WET AIR OXIDATION

Wet air oxidation (WAO), involving oxidation at high temperature (125-320 degrees C) and pressure (0.5-20 MPa) conditions, is useful for the treatment of hazardous, toxic, and nonbiodegradable waste streams. The process becomes self-sustaining when the feed chemical oxygen demand (GOD) is about 20 000 mg/L and can be a net energy producer at sufficiently higher feed COD's. All the published information on WAO has been analyzed and presented in a coherent manner. Wet air oxidation studies on pure compounds have been critically reviewed. Mechanism, kinetics, and structure-oxidizability correlation for WAO of carboxylic acids, phenols, cyanides, and nitriles have been described. The industrial applications discussed include municipal sewage sludge treatment, distillery waste treatment, black liquor treatment, cyanide and nitrile wastewater treatment, spent carbon regeneration, and energy and resource regeneration. Waste streams from other sources and some miscellaneous applications of WAO have also been included. Special emphasis is given to WAO under supercritical conditions (above the critical temperature of water) and oxydesulfurization of coal. In addition to the industrial applications, some other aspects (like various catalysts and oxidizing agents) of WAO have also been discussed. Recommendations and suggestions for further investigations have been made.