Scholarly article on topic 'Treatment of Effluent from a Factory of Paints Using Solar Photo-Fenton Process'

Treatment of Effluent from a Factory of Paints Using Solar Photo-Fenton Process Academic research paper on "Chemical engineering"

Share paper
Academic journal
International Journal of Photoenergy
OECD Field of science

Academic research paper on topic "Treatment of Effluent from a Factory of Paints Using Solar Photo-Fenton Process"

Hindawi Publishing Corporation International Journal of Photoenergy Volume 2013, Article ID 340347, 9 pages

Research Article

Treatment of Effluent from a Factory of Paints Using Solar Photo-Fenton Process

Alam Gustavo Trovó,1 Oswaldo Gomes Jr.,1 and Antonio Eduardo da Hora Machado1,2

1 Instituto de Química, Universidade Federal de Uberlandia, 38400-902 Uberlandia, MG, Brazil

2 Departamento de Química, Universidade Federal de Goias, 75704-020 Catalao, GO, Brazil

Correspondence should be addressed to Alam Gustavo Trovó; Received 31 May 2013; Revised 31 August 2013; Accepted 31 August 2013 Academic Editor: Mika Sillanpaa

Copyright © 2013 Alam Gustavo Trovó et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

We evaluated the use of Fenton reactions induced by solar radiation in the treatment of effluent from a factory of paints for buildings, after prior removal of the suspended solids. The increase of H2O2 concentration from 100 to 2500 mg L-1 for a [Fe2+] = 105 mg L-1 contributed to the reduction of DOC, COD, and toxicity. Our best results were achieved using

DOC and COD removal and a complete removal of the toxicity with respect to Artemia salina. Additionally, through increasing Fe2+ concentration from 15 to 45 mg L-1, the DOC removal rate increased 11 times, remaining almost constant in the range above 45 until 105 mgL-1. Under our best experimental conditions, 80% of DOC removal was achieved after an accumulated dose of 130 kJm-2 of UVA radiation (82 ± 17 min of solar irradiation under an average UVA irradiance of 34.1 ± 7.3 W m-2), while 40% of DOC removal was reached after 150 min under only thermal Fenton reactions. The results suggest the effectiveness of implementation of solar photo-Fenton process in the decontamination and detoxification of effluents from factories of paints for buildings.

1. Introduction

Wastewaters containing toxic compounds may originate from household and personal care activities as well as from industrial processes. Most of the compounds present in these wastewaters are not treatable by conventional technologies due to the high stability, toxicity, and/or lowbiodegradability [1,2].

Having regard to the above information, many studies aimed at the elimination of toxic and recalcitrant compounds are based on the application of advanced oxidation processes (AOPs) [3-8], since the nonselective attack of the hydroxyl radicals usually converts toxic compounds into carbon dioxide, water, and inorganic ions [9]. However, the main disadvantage of AOPs is high cost of maintenance of the artificial sources of radiation and equipment for ozone production. On the other hand, solar radiation can be used as radiation source in heterogeneous photocatalysis and photo-Fenton process, reducing the energetic costs [10-13]. The photo-Fenton process has the advantage to be a homogeneous process, favouring a better contact between reagent species

and also avoiding an additional step for removal of catalyst, which is usual when dealing with heterogeneous processes.

Although the photo-Fenton process has been applied in the treatment of wastewaters of different compositions (containing pesticides, pharmaceuticals, petroleum, dyes, and colorants, among other compounds), no attempts have been published concerning the use of the photo-Fenton process combined with solar radiation as an alternative to the treatment of effluent from factories of paints for buildings, searching its decontamination and detoxification. Most of the articles published concerning the treatment of wastewaters containing dyes and pigments involve the study of synthetic effluents containing one or more target compounds in ultrapure water and/or using artificial irradiation, a situation far from the reality [14-18]. Few studies have been reported using real effluents [10,11,19,20].

Therefore, the aim of the present work is to evaluate at lab scale the influence of H2O2 concentration on the soluble fraction of the organic load (dissolved organic carbon (DOC) and chemical oxygen demand (COD)), as well as on the toxicity removal during the application of the solar

photo-Fenton process in the treatment of a real effluent, seeking to meet discharge standards and/or reuse in the manufacturing process or in other activities inherent to the industrial plant. Under the best concentration defined in this study for H2O2, the influence of Fe2+ on the kinetics of DOC removal was evaluated, aiming to know the time of treatment and estimate its potential of application. The evaluation of the concentration of Fe2+ and H2O2 is determinant to establish the process efficiency. This information is necessary for an economic and operational evaluation before scaling up to a large scale. In addition, the knowledge about the behaviour of the effluent toxicity during application of the photocatalytic process allows us to make the necessary adjustments so that the process is feasible in large-scale applications.

2. Materials and Methods

2.1. Reagents. All solutions, except the effluent, were prepared using ultrapure water.

FeSO4-7H2O (Vetec) was used to prepare aqueous 0.25 molL-1 Fe2+ stock solution; H2O2 (30% w/w), H2SO4, NaOH, and Na2SO3, all from Vetec, were used as received. A solution of ammonium metavanadate (Vetec) was prepared at a concentration of 0.060 mol L- in used for H2O2 quantification.

The effluent was kindly provided by a factory of paints for buildings, whose main activity is the production of acrylic paints. The composition of the effluent was not made available by the company. In general, this kind of effluent must contain acrylic resin, organic and inorganic pigments (titanium dioxide, phthalocyanines, etc.), charges (carbonates, silicates, etc.), additives (dispersants, humectants, surfactants, etc.), and organic and inorganic salts, among others [21].

2.2. Photodegradation Procedure and Solar Irradiance Measurements. All experiments were carried out between 10 am and 14 pm, in a range of temperatures varying between 27 and 33°C, during autumn using a batch reactor located in our lab, in Uberlandia, Brazil (18°55'08"S; 48°16'37" W). The solutions containing reagents and effluent, after adjustment of pH and filtering, were exposed to sunlight under clear sky conditions, in open vessels of dark glass (same deep, but with different surface area), and maintained under constant magnetic stirring. Three types of glass containers were used: the first one with 0.21 x 0.21 m (volume of 3.3 L and surface area of 0.044 m2), the second with 13 cm of diameter (volume of 0.98 L and surface area of 0.013 m2), and the third with diameter of 6 cm (volume of 0.21 L and surface area of 0.0028 m2), all with 7.2 cm of depth. Each glass container was filled with the effluent, resulting in a depth of 7 cm.

Two sets of experiments involving the photo-Fenton treatment were performed. One is controlled dosing of H2O2 (ranging from 100 up to 2500 mgL- ), monitoring Fe + and Fe3+ concentrations, the removal of DOC and COD as well as the toxicity. The second set is evaluating the effect of different iron concentrations (15, 45, 75, and 105 mg L-1) on the kinetics of DOC removal and consumption of H2O2.

The first one was done using containers of 0.21 x 0.21 m and 105 mg L-1 Fe2+. For these experiments, H2O2 was added

to the containers in small portions, in the order of a few mgL-1. The consumption of H2O2 was monitored during solar exposure without control of the dose of the incident UVA radiation. After consuming all H2O2, an aliquot was taken for analyses. A new portion of H2O2 was added, and another sample was taken after consumption of all the H2O2. This cycle was repeated until a cumulative concentration of 2500mgL-1 of H2O2 has been added. The procedure described as "addition, total consumption, sample collection, and new addition" is important as it prevents the occurrence of reactions in the dark during storage after collection of the sample and possible interference in toxicity tests and the analysis of COD. In these experiments, aliquots (70 mL) of the photolysed solution were collected immediately after the confirmation of the total consumption of the added H2O2. Considering this procedure, it is recommended that the experimental data must be expressed in terms of H2O2 consumption and not on the basis of the accumulated radiation dose or even the reaction time.

In the second set of experiments (kinetic experiments), containers of 13 cm diameter were used. Two sets of experiments were performed: the first one involves the correlation between reaction time and accumulated dose of UVA, and the other relates the reaction directly to the dose of UVA radiation. In the first set of experiments, aliquots of 30 mL were collected at intervals of 20 min up to 60 min of reaction and at very 30 min above 60 min of reaction up to 150 min. For the second, aliquots were collected after exposure to the same dose of UVA radiation. This procedure was done to facilitate the comparison of results, since for the same dose of UVA, the same amount of photons is obtained, providing the same level of degradation for a similar exposition [10, 11, 22]. The measurements of UVA irradiance and dose were done using a solar light PMA2100 photometer/radiometer, equipped with a UVA detector (320-400 nm).

We used an initial concentration of H2O2 equal to 1600 mg L-1, determined in previous experiments, which is able to induce an almost complete reduction in DOC and COD. Due to the fast consumption of H2O2, new additions were done at each 78.3 kJm-2 accumulated, in the experiments when 45mgL-1 Fe2+ were used, and at each 47.1 kJm-2 of UVA, when 75 or 105 mg L- Fe + were used.

Before photo-Fenton experiments, the initial pH of the effluent was adjusted between 2.5 and 2.8, the optimum pH range for Fenton reactions [23,24], using a solution of H2SO4, which caused the precipitation of the suspended solids. The suspended solids in the effluent were, then, removed by filtration, using membranes with mean pore size of 0.45 ^m, after a previous decantation. An aqueous solution containing Fe2+, acidified with sulfuric acid, was added to the filtered effluent. Acidification of this solution was to prevent the oxidation of Fe2+ to Fe3+. Shortly after the addition of Fe2+, a new adjustment of pH to the range between 2.5 and 2.8 was done. So, before exposing the solution to sunlight, the H2O2 was added.

After sampling and before analysis, for the experiments involving the controlled dosage of H2O2, the pH of the aliquots was adjusted to the range between 6 and 8 before filtration through membranes with mean pore size

Table 1: Composition of the studied effluent.


Dissolved organic carbon (mgC L- ) Dissolved organic carbon (mgC L-1)c Dissolved inorganic carbon (mg C L-1)b Dissolved inorganic carbon (mg C L-1)c Chemical oxygen demand (mgO2 L-1)b Chemical oxygen demand (mgO2 L-1)c Toxicity (A. salina) (%)c

Solids in suspension (mgL-1)a Total dissolved iron (mgL-1)b Total chloride (mg L-1)b Total chloride (mg L-1)c Total phosphorus (mg L-1)c Total N(mgL-1)b Total N(mgL-1)c N-NH4+ (mgL-1)b N-NH4+ (mgL-1)c

Colora Colorb Colorc Odora Odorb Odorc

307 237 83.5 6.2 1232 672 100 7.6 2040 0.05 8.2

3.2 34.9 28.1 28.5 26.9 Lilac Lilac


Fetid Fetid

Similar but less intense

aRaw effluent. b

Raw effluent, after filtration using 0.45 ^m mean pore size membranes. cAfter pH adjustment between 2.5 and 2.8, precipitation, and filtration using 0.45 ^m mean pore size membranes.

of 0.45 ^m, while for the kinetics experiments, an excess of a 2.0molL-1 solution of Na2SO3 was added to the samples before pH adjustment and filtration, ensuring the removal of the remaining H2 O2 and stopping the Fenton reactions. For the kinetics experiments, only DOC and H2O2 analyses were done, since the presence of sulfite does not cause interference in these analyses.

Control experiments (direct photolysis, H2O2/solar, H2O2 dark, Fe2+/solar, and Fenton) were also performed in containers with 6 cm diameter using 105 mg L-1 Fe2+.

2.3. Analytical Determinations and Toxicity Bioassays. The efficiency of the photo-Fenton process was evaluated by monitoring the following experimental parameters: electronic absorption, consumption of H2O2, amount ofFe2+ and Fe3+, COD, DOC, and toxicity, evaluated using Artemia salina.

The DOC decay was followed using a TOC analyser (Shi-madzu TOC-VCPH/CPN) equipped with an ASI-V autosam-pler. COD determinations were carried out according to the 5220D Standard Methods [25]. The H2O2 concentration was estimated using a photometric method proposed by Nogueira et al. [26]. The absorbance values were obtained from UV-Vis spectra in the range between 190 and 800 nm, using a Shimadzu UV-1650 PC spectrophotometer. The Fe2+

content was determined directly, using a methodology based on the reaction between Fe2+ and 1,10-phenantroline [25]. The concentration of Fe3+ was estimated by the difference between the total iron, determined after reduction with hydroxylamine, and the content of Fe2+. The toxicity tests were done evaluating the immobilization of A. salina [27].

3. Results and Discussion

3.1. Characterization of the Effluent. Paints for buildings can be considered as a stable mixture, in basic medium, of solids in a volatile component (water or organic solvent, in this case, water). A third group of components is the additives. Although they represent a small fraction of the composition, they are responsible for important features for the paints, as wetting and dispersing action for pigments and charges and corrosion protection, among others.

A brief characterization of the effluent used in this study is presented in Table 1. The raw effluent, a mixture of different dyes, is opaque with a milky appearance and a slightly lilac color, possessing an expressive amount of suspended solids (2040 mgL-1) and a pH close to neutrality. The soluble fraction has a moderate organic load (DOC = 307.0 mg C L-1 and COD = 1232 mg O2 L-1).

Considering that the optimum pH range for Fenton reactions occurs between 2.5 and 2.8 [23, 24], the pH of the effluent was adjusted to this range before performing the photo-Fenton experiments. However, after acidification, the equilibrium that kept the solids suspended due to the dispersant action of the additives, was compromised, leading to a rapid precipitation. Simultaneous to precipitation, a complete color removal was observed, most likely due to the adsorption of the pigments on the surface of the solids. With the removal of the suspended solids, a partial but expressive DOC and COD reduction, respectively, from 307 to 237 mgL-1 and from 1232 to 672 mgL-1 (Table 1), was quantified. Similar behavior was also observed for the inorganic fraction (total chloride and nitrogen and nitrogen as ammonium). In addition, the pH adjustment contributed to the elimination of carbonates and bicarbonates, reducing the dissolved inorganic carbon from 83.5 to 6.2mgCL-1 (Table 1), which is extremely advantageous since these species act as scavengers of hydroxyl radicals [28]. On the other hand, although a complete color removal was reached after pH adjustment and filtration of solids, much of the organic load remained in solution, which presented 100% of toxicity to A. salina (Table 1).

From this point, the authors decided to apply the photo-Fenton process as an alternative to degrade only the soluble fraction of the organic load to discharge standards and/or its reuseain, and not the solid phase. So, before all photodegradation experiments and after pH adjustment, the effluent was submitted to decantation and filtration using 0.45 ^m mean pore size membranes.

The UV-Vis absorption spectrum of the effluent after pretreatment reveals a high absorbance only in the UV region (190-400 nm), probably due to the presence of aromatic compounds (Figure 1(b)).

0 300 -

600 1200 1800 2400 H2O2 (mg L-1)

■- DOC 1- COD

200 250 300 350

Wavelength (nm)

- 0 - 1000

— 100 mg L-1 H2O2 ...... 1200

200 - 1600

- 300 - 2500

Figure 1: Influence of the H2O2 concentration on the soluble fraction of the (a) organic load DOC and COD, (b) UV absorbance removal of the effluent, obtained during solar photo-Fenton reaction, using different H2 O2 concentrations. Experimental conditions: initial DOC = 237 mg CL-1; initial COD = 672 mg O2 L-1; Fe2+ = 105 mg L-1; and pH = 2.5-2.8.

3.2. Application of Photo-Fenton Process Mediated by Solar Radiation

3.2.1. Influence of the H2O2 Concentration. The H2O2 concentration is an important operational parameter for Fenton reactions, since an excess of this reagent, or its absence, tends to reduce drastically the efficiency of the process. The excess ofH2O2 favors self-decomposition reactions (1) and reactions that consume hydroxyl radicals without however promoting the degradation of organic matter (2)-(4), committing the efficiency of the process [27,29-32]. In view of this, in the first part of this study, a set of experiments was carried out aiming to find the best H2O2 concentration in the range from 100 to 2500mgL-1, in the presence of 105mgL-1 Fe2+, capable to maximize DOC and COD removal (Figure 1). In addition, the toxicity of the effluent was monitored throughout the process in order to assess the viability and the potential use of photo-Fenton reactions in the treatment of this kind of effluent. In these experiments, the dose of UVA radiation was not controlled the solutions were exposed to the sunlight until the total consumption of the H2O2 was added:

HO^ + •oh

k=5.2x 109 M-1 s-1

H2O2 + H2O2

2 H2O + O2

H2O2 + HO^ H2O + HO/ к = 3.3 x 107 M-1 s-1 (2)

HO/ + •OH H2O + O2 к = 0.71 x 1010 M-1 s-1 (3)

For the experiments with controlled H2O2 dosage, after addition of the first dose of 100mgL-1 of this reagent, the color of the effluent changed from light orange to dark gray, suggesting the formation of dark colored intermediates. New additions of H2O2 up to 2500 mg L-1 were done. Although there has not been a complete removal of color of the solution, there was a significant reduction in its intensity. This suggests the persistence of the colored intermediates. Despite that the color of the effluent can limit the action of the incident radiation, a fast COD decay from 672 to 250 mg O2 L-1 was achieved using 400mgL- H2O2, and 105mgL- Fe +, under solar irradiation. Using 1600mgL-1 H2O2 a COD of 70mgO2 L- was reached (Figure 1(a)).

Only a slight improvement in COD removal was observed when increasing the H2O2 concentration from 1600 up to 2500mgL-1, respectively, 70 to 57mgO2 L-1, probably due to the formation of acids of low molecular weight, refractory to oxidation [33,34]. Similar behavior was observed for DOC removal (Figure 1(a)) and for the absorption maxima at 224 and 272nm (Figure 1(b)). Using 1600mgL-1 H2O2, 90% of DOC removal and 100% of removal of the absorbance peaks at 224 and 272 nm were obtained (Figure 1), suggesting a high efficiency of the photo-Fenton process in removing the organic load and decontamination of this class of effluent. Therefore, the use of H2O2 concentrations higher than

600 1200 1800 H2O2 (mg L-1)

-•- Fe -.- Fe3+ —Total iron

Figure 2: Dependence on Fe2+, Fe3+, and total dissolved iron concentrations and different concentrations of hydrogen peroxide, during photo-Fenton treatment of the soluble fraction of the effluent. Experimental conditions: DOC = 237mgCL-1; COD = 672 mg O2 L-1 ; Fe2+ = 105 mg L-1 ; and pH = 2.5-2.8.

1600 mg L-1 is not justifiable (Figure 1). The H2O2 concentration defined as the best in this study (1600 mg L-1), is very near to the stoichiometric ratio of H2O2 (1428 mg L- ), considering that 1 g COD = 0.03125 mol O2 = 0.0625 mol H2O2 = 2.125 gH2O2 [35].

Parallel to DOC, COD, and absorbance analysis, the concentrations of Fe2+, Fe3+ and the total dissolved iron (Fe2+ + Fe3+) were also evaluated for different concentrations of H2O2 (Figure 2). These are also important parameters to determine the efficiency of the photo-Fenton process in the degradation of the organic load, since in most cases part of the iron added tends to be complexed by degradation of byproducts [19]. In view of this, new additions of iron ions could be required to reach adequate degradation efficiency. In addition, it is important to know the changes in the concentration of Fe + and Fe +, since the amount ofhydroxyl radicals generated by reactions mediated by Fe2+ (5) is higher than that generated by Fe +, once the regeneration of ferrous ions from ferric ions ((6) and (7)) is the limiting step in the catalytic cycle of iron:

Fe + H2O2 Fe + OH- + •QH к = 63.0 M-1 s

Fe3+ + H2O2 — FeIII(HO2)2+ + H+ fc = 3.1 x 10-3 (6) FeIII(HO2)2+ Fe2+ + HO/ к = 2.7 x 10-3 s-1 (7)

As before mentioned, the presence of colored intermediates was observed for concentrations of H2O2 up to 2500mgL-1. This tends to affect the photochemical regeneration of ferrous ions since the absorption of photons by Fe3+ complexes is more difficult in strongly colored solutions, even under stirring (Figure 2) [36]. Considering this, we can consider that at the beginning of the experiments, the thermal Fenton process probably prevails over the photo-Fenton. Therefore, the regeneration of ferrous ions probably should occur, in this case, by the action of H2O2 ((6)-(7)).

As presented in Figure 2, between 75 and 90% of the initial concentration of Fe + was converted to Fe +, when the H2O2 added resulted in an initial concentration between 1000 and 1600mgL-1. As discussed before, the increase in the initial concentration of H2O2 from 1600 to 2500mgL-1 contributed only to a minimal improvement in COD and DOC removal. Besides the formation of carboxylic acids of low molecular weight, the low COD and DOC removal may also be associated with the low concentration of Fe + and high concentration of Fe3+ in the reaction medium after adding H2O2, giving an initial concentration between 1000 and 1600 mgL-1 (Figure 2), which helps to reduce the efficiency of generation ofhydroxyl radicals ((5)-(7)). In other words, once the regeneration of ferrous ions is very slow ((6)-(7)), the degradation of the organic load will depend on the rate of regeneration of Fe + from Fe +, mediated by H2O2 ((6)-(7)).

A probable consumption of H2O2 (Figure 1(a)) without apparent contribution in the removal of COD and DOC could have occurred due to the regeneration of Fe2+ ((6)-(7)) [31, 32] as well as self-decomposition reactions and scavenging ofhydroxyl radicals ((1)-(4)).

The role of H2O2 concentration in the toxicity during the photo-Fenton process was also evaluated, once the soluble fraction of the effluent presented 100% toxicity to A. salina (Figure 3). After the photo-Fenton process using H2O2 in the range of 100 up to 1600 mg L- , the toxicity was reduced to 0%. On the other hand, for an H2O2 concentration of 2500 mgL-1, the reduction of toxicity was from 100 to 23% (Figure 3). It is probable that this effect is related to the formation of carboxylic acids, that tend to be toxic to A. salina [33], as also reported in studies involving Daphnia magna in the degradation of sulfamethoxazole and amoxicillin [37,38].

As presented and discussed above, the results demonstrate the feasibility and potential of photo-Fenton process both in decontamination (Figure 1) and detoxification (Figure 3) of effluent from factories of acrylic paints for buildings. Considering using concentrations of H2O2 of 1600mgL-1, COD, DOC, and toxicity removal between 90 and 100% were obtained, an initial concentration of 1600 mgL-1 H2O2 was used for the kinetics experiments, evaluating the iron ions concentration.

3.2.2. Influence of the Fe2+ Concentration. The initial Fe2+ concentration is important in two aspects, one is related to the penetration of light through the solution, and the other is related to the efficiency of the photo-Fenton process in generating hydroxyl radicals since Fe2+ catalyzes the decomposition of H2O2, generating hydroxyl radicals (5). However,

Figure 3: Evaluation of the toxicity to A. salina during photo-Fenton treatment of the soluble fraction of the effluent, using different concentrations of H2O2. Experimental conditions: DOC = 237 mg C L-1; COD = 672 mg O2 L-1; Fe2+ = 105 mg L-1; and pH = 2.5-2.8.

it is known that an excess of Fe2+ can act as scavenger of hydroxyl radicals (8), compromising the efficiency of the process [31]:

Fe2+ + HO^ Fe3+ + HO- fc = 3.2 x 108 M-1 s-1 (8)

The effect of the iron concentration on Fenton and photo-Fenton processes was evaluated in previous studies. It was observed that the rate of degradation increases with a given concentration of iron ions, regarded as the concentration that results in the best experimental conditions, which, on the other hand, is dependent on the composition of the effluent and type of reactor [10,11,19, 27, 39, 40].

In this study, four sets of experiments using different iron concentrations (15, 45, 75, and 105 mgL- ) were done using an initial H2O2 concentration of 1600mgL-1. As the initial dose of H2O2 was rapidly consumed, new additions were done at each 78.3 kJ m-2 of accumulated dose of UVA radiation in the assays done with 45mgL-1 Fe2+ and at each 47.1 kJ m-2 of accumulated dose of UVA radiation in the assays done with 75 and 105 mg L-1 Fe2+. Using the lower iron concentration (15mgL-1), a low rate for DOC removal was verified when compared to the other iron concentrations (45, 75, and 105 mg L-1) (Figure 4(a)).

It can be observed in Figure 4(a), the occurrence of an induction period in the reactions is induced by the lowest iron concentration. For the largest concentrations of iron, induction periods were not observed, suggesting that the limiting step of the reaction for the lower iron concentrations must be the regeneration of Fe2+ [39, 40], once these experiments also showed an initial darkening of the effluent, in

general attributed to the formation of reaction intermediates [8,34,37]. However, after a period between 5 and 50 minutes, there was a complete removal of the dark color, which occurs faster (5-10 min) when the larger concentrations of Fe2+ were employed.

The curve of DOC removal can be divided into two parts (up to 78.3 kJm-2 and above 78.3 kJm-2), Figure 4(a), with exception of the experiment in the presence of 15 mg L-1 Fe2+. In the first part, the curve of DOC removal presents apparent pseudo first-order kinetics (fc = 0.014, 0.16, 0.18, and 0.20 kJ-1 m2, resp., for the initial dose of Fe2+ of 15,45,75, and 105 mg L-1). The second part of the curve is characterized by a slow DOC removal rate, due to formation of carboxylic acids of low molecular weight, refractory to oxidation, and because they are able to form complexes with dissolved iron ions [39], reducing the efficiency of the Fenton reactions.

An increase in the rate of DOC removal by a factor of 11 was achieved when the Fe2+ concentration increased from 15 to 45mgL-1, considering an accumulated dose of 78.3kJm-2 of UVA radiation (Figure 4(a)). On the other hand, in increasing the Fe + concentration from 45 to 75 and 105 mg L-1 no significant improvement was obtained in DOC removal (Figure 4(a)). These results suggest that an iron concentration of 45mgL-1 is enough to trigger the photocatalytic process induced by solar irradiation. So, using 45mgL-1 Fe2+, the photocatalytic regeneration of ferrous ions from ferric was fast enough (Figure 4(b)), ensuring the availability of ferrous ions to consume H2O2 and produce more hydroxyl radicals.

After an accumulated dose of 130kJm-2 of UVA (82 ± 17 min of solar irradiation, equivalent to an average intensity of UVA radiation of 34.1 ± 7.3 Wm- ), in the presence of 45mgL-1 of Fe2+, 80% of DOC removal was reached for a consumption of 1650mgL- H2O2 (Figure 4(a)). This result reinforces the results obtained in experiments using controlled dosing of H2O2, in which 90% of DOC removal was achieved using 1600 mg L-1 H2O2 (Figure 1(a)). In addition, an increase in the time of exposure to solar radiation did not result in significant improvement in DOC removal (Figure 4(a)), probably due to at least three factors: the formation of carboxylic acids of low molecular weight, recombination reactions ((2)-(4)), and scavenging of hydroxyl radicals by Fe2+ (8).

Control experiments using the soluble fraction of the effluent were also carried out under the following conditions: (a) absence of Fe2+ and H2O2 (direct photolysis at pH 2.5-2.8); (b) photolysis without adding Fe2+, in presence of 1600mgL-1 H2O2 at pH 2.5; (c) photolysis involving a hydrated complex of iron, using 45mgL-1 Fe2+ at pH 2.52.8, without H2O2; and (d) Fenton process in the dark using 105mgL-1 Fe2+ and 1600mgL-1 H2O2. These experiments were important to assure that the results found during the photocatalytic assays were consistent and not due to direct photolysis and/or thermal Fenton reactions (Fenton reactions in the dark). No degradation was observed in the conditions from (a) to (c), while 40% of DOC removal was reached in the thermal Fenton reaction in the presence of 105mgL-1

> T ttf

II <> /

0 600 1200 1800 2400 H2O2 (mg L-1)

—•— A. salina

250 "t.

•d 150 -

- 3000

50 100 150 200 Energy dose (kJ m-2)

■- 15 mg L-1 75

•- 45 105

Energy dose (kJ m-2)

-■- 15 mg L

75 105

Figure 4: Influence of Fe2+ concentration on (a) kinetics of DOC removal of the effluent (solid symbols) and consumption of H2O2 (open symbols); (b) dissolved iron species (solid symbols: Fe2+ concentration, open symbols: Fe3+ concentration) during the solar photo-Fenton treatment of the soluble fraction of the effluent under study. Experimental conditions: DOC = 247 mgC L-1; H2 O2 = 1600 mgL-1 replaced in 78.3 kJ m-2 to 45 mg L-1 Fe2+ and 47.1 kJ m-2 to 75 and 105 mg L-1 Fe2+; and pH = 2.5-2.8. Irradiation time: 128 ± 23 min (238 kJ m-2) and solar light average intensity: 39.6 ± 5.6 W m-2.

Fe2+, after 150 min of reaction (data not shown), equivalent to the period required to accumulate a dose ofUVA radiation of 238 kJ m-2 in the experiments under solar irradiation. The lower DOC removal obtained in the thermal Fenton reaction, (d), when compared to the photo-Fenton process induced by solar radiation (90% of DOC removal), suggests a synergetic effect caused by both Fenton processes.

For thermal Fenton reactions, the concentrations of Fe2+ and Fe3+ and total dissolved iron (Fe2+ + Fe3+) were also monitored. During the reaction interval (150 min), the concentration of Fe2+ decreased from 102 to 20 mg L-1 after a consumption of 1260mgL-1 H2O2. At the same time, no increase in the concentration of Fe2+ has been observed (data not shown). This agrees with the results obtained using controlled dosing of H2O2 (Figure 2).

4. Conclusions

Although, respectively, 62 and 75% of DOC and COD removal were reached using 800mgL-1 H2O2 and [Fe2+] = 105mgL-1, no reduction in the toxicity was observed. This suggests that the earliest intermediates of oxidized pretreated effluent obtained using a low dose of H2O2 (up to 800 mg L-1 ) still present acute toxicity to A. salina. A photo-Fenton process involving a H2O2 concentration over 1000 mg L- tends to produce oxidized intermediates with low toxicity (below 20%). Our best results were obtained using a concentration

of H2O2 of 1600 mgL-1 and [Fe2+]= 105 mgL-1. Under these conditions, a removal of 90% of DOC and COD and of 100% of toxicity was obtained. Only a slight improvement in DOC and COD removal could be observed when increasing the H2O2 concentration above 1600 up to 2500mgL-1 (decay from 26 to 19mgCL- and from 70 to 57mgO2 L- , resp.) probably due to the formation of carboxylic acids, refractory to oxidation.

The curve of DOC removal is consistent with apparent pseudo first-order kinetics (fc = 0.014, 0.16, 0.18, and 0.20 kJ-1 m2, resp., for the initial doses of iron of 15, 45, 75, and 105 mg L-1 Fe2+), and an improvement of 11 times on the DOC removal rate was reached when the iron concentration increased from 15 to 45 mg L-1, keeping almost constant from 45 up to 105 mg L-1. Under our best experimental conditions ([Fe2+] = 45mgL-1 and [H2O2] = 1600mgL-1), 80% of DOC removal was achieved after exposure to 130 kJm-2 (82 ± 17 min of solar irradiation and average UVA irradiance of 34.1 ± 7.3 Wm-2), while 40% of DOC removal was reached under only thermal Fenton reaction ([Fe2+ ] = 105 mg L-1 and [H2O2] = 1600 mg L-1), after 150 min, suggesting a synergetic effect for the combination among the reactions of Fenton and irradiation in the ultraviolet.

These results demonstrate the viability of application of Fenton reactions to the decontamination and detoxification of effluent from factories of paints for buildings, using solar radiation.


The authors thank CNPq (Project no. 2011-EXA022) for the scholarship to O. Gomes Jr. and FAPEMIG (CEX-APQ-00915-11, CEX-APQ-01798-11, CEX-APQ-02425-10, and CEX-APQ-01217-12), CAPES/PVNS, CNPq (304.576/2011-5) for the financial support of this work. The authors also thank Mr. Paulo Souza MUller Jr. for technical support. A. E. H. Machado is particularly indebted to CNPq and CAPES for his research grants. This work is a collaborative research project between members of the Rede Mineira de Química (rQ-MG), partially supported by FAPEMIG (Project no. REDE-113/10).


[1] M. E. DeLorenzo, G. I. Scott, and P. E. Ross, "Toxicity of pesticides to aquatic microorganisms: a review," Environmental Toxicology and Chemistry, vol. 20, no. 1, pp. 84-98, 2001.

[2] K. Kummerer, "Antibiotics in the aquatic environment: a review—part I," Chemosphere, vol. 75, no. 4, pp. 417-434, 2009.

[3] A. Goi, Y. Veressinina, and M. Trapido, "Fenton process for landfill leachate treatment: evaluation of biodegradability and toxicity," Journal of Environmental Engineering, vol. 136, no. 1, pp. 46-53, 2010.

[4] A. Zapata, T. Velegraki, J. A. Sánchez-Pérez, D. Mantzavinos, M. I. Maldonado, and S. Malato, "Solar photo-Fenton treatment of pesticides in water: effect of iron concentration on degradation and assessment of ecotoxicity and biodegradability," Applied Catalysis B, vol. 88, no. 3-4, pp. 448-454, 2009.

[5] A. Zapata, I. Oller, C. Sirtori et al., "Decontamination of industrial wastewater containing pesticides by combining large-scale homogeneous solar photocatalysis and biological treatment," Chemical Engineering Journal, vol. 160, no. 2, pp. 447-456,2010.

[6] C. Sirtori, A. Zapata, I. Oller, W. Gernjak, A. Agüera, and S. Malato, "Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment," Water Research, vol. 43, no. 3, pp. 661-668, 2009.

[7] L.-A. Lu, Y.-S. Ma, M. Kumar, and J.-G. Lin, "Photo-Fenton pretreatment of carbofuran—analyses via experimental design, detoxification and biodegradability enhancement," Separation and Purification Technology, vol. 81, no. 3, pp. 325-331, 2011.

[8] B. Lopez-Alvarez, R. A. Torres-Palma, F. Ferraro, and G. Penuela, "Solar photo-Fenton treatment of carbofuran: analysis of mineralization, toxicity, and organic by-products," Journal of Environmental Science and Health A, vol. 47, no. 13, pp. 21412150, 2012.

[9] A. Machulek Jr, F. H. Quina, F. Gozzi, V O. Silva, L. C. Friedrich, and J. E. F. Moraes, "Fundamental mechanistic studies of the photo-Fenton reaction for the degradation of organic pollutants," in Organic Pollutants Ten Years after the Stockholm Convention—Environmental and Analytical Update, pp. 271-292, InTech, Rijeka, Croatia, 2012.

[10] A. E. D. H. Machado, T. P. Xavier, D. R. De Souza et al., "Solar photo-fenton treatment of chip board production waste water," Solar Energy, vol. 77, no. 5, pp. 583-589, 2004.

[11] C. Sattler, L. de Oliveira, M. Tzschirner, and A. E. H. Machado, "Solar photocatalytic water detoxification of paper mill effluents," Energy, vol. 29, no. 5-6, pp. 835-843, 2004.

[12] E. S. Elmolla and M. Chaudhuri, "Comparison of different advanced oxidation processes for treatment of antibiotic aqueous solution," Desalination, vol. 256, no. 1-3, pp. 43-47, 2010.

[13] A. Durán, J. M. Monteagudo, and I. San Martin, "Photocatalytic treatment of an industrial effluent using artificial and solar UV radiation: an operational cost study on a pilot plant scale," Journal of Environmental Management, vol. 98, no. 1, pp. 1-4, 2012.

[14] M. Kositzi, A. Antoniadis, I. Poulios, I. Kiridis, and S. Malato, "Solar photocatalytic treatment of simulated dyestuff effluents," Solar Energy, vol. 77, no. 5, pp. 591-600, 2004.

[15] F. Ay, E. C. Catalkaya, and F. Kargi, "A statistical experiment design approach for advanced oxidation of Direct Red azo-dye by photo-Fenton treatment," Journal of Hazardous Materials, vol. 162, no. 1, pp. 230-236, 2009.

[16] M. Jonstrup, M. Punzi, and B. Mattiasson, "Comparison of anaerobic pre-treatment and aerobic post-treatment coupled to photo-Fenton oxidation for degradation of azo dyes," Journal of Photochemistry and Photobiology A, vol. 224, no. 1, pp. 55-61, 2011.

[17] M. Punzi, B. Mattiasson, and M. Jonstrup, "Treatment of synthetic textile wastewater by homogeneous and heterogeneous photo-Fenton oxidation," Journal of Photochemistry and Photobiology A, vol. 248, pp. 30-35, 2012.

[18] E. R. Bandala, M. A. Pelaez, A. J. Garcia-Lépez, M. D. J. Salgado, and G. Moeller, "Photocatalytic decolourisation of synthetic and real textile wastewater containing benzidine-based azo dyes," Chemical Engineering and Processing, vol. 47, no. 2, pp. 169-176, 2008.

[19] V. J. P. Vilar, L. X. Pinho, A. M. A. Pintor, and R. A. R. Boaventura, "Treatment of textile wastewaters by solar-driven advanced oxidation processes," Solar Energy, vol. 85, no. 9, pp. 1927-1934, 2011.

[20] E. GilPavas, I. Dobrosz-Gomez, and M. A. Gomez-Garcia, "Decolorization and mineralization of Diarylide Yellow 12 (PY12) by photo-Fenton process: the response surface methodology as the optimization tool," Water Science and Technology, vol. 65, no. 10, pp. 1795-1800, 2012.

[21] "CETESB—Companhia de Tecnologia de Saneamento Ambiental," 2013, Guia Tecnico Ambiental Tintas e Vernizes— Serio P+L., limpa/documentos/tintas.pdf.

[22] R. F. P. Nogueira, A. G. Trové, and W. C. Paterlini, "Evaluation of the combined solar TiO2/photo-Fenton process using multivariate analysis," Water Science and Technology, vol. 49, no. 4, pp. 195-200, 2004.

[23] R. F. Pupo Nogueira and J. R. Guimaraes, "Photodegradation of dichloroacetic acid and 2,4-dichlorophenol by ferrioxal-ate/H2O2 system," Water Research, vol. 34, no. 3, pp. 895-901, 2000.

[24] J. J. Pignatello, "Dark and photoassisted Fe3+-catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide," Environmental Science and Technology, vol. 26, no. 5, pp. 944951, 1992.

[25] APHA/AWWA/WEF, Standard Methods for the Examination of Water and wasteWater, American Public Health Association, New York, NY, USA, 12th edition, 1998.

[26] R. F. P. Nogueira, M. C. Oliveira, and W. C. Paterlini, "Simple and fast spectrophotometric determination of H2O2 in photo-Fenton reactions using metavanadate," Talanta, vol. 66, no. 1, pp. 86-91, 2005.

[27] A. G. Trovó, T. F. S. Silva, O. Gomes Jr. et al., "Degradation of caffeine by photo-Fenton process: optimization of treatment conditions using experimental design," Chemosphere, vol. 90, no. 2, pp. 170-175, 2013.

[28] A. G. Trovó and R. F. P. Nogueira, "Diclofenac abatement using modified solar photo-Fenton process with ammonium iron(III) citrate," Journal ofthe Brazilian Chemical Society, vol. 22, no. 6, pp. 1033-1039, 2011.

[29] S. A. S. Melo, A. G. Trovó, I. R. Bautitz, and R. F. P. Nogueira, "Degradation of residual pharmaceuticals by advanced oxidation processes," Quimica Nova, vol. 32, no. 1, pp. 188-197, 2009.

[30] C. Jiang, S. Pang, F. Ouyang, J. Ma, and J. Jiang, "A new insight into Fenton and Fenton-like processes for water treatment," Journal of Hazardous Materials, vol. 174, no. 1-3, pp. 813-817, 2010.

[31] J. De Laat and H. Gallard, "Catalytic decomposition of hydrogen peroxide by Fe(III) in homogeneous aqueous solution: mechanism and kinetic modeling," Environmental Science and Technology, vol. 33, no. 16, pp. 2726-2732,1999.

[32] R. F. Pupo Nogueira, A. G. Trovó, M. R. A. Da Silva, R. D. Villa, and M. C. De Oliveira, "Fundaments and environmental applications of Fenton and photo-Fenton processes," Quimica Nova, vol. 30, no. 2, pp. 400-408, 2007.

[33] A. G. Trovó, O. Gomes Jr., A. E. H. Machado, W. Borges Neto, and J. O. Silva, "Degradation of the herbicide paraquat by photo-Fenton process: optimization by experimental design and toxicity assessment," Journal of the Brazilian Chemical Society, vol. 24, no. 1, pp. 76-84, 2013.

[34] A. G. Trovó, R. F. P. Nogueira, A. Aguera, A. R. Fernandez-Alba, and S. Malato, "Paracetamol degradation intermediates and toxicity during photo-Fenton treatment using different iron species," Water Research, vol. 46, no. 16, pp. 5374-5380, 2012.

[35] W. Gernjak, T. Krutzler, A. Glaser et al., "Photo-fenton treatment of water containing natural phenolic pollutants," Chemosphere, vol. 50, no. 1, pp. 71-78, 2003.

[36] S. Malato, P. Fernández-Ibánez, M. I. Maldonado, J. Blanco, and W. Gernjak, "Decontamination and disinfection of water by solar photocatalysis: recent overview and trends," Catalysis Today, vol. 147, no. 1, pp. 1-59, 2009.

[37] A. G. Trovó, R. F. P. Nogueira, A. Aguera, A. R. Fernandez-Alba, C. Sirtori, and S. Malato, "Degradation of sulfamethoxazole in water by solar photo-Fenton. Chemical and toxicological evaluation," Water Research, vol. 43, no. 16, pp. 3922-3931,2009.

[38] A. G. Trovó, R. F. Pupo Nogueira, A. Agüera, A. R. Fernandez-Alba, and S. Malato, "Degradation of the antibiotic amoxicillin by photo-Fenton process—chemical and toxicological assessment," Water Research, vol. 45, no. 3, pp. 1394-1402, 2011.

[39] E. M. R. Rocha, V. J. P. Vilar, A. Fonseca, I. Saraiva, and R. A. R. Boaventura, "Landfill leachate treatment by solar-driven AOPs," Solar Energy, vol. 85, no. 1, pp. 46-56, 2011.

[40] S. M. Rodríguez, J. B. Galvez, M. I. M. Rubio et al., "Engineering of solar photocatalytic collectors," Solar Energy, vol. 77, no. 5, pp. 513-524, 2004.

Copyright of International Journal of Photoenergy is the property of Hindawi Publishing Corporation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.