Enhanced treatment of recalcitrant landfill leachate via CFA/FE-catalyzed Fenton process and subsequent activated sludge adaptation

Abstract

Landfill leachate contains significant levels of organic and inorganic substances as well as pathogens. The high concentration of chemical oxygen demand (COD) and low biochemical oxygen demand-to-chemical oxygen demand (BOD/COD) ratio indicate the leachate is poorly biodegradable and consist of substantial recalcitrant organic matter, making it difficult to treat by conventional biological wastewater treatment processes. The Fenton reaction is an advanced oxidation process that is based on the reaction between iron ions and hydrogen peroxide, generating hydroxyl radicals. This study utilises coal fly ash modified by the iron precipitation method as a Fenton catalyst. Catalyst characterization using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), x-ray diffraction (XRD), and the acid digestion method confirmed the presence of a substantial iron content in the form of magnetite. Batch Fenton experiments showed that decolourisation of leachate was affected by pH solution, the dosage of iron catalyst, and H₂O₂. Under the following operating conditions: 2 g L^-1 CFA/Fe, 4800 mg L^-1 H₂O₂, pH 3, colour and dissolved organic carbon (DOC) removal reached up to 81.46% and 42.98%, respectively. Furthermore, the subsequent biological activated sludge treatment after Fenton oxidation showed that the activated sludge process could adapt to residual Fenton’s reagents.

Keywords: activated sludge, heterogeneous Fenton, hybrid wastewater treatment, landfill leachate.