Electrodialytic concentration of landfill leachate effluent: Lab- and pilot-scale test, and assessment

Abstract

The treatment of landfill leachate, which is highly polluted wastewater, is a critical challenge for waste-to-energy power plants in China. In recent years, pressure-driven membrane processes such as ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and disk-tube reverse osmosis (DTRO) have been used to treat landfill leachate for water recovery. However, the water recovery ratio is relatively low because of the high osmotic pressure of the concentrated landfill leachate, and the treatment of DTRO concentrate is still a key issue. In this study, electrodialysis (ED), an electro-driven membrane process, was integrated into the current pressure-driven membrane processes to separate and concentrate the UF permeate. The results indicate that the optimal ion exchange membranes for assembly in the ED stack are the CJMC-2S/CJMA-2S membranes, and the voltage drop of the membrane stack was optimised to achieve a feasible voltage across the cell pair (0.5–0.6 V), as well as low specific energy consumption; the flow velocity of the dilute solution and concentrate was optimised at 4 cm/s. The conductivity of the ED concentrate could reach a value as high as > 120 mS/cm when the volume ratio of the initial concentrate to the dilute solution was 1:20, where the specific energy consumption was 3.76 kWh/m3. The chemical oxygen demand (COD) and salt reduction ratios were 12.5% and 79.9%, respectively. Additionally, the ED operating process was stable in ten-batch lab-scale operation and continuous pilot-scale application for the treatment of the UF permeate of landfill leachate. Hence, the ED process exhibits excellent performance and can be potentially integrated into the current method for treating landfill leachate.