Degradation of metoprolol by means of advanced oxidation processes

Abstract

For this study the emerging contaminant ß-blocker Metoprolol (MET) has been selected due that it is a highly prescribed pharmaceutical and it has been detected in waste water treatment plants influents, thus, in natural waters. Several studies, focused on the toxicological potential of Metoprolol, indicate its potential environmental relevance and its recalcitrant nature. To remove MET from water, different Advanced Oxidation Processes (AOPs) were used.

MET removal was studied, in different reactors with natural and artificial light, by photolysis, UVC/H2O2, photocatalysis, Fenton, photo-Fenton, bicarbonate-activated hydrogen peroxide (with cobalt or iron) processes. The different set-ups and technologies tested have been compared in order to establish the efficiency of the processes.

The experiments were normally carried out with 50 mg/L of initial MET in Milli-Q water, free pH, and 25 ± 5 ºC.

Thus, photolysis experiments were done in (solarbox (SB), Compound Parabolic Collector (CPC), Black light blue lamps (BLB) and UVC254 nm (UVC) reactors). The best result obtained was 93.5% of MET removal in UVC reactor after 240 minutes.

UVC/H2O2 experiments were carried out in UVC reactor. Different H2O2 concentrations and pH were tested and the maximum removals were MET (98%) and TOC (70.7%) for 125 mg H2O2/L.

Photocatalysis was carried in SB and CPC with different TiO2 concentrations (0.05, 0.10 and 0.40 g /L). Experiments were also carried out varying the initial MET concentration (25, 50 and 100 mg/L), pH and the water matrix with 0.4 g TiO2/L in SB or adding 25 and 150 mg/L of H2O2. The best results obtained were a complete MET removal and 45.7% of mineralization in SB and 81.5% of MET degradation and 29.2% of mineralization in CPC.

The dark-Fenton experiments were carried out at pH in a reactor of 2 L. Two different concentrations of Fe (II) (2.5 mg/L or 10 mg/L) and H2O2 (25 mg/L or 150 mg/L) were used. To improve the Fenton process, the total Iron (II) concentration was divided in equal parts (5) and added at constant periods of time (12 minutes) during 1 hour. With the highest concentrations of iron and H2O2 the maximum MET conversion was 87.0% and mineralization 15.6%.

Photo-Fenton experiments were done at pH 3, and temperature of 14 or 25 ºC in four reactors (BLB, SB, CPC and UVC). Two different concentrations of Fe (II) (2.5 mg/L or 10 mg/L) and H2O2 (25 mg/L or 150 mg/L) were used. With the highest iron and H2O2 concentrations, the best results in MET degradation were observed (BLB: 100% in 7 min; SB: 97.3% in 7 min; CPC: 98.3% in 3 min).

The dark- Bicarbonate/hydrogen peroxide experiments were carried out with 5 mg/L of MET in drinking water, pH 6.2, and room temperature in a reactor of 0.5 L. To improve the process, cobalt (II) or iron (II) as catalyzer were added in the batch reactor. A complete MET conversion in 40 minutes was achieved.

The efficiency of different AOPs and reactors tested was compared from the ratio between accumulated energy and MET eliminated. The energy is better used in CPC (0.065 kJ/mg) than in SB (0.275 kJ/mg). For photo-Fenton process (0.04 kJ/mg) UVC and (0.05 kJ/mg) BLB reactors exhibit a much better performance than (0.30 kJ/mg) SB and (0.26 kJ/mg) CPC reactors.

From the intermediates identified, a possible MET fragmentation was proposed for the different processes, where, mainly oxidative attacks were detected.

On the other hand, the irradiation in the photocatalytic reactor (SB) was measured by o-NB actinometry, based on pH or o-NB concentration. In addition, this work has demonstrated that the o-NB actinometry, followed by o-NB concentration consumption, could be used in the presence of the catalyst TiO2.

En este trabajo se ha estudiado la eficacia de varios Procesos de Oxidación Avanzada (UVC/H2O2, fotocatálisis, Fenton, foto-Fenton, bicarbonato/H2O2 con y sin catalizador) para degradar el fármaco Metoprolol (MET).

Además se ha comparado la eficiencia energética de los diferentes procesos y diferentes instalaciones en la eliminación de MET. Los experimentos se realizaron con 50 mg/L iniciales de MET en agua Mili-Q, pH libre y 25ºC.

En el caso de la fotólisis, se usaron cuatro instalaciones (solarbox (SB), concentradores parabólicos compuestos (CPC), lámparas black light blue (BLB) y UVC254 nm (UVC)) y el mejor resultado obtenido fue (UVC: 93,5%).

Los experimentos UVC se realizaron a diferentes pH y concentraciones de H2O2 con una eliminación de MET de 98%.

Los experimentos de fotocatálisis se llevaron a cabo con luz natural y artificial, variando la concentración de TiO2 (0,05, 0,10 y 0,40 g/L). También se realizaron experimentos con 0,4 g/L TiO2 pero variando la concentración inicial del MET (25, 50 y 100 mg/L), el pH, la matriz acuosa y adicionando peróxido de hidrógeno. Los mejores resultados fueron (CPC: 81,5% y SB: 100%).

Los experimentos de Fenton se realizaron a pH 3,0 en un reactor de 2 L. Para mejorar el proceso, la adición del Fe (II) se dividió en 5 adiciones realizadas a intervalos constantes de tiempo durante 60 minutos. La mejor degradación de MET fue 87%.

Los experimentos de foto-Fenton se realizaron a pH 3,0 y temperaturas de 14ºC y 25ºC en cuatro instalaciones diferentes (BLB, SB, CPC y UVC). Los mejores resultados obtenidos para la eliminación de MET fueron (BLB: 100%; SB: 97,3% y CPC: 98,3%).

Los experimentos con bicarbonato/H2O2 se realizaron con 5 mg/L iniciales de MET en agua potable, pH libre y temperatura ambiental en un reactor de 0,5 L. Adicionalmente se utilizó Co (II) y Fe (II) como catalizadores. Eliminación de MET de 100%.

Se realizó la identificación de los diferentes intermedios y se han establecido los posibles caminos de degradación del MET.

Finalmente se realizó un estudio de un método actinométrico para poder realizar mediciones de radiación en un reactor fotocatalítico en presencia de un catalizador en suspensión.