Many pharmaceuticals (e.g. antibiotics, contrast media, beta blockers) are excreted unmetabolized and enter wastewater treatment plants (WWTPs) through the domestic sewage system. Research has shown that many of them are not effectively removed by conventional wastewater treatment and therefore are detected in surface waters. Reverse osmosis (RO) is one of the most effective means for removing a wide range of micropollutants in water recycling. However, one significant disadvantage is the need to dispose the resultant RO concentrate. Due to the fact that there are elevated concentrations of micropollutants in the concentrate, a direct disposal to surface water could be hazardous to aquatic organisms. As a consequence, further treatment of the concentrate is necessary. In this study, ozonation was investigated as a possible treatment option for RO concentrates. Concentrate samples were obtained from a RO-membrane system which uses municipal WWTP effluents as feeding water to produce infiltration water for artificial groundwater recharge. In this study it could be shown that ozonation is efficient in the attenuation of selected pharmaceuticals, even in samples with high TOC levels (46 mg C/L). Tests with chlorinated and non-chlorinated WWTP effluent showed an increase of ozone stability, but a decrease of hydroxyl radical exposure in the samples after chlorination. This may shift the oxidation processes towards direct ozone reactions and favors the degradation of compounds with high apparent second order rate constants. Additionally it might inhibit an oxidation of compound predominantly reacting with OH radicals. Ozone reaction kinetics were investigated for beta blockers (acebutolol, atenolol, metoprolol and propranolol) which are permanently present in WWTP effluents. For beta blockers two moieties are common which are reactive towards ozone, a secondary amine group and an activated aromatic ring. The secondary amine is responsible for a pH dependence of the direct ozone reaction rate, since only the deprotonated amine reacts very quickly. At pH 7 acebutolol, atenolol and metoprolol reacted with ozone with an apparent second order rate constant of about 2000 M-1 s-1, whereas propranolol reacted at ~1.0 105 M-1 s-1. The rate constants for the reaction of the selected compounds with OH radicals were determined to be 0.5-1.0 x 1010 M-1 s-1. Oxidation products (OPs) formed during ozonation of metoprolol and propranolol were identified via liquid chromatography (LC) tandem mass spectrometry. Ozonation led to a high number of OPs being formed. Experiments were carried out in MilliQ-water at pH 3 and pH 8 as well as with and without the radical scavenger tertiary butanol (t-BuOH). This revealed the influence of pH and the OH radical exposure on OP formation. The OH radical exposure was determined by adding the probe compound para-chlorobenzoic acid (pCBA). Metoprolol: To define the impacts of the protonated and non protonated metoprolol species on OH radical formation, the measured pCBA attenuation was compared to modeled values obtained by a simplified kinetic model (Acuchem). A better agreement with the measured results was obtained, when the model was based on a stoichiometric formation of OH radical precursors (O2-) during the primary ozone reaction of metoprolol. However, for reaction of a deprotonated molecule (attack of the aromatic ring) a formation of O2- could be confirmed, but an assumed stoichiometric O2- formation over-estimated the formation of OH radicals in the system. Analysis of ozonated raw wastewater and municipal WWTP effluent spiked with 10 μM metoprolol exhibited a similar OP formation pattern as detected in the reaction system at pH 8 without adding radical scavenger. This indicated a significant impact of OH radical exposure on the formation of OPs in real wastewater matrices. Propranolol: The primary ozonation product of propranolol (OP-291) was formed by an ozone attack of the naphthalene ring, which resulted in a ring opening and two aldehyde moieties being formed. OP-291 was further oxidized to OP-307, presumably by an OH radical attack, which was then further oxidized to OP-281. Reaction pathways via ozone as well as OH radicals were proposed and confirmed by the chemical structures identified with MS2 and MS3 data. It can be concluded that ozonation of WWTP effluent results in the formation of a high number of OPs with an elevated toxic potential (i.e. formation of aldehydes).