Treated municipal wastewater may contain pathogenous micro-organisms and persistent trace organics leading to problems when being discharged into the surface waters. The investigations of the research project PILOTOX aimed at their elimination from treated municipal wastewater through subsequent oxidation by ozone. For this purpose, the TU Berlin (department of Water Quality Control) in cooperation with the Berliner Wasserbetriebe at the WWTP Berlin-Ruhleben, carried out several tests with a pilot plant by the company WEDECO aiming at the ozonation of the effluent. The results show that ozonation is a suitable procedure to remove and transform respectively, substantial quantities of the pharmaceutical residues detected in the effluent of the Ruhleben WWTP and, at the same time, to achieve a germ reduction complying with the threshold values stipulated in the European directive on bathing water. It was found that many trace organics such as the anti-epilepticum carbamazepin or the hormone estron can be removed at a very low ozone dosage to below their analytic detection limit. The X-ray contrast media however, turned out to be more resistant: even at a high ozone dosage, their concentrations could be reduced only partially. In this context, the tests detected that through the combination of H2O2 and ozone, an elevated elimination rate for the substances iopamidol and iohexol can be achieved. The elimination of the analysed trace organics correlated with the decrease of the water’s UV activity. Thus, it is advisable to use the rapidly and simply traceable parameter SAK254 as process control parameter to determine the necessary ozone dosage. In addition, it could be proven that ozonation increases the biological degradability of water components. Laboratory test looking at recontamination levels however, indicate that the threshold values stipulated in the EU directive on bathing water will not be exceeded if the ozone-treated effluent is mixed with water originating from the River Spree. A study regarding the water’s acute and chronic toxicity, to its gene toxicity and endocrine impacts, revealed that – compared to the untreated effluent - no eco-toxicological risk potential can be detected in the ozone-treated water samples.The specific treatment cost covering the large-scale application of ozone treatment at the WWTP Ruhleben range between 1,0 cent/m3 and 2,2 cent/m3, of which the investment costs account for a percentage of 20-30 %.