Feasibility study of landfill leachate treatment by hydrothermal oxidation

Resumen

The aim of this work is to present the results obtained in the application of the Hydrothermal Oxidation (HO) process of a landfill leachate. Few reports about landfill leachate hydrothermal oxidation process have been found. This wastewater is the liquid that moves through or drains from a landfill of urban solid waste and industrial solid waste. This liquid may either exist already in the landfill and also it may be created after rainwater mixes with the chemical waste. Typically, landfill leachate has high concentrations of nitrogen, iron, organic carbon, manganese, chloride and phenols. Other chemicals including pesticides, solvents and heavy metals may also be present. At first, Wet Air Oxidation (WAO) experiments were carried out in a batch reactor with a pressure of 180 bar, a temperature of 275ºC and using air as oxidant. In a second stage, WAO and Supercritical Water Oxidation (SCWO) experiments were carried out in an isothermal plug flow reactor with low concentrations, at a constant pressure of 25 MPa and different temperatures ranging from 350 to 500 ºC. Pure oxygen, from hydrogen peroxide decomposition, was used as oxidant with an oxygen excess coefficient upper than n>1 that means no oxygen limitations. As the wastewater studied is a complex mixture of several compounds, the oxidation process efficiency was followed in terms of the reduction of both chemical oxygen demand (COD) and total organic carbon (TOC). The composition of the gas phase generated in the process has been also analyzed (on-line). In WAO experiments, a maximum COD removal of 75% was obtained after 120 min at a temperature of 275 ºC and a pressure of 180 bar. SCWO experiments have demonstrated that the high content of salts present in the wastewater produce plugging in the tubular reactor after several hours of treatment. Besides, the presence of chlorides may generate corrosion, so it is necessary to carry out some pretreatments to remove the salts and chlorides presents in the wastewater or they must be treated in another reactor configuration as a transpiring wall.