The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15–30min), temperature (160–200°C), Cu2+ concentration (250–750mgL‐1) and H2O2 concentration (0–1500mgL‐1) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two‐stage, sequential process comprising the heating‐up of the reactor and the actual WAO. The leachate, at an initial COD of 4920mgL‐1, was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45min long heating‐up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H2O2 to reactive hydroxyl radicals. WAO at 2.5MPa oxygen partial pressure advanced treatment further; for example, 22min of oxidation at 200°C, 250mgL‐1 Cu2+ and 0–1500mgL‐1 H2O2 resulted in an overall (i.e. including acidification and heating‐up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating‐up and WAO stages, while H2O2 concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H2O2 concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.
