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This work was carried out to improve the performance of an ozonation system used for wastewater treatment in the pharmaceutical industry. Ferrous sulfate was applied as a catalyst to the reaction system in order to improve the mineralization of organic matter. After this, the pH of the water was adjusted to 8.5-10 so that the process flows under alkaline conditions. Finally, O3 was injected through a Venturi tube to improve the mass exchange between gas and water. Preliminary data on the operation of the treatment system indicate a COD removal of less than 10%. The tests were carried out at full scale and the water quality variables were analyzed at different reaction times. Results allowed us to determine that an ozone dose equal to 10 g/h and 10 mg/L of Fe2+ and an initial pH of water of 9 require a total of 4.5 hours to achieve a 30.73% reduction of COD and 36.85% reduction of TOC. The results obtained at an initial pH higher than 9.5 indicate that the effectiveness of the process is lowered under this condition, which may be due to the rapid formation of insoluble Fe(OH)3, thus reducing the availability of catalyst for the formation of OH* radicals in the water. [ABSTRACT FROM AUTHOR]