Polycyclic aromatic hydrocarbons (PAHs) are considered priority compounds due to their toxic and carcinogenic nature. The concern about water contamination and the consequent human exposure has encouraged the development of new methods for PAHs removal. The purpose of this work was to study the feasibility of a degradation process of benzo(a)pyrene (BaP) in aqueous matrices by oxidation with Fenton reagent. A laboratory unit was designed to optimize the factors which may influence the process: pH (3.5 to 6.0), temperature (30 to
In these last years, an increasing concern about monitoring water quality has been reflected in many studies. The amount of freshwater on Earth is limited and its quality constantly threatened. Hence there is a demand for the protection of water resources, in order to prevent their contamination by toxic compounds and pathogenic agents. Nowadays, the major concern is focused on organic pollutants such as polycyclic aromatic hydrocarbons (PAHs).
PAHs are compounds with two or more fused aromatic rings, containing only carbon and hydrogen [
The Water Framework Directive (2000/60/EC) outlined a strategy to combat water pollution and also demanded the establishment of a list of priority pollutants [
Benzo(a)pyrene (
Given the risks posed by these compounds to public health, several methodologies for the decontamination of environmental matrices have been developed. Some authors suggest removal through volatilization, oxidation, adsorption to soil particles, and biodegradation [
There are few studies about the degradation of PAHs via Fenton oxidative process in aqueous matrices. Beltrán et al. [
There are several studies describing PAHs degradation in other matrices such as soils and sediments [
The present work pretends to evaluate the feasibility of
A commercial solution of benzo(a)pyrene (1000
Hydrogen peroxide in stable form (30% Perhydrol, p.a.) and iron (II) sulfate heptahydrate were purchased from Merck (Darmstadt, Germany). The pH of the PAH solutions was adjusted with
The experiments were conducted in a 250 mL jacketed thermostatic batch reactor (inner diameter: 7.5 cm, height: 11.5 cm). The outside of the reactor was covered with aluminium foil to protect from light, and an inlet for temperature measuring was placed on the top of the reactor. Homogeneous mixing was provided using a magnetic stirring bar and the temperature was kept constant with a thermostatic bath (Figure
Scheme of the experimental device.
In each experiment, 100 mL of
Experimental conditions used in Fenton’s reaction.
Run no. | pH | ||||
---|---|---|---|---|---|
1 | 3.5 | 40 | 10 | 200 | 5.50 |
2 | 6.0 | 40 | 10 | 200 | 5.50 |
3 | 3.5 | 30 | 10 | 200 | 5.50 |
4 | 3.5 | 50 | 10 | 200 | 5.50 |
5 | 3.5 | 70 | 10 | 200 | 5.50 |
6 | 3.5 | 40 | 10 | 20 | 3.75 |
7 | 3.5 | 40 | 10 | 50 | 3.75 |
8 | 3.5 | 40 | 10 | 150 | 3.75 |
9 | 3.5 | 40 | 10 | 100 | 2.75 |
10 | 3.5 | 40 | 10 | 100 | 5.50 |
11 | 3.5 | 40 | 10 | 100 | 3.75 |
12 | 3.5 | 40 | 20 | 50 | 3.75 |
13 | 3.5 | 40 | 60 | 50 | 3.75 |
14 | 3.5 | 40 | 100 | 50 | 3.75 |
HPLC analyses were performed with a Merck Hitachi LaChrom Elite system (Darmstadt, Germany) equipped with an L-2130 pump, L-2200 autosampler, and a L-2480 fluorescence detector. Data were acquired and processed by EZChrom Elite software from Agilent (Santa Clara, CA, USA). For chromatographic separation, a reversed-phase RP-18 endcapped Purospher STAR (250 mm
The method linearity was verified in the 1 to 100
As mentioned above, Fenton’s reagent is a strong oxidant mixture consisting of hydrogen peroxide and iron (II) salt that acts as a catalyst. In this process, the hydroxyl radicals are formed in situ and depend on several factors such as pH, temperature, and the initial concentrations of hydrogen peroxide, ferrous ion, and
The standards of
The Fenton’s reaction is pH dependent, because this value affects the hydroxyl radicals generation and, consequently, the oxidation efficiency. For this degradation process, the optimal pH range mentioned in literature is 3 to 6. Therefore, in this work the 3.5 and 6.0 pH values were studied and the results are shown in Figure
Effect of pH on
Experiments were conducted under the same conditions at four different temperatures between 30 and
Effect of temperature on
Experiments were performed to determine the effect of hydrogen peroxide concentration on the process (Figure
Influence of hydrogen peroxide concentration on
Experiments were conducted in order to investigate the effect of ferrous ion concentration (catalytic agent) on the process. Figure
In 1996, Béltran et al. [
The homogeneous Fenton process has the disadvantage of commonly using high concentrations of ferrous ion (50 to 80 mg
Effect of the initial concentration of ferrous ion on
Thinking about a possible application of this method to naturally contaminated samples, it is important to study the dependence of the degradation efficiency on the initial concentration of the analyte. In wastewater treatment plants, the analyte concentration present in the effluent is usually unknown. Therefore, it is essential to determine the maximum amount of pollutant that would be degraded with a fixed reagent concentration. As seen in Figure
Effect of
The main conclusion of the present work is that Fenton’s reagent is an appropriate method for the total degradation of benzo(a)pyrene in water matrices, providing that the ferrous ion and hydrogen peroxide are present in suitable concentrations. These parameters as well as temperature are important variables for the process. It was shown that an increase in temperature from 30 to
Future work will consider a scale-up optimization as well as the identification of the reaction by-products, if they appear.
The authors wish to thank the Fundação para a Ciência e a Tecnologia (FCT), Portugal, for financial support (SFRH/BD/38694/2007).