Accurate separation and recovery of humic substances from landfill leachate concentrate by triethanolamine-based loose nanofiltration membranes

The treatment of landfill leachate concentrate poses significant environmental challenges, particularly in the separation and recovery of valuable humic substances from high salt concentrations. In this study, a novel loose nanofiltration (LNF) membrane was fabricated using 0.5 wt% triethanolamine (TEOA) and 0.1 wt% trimesoyl chloride (TMC) via interfacial polymerization for the accurate separation of humic substances from inorganic salts in landfill leachate concentrate. The optimized TEOA membrane exhibited high permeate flux about 67.6 ​L ​m⁻² ​h⁻¹·bar⁻¹ and over 90 ​% transmission for ions, while achieving the rejection of humic substances above 92 ​%. The effects of operating conditions were investigated. Results showed that increasing inorganic salt concentration led to a notable decrease in inorganic salt rejection due to intensified concentration polarization and weakened electrostatic interactions. Rising humic substance concentration further intensified membrane fouling and concentration polarization, resulting in reduced flux and increased humic substance and inorganic salt rejections. Higher temperatures and alkaline pH increased flux and maintained stable rejections. In addition, a two-stage membrane filtration process was subsequently applied to actual landfill leachate concentrate samples. The humic substance concentration was enriched from 1.5 to 37.4 ​g ​L⁻¹, achieving a recovery rate over 60 ​% at a concentration factor of 12.5. The recovered humic substances complied with the standards of water-soluble fertilizers containing humic-acids (NY1106-2010), highlighting the LNF membrane's potential in sustainable landfill leachate concentrate management and resource recovery.