Wet air oxidation (WAO) process is one of the most economical and environmentally-friendly advanced oxidation processes. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. The advantages of the process include low operating costs and minimal air pollution discharges. Wet air oxidation (WAO) process is proper to a high organic loading at high flow rate and can partially cover the application range of incineration and biological methods. Wet air oxidation (WAO) process has a great potential for the treatment of effluent containing a high content of organic matter and/or toxic contaminants for which direct biological treatment is not feasible. By using Wet air oxidation (WAO) process, the organic pollutants are either partially oxidized into biodegradable intermediates or mineralized to carbon dioxide, water, and innocuous end products.