**3. Experimental methodology**

During this research work, a set of experiments under different test scenarios were performed in order to assess the antibiotic removal efficiency and to characterize its photo-oxidation kinetics, using two different lab-scale photoreactors. In the first one (PR1), the heterogeneous photocatalysis was performed using suspended TiO<sup>2</sup> nanoparticles as catalyst to remove the antibiotic from water. In the second (PR2) one, a photocatalytic filtration was performed using a granular porous medium coated by immobilized TiO<sup>2</sup> nanoparticles.

In these experiments, the antibiotic used to prepare all synthetic solutions was the oxytetracycline hydrochloride (MW = 496.89, CAS# 2058-46-0), supplied by Sigma-Aldrich with a purity higher than 95%. The OTC concentrations were always measured using a UV-VIS spectrophotometer, Shimadzu UV-1800, at 354-nm wavelength. Titanium dioxide (TiO<sup>2</sup> ) used was Degussa (Aeroxide®) P-25 (80% anatase and 20% rutile).

The intensity of solar radiation is measured by a global UV radiometer (OHM – HD 9021), which was placed next to the solar reactors, in order to provide data in terms of incident solar radiation intensity (W/m2 ). A reagent kit for rapid analysis of the amount of iron (Aquaquant®, E. Merck Darmstadt Germany) was also used.

Test scenarios were defined aiming to assess the effect on OTC removal efficiency of some abiotic parameters (e.g., OTC initial concentration, pH, hydraulic conditions, UV radiation source, and water matrices).
