Landfill leachate treatment by hydroxyl and sulfate radical-based advanced oxidation processes (AOPs)

Abstract

A negative aspect of landfilling is the formation of multicomponent dark liquids that contain a variety of chemical pollutants and substances. Given the environmental risk, treatment methods must be developed and applied, in order to degrade and destroy the target pollutants. This work evaluates the efficacy of UV/Fe2+/H2O2 and UV/Fe2+/S2O82− processes for the degradation of landfill leachate and examines the influence of [Fe2+]/[Oxidant] ratio, UV light, dosing mode and pretreatment by a physicochemical process. Regarding photo-Fenton, best removal efficiencies (65.58 % COD, 48.12 % TOC, 86.65 % Color Index) were achieved under operating conditions as CODo:H2O2 mass ratio = 1:1, [Fe2+]/[H2O2] = 1:10, pH = 3.5 and treatment time = 60 min. UV/Fe2+/S2O82− process showed better performance (76.34 % COD, 71.44 % TOC, 88.94 % Color Index) in the respective conditions, albeit its efficacy was significantly affected by sulfate radical selectivity. Additionally, a series of experiments proved that oxidant dosing and coagulation/flocculation had a positive impact on the effectiveness of the photocatalytic applications. On the contrary, UV light didn't have a significant effect on dark Fenton's ability to degrade landfill leachate, as a result of the dark color of the sample and the solids generated in the beginning of the processes. Finally, a dual-oxidant catalytic process (UV/Fe2+/H2O2/S2O82−) was applied, exhibiting lower performance than that of UV/Fe2+/H2O2 (or UV/Fe2+/ S2O82−).