The objective of this study was to compare the efficiency of O-3/granular activated carbon (GAC) to enhance ozone transformation into circle OH radicals, with the common advanced oxidation processes (O-3/OH-, O-3/H2O2). The results obtained with model systems under the given experimental conditions showed that the system O-3/OH- (pH 9) and O-3/H2O2 (pH 7, [H2O2] = 1 circle 10(-5) M) are more efficient than O-3/GAC (pH 7, [GAC] = 0.5 g/L) to enhance ozone transformation into circle OH radicals. However, in Lake Zurich water the O-3/GAC process has a similar efficiency as O-3/H2O2 for ozone transformation into circle OH radicals. The results also show that the presence of GAC during Lake Zurich water ozonation leads to (i) removal of hydrophilic and hydrophobic micropollutants, (ii) reduction of the concentration of CO32-/HCO3-, and (iii) decrease of the concentration of dissolved organic carbon (DOC) present in the system.