Pre-treatment of Propranolol Effluent by Advanced Oxidation ... - RACO

Pre-treatment of Propranolol Effluent by Advanced Oxidation Processes Valderice P.A. Baydum*, Renato F. Dantas, Allan Teixeira, José G. A. Pacheco, Valdinete L. Silva*. Department of Chemical Engineering, Federal University of Pernambuco, Av. Prof. Arthur de Sá, s/n. CEP 50740-560. Cidade Universitária – Recife, BRAZIL

Pre-tratamiento de efluentes de Propranolol mediante procesos avanzados de oxidación Pre-tractament d’efluents de Propranolol mitjançant processos avançats d’oxidació Recibido: 16 de mayo de 2012; aceptado: 6 de agosto de 2012

RESUMEN

RESUM

Se estudiaron los índices de degradación y las eficacias de eliminación de Propranolol utilizando fotólisis directa UV-C, H2O2, UV-C/H2O2, UV-C/ Fe2+, H2O2/Fe2+ y UV-C/ H2O2/Fe2+. Se comparan los distintos procesos para la eliminación del fármaco Propranolol. Los resultados experimentales mostraron que aumentando las concentraciones de peróxido del hidrógeno durante el tratamiento UV-C/ H2O2, aumentó el índice de oxidación. Por otro lado, añadiendo más iones ferroso aumentó el índice de oxidación para los procesos H2O2/Fe2+ y UV-C/ H2O2/Fe2+. Se discuten las principales ventajas y desventajas de cada proceso y la complejidad de comparar los distintos procesos de oxidación avanzada (AOPs). En el proceso foto-fenton fue posible eliminar más del 80% de una concentración de propranolol de 20 mg.L-1 en 5 minutos.

Es van estudiar els índexs de degradació i les eficàcies d’eliminació de Propranolol utilitzant fotólisis directa UV-C, H2O2, UV-C/H2O2, UV-C/ Fe2+, H2O2/Fe2+ y UV-C/H2O2/Fe2+. Es comparen els diferents processos per a l’eliminació del fàrmac Propranolol. Els resultats experimentals van mostrar que augmentant les concentracions de peròxid de l’hidrògen durant el tractament UV-C/H2O2, va augmentar l’índex d’oxidació. D’altra banda, afegint més ions ferrós va augmentar l’índex d’oxidació per als processos H2O2/ Fe2+ y UV-C/ H2O2/Fe2+. Es discuteixen els principals avantatges i desavantatges de cada procés i la complexitat de comparar els diferents processos d’oxidació avançada (AOPs). En el procés foto-fenton va ser possible eliminar més del 80% d’una concentració de propranolol de 20 mg.L-1 en 5 minuts.

Palabras clave: proceso de oxidación avanzada, propranolol, cinética, fenton, foto-fenton, UV-C/H2O2.

Paraules clau: procés d’oxidació avançada, propranolol, cinètica, fenton, foto-fenton, UV-C/H2O2.

SUMMARY Degradation rates and removal efficiencies of Propranolol using UV-C direct photolysis, H2O2, UV-C/H2O2, UV-C/ Fe2+, H2O2/Fe2+ and UV-C/H2O2/Fe2+ were studied. The different processes were compared for the removal of the pharmaceutical Propranolol. Experimental results showed that increasing the hydrogen peroxide concentrations during the UV-C/H2O2 treatment the oxidation rate was increased. On the other hand, adding more ferrous ions enhanced the oxidation rate for the H2O2/Fe2+ and UV-C/ H2O2/Fe2+ processes. The main advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes (AOPs) are discussed. In the photo-fenton process it was possible to remove more than 80% from propranolol concentration of 20 mg. L-1 in 5 minutes. Keywords: advanced oxidation process, propranolol, kinectics, fenton, photo-fenton, UV-C/H2O2.

Afinidad LXIX, 559, Julio - Septiembre 2012

*Corresponding author: [email protected]; [email protected], Tel. +55-0-81-21268711, Fax +55-0-8121267278.

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1. Introduction Pharmaceutical substances and personal care products are an emerging class of aquatic contaminants that have been increasingly detected in ground and surface water in the range of mg.L-1 and ng.L-1 [1-9]. These compounds reach waterways mainly through the discharge of sewage wastewaters and effluents. Important pollution sources such as direct emissions from the pharmaceutical industry and improper disposal of drugs are responsible for great part of this contamination. Pharmaceuticals are often not completely removed in biological treatment plants [10] and therefore, they are emitted to the environment. Hence, it is necessary to treat adequately this type of effluents before their discharge into the environment. Propranolol is a non-selective β-adrenergic receptor (β-blocker) extensively used throughout Brazil for treating hypertension and cardiac arrhythmias [11]. Thus, it has been chosen to represent the class of pharmaceuticals in this study. The chemical and physical characteristics of Propranolol are summarized in Table 1. Table 1 - Physical and chemical properties Propranolol a MW (gmol-1) Water solubility (gl-1) pKa

259,4 100 9.5

Molecular structure

a

[24,25,26,27]

It is a non-biodegradable substance [12] and its removal is not properly performed by conventional sewage treatment, moreover it can be accumulated in aquatic environment [13]. Propranolol was detected in wastewater in different countries and its concentration is given in Table 2 [14]. Despite the small concentration in wastewater, as low as 50 ng.L-1, in industry effluents propranolol has higher concentrations, as high as 20 mg L-1. Table 2 - Propranolol concentration in wastewater treatment plants. Concentration (mg/L)

Wastewater

0.05

STP influents / Sweden [28]

0.03

STP effluents / Sweden [28]

0.03

STP effluents/France [29]

0.01

STP effluents /Greece [29]

0.04

STP effluents /Italy [29]

0.17

STP effluents / Germany [21]

One of the novel technologies for treating effluents is the advanced oxidation processes (AOPs) in which hydroxyl radicals are generated in order to degrade organic pollutants [15]. AOPs can be applied to fully or partially oxidize pollutants and also as a pre-treatment to improve the biodegradability of the effluent in combination with further biological treatment [16]. AOPs processes include Technologies such as UV/H2O2, UV/O3, UV/ H2O2/O3, UV/H2O2/ Fe2+(Fe3+) and UV/TiO2. The efficiency of the various AOPs depend both on the rate of generation of the free radicals

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and the extent of contact between the radicals and the organic compound [17]. It is assumed that a combination of single oxidation processes should result in better degradation rates and efficiencies as compared to individual processes. The Fenton and photo-Fenton systems have been widely applied in the treatment of non-biodegradable compounds in wastewater. Oxidation with Fenton’s reagent is based on ferrous ion and hydrogen peroxide, and exploits the reactivity of the hydroxyl radicals produced in acidic solution by the catalytic decomposition of H2O2 [10]: Fe2+ +H2O2→ Fe3+ +OH− + HO•

(1)

Hydroxyl radicals may be scavenged by the reaction with another Fe2+: HO• + Fe2+→ OH− + Fe3+

(2)

Fenton’s reagent appears to be a very powerful oxidizing agent. The chemicals are readily available at moderate cost and without needing special equipment. In addition to the above reactions, the photo-Fenton process produces hydroxyl radicals in the following way [18]. Fe3+ +H2O+hν→ HO• + Fe2+ +H+ (3) Fe(OH)2+ +hν→ HO• + Fe2+ (4)

The rate of organic pollutant degradation could be increased by irradiation of Fenton’s reagent with UV light (photo-Fenton process). The illumination leads not only to the formation of additional hydroxyl radicals but also to the recycling of the ferrous catalyst by converting Fe3+ into Fe2+. Among the AOPs, the oxidation using Fenton’s reagent and photo-Fenton’s reagent have been found to be promising and attractive treatment methods for the effective degradation of pharmaceuticals. The objective of this study was to evaluate the degradation of propranolol by AOPs in a synthetic effluent, similar to a pharmaceutical industry stream, as a pre-treatment before biological oxidation. AOPs investigated were: UV-C/H2O2, UV-C/ Fe2+, H2O2/ Fe2+, UV-C/ H2O2/ Fe2+, UV-C (Photolysis) and H2O2. Degradation rates and efficiencies were compared among the various oxidation processes studied. The difficulty in comparing these processes on an equal basis is discussed. Table 3 – Variable and levels used in Fenton experiments. Symbol

Variable

[H2O2] [H2O2] / [Fe 2+]

Peroxide concentration (mg/L) Mass ratio

Levels low (-1) high (+1) 50 100 2 6

Table 4 – Variable and levels used in photo-Fenton experiments. Symbol

Variable

[H2O2] [H2O2] / [Fe 2+] t

Peroxide Concentration (mg/L) Mass ratio Time (min)

Levels low (-1) high (+1) 50 100 2 6 15 30

2. Materials and Methods The target substance, a racemic mixture of propranolol hydrochloride, i.e. (±)-1-isopropyl-amino-3-(1-naphthyloxy) propan-2-ol hydrochloride (99.8% purity) was supplied by the state pharmaceutical laboratory of Pernambuco, Brazil. Fenton and Photo-Fenton experiments were carried out using heptahydrated ferrous sulphate (FeSO4.7H2O) (99.5% w/w, F. Maia), hydrogen peroxide (30% w/w, F. Maia); sulphuric acid (97–98% w/w, Merck) was used for


Table 5 – Representative studies for propranolol removal. Process

Initial concentration

UV-C UV-C Fenton-like + fungus Photolysis SPF EF Fenton

100 mg/L 100 mg/L 10 mg/L 2 x 10-5 M 100 mg/L 100 mg/L 2 mg/L

Fe (II) 100-300mM* 10 x 10-6M 0.5mM 0.5mM 20mg/L

H2O2

% Removal

Reference

20mM 20mM 50mg/L

30 in 8 h 60 in 24 h 80 in 6 h 90 in 60 min** 97 in 6 h 66 in 6 h complete in 30 min

[19] [19] [30] [31] [32] [32] [33]

* Fe(III);** pH 5; Solar Photoelectro-fenton (SPF); Electro-Fenton (EF)

pH adjustment. Hydrogen peroxide consumption was monitored using Merckoquant® peroxide analytical test strip (range 0.5–25 y 1–100 mg L−1 H2O2) (Merck). All solutions were prepared with distilled water.

A calibration curve of propranolol concentration was done from 0 to 20 mg L-1.

2.1. Experimental setup To perform the runs, propranolol solutions (20 mg L -1, 100 mL of deionized water) were transferred into borosilicate glass reaction vessels, with magnetic stirring. To ensure reproducibility, each experiment was conducted in duplicate.

3.1. Preliminary AOPs studies

3. Results and discussion

2.2. UV-C irradiation system Irradiation experiments were carried out with UV lamp (Philips 30W), which emitted radiation at 253.7 nm [19]. Hydrogen peroxide assisted photodegradation was studied by adding 50 or 100 mg L-1 of H2O2 in propranolol aqueous solution at pH 3. 2.3. Degradation kinetics In each experiment, an Erlenmeyer containing 100 mL of Propranolol solution was placed on a table stirrer at 300 rpm during 5, 10, 15, 20 and 30 minutes. Any residual hydrogen peroxide was destroyed by the enzyme catalase from bovine liver (2950 U/mg) whenever residual H2O2 in the treated sample was not determined. After each time the samples were filtered through 0.45 µm glass fibre filter from Whatman and the residual concentrations were quantified. The experiments were carried out in duplicates; the measurements average was calculated. 2.4. Experimental design The effect of Fe(II) and H2O2 initial concentration on propranolol oxidation was studied by using a 23 experimental design and a surface-response analysis [20]. Propranolol initial concentration (20 mg L−1), temperature (25ºC) and initial pH (3.0) were kept as constant parameters. Tables 3 and 4 present the variables and levels of Fenton and photo-Fenton experiments respectively. 2.4.1. Fenton and photo-Fenton processes Fenton and photo-Fenton oxidation were carried out at initial pH of 3.0. Hydrogen peroxide, at initial concentration of 50 mg L-1 or 100 mg L-1, and ferrous ions (as ferrous sulphate salt) at initial concentrations of 8 to 50 mg L-1 were added into the Propranolol solution to initiate the oxidation reactions. These concentrations were chosen at levels that would allow measurable degradation over a period of 15 to 30 min, which corresponded to the UV-C exposure time. 2.6. Analytical methods The total organic carbon (TOC) content of the initial samples was determined in a Shimadzu TOC-V analyzer. A Perkin Elmer spectrophotometer UV-Vis Lambda 35 was used to determine propranolol concentration at 289 nm.


ation efficiency and minimize sludge production is a major drawback in many natural waters.

Figure 1 - Chemical degradability of Propranolol under different conditions. Initial conditions: pH 3, [Propranolol]0 = 20 mg/L, [Fe2+]0 = 50 mg/L, in Fenton and Photo-fenton process [H2O2]0 = 100 mg/L.

Figure 1 shows that simple H2O2 oxidation and UV-C photolysis reactions lead to limited propranolol degradation: 2% and 16%, respectively, after 60 min reaction. The combined action of UV-C and H2O2 caused degradation of 89% and 93% after 60 min, respectively with 50 and 100mg/L of peroxide initial concentration. For UV-C and Fe2+ observed Propranolol removal was 44% in 60 min. In the Fenton process Propranolol removal was 93% at 60 min. For photo-Fenton process 93% of degradation was obtained at 30 min. Others studies for propranolol removal are showed in Table 7. Table 8 – Pseudo First-order rate kinetics (k) and half-life (t1/2) of Propranolol degradation Type of oxidation process UV+Fe

2+

k (min−1) 0,05

t1/2 (min) 13,86

UV+H2O2

0,16

4,33

Fenton (Fe2++H2O2)

0,38

1,82

photo-Fenton (Fe2++ UV+H2O2)

0,58

1,19

This result shows that out of the various oxidation pathways, the removal of Propranolol is most efficiently carried out by the photo-Fenton process. The relative efficiencies

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of the above discussed processes are in the following order: Fe2+ + H2O2 +UV-C (photo-Fenton) > Fe2+ + H2O2 (Fenton)>UV-C+ H2O2 >UV-C+ Fe2+ >UV-C> H2O2. The high efficiency of the photo-Fenton process is due to the formation of more hydroxyl radicals than the other processes. This process significantly increased the rate of oxidation mainly due to the photo-reduction of Fe3+ to Fe2+, which reacts with H2O2 establishing a cyclic mechanism of generating additional hydroxyl radicals (Eq. 3). Furthermore, the effect of UV-C light was also attributed to direct hydroxyl radical formation and regeneration of Fe2+ from the photolysis of the Fe(OH)2+ complex in solution [18]. It was known that the existing form of ferrous iron is related to the solutions acidity. At pH 3, part of ferrous iron would exist in the form of Fe(OH)2+, which photolysis under UV-C radiation could directly produce OH• radicals and Fe2+[8]. The main advantage of the photolytic oxidation based processes are the operation at room temperature conditions and mild pressure, besides the possibility to effectively use sunlight, which should result in considerable economic savings especially for large-scale operations [17]. Nevertheless, photolytic methods may result in expensive high - energy requirements [22]. Highly complicated apparatus which could help in the transition from laboratory scale to a large scale are not required [23]. A major disadvantage of these processes is strong dependence on the aqueous solution pH and the concentrations of hydrogen peroxide and ferric/ferrous ion. The requirement for acidic pH 3–4 in order to achieve high degrad Table 8 - Comparison between the degradation and TOC removal of Propranolol by Fenton and photo-Fenton reactions. oxidation process Fenton photo-Fenton

Degradation (%) 90 99

TOC (%) 52 69

Experimental conditions: reaction time = 30 min, [Propranolol]0 = 20 mg/L, [Fe2+]0 = 50 mg/L, [H2O2]0 = 100 mg/L and pH 3.

3.2. Degradation kinetics A plot of [Propranolol/Propranolol0] versus time is presented in Fig. 5. Propranolol and Propranolol0 represent the concentration of Propranolol from 0 to 30 min and its initial concentration, respectively. The experimental data in Fig. 5 show that photo-Fenton processes had a significant accelerating effect on the rate of oxidation of Propranolol. The disappearance of Propranolol could be described in pseudo first-order reaction kinetics with regard to pharmaceutical concentration. Degradation rate constants, k (in min−1), were determined from the slope of −ln(C/C0) = f(t (min)) plots, where Propranolol0 and Propranolol are the concentration of Propranolol at times 0 and t. The apparent rate constant has been chosen as the basic kinetic parameter to compare the different systems, since it is independent of the concentration and thus enables one to determine the catalytic activity. Furthermore, to gain a better understanding of the degradation processes, the necessary time to reduce to 50% the initial concentration of Propranolol (i.e. the half-life) was calculated and is termed (t1/2). The results are listed in Table 8. The data in Table 8 show that adding Fe2+ to the UV+H2O2 system enhanced the rate of Propranolol oxidation by a

214

maximum factor 3.6, over the UV+H2O2 system, depending on both H2O2 and Fe concentrations. This phenomenon of enhanced removal efficiency is also known from other researches with Fe2+ and Fe3+ [22]. As listed in Table 8, the addition of UV light to the Fenton reaction led to a 1.5 times increase in the reaction rate constant for Propranolol degradation (from 0.38 to 0.58 min−1). However, the use of a simple UV lamp in Fenton reaction may be very important to increase the degradation capacity of Propranolol after few minutes. This is because UV light wavelength can significantly influence direct formation of OH• radicals as well as the photo-reduction rate of Fe3+ to Fe2+ (Eq. (3)). 3.3. Experimental design 3.3.1. Fenton and photo-Fenton process

Figure 2 – Three-dimensional representation of the response surface for the Propranolol removal percentage after 30 min of reaction with Fenton’s reagent. [H2O2] and [H2O2]/[Fe2+] load are represented in coded values in the abscissa. Removal percentage is shown in the legend. Temperature is fixed at 25 °C (the lowest value).

A total of four runs were conducted for Fenton process and eight runs were conducted for photo-Fenton process. Data analysis and optimisation were carried out using Statistical commercial software. Statistical validation was carried out by testing at a 95% confidence level. Degradation rate and efficiency of Propranolol was promoted with increasing the peroxide by Fenton reaction as shown in Figure 2. Analyzing the values in Figure 3 shows the Pareto chart for all study variables and their interactions for the planned usage Photo-fenton. All Pareto chart values greater than the P value (0.05) are statistically significant. Thus, it can be observed in Figure 3 that only the time is statistically significant. In Figure 4 it is observed that the best results of the Propanolol removal were obtained from experiments with smaller molar ratio [H2O2]/[Fe2+] and larger time and peroxide concentration. The same operating parameters (volume, pH) were applied in Fenton and Photo-fenton processes in order to compare their efficiency for the degradation of Propranolol. On a time basis, the removal of Propranolol was more effective using the photo-Fenton reaction compared to a normal Fenton reaction.


Figure 3 – Pareto chart of standardized effects and their interactions for the Photo-fenton factorial plan 23 design.

Figure 5 – Kinetic Degradation of Propranolol using differing reagent.

4. Conclusions

Figure 4 – Cube showing the results in terms of % Propranolol removal for Photo-fenton reaction.

3.4. Mineralisation study In order to assess the degree of mineralisation reached during AOPs, the decreasing of the total organic carbon (TOC) is generally estimated. To study the mineralisation of Propranolol in Fenton and photo-Fenton processes, the Propranolol degradation experiments were conducted at Propranolol initial concentration of 20 mg/l. The amount of TOC produced by the degradation reaction was measured. Productivity of TOC was regarded as mineralisation efficiency. The results are shown in Table 8. As can be seen, pharmaceutical degradation is much higher than TOC removal even in Fenton and photo-Fenton. Although, it is clear from these results that photo-Fenton processes presents a TOC removal higher than Fenton process, 69% and 52%, respectively. It is possible to conclude that the UV lamp is very useful in Fenton system to aid the Propranolol mineralisation. The great difference between degradation efficiency and mineralization efficiency also implied that the products of Propranolol oxidation mostly stayed at intermediate product stages under the present experimental conditions.


The following conclusions can be drawn from the present study: • Degradation of Propranolol by photolysis was found to be less effective as compared to UV-C/H2O2 oxidation. • Increasing the concentration of hydrogen peroxide promoted the oxidation under UV-C/H2O2 treatment. • The optimum conditions for the degradation of Propranolol in Fenton and photo-Fenton processes were observed at [H2O2]/[Fe] 2, with an initial H2O2 concentration of 100 mg/L at t = 30 min with a pharmaceutical concentration of 20 mg/L. • Highest removal efficiency in terms of TOC could be achieved via photo-Fenton’s reagent. • Fenton and photo-Fenton processes are powerful methods for Propranolol degradation, but photo-Fenton process is more efficient. • The advantages of the photo-Fenton process as an oxidative treatment are low cost, rapid degradation, and simple handling. • H2O2/Fe2+/UV system could be applied to wastewater treatment works as a new developing methodology for reducing levels of other pharmaceuticals.

Acknowledgements The authors wish to thank the LAFEPE Pharmaceutical Company for the supply of active substance. We acknowledge the financial support of FACEPE under research project IBPG-0200-3.06/08.

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