Ozone and photocatalytic processes to remove the antibiotic sulfamethoxazole from water

In this study, water containing the pharmaceutical compound sulfamethoxazole (SMT) was subjected to the various treatments of different oxidation processes involving ozonation, and photolysis and catalysis under different experimental conditions. Removal rates of SMT and total organic carbon (TOC), from experiments of simple UVA radiation, ozonation (O3), catalytic ozonation (O3/TiO2), ozone photolysis (O3/UVA), photocatalytic oxidation (O2/TiO2/UVA) and photocatalytic ozonation (O3/UVA/TiO2), have been compared. Photocatalytic ozonation leads to the highest SMT removal rate (pH 7 in buffered systems, complete removal is achieved in less than 5 min) and total organic carbon (in unbuffered systems, with initial pH = 4, 93% TOC removal is reached). Also, lowest ozone consumption per TOC removed and toxicity was achieved with the O3/UVA/TiO2 process. Direct ozone and free radical reactions were found to be the principal mechanisms for SMT and TOC removal, respectively. In photocatalytic ozonation, with buffered (pH 7) aqueous solutions phosphates (buffering salts) and accumulation of bicarbonate scavengers inhibit the reactions completely on the TiO2 surface. As a consequence, TOC removal diminishes. In all cases, hydrogen peroxide plays a key role in TOC mineralization. According to the results obtained in this work the use of photocatalytic ozonation is recommended to achieve a high mineralization degree of water containing SMT type compounds.