Advanced Oxidation Processes (AOPs) have been widely used for wastewater treatment. Persulfate (PS) activation through different pathways has attracted a lot of attention; due to the generation of sulfate radicals which have high oxidation potential. In this study, a series of laboratory-scale experiments were conducted on landfill leachate, using PS/Fe2+/H2O2 and PS/Fe2+/SO3 2� systems. A statistical design of experiments was adopted using Design Expert 11 software. COD removal efficiency for both systems was evaluated and the optimum operating conditions were determined using Response Surface Methodology. The effects of the independent variables (pH, chemical doses, and reaction) on the removal of COD were studied. The optimised COD removal was 68 at pH 5 for PS/Fe2+/H2O2 system. Fe2+, H2O2, and PS doses were 1.95 mM, 0.05 mM, and 0.50 mM, respectively, with 10 min reaction time. 90 COD removal was obtained at pH 3.67, Fe2+ dose of 0.5 mM, SO3 2� dose of 0.5 µM, and PS dose of 1.5 mM with 17 min reaction time for PS/Fe2+/SO3 2� system. © 2024, Institute of Technology PETRONAS Sdn Bhd.