration of 350 mg T[Cu] L−1, copper removal efficiency of 96% was obtained at pH = 9.0 within 12 h (with △Cu/△COD = 1.24), 84% was obtained at pH = 3.0 within 8 h (with △Cu/△COD = 1.72). Cu(NH3)42+ was reduced as polyhedral deposits on the cathode.

► The feasibility of complex copper recovery using a dual chamber MFC was confirmed.
► Up to 96.26% of complex copper(II) removal was achieved in MFC from ammonia solution within 12 h.
► By acidifying catholyte, the structure of complex-copper(II) compound can be destabilized, then facilitate copper reduction.
► The deposited solid-state reduction products allowed for copper recovery.