Landfill leachate treatment by direct contact membrane distillation: Impacts of landfill age on contaminant removal performance, membrane fouling and scaling

The imperative for sustainable urban development necessitates the proper treatment of landfill leachate (LFL), driven by its high level of contaminants. Although membrane distillation (MD) effectively captures non-volatile contaminants, impediments persist in practical implementation in LFL, notably membrane fouling and scaling induced by organic and inorganic substances. These challenges are particularly salient in treating LFL with varying contaminant concentrations contingent upon its age. This study comprehensively investigated the treatment efficiency of direct contact membrane distillation (DCMD) for both young landfill leachate (YLFL) and aged landfill leachate (ALFL), along with an examination of the associated membrane fouling and scaling conditions over a 15-d period. The results demonstrated that chemical oxygen demand (COD) and metal ions in both YLFL and ALFL were effectively retained by DCMD, with rejection rates exceeding 99 %. Nevertheless, escalating membrane fouling led to diminished distillate fluxes, with reductions of 26 %-32 % for YLFL and 63 %-86 % for ALFL. The fouling mechanisms differed between YLFL and ALFL treatments. YLFL primarily induced organic fouling through biopolymers and humic acid (HA), while ALFL introduced inorganic salt ions (e.g., Ca2+ and Mg2+) and organics, resulting in scaling and hybrid organic -inorganic fouling. Acid cleaning proved more efficacious than alkali cleaning for ALFL treatment, as it dissolved ions and disrupting the crystal -organic crosslinked fouling layer. This study sheds new light on membrane fouling control during DCMD-based treatment of LFL at varying ages.