An innovative approach for landfill leachate treatment based on selective adsorption of humic acids with carbon nitride

Selective adsorption of humic acids is innovative in landfill leachate treatment, since it can both address the UV quenching substance (UVQS) problems and recover humic acids as liquid fertilizers applied in agriculture and forestry. However, due to lacking available adsorbents, it remains a great challenge. Herein, we evaluated the application of graphitic carbon nitride (g-CN) for selective adsorption of humic acids from landfill leachate. First, 10 types of leachate were considered and characterized, and the leachate contained humic acids of different contents. The common method was used to prepare g-CN with similar properties to the previously reported counterparts. Then, kinetics, isotherms, and removal for adsorption of the leachate by g-CN were studied. It was found that the adsorption was fast and controlled by the surface and intraparticle diffusion. For all the leachate, the removal of UV absorbance at 254 nm (UV254) was 30 -70%, much greater than that for total organic carbon. In particular, the UV254 removal was mainly contributed by the selective adsorption of humic acids with a high selectivity coefficient (>3.06). The recovery rate and purity of the adsorbed humic-like components were 100% in some cases. Finally, the mechanisms for selective adsorption were elucidated. The results revealed that, in addition to the major n-n interactions, the adsorption was affected by electrostatic interactions and hydrogen bondings, along with the newly proven conformation-variation effect. The findings will expand a promising direction for disposal of landfill leachate.