Landfill leachate treatment by subcritical water oxidation with potassium permanganate in a batch reactor

Introduction: the treatment of landfill leachate by oxidation in subcritical water using potassium permanganate as oxidant was studied in a batch reactor.Objective: to evaluate the effect of temperature, reaction time, and oxidant excess on the chemical oxygen demand (COD) conversion in the process.Methodology: a temperature range of 300–350 °C, reaction time of 20–40 min, and oxidant excess from 0% (stoichiometric) to 25% were considered, using a factorial design 23. Pressure was kept constant at 2500 psi (17.3 MPa). COD was measured in the liquid phase, and the effect of the factors on conversion was determined through ANOVA analysis.Results: all runs yielded a yellowish liquid and a brown sludge that was difficult to resuspend. ANOVA results indicated that temperature was the only significant factor, with no relevant interactions. High COD conversions were obtained at 350 °C, 20 min, and stoichiometric oxidant. Total nitrogen, analyzed in selected samples, showed conversions above 90% at temperatures lower than those required in supercritical water oxidation (>500 °C) to achieve similar values. Total volatile solids analysis revealed that the sludge consisted of both organic and inorganic substances, possibly resulting from coagulation and adsorption by the manganese oxide byproduct.Conclusions: the high conversions obtained, together with less stringent conditions than those required for supercritical water oxidation, represent an opportunity for the development of an efficient treatment for leachates, taking into account the management of the sludge generated.