Landfill leachate treatment by batch supercritical water oxidation

Abstract

Landfill leachate treatment has been the focus of a great deal of research through different physicochemical and biological methods. However, no single method successfully addresses the required destruction efficiencies regarding organic matter and nitrogen, which is why the treatment is done employing combined technologies. Supercritical water oxidation (SCWO), a process that takes place at temperatures and pressures above the critical point of water and in the presence of a source of oxygen, has been successfully applied to the treatment of different types of wastewaters in an efficient way. Therefore, this paper presents an experimental study of the supercritical water oxidation of landfill leachate in a batch reactor in the temperature range 400-500°C, reaction times from 15 to 30 minutes and oxygen excess (OE) from 100% to 300 %. Total organic carbon (TOC) and Total nitrogen (TN) destruction efficiencies were measured in the reactor effluent samples and the combined effect of the studied factors was analyzed by means of the Analysis of Variance (ANOVA). Optimal operation conditions for TOC destruction were 400°C, 30 min and 100 % OE, being 500°C, 30 min and 100 % OE for TN destruction. Contrary to what has been reported in similar studies, the results suggest that it is possible to accomplish the simultaneous TOC and TN destruction in leachate wastewater by SCWO treatment at 400°C, 100 % OE and residence times longer than 30 min and without using a catalyst, either in batch or in a continuous process, as long as both the oxidant and the wastewater are mixed and heated together at the reaction temperature.