Removal of micropollutants in wastewaters has gained importance in recent years. Advanced treatment processes such as ozone oxidation, activated carbon adsorption, and membrane filtration are required to remove the micropollutants from wastewaters. In this study, extended ozonation was applied at different stages of a wastewater treatment plant (WWTP) to determine its effect on the removal efficiencies of both macro and micropollutants. At the first experimental study, wastewater that was obtained from the effluent of the aerated grit chamber of a conventional full-scale municipal WWTP, was treated with a concentration of 30 mg/L FeCl3 through a laboratory scale jar test system followed by a laboratory-scale ozonation unit. According to the results, chemically enhanced primary treatment (CEPT) achieved removal efficiencies over 75% for chemical oxygen demand (COD), 50% for total phosphorus (TP) and 90% for total-suspended solids (TSS), while ozonation followed by the CEPT resulted with an overall COD removal efficiency up to 93%. As a second experimental study, effluent of the overloaded conventional activated sludge (CAS) system of the same WWTP was solely post ozonated. 90 min of post-ozonation resulted with a decrease by 70% and an increase by 50% in ammonium and nitrate concentration, respectively. Over 99% removal efficiency of diclofenac was achieved in each experimental study (CEPT+O-3 and CAS+O-3). Results of each experimental study were evaluated in terms of both efficiency and feasibility. Since the ozonation results with an increase in the concentration of oxidized nitrogen; applying ozonation to a preliminary-treated wastewater after CEPT can be advantageous in some cases, where nitrate can be used as electron acceptor in anoxic environments for deep-sea discharges.