Integration of US/Fe²⁺ and photo-Fenton in sequencing for degradation of landfill leachate

The landfill leachate treated by sonication in presence of Fe²⁺ (US/Fe²⁺) and then by photo-Fenton achieved the highest total organic carbon (TOC) removal efficiency among the screened processes. The lower initial pH, dosage of Fe²⁺ and initial concentration of leachate were helpful in raising TOC removal efficiency of leachate by US/Fe²⁺. The optimal conditions for the US-photo-Fenton process were as follows: initial pH at 3.0, [H₂O₂]/[TOC₀] at 2, [H₂O₂]/[Fe²⁺] at 5 and initial concentration of landfill leachate at 600 mg/L. The removal efficiency of TOC, chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD₅) were 68.3, 79.6 and 58.2%, while the BOD₅/COD rose from 0.20 to 0.43 at optimum condition. Based on gas chromatography–mass spectrometry (GC-MS) results, 36 of a total of 56 pollutants were completely degraded by US-photo-Fenton treatment.