Membrane distillation combined with electrocoagulation and electrooxidation for the treatment of landfill leachate concentrate

The landfill leachate concentrate is a kind of waste water containing salt and refractory organics produced by the membrane bioreactor-nanofiltration/reverse osmosis process. In the present work, three integrated processes of electrocoagulation (EC)-direct contact membrane distillation (DCMD), electrooxidation (EO)-DCMD and EC-EO-DCMD were used to treat the leachate concentrate. The results show that the total organic carbon (TOC), Ca2+ and Mg2+ removal rates of the EC process were 40.52%, 98.03% and 88.84%, respectively, under the optimal operating conditions. The TOC removal rate of the EO process was 64.62% under the optimal operating conditions. The removal rates of TOC, Ca2+ and Mg2+ by combined EC-EO process were 82.16%, 99.04% and 94.22%, respectively. When the MD was applied together with the EC and EO steps, the flux improved 23%∼42%, which was confirmed by the SEM-EDS, FTIR and XRD analysis that only quite a small amount of humic acid and fulvic acid substances was observed to be randomly deposited on the membrane surface. During 72 h operation, the permeate had a lower conductivity than 15 μS/cm, and only a small amount of organic (TOC < 9.6 mg/L) was detected. These results clearly demonstrated that the EC and EO processes can effectively reduce the refractory organics and scaling inorganics, and coupled with MD can synergistically to remove the pollutant that providing a better choice for the treatment of leachate concentrate.