Municipal solid waste (MSW) leachate, mostly comprised of organic and inorganic substances originated from discarded organic matters, chemicals, and liquors at MSW dumpsite. Pollutant composition and toxic compounds of leachate necessitate the effective treatment before its disposal. In the current study, advanced oxidation processes; ozonation, peroxone process and photolytic ozonation were employed for the treatment of complex MSW leachate. Central Composite Design (CCD) of Response Surface Methodology (RSM) was applied to optimize the various operating parameters in the treatment system. The optimized condition of pH: 9.0; contact time: 60 min and Ozone dose: 5 g/h for a litre of leachate provided the maximum COD and NH3–N reduction of 72 % and 80 % respectively for photolytic ozonation (under 15 W–UVC; λ:254 nm) whereas under the same operating conditions, ozonation process provided 45 % of COD removal and 50 % of NH3-N removal. Peroxone process with H2O2 concentration of 800 mg/L, showed the maximum COD and NH3-N removal efficiencies of 61 % and 59.7 % respectively. The developed models have confirmed the interaction between the selected parameters; have good agreement with each other; have the best fit. The present approach provided the knowledge to adopt an efficient way of treatment to the complex MSW leachate to proceed further for pilot-scale treatment. © 2020 Institution of Chemical Engineers