Maria Carbajo

UV-C radiation based methods for aqueous metoprolol elimination.

The endocrine disruptor metoprolol has been oxidised in aqueous solution by means of the systems UV-C, UV-C/H(2)O(2), UV-C/percarbonate, UV-C/monopersulfate, UV-C/TiO(2), UV-C/H(2)O(2)/TiO(2) and photo-Fenton. From simple photolysis experiments the quantum yield of metoprolol has been calculated (roughly 5x10(-3) mol Einstein(-1) at circumneutral pH). Addition of free radicals promoters significantly enhanced the metoprolol depletion rate. Mineralization degree was negligible when no promoter was added, while low values were achieved in the presence of either inorganic peroxides or titanium dioxide. The combination of radiation, hydrogen peroxide and TiO(2) increased the mineralization level up to values in the proximity of 45-50% under the best conditions investigated. The photo-Fenton process was the best system in terms of total oxidation (mineralization degree 70%) when optimum conditions were applied.

Comparison of different advanced oxidation processes (AOPs) in the presence of perovskites.

The efficacy of the oxidation systems: O3, UV radiation, O3/UV radiation, O3/perovskite, UV radiation/perovskite, O3/UV radiation/perovskite, H2O2/UV radiation, H2O2/UV radiation/perovskite, has been investigated by using pyruvic acid as probe compound. Under the operating conditions used, the combination of UV radiation and hydrogen peroxide (with or without perovskites) leads to the fastest pyruvic acid removal while the best results in terms of mineralization degree are obtained when combining O3/UV radiation/perovskite. The effect of the variables: inlet ozone (15-75 mg L(-1)) and initial pyruvic acid (10(-3) to 10(-2)M) concentrations, catalyst load (0.01-1.5 g L(-1)) and pH (2-9) was investigated for the photocatalytic ozonation. The most influencing parameter was the ozone concentration fed to the photoreactor. A zero order was observed for pyruvic acid concentration and close to zero for catalyst load. Some deactivation is observed after reusing the catalyst, likely due to leaching of the active phase.

UV-C photolysis of endocrine disruptors. The influence of inorganic peroxides

Norfloxacin, doxycycline and mefenamic acid have been photolysed with UV-C radiation (254 nm) in the presence and absence of inorganic peroxides (hydrogen peroxide or sodium monopersulfate). Quantum yields in the range (1.1-4.5)x10(-3) mol Einstein(-1) indicate the low photo-reactivity of these pharmaceuticals. Inorganic peroxides considerably enhanced the contaminants conversion, although no appreciable mineralization could be obtained. A simplistic reaction mechanism for the hydrogen peroxide promoted experiments allowed for a rough estimation of the rate constant between hydroxyl radicals and norfloxacin (k>1 x 10(9)M(-1)s(-1)), doxycycline (k>1.5 x 10(9)M(-1)s(-1)) and mefenamic acid (k>11.0 x 10(9)M(-1)s(-1)).

Kinetics of the Ozone-p-Chlorobenzoic Acid Reaction

The kinetics of p-chlorobenzoic acid ozonation was investigated. From experiments carried out at acidic pH it was suggested that the direct rate constant between the ozone molecule and p-chlorobenzoic acid is higher than the reported value of 0.15 M−1s−1. Runs completed in homogeneous contact pattern allowed for the calculation of the direct rate constant with a value of approximately 4.5 M−1s−1. Additionally, some competitive experiments were carried out in the presence of a reference compound (atrazine or simazine). From these competitive runs conducted at pH 1, values of 3.1 and 6.7 M−1s−1 were obtained by considering the presence of hydroxyl radicals. If the occurrence of these radicals is ruled out, the new values obtained are 3.6 and 2.2 M−1s−1. In any case, apparently the ozonation of p-chlorobenzoic acid seems to be faster than stated in the literature. However, the addition of tert-butyl alcohol either in homogeneous or heterogeneous experiments completely inhibited the p-chlorobenzoic acid oxidation, suggesting the generation of radical species even at strongly acidic conditions.

Photocatalytic ozonation of phenolic wastewaters : Syringic acid, tyrosol and gallic acid

The photocatalytic ozonation of a mixture of 3 phenols (gallic acid, tyrosol and syringic acid) has been conducted under different operating conditions. The individual adsorption of the phenol type compounds onto titanium dioxide (photocatalyst) has been first evaluated. Equilibrium conditions are attained in less than an hour while the isotherm curves reveal that adsorption intensity increases in order: syringic acid < tyrosol < gallic acid. When the photocatalytic ozonation is applied, an optimum in titanium dioxide concentration is experienced (1.5 g L− 1). Direct comparison of the photocatalytic ozonation to other less sophisticated oxidation systems (i.e., single ozonation, catalytic ozonation, photo-ozonation, etc.) indicates a higher efficiency of the former in terms of ozone uptake.

Effects of different catalysts on the ozonation of pyruvic acid in water

Removal of pyruvic acid from water has been studied through catalytic ozonation. Copper or cobalt impregnated MCM-41, Ru-Al2O3, Ru-CeO2, FeO(OH) and LaTi1-xCuxO3 and LaTi1-xCoxO3 Perovskites have been used as catalysts. Only perovskites and Ru-CeO2 catalysts did show significant catalytic activity to increase the ozonation of pyruvic acid.

Homogeneous Catalyzed Ozone Decomposition in the Presence of Co(II).

The homogeneous decomposition of ozone in the presence of a Co(II) catalyst has been investigated in aqueous solution. Under the conditions investigated (Co(II) concentration: 0.0 – 2.0 ppm, pH: 1.6- 8.4, O3 concentration: 5 10−5 – 2.0 104 M) the process can be assumed to follow pseudo first order kinetics with respect to ozone. Cobalt concentration dependency also obeys first order kinetics although it may be considered to reach a steady state concentration. pH exerts a positive influence on the decomposition rate from 1.6 to 7.1, the process leveling off at pH 8.4. An Arrhenius analysis of the temperature effect gave a moderate activation energy of the global reaction (E=10917 cal mol−1). A more detailed radical mechanism than a simple pseudo first order reaction can be postulated for simulation purposes. By numerical optimization of some unknown kinetic constants the influence of several operating variables can be adequately predicted.