A combined microbial desalination cell and electrodialysis system for copper-containing wastewater treatment and high-salinity-water desalination

A new concept for heavy metal removal by forming hydroxide precipitation using alkalinity produced by microbial desalination cell (MDC) was proposed. Four five-chamber MDCs were hydraulically connected to concurrently produce alkalinity to treat synthetic copper-containing wastewater and salt removal. There was nearly complete removal of copper, with a maximum removal rate of 5.07 kg/(m3 d) under the initial copper concentration of 5000 mg/L (final pH of 7). The final copper concentration met the emission standard for electroplating of China (0.5 mg/L, GB 21900-2008). XRD analysis indicated copper was precipitated as Cu2Cl(OH)3. The best performance of MDCs in terms of average power density, salt removal and COD removal rate achieved in stage 3 were 737.3 ± 201.1 mW/m2, 53.6 ± 0.8 kg/(m3 d), and 1.84 ± 0.05 kgCOD/(m3 d) respectively. For purposes of water recovery, an electrodialysis (ED) system was presented based on in-situ utilization of generated electricity by MDCs as post-desalination treatment for salt effluent after sedimentation. The maximum discharging voltage of 12.75 ± 1.26 V at switching time (Ts) of 15 min using a capacitor-based circuit produced a maximum desalination efficiency of 30.4 ± 2.6%. These results indicated that this combined system holds great promise for real-world treatment of copper-containing wastewater and deep desalination of high-salinity-water.