Sustainable Remediation of Landfill Leachate Through Sludge-Based Adsorbents: A Critical Review of Synthesis, Performance, and Circularity.

The complex composition of landfill leachate, characterized by high concentrations of refractory organic matter, ammonium nitrogen, and heavy metals, requires efficient and sustainable treatment technologies. Recently, sludge-based adsorbents (SBAs) obtained from wastewater treatment plants (WWTPs) sludge have emerged as promising alternatives to the conventional activated carbon materials for landfill leachate. This review critically evaluates the recent literature related to the transformation of sludge waste and municipal solid waste-based adsorbents into high-efficiency SBAs as a circular economy strategy for leachate remediation. The correlation of the physicochemical characteristics of landfill leachate with the properties of SBAs to enhance the removal of specific contaminants is discussed. The treatment strategies for landfill leachate including physicochemical, biological, and integration of those are summarized. By correlating adsorption performance with SBAs's properties and circular economy principles, this review identifies the key knowledge gaps and provides guidance for the development and large-scale implementation of sustainable leachate treatment technologies. Furthermore, the prospects for the application of SBAs in the closed-loop landfill leachate treatment system are addressed.