Degradation and mineralization of the emerging pharmaceutical pollutant sildenafil by ozone and UV radiation using response surface methodology

Pharmaceuticals and their degradation products which are present in wastewater and superficial waters are becoming an ecological issue. This research investigated the degradation and mineralization of synthetic solutions of the pharmaceutical compound sildenafil citrate (SC) by single ozonation and ozonation jointed with UV radiation (O/UV). The effects of initial drug concentration (50–125 mg L), inlet ozone concentration (35–125 g Nm), and UV radiation on SC degradation and decrease of total organic carbon (TOC) were investigated using response surface methodology based on a central composite experimental design. Through the RSM analysis, it was possible to confirm the removal of SC for the entire experimental range. Major intermediates of SC degradation were identified and a degradation pathway was proposed. The kinetics of SC degradation was modeled as a pseudo-first-order reaction with a rate constant ranging between 0.072 and 1.250 min. The SC degradation and TOC removal were strongly enhanced by increasing the concentration of gaseous ozone at the inlet and incorporating UV radiation. The highest TOC removal reached at 60 min was 75%, in the O/UV system, with initial SC content of 50 mg L and inlet ozone concentration of 125 g Nm. The degradation rate of SC was increased 3 to 9 times in the presence of UV radiation. Ozone-based advanced oxidation processes appear as a suitable alternative for treatment of the emerging pollutant SC.