The efficiency of ozone-based processes under various conditions was studied for the treatment of a surface water (Lake Zurich water, Switzerland) spiked with 19 micropollutants (pharmaceuticals, pesticides, industrial chemical, X-ray contrast medium, sweetener) each at 1 mu g L-1. Two pilot-scale ozonation reactors (4-5 m(3) h(-1)), a 4-chamber reactor and a tubular reactor, were investigated by either conventional ozonation and/or the advanced oxidation process (AOP) O-3/H2O2. The effects of selected operational parameters, such as ozone dose (0.5-3 mg L-1) and H2O2 dose (O-3:H2O2 = 1:3-3:1 (mass ratio)), and selected water quality parameters, such as pH (6.5-8.5) and initial bromide concentration (15 200 Lig L-1), on micropollutant abatement and bromate formation were investigated. Under the studied conditions, compounds with high second-order rate constants k03>104 M-1 s(-1) for their reaction with ozone were well abated (>90%) even for the lowest ozone dose of 0.5 mg L-1. Conversely, the abatement efficiency of sucralose, which only reacts with hydroxyl radicals (center dot OH), varied between 19 and 90%. Generally, the abatement efficiency increased with higher ozone doses and higher pH and lower bromide concentrations. H2O2 addition accelerated the ozone conversion to "OH, which enables a faster abatement of ozone-resistant micropollutants. Interestingly, the abatement of micropollutants decreased with higher bromide concentrations during conventional ozonation due to competitive ozone-consuming reactions, except for lamotrigine. due to the suspected reaction of HOBr/ORC with the primary amine moieties. In addition to the abatement of micropollutants, the evolution of the two main transformation products (TPs) of hydrochlorothiazide (HCTZ) and tramadol (TRA), chlorothiazide (CTZ) and tramadol N oxide (TRA-NOX), respectively, was assessed by chemical analysis and kinetic modeling. Both selected TPs were quickly formed initially to reach a maximum concentration followed by a decrease of their concentrations for longer contact times. For the studied conditions, the TP's concentrations at the outlet of the reactors ranged from 0 to 61% of the initial parent compound concentration, CTZ being a more persistent TP against further oxidation than TRA-NOX. Finally, it was demonstrated in both reactors that the formation of bromate (BrOi), a potentially carcinogenic oxidation by-product, could be controlled by H2O2 addition with a general improvement on micropollutant abatement. Post-treatment by granular activated carbon (GAC) filtration enabled the reduction of micropollutants and TPs concentrations but no changes in bromate were observed. The combined algae assay showed that water quality was