*2.1.1. Industrial application of wet air oxidation*

WAO technologies have been commercialized around 60 years ago. Applying different temperatures, one can mention three different oxidation categories, namely: low temperature oxidation, medium temperature oxidation, and high temperature oxidation.

Commercial application of low-temperature oxidation (100°C-200°C) involves low-pressure thermal conditioning (LPO) of activated sludge and the treatment of low-strength sulfidic spent caustic. The most prevalent WAO applications are for ethylene plant spent caustic and refinery spent caustic.

The ethylene plant spent caustic is traditionally oxidized at low temperatures in the range of 120°C-220°C; the main purpose is to destroy the odorous sulfide content of this effluent. The refinery spent caustic WAO application operates at 240°C-260°C that already fits the medium temperature category, as well as the WAO of some organic wastes. Other industrial wastes treated by low-temperature oxidation include cyanide and phosphorous wastes, as well as non-chlorinated pesticides. High-temperature oxidation 260°C-320°C is used for refinery spent caustic, sludge destruction, and most WAO treated industrial wastewaters. Most organic industrial wastes are oxidized in this temperature range, including pharmaceutical wastes as well as pesticides, solvents, and the complete destruction of liquid wastes of pulp and paper production and other organic sludges.
