Combining ozonation with aerobic wastewater treatment by using pre- and post-ozonation or other schemes is a known method for improving purification of industrial wastewaters. The application of mentioned methods is usually restricted due to the need of high ozone doses that significantly increases the cost of the purification process. The method of combining of ozonation and aerobic bio-oxidation into single integrated process, described in the current paper, has been found to improve wastewater purification efficiency when small ozone doses are applied. It is demonstrated how small ozone doses improve the performance of the aerobic bio-oxidation process over the conventional aerobic bio-oxidation process. Results revealed that the measurement of mixed liquor suspended solids (MLSS) is not suitable for evaluation of the activated sludge concentration in bioreactor. The measurement of ATP concentration proved to be superior over the MLSS concentration, as its response to ozone attack was immediate