An integrated photothermal–photocatalytic strategy for in situ treatment and water reuse of landfill leachate

Landfill leachate (LFL) typically contains a wide range of potential pollutants, making it difficult to treat and inefficient in resource utilization. This work developed a new multifunctional evaporator that integrated photothermal evaporation with photocatalytic degradation to enable in situ purification and water recovery. The device was fabricated by immobilizing a hydrothermally synthesized Nickel Oxide- Titanium Dioxide- Carbon Nanotube (NiO-TiO₂-CNT) composite on a melamine sponge via sodium alginate crosslinking, forming a synergistic evaporation–degradation interface. Under 1 kW·m⁻² solar irradiation, the system achieved an evaporation rate of 2.25 kg·m⁻²·h⁻¹ , where the addition of 1 mmol·L⁻¹ PMS boosted phenol removal efficiency to 90 %. When applied to real LFL, COD was reduced from 4266 to 53 mg·L⁻¹ , and phosphate was completely removed to below detection limits (<0.01 mg·L⁻¹). Although ammoniacal nitrogen levels remained relatively high at 354 mg·L⁻¹ , post treatment phytotoxicity tests involving irrigation of wheat with leachate resulted in a 90 % germination rate, which increased to 100 % after dilution. This indicated the treated leachate was safe and could potentially be used as a nitrogen-rich liquid fertilizer. A techno-economic analysis showed that the system could be operated at a cost of only 10.33 USD per metric ton, significantly lower than conventional treatments. This work thus provides a cost-effective sustainable strategy for simultaneous pollutant control, water reuse, and ecological restoration of landfill sites.