Wet air oxidation for the treatment of industrial wastes. Chemical aspects, reactor design and industrial applications in Europe

Aqueous wastes containing organic pollutants can be efficiently treated by wet air oxidation (WAO), i.e. oxidation (or combustion) by molecular oxygen in the liquid phase, at high temperature (200–325°C) and pressure (up to 175 bar). This method is suited to the elimination of special aqueous wastes from the chemical industry as well as to the treatment of domestic sludge. It is an enclosed process, with a limited interaction with the environment, as opposed to incineration. Usually, the operating cost is lower than 95 Euro m−3 and the preferred COD load ranges from 10 to 80 kg m−3. Only a handful of industrial reactors are in operation world-wide, mainly because of the high capital investment they require. This paper reviews the major results obtained with the WAO process and assesses its field of possible application to industrial wastes. In addition, as only a very few studies have been devoted to the scientific design of such reactors (bubble columns), what needs to be known for this scientific design is discussed. At present, a computer program aimed at determining the performance of a wet air oxidation reactor depending on the various operating parameters has been implemented at the laboratory. Some typical results are presented, pointing out the most important parameters and the specific behavior of these units.