Air Products uses their CHEMOXTM process for advanced oxidation of a variety of waste waters, e.g. landfill leachate. The centrepiece of the CHEMOXTM process is the Impinging Zone Reactor (IZR) developed by the University of Clausthal. In the IZR waste water is intensively mixed with an ozone/oxygen mixture under atmospheric pressure and ambient temperature. Due to the excellent gas mass transfer performance of the IZR no expensive pressure vessels or gas compressors are required. Pilot plant trials were performed very successfully on a landfill leachate in Germany in 1995. Results from parallel operations with a commercial venturi/bubble column system and the CHEMOXTM process show a decrease in hydraulic retention time of 10.3 vs. 3.3 [h], a reduction of the O3/COD ratio of 3.2 vs 1.8 [kg/kg], and an energy consumption (without ozone generation) of 8.0 vs. 4.3 [kWh/kg ozone consumed] (meter reading) respectively. State-of-the-art, process controlled, mobile pilot plants provide the customer with the required information to accurately design and cost an effective ozone waste water treatment process.