Elimination of phenol from phenolic wastewater of an olefin plant using ozone is reported. In this work a bench-scale semi-batch ozonation system was set up in the Environmental Engineering Research Center (EERC). A venturi injection and a circulation system was used for injection of ozone into the ozonation contactor. Samples were taken from buffered aqueous phenol solutions at different pH values with an initial concentration of 80 +/- 5 ppm. Experimental results revealed that phenol removal efficiency increased with increasing pH and reached >99.5% after 15 min ozonation at a pH of 11. With increasing pH, ozone consumption (i.e. mol O-3 per mol phenol) decreased from 6.1 to 5.1. The results were compared with Roth's model, which was used to describe the global reaction rate of ozonation of phenol. Using Roth's model and results of bench-scale system a pilot scale ozonation system was designed and set up in a petrochemical complex. From the results of steady-state pilot scale tests, it was shown that ozonation could significantly reduce phenol concentration to the desired level in actual wastewater.