Comparing the photocatalytic oxidation of Metoprolol in a solarbox and a solar pilot plant reactor

Abstract

Abstract The aim of this work is to study and compare the removal of Metoprolol (MET) “1-(isopropylamino)-3-[p(β-methoxyethyl)phenoxy]-2-propanol” by photolysis, photocatalysis/TiO 2 , UV–Vis/H 2 O 2 and UV–Vis/H 2 O 2 /TiO 2 processes using two different experimental devices: solarbox (SB) with a Xe lamp and a solar pilot plant reactor with compound parabolic collectors (CPCs). Photolysis shows low MET removal (14% and 8%) with SB and CPCs respectively, and TOC almost negligible. Different TiO 2 concentrations (0.05, 0.1 and 0.4 g/L) were used in both devices and the best results were obtained for 0.4 g/L, after 360 min of irradiation ( Q = 19 kJ/L) with complete MET elimination and 55% of TOC removal in SB. Tests done with real matrix water show a decrease in MET removal to 21% due the competition of the organic matter present for light and catalyst. The UV–Vis/H 2 O 2 /TiO 2 process represents an improvement with respect to the photocatalytic process (without H 2 O 2 ) and times required to achieve the same MET o TOC removal are shortened in both devices, for instance, 120 min for total MET removal in SB. The best mg H 2 O 2 /mg MET ratio was 3. The MET photocatalysis (in solarbox) increases biodegradability and the treated solutions can be coupled to biological process after 360 min of irradiation and the solution treated in CPC reactor, after 270 min, remains not biodegradable. A pseudo-first order kinetics in photocatalytic processes were calculated in SB and CPC reactors. The toxicity, measured by Vibrio Fischeri method, decreases when MET is degraded by photocatalysis/TiO 2 and UV–Vis/H 2 O 2 /TiO 2 processes in both devices. The major reaction intermediates in UV–Vis/H 2 O 2 /TiO 2 process were identified by ionization/mass spectrometry and a MET photo-degradation pathway was proposed. Finally, in photocatalysis (0.4 g/L TiO 2 ) the energy needed to degrade 1 mg of MET, at 240 min was evaluated, being 0.275 and 0.065 kJ/mg MET for SB and CPCs respectively.