Supercritical water oxidation of landfill leachate

In this paper, ammonia as an important ingredient in landfill leachate was mainly studied. Based on Peng-Robinson formulations and Gibbs free energy minimization method, the estimation of equilibrium composition and thermodynamic analysis for supercritical water oxidation of ammonia (SCWO) was made. As equilibrium is reached, ammonia could be totally oxidized in SCW. N-2 is the main product, and the formation of NO2 and NO could be neglected. The investigation on SCWO of landfill leachate was conducted in a batch reactor at temperature of 380-500 degrees C, reaction time of 50-300 s and pressure of 25 MPa. The effect of reaction parameters such as oxidant equivalent ratio, reaction time and temperature were investigated. The results showed that COD and NH3 conversion improved as temperature, reaction time and oxygen excess increased. Compared to organics. NH3 is a refractory compound in supercritical water. The conversion of COD and NH3 were higher in the presence of MnO2 than that without catalyst. The interaction between reaction temperature and time was analyzed by using response surface method (RSM) and the results showed that its influence on the NH3 conversion was relatively insignificant in the case without catalyst. A global power-law rate expression was regressed from experimental data to estimate the reaction rate of NH3. The activation energy with and without catalyst for NH3 oxidation were 107.07 +/- 8.57 kJ/mol and 83.22 +/- 15.62 kJ/mol, respectively. (C) 2011 Elsevier Ltd. All rights reserved.