Hydrothermal Oxidation of Oily Wastes: an Alternative to Conventional Treatment Methods

Under current legislations most oils used are considered hazardous wastes and its safe collection and disposal must be ensured. Since conventional treatment methods are often inefficient or environmentally unacceptable, the development and application of new technologies is highly necessary. Wet Air Oxidation (WAO) and Supercritical Water Oxidation (SCWO) are two forms of hydrothermal oxidation that have been proved to be effective processes to treat a wide variety of industrial wastes, but they have hardly been tested for oily wastes. In this work, the suitability of hydrothermal oxidation to the treatment of oily wastewaters is described by the results obtained with three different substrates: free fatty acids, cutting oils and bilge wastes. The efficiency of the treatment process is demonstrated for the three oily wastes tested. At temperatures below 350 degrees C and reaction times of 40 minutes, a 70--90 % of COD elimination is achieved, obtaining an effluent with low molecular weight compounds, mainly carboxylic acids. At 500 degrees C, a 99 % of COD removal is achieved in less than one minute. At this temperature the reaction seems to proceed mainly through total mineralization to carbon dioxide and water.