A new constructed wetland combined with microbial desalination cell and its application

Abstract Wastewater recycling can alleviate the shortage of water resources. Saline water is seldom treated with biological processes and the recycling utilization is low. Constructed wetland (CW) is a safe and economical ecological water treatment. However, the saline water treatment performance of CW is not good. Microbial desalination cell (MDC) utilizing the bioelectro-chemical principle achieves the functions of desalination and power generation. In this study, MDC was used to strengthen CW to form a composite system, MDC-CW, through optimizing design parameters. MDC-CW was applied in the treatment of salt-containing water. The average total nitrogen removal rate in MDC-CW-P1 reached 87.33% and the average COD removal rate was 92.79%. The average desalination rate of MDC-CW-P1 was 55.78% and the average voltage of MDC-CW-P1 reached 0.40 mV. It was found that planting canna indica in the MDC-CW was conducive to the functions of desalination and power generation. The above results were also verified by the microbial testing results of gravels in substrate, plant rhizosphere and electrodes. In addition, the decontamination of the device mainly depended on the functions of the bacteria commonly used in water treatment, such as Proteobacteria and Bacteroidetes, whereas the generation of power depended on the function of Geobacter. Salt ions moved spontaneously to the cathode and anode under the premise of current generation, so that the desalination function was realized under the selective isolation function of exchange membranes. The device design and laboratory application of MDC-CW experimentally accomplished the electrochemical technology and enlarged the treatment scale of CW.