Tailored monovalent selective dialysis membranes enable fouling-resistant ammonia recovery from landfill leachate via diffusion dialysis–membrane distillation

Membrane distillation (MD) has high ammonia removal rate when treating the landfill leachate, but fouling by organics and salts limits its performance. In addition, the pH and temperature adjustments required by MD can affect subsequent treatment. In this study, the cation exchange membrane Selemion-CMV (CMV membrane) has been modified with polypyrrole (Ppy) and Nafion, respectively, to achieve monovalent cation selectivity. They were then used in the diffusion dialysis (DD)-MD process to continuously remove ammonia from landfill leachate without changing the water quality, protecting MD process from the influence of organics, Ca 2+ and Mg 2+ . With characterizations and performance testing of the two modified membranes under different conditions, it was found that the Ppy membrane achieved monovalent cation selectivity through electrostatic repulsion and pore size sieving effects, while the Nafion membrane relied on hydration energy differences and a “dissociation–reassociation” mechanism for NH 4 + transport. When applied to actual landfill leachate treatment, Ppy membrane exhibited a relatively low NH 4 + flux of 1.55 mol m −2  h −1 but demonstrated excellent selectivity with P NH 4+ /K , P NH4+/Ca , and P NH4+/Mg of 2.8, 11.27, and 14.21, respectively. In contrast, Nafion membrane exhibited a higher flux of 2.34 mol m −2  h −1 , but slightly lower selectivity, with P NH4+/K , P NH4+/Ca , and P NH4+/Mg of 6.21, 9.17, and 11.21. The DD-MD process achieved continuous ammonia recovery and successfully shielded the MD membrane from fouling, which provides a promising strategy to use membrane technology for efficient resource recovery from complex landfill leachate treatment.