Indanthrene Blue Dye Degradation by UV/H 2 O 2 Process: H 2 O 2 as a Single or Fractioned Aliquot?

Abstract

Organic dyes are relatively resistant to conventional treatment methods and some of them produce carcinogenic by-products, making necessary the development of technologies for the removal of dyes and their breakdown products in wastewater. In this study, the influence of the addition of single or fractionated aliquots of H₂O₂ on the removal of indanthrene blue dye contained in aqueous solutions through the UV/H₂O₂ system was studied. Experimental parameters studied were temperature, pH, and H₂O₂ concentration, using single and fractional H₂O₂ additions. Maximum efficiency was observed at the highest H₂O₂ concentration in acid media. Fractional addition of H₂O₂ has a positive influence on the overall efficiency of the oxidative processes. Treatment carried out at 40°C, pH 5, and 1,500 mg/L of H₂O₂ (fractional addition) resulted in a drastic enhancement of the dye degradation/mineralization rate, reducing 98.6% chemical oxygen demand, 100% color, 92% total organic carbon, and 99% H₂O₂, demonstrating that this system was effective in the treatment of effluent containing indanthrene blue dye.

Introduction

The textile industry produces large quantities of colored wastewater that contain high levels of organic matter (Nidheesh et al., 2013). These effluents have extremely heterogeneous compositions with a large amount of toxic and recalcitrant compounds, which make their treatment very difficult. These wastewaters are characterized by strong coloration, high loads of suspended solids, highly fluctuating pH values, high values of chemical oxygen demand (COD), and substantial concentrations of metal ions, chlorinated organic compounds, and surfactants (Nagel-Hassemer et al., 2012).

Dyes contribute significantly to environmental pollution, especially in water resources, hindering the penetration of sunlight and damaging the photosynthetic metabolism of some species such as marine microalgae (cyanobacteria and chlorophyte). Moreover, they are potentially carcinogenic (Salgado, 2009).

More than 10,000 different types of dyes and pigments are used worldwide in the textile industry. Approximately 20% of these dyes are unfixed in the dyeing stages and are lost in the textile wastewater, thus generating an environmental problem when discarded inappropriately (Guarantini and Zanoni, 2000; Park et al., 2007; Parshetti et al., 2010). In addition, these dyes are relatively resistant to conventional treatment methods and some of them produce carcinogenic by-products. Therefore, it is necessary to develop technology systems for the removal of dyes and their breakdown products in wastewater.

Dye is composed of a chromophore group and a group responsible for fixing the dye to a fiber structure. Between the groups of dyes, determined based on the chromophore groups, the Society of Dyers and Colourists (1976) classifies the dyes and pigments in 26 types such as azina, azo, anthraquinone, nitro, thiazine, and others. About 20–30% can be identified, of which azo (70%) and anthraquinone (15%) dyes are most commonly used (Moussavi and Mahnoudi, 2009).

Anthraquinone dyes are mainly used in the coloration of cotton and cellulose fibers (Novotny et al., 2006) and are applied as primary and secondary dyes in trichromatic compositions (Epolito et al., 2005). They pose serious health risks not only from their presence in the environment but also because of their secondary products, such as potentially carcinogenic aromatic amines (Novotny et al., 2006). The indanthrene dyes fall into this classification, and there are a few studies addressing the removal of this type of dye and its degradation reaction intermediaries (Hihara et al., 2002; Roessler and Crettenand, 2004; Pupo et al., 2013). Therefore, the importance of the investigations studying routes of treating wastewater containing anthraquinone-based dyes is evident, according to the environmental and health risks that they present (Fanchiang and Tseng, 2009).

Biological treatments, the most widely utilized, do not present a complete solution to the problem, owing to the low biodegradability of many dyes (Galindo et al., 2001). Techniques such as adsorption on wheat bran (Çiçek et al., 2007), adsorption on activated carbon (Órfão et al., 2006), coagulation/flocculation (Lee et al., 2006), ultrafiltration (Zaghbani et al., 2007), and reverse osmosis (Sostar-Turk et al., 2005) have been reported for the removal of textile dyes. However, they are more expensive than biological processes and only realize the phase transfer of the pollutant requiring postprocessing of solid wastes generated or the regeneration of the adsorbent material.

Owing to the deficiencies presented by conventional treatment systems, new treatment alternatives have been proposed. Very promising alternatives are the advanced oxidation processes (AOPs), which are characterized by generating highly reactive oxygen radicals in aqueous solution, particularly the hydroxyl radical (•OH) from the combination of different chemical oxidants, with or without a radiation source. Hydroxyl radicals are not selective and attack all organic molecules. The great advantage of these processes is their destructive character, that is, the contaminant is not simply transferred from the phase, but rather it is degraded through a series of chemical reactions (Benitez et al., 2002; Al-Qodah et al., 2007).

Hydrogen peroxide (H₂O₂) is one of the most common sources of •OH radicals, either by its catalytic decomposition in the presence of metal ions or semiconductor oxides, or by irradiation with ultraviolet light (UV). •OH radicals are extremely reactive and are strong oxidants (E = 2.8 V), which are able to mineralize organic contaminants by successive oxidation reactions (Gogate and Pandit, 2004; Raj and Quen, 2005; Salgado, 2009).

Compared to other AOPs such as Fenton, ozone, UV/O₃, UV/TiO₂, and so forth, the photolysis of H₂O₂ has some advantages such as complete water miscibility, stability, and commercial availability. Moreover, H₂O₂ presents no problems for phase transfer, and the investment costs are relatively low compared to other processes (Raj and Quen, 2005).

Thus, in this article, we study the influence of the addition of single and fractionated aliquots of H₂O₂ on the removal of indanthrene blue dye contained in aqueous solutions through the UV/H₂O₂ AOP. The variables studied for the synthetic wastewater treatment were as follows: temperature, pH value, and H₂O₂ concentration.

Materials and Methods

For this article, we used the dye, indanthrene blue (CAS Number: 81-77-6), which has a melting point of 470–500°C, a pH value of 8, maximum absorbance at 290–300 nm, solubility of 0.1 g/100 mL in water at room temperature, and is soluble in sulfuric acid as well as in alkaline solutions. Figure 1 shows the chemical structure of indanthrene blue. The complex aromatic molecular structure of indanthrene blue makes it very stable and difficult to degrade.

FIG. 1.

Chemical structure of indanthrene blue dye.

All experiments were carried out in a thermostatic photochemical reactor with a capacity of 0.5 L, coupled to an ultrathermostatic bath (Nova Ética, Brazil), and operated in batch mode. A mercury vapor lamp (125 W without the protective bulb) was used as the radiation source, which was placed into a quartz bulb and immersed into the solution (Fig. 2).

FIG. 2.

Schematic representation of photochemical reactor used for UV/H₂O₂ treatment of indanthrene blue dye solutions (60 mg/L). UV, ultraviolet light.

All treatments were held under agitation at 500 rpm, provided by a magnetic stirrer, with oxygenation of 10 L/min by an air compressor. The variants of the treatment were temperature (20°C, 30°C, and 40°C), which was maintained by a cooling jacket, pH value (5, 7, and 9), adjusted by HCl or NaOH solutions (0.5 M), the concentration of H₂O₂ (500, 1,000, and 1,500 mg/L) (Cisneros et al., 2002; Martins et al., 2011), and dye concentration (60 mg/L). The treatment time was set at 60 min. The determination of color, total organic carbon (TOC), chemical oxygen demand (COD), pH value, and residual peroxide was performed after each treatment of the samples.

The determination of COD was performed according to the standard American Public Health Association (APHA) method (Alpha, 2005). The ampoules were placed into a digester (HACH DRB 200), with further reading of the absorptivity at a wavelength of 600 nm in a HACH DRB 5000 spectrophotometer. The values of TOC were determined using the test tube HACH method No. 10128.

The pH value of the obtained effluent sample was determined by a pH meter (PM608; Analion). The determination of color was carried out according to standard methodology, CPPA (1975) modified (CPPA, 1975; Queissada, 2009), using a spectrophotometer (HACH DRB 5000).

H₂O₂ concentration was determined according to the procedure adapted from Queissada (2009), using a HACH DRB 5000 spectrophotometer. The H₂O₂ concentration in the sample was obtained by interpolation of absorbance, which was measured in the sample from the calibration curve that was previously constructed.

After determination of the best conditions of variables treatment, a more detailed study was performed in terms of H₂O₂ use. Therefore, the addition of the H₂O₂ was performed at a single rate (at the start of treatment) or with fractional rates (three fractions, every 20 min and six fractions, every 10 min).

Results and Discussion

Treatment using single addition of H₂O₂

All experiments were performed in triplicate for increased reliability of the results. Treatments were performed at pH 5, 7, and 9, with H₂O₂ concentrations of 500, 1,000, and 1,500 mg/L, and temperature variation of 20°C, 30°C, and 40°C.

The effect of UV radiation on the degradation of the dye, without adding hydrogen peroxide, was initially evaluated before starting the study of other variables. The effect of photolysis of indanthrene blue dye in the absence of H₂O₂ is presented in Figure 3. Removals of 0.8% and 0.6% for color and COD were observed, respectively. Thus, the UV radiation alone is not capable of degrading the dye in a considerable rate and the addition of H₂O₂ is needed to enhance the process.

FIG. 3.

Decrease of color and chemical oxygen demand (COD) of indanthrene blue dye solution (60 mg/L) as a function of treatment time without the addition of hydrogen peroxide.

Effect of H₂O₂ concentration

Discoloration and degradation of indanthrene blue dye increased with increasing concentration of H₂O₂ (Table 1). The use of higher concentrations of H₂O₂ in conjunction with UV light increases degradation and discoloration of the colorant, owing to higher amounts of •OH radicals generated by the photolysis of H₂O₂ (Salgado, 2009).

Table 1.

Physical and Chemical Characterization of Effluent After UV/H₂O₂ Treatment

Dye concentration (mg/L)	H₂O₂ concentration mg/L	Initial pH	Final pH	Temperature (°C)	COD reduction (%)	Color reduction (%)	H₂O₂ reduction (%)
60	500	5 ± 0.1	4.2 ± 0.1	20 ± 0.1	62.4 ± 1.5	90 ± 2.4	97 ± 1.5
60	1,000	5 ± 0.1	4.1 ± 0.1	20 ± 0.1	83.8 ± 2.3	92 ± 3.8	98 ± 2
60	1,500	5 ± 0.1	4.1 ± 0.1	20 ± 0.1	90.5 ± 2.6	95 ± 2.2	96 ± 0.5
60	500	7 ± 0.1	6.8 ± 0.1	20 ± 0.1	57.0 ± 4.2	82 ± 1.4	97 ± 1.4
60	1,000	7 ± 0.1	6.7 ± 0.1	20 ± 0.1	77.2 ± 1.8	89 ± 0.8	97 ± 0.6
60	1,500	7 ± 0.1	6.8 ± 0.1	20 ± 0.1	88.6 ± 2.6	92 ± 1.4	96 ± 2.4
60	500	9 ± 0.1	8.2 ± 0.1	20 ± 0.1	52.9 ± 2.8	72 ± 2.6	96 ± 2.1
60	1,000	9 ± 0.1	8.0 ± 0.1	20 ± 0.1	70.0 ± 1.4	84 ± 2.5	96 ± 0.5
60	1,500	9 ± 0.1	7.9 ± 0.1	20 ± 0.1	85.6 ± 1	90 ± 4.7	95 ± 1.7

COD, chemical oxygen demand; UV, ultraviolet light.

The discoloration of the dye solution occurs due to the reaction between the dye molecule and the hydroxyl radicals, which are simultaneously generated in a solution from hydrogen peroxide, UV irradiated [Eq. (1)]. \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}H_2 O_2 + hv \rightarrow 2 \ {\bullet} \ OH \tag{1}\end{align*} \end{document}

The hydroxyl radicals are very strong oxidizing agents, they can react with the dye molecules producing intermediates, which can cause discoloration of the initial solution. At higher hydrogen peroxide concentrations, the solution consumes •OH radicals to produce peroxyl radicals— \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$HO_2^{\bullet}$$ \end{document} [Eq. (2)] (Chang et al., 2010; Ghodbane and Hamdaoui, 2010). \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}H_2 O_2 + {\bullet} \ OH \rightarrow H_2 O + HO^{\bullet}_2 \tag{2}\end{align*} \end{document}

Effect of pH

Some reports have already shown that aqueous solutions containing dyes can be discolored more efficiently by the H₂O₂/UV process in acid media (Hihara et al., 2002; Rathi et al., 2003; Aleboyeh et al., 2005; Rodriguez et al., 2007). The results are listed in Table 1 and show that the lower the pH value, the higher the reduction of both color and COD, also highlighting the faster consumption of H₂O₂ in acidic conditions. This behavior is rationalized by considering that the reduction potential of the hydroxyl radical decreases with increasing pH, and in acid pH values (i.e., pH 3), its reduction potential is 2.80 V, whereas at pH 7.0, it drops to 1.80 V (Aleboyeh et al., 2005). This explains why the best results in Table 1 were obtained under acidic conditions.

Furthermore, according to Rathi et al. (2003), the degradation rates of organic compounds become faster at acidic pH compared to neutral or alkaline pH systems. At acidic pH values, the •OH radical is the predominant reactive oxidant, but at alkaline pH values, weaker hydroperoxyl radicals [Eq. (2)] are formed through the reaction of hydroxyl radicals with H₂O₂, which decreases the efficiency of the oxidation process, and the dissociated hydroperoxy anion [Eq. (3)] will consume the hydroxyl radicals, as shown by reactions in Equations (4) and (5): \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}H_2 O_2 \leftrightarrow H^{ +} + HO^{ -}_2 \tag{3}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{\bullet} \ OH + HO^{ -}_2 \rightarrow OH^{ -} + HO_2 \ {\bullet} \tag{4}\end{align*} \end{document} \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}{\bullet} \ OH + HO^{ -}_2 \rightarrow H_2 O + O_2 \ {\bullet} \tag{5}\end{align*} \end{document}

The pH of the solutions decreases after the treatments, indicating the formation of carboxylic acids through the oxidation of the organic compounds present in the solutions (Mattos et al., 2003).

Effect of temperature

Rodriguez et al. (2007) studied the effect of temperature on the discoloration of aqueous solutions containing indigo carmine dye in an acidic medium and realized that this variable does not cause a significant effect on the discoloration or degradation of the dye. This indicates that the activation of the UV/H₂O₂ process occurs by means of a photochemical pathway and not through a thermal process.

Table 2 shows the reduction in COD, color, and H₂O₂ upon varying the temperature of the treatment in an alkaline medium (pH 9). From Table 2, it is possible to observe a slight increase in the reduction of COD and color with increasing temperature. A similar behavior was noted at pH values of 5 and 7. This occurs because increasing the temperature decreases the energy needed to reach the activation energy of the reaction, resulting in an increase in the rate of the oxidation reaction.

Table 2.

Reduction of COD, Color, and H₂O₂ Upon Varying Both Temperature and H₂O₂ Concentration During H₂O₂/UV Treatment AT pH 5, 7, and 9

Dye concentration (mg/L)	Initial pH	Final pH	Temperature (°C)	H₂O₂ concentration (mg/L)	COD reduction (%)	Color reduction (%)	H₂O₂ reduction (%)
60	5.0 ± 0.1	4.2 ± 0.1	20 ± 0.1	500	62.9 ± 2.7	90.0 ± 3.8	97.0 ± 2.8
60	5.0 ± 0.1	4.1 ± 0.1	30 ± 0.1	500	63.0 ± 3.1	90.0 ± 2.2	99.0 ± 1.4
60	5.0 ± 0.1	4.0 ± 0.1	40 ± 0.1	500	63.1 ± 1.8	90.0 ± 1.4	99.0 ± 0.8
60	5.0 ± 0.1	4.1 ± 0.1	20 ± 0.1	1,000	83.8 ± 1.1	92.0 ± 2.4	98.0 ± 1.8
60	5.0 ± 0.1	4.2 ± 0.1	30 ± 0.1	1,000	80.0 ± 0.9	98.0 ± 3.2	98.0 ± 1.2
60	5.0 ± 0.1	4.2 ± 0.1	40 ± 0.1	1,000	86.5 ± 1.5	99.0 ± 1.9	99.0 ± 1.8
60	5.0 ± 0.1	4.1 ± 0.1	20 ± 0.1	1,500	90.5 ± 1.1	95.0 ± 0.8	96.0 ± 2.7
60	5.0 ± 0.1	4.2 ± 0.1	30 ± 0.1	1,500	94.7 ± 1.8	100.0 ± 0.4	99.0 ± 0.7
60	5.0 ± 0.1	4.2 ± 0.1	40 ± 0.1	1,500	96.3 ± 2.4	100 ± 1.2	99.0 ± 1.1
60	7.0 ± 0.1	6.8 ± 0.1	20 ± 0.1	500	57.0 ± 2.2	82.0 ± 2.1	97.0 ± 2.5
60	7.0 ± 0.1	7.0 ± 0.1	30 ± 0.1	500	57.0 ± 3.1	90.0 ± 1.4	99.0 ± 2.1
60	7.0 ± 0.1	7.0 ± 0.1	40 ± 0.1	500	58.1 ± 1.2	95.0 ± 2.1	98.0 ± 0.2
60	7.0 ± 0.1	6.7 ± 0.1	20 ± 0.1	1,000	77.2 ± 2.4	89.0 ± 5	97.0 ± 0.7
60	7.0 ± 0.1	7.0 ± 0.1	30 ± 0.1	1,000	78.0 ± 1.7	97.0 ± 1.4	98.0 ± 0.9
60	7.0 ± 0.1	7.0 ± 0.1	40 ± 0.1	1,000	84.2 ± 2.4	99.0 ± 1.6	98.0 ± 1.6
60	7.0 ± 0.1	6.8 ± 0.1	20 ± 0.1	1,500	88.6 ± 1.8	92.0 ± 2.6	96.0 ± 1.7
60	7.0 ± 0.1	6.8 ± 0.1	30 ± 0.1	1,500	89.0 ± 1.5	100.0 ± 0.4	97.0 ± 2.9
60	7.0 ± 0.1	6.8 ± 0.1	40 ± 0.1	1,500	93.4 ± 3.4	100.0 ± 1.1	96.0 ± 4.4
60	9.0 ± 0.1	8.2 ± 0.1	20 ± 0.1	500	52.9 ± 2.9	73.0 ± 1.6	96.0 ± 0.7
60	9.0 ± 0.1	7.7 ± 0.1	30 ± 0.1	500	53.8 ± 2.6	81.0 ± 0.7	98.0 ± 1.5
60	9.0 ± 0.1	7.8 ± 0.1	40 ± 0.1	500	56.4 ± 1.5	85.0 ± 2.2	97.0 ± 2.8
60	9.0 ± 0.1	8.0 ± 0.1	20 ± 0.1	1,000	70.1 ± 3.7	81.0 ± 2.9	96.0 ± 3.8
60	9.0 ± 0.1	8.1 ± 0.1	30 ± 0.1	1,000	70.5 ± 2.3	86.0 ± 1.7	97.0 ± 0.8
60	9.0 ± 0.1	8.2 ± 0.1	40 ± 0.1	1,000	74.5 ± 1.6	95.0 ± 3.7	97.0 ± 1.4
60	9.0 ± 0.1	7.9 ± 0.1	20 ± 0.1	1,500	85.6 ± 1.8	89.0 ± 0.6	95.0 ± 3.5
60	9.0 ± 0.1	8.0 ± 0.1	30 ± 0.1	1,500	87.0 ± 1.6	90.0 ± 1.8	96.0 ± 1.4
60	9.0 ± 0.1	8.1 ± 0.1	40 ± 0.1	1,500	90.3 ± 2.8	100.0 ± 0.4	95.0 ± 0.8

Pearson correlation

The Pearson linear correlation between COD × temperature, color × temperature (relative to pH shift), COD × pH, and color × pH (relative to the temperature change) was used to observe a possible relationship between these parameters. The results of these studies are listed in Table 3.

Table 3.

Linear Pearson Correlation Between the Parameters: Color Reduction × Concentration, COD Reduction × Temperature (Relative to the Change in pH), Color Reduction × pH and COD Reduction × pH (Relative to the Change in Temperature)

Dye concentration (mg/L)	pH	Correlation (r) COD × temperature	Correlation (r) color × concentration	Temperature (°C)	Correlation (r) COD × pH	Correlation (r) color × pH
60	5	0.987	0.817	20	−0.857	0.364
60	7	0.614	0.953	30	−0.439	−0.632
60	9	0.736	0.697	40	−0.795	0.268

Pearson linear correlation showed a significant positive correlation between the reduction of COD and temperature, that is, when the correlation coefficient (r) is close to 1, it indicates the existence of a direct correlation between the variables. Thus, the higher the temperature increases, the greater the COD reduction. Similar behavior was obtained between the concentration of H₂O₂ and the color reduction.

In the correlation between pH and reduction of COD, a significant negative correlation was observed, indicating an inverse correlation, namely, the increase in pH causes a decrease in the COD reduction.

Treatment with fractionated aliquot of H₂O₂

From the data in Table 2, the highest rates of reduction of COD, color, and H₂O₂ occurred at 40°C using 1,500 mg/L of H₂O₂ at pH values of 5, 7, and 9. Thus, the effect of the use of fractional aliquots of H₂O₂ was studied using these optimized conditions. The aliquot of H₂O₂ was fractionated into three parts (3 × 375 mg/L), which were injected every 20 min throughout the treatment. This procedure was performed to optimize the treatment of the H₂O₂/UV system for the possible degradation of compounds that were not degraded during the treatment with a single aliquot of H₂O₂ and to avoid the formation of hydroperoxyl radicals, with a consequent decrease in the •OH concentration.

Results of the reduction processes for COD and color, after UV/H₂O₂ treatment using a fractional aliquot of H₂O₂ (Table 2), showed that the H₂O₂ was almost completely consumed (99%) in all treatments, independent of the pH value that was used. This is extremely important, as residues of H₂O₂ can be toxic when this effluent is discarded into aquatic environments (Mattos et al., 2003).

The greatest COD (98.6%) and color (100%) reductions occurred with treatment parameters using pH 5 and aliquots of 375 mg/L H₂O₂. Nevertheless, the process for the same conditions, but using a single aliquot, was to some extent less effective (96.3% COD reduction). This may be attributed to the fact that the initial concentration of H₂O₂ (1,500 mg/L) at the beginning of the treatment becomes somewhat excessive, decreasing the efficiency of the process (Fig. 4). Fernandez et al. (1999) evaluated the addition of H₂O₂ concerning the rate of mineralization of the Orange II dye. An increase in the rate of mineralization with the gradual addition of peroxide during elapsing of reaction was observed. Rate of H₂O₂ addition can influence the mineralization of the target compound. These authors verified an increase in the rate of mineralization with the progressive addition of peroxide in the reaction, rather than adding it at the beginning of the reaction. Such behavior may have been raised by the fact that H₂O₂, even in optimum conditions of operation, can act as a •OH radical-capturing source [Eq. (2)], and the intermediaries generated can compete with the dye for the •OH radical.

FIG. 4.

Decrease of COD using a single aliquot and fractional aliquot of H₂O₂ (1,500 mg/L) in UV/H₂O₂ treatment of indanthrene blue dye solutions (60 mg/L) at 40°C. (A) pH 5, (B) pH 7, and (C) pH 9.

Results are shown in Figure 5. Through the graphs, it can be observed that COD reduction occurs rapidly during the first 20 min of the treatment, with a lower reduction rate in the subsequent minutes of treatment. It is believed that the photolysis of H₂O₂ molecules in •OH radicals [Eq. (1)] performed the degradation of much of the dye in the first 20 min, producing intermediaries. The intermediaries generated can present a more complex chemical structure, which hampers their degradation, and compete with the dye molecules for the •OH radicals. This would explain why in the final 40 min of the treatment, the COD decrease occurred slowly, even with the additions of H₂O₂.

FIG. 5.

Reduction kinetics of COD and H₂O₂ during treatment of indanthrene blue dye solutions (60 mg/L) with UV/H₂O₂ (fractional rate) [1,500 mg/L] at 40°C. (A) pH 5, (B) pH 7, and (C) pH 9.

In contrast, the TOC is a direct measurement of the amount of carbonaceous organic matter in an effluent sample. In this study, we selected the treatments that showed the highest reduction of COD, color reduction, and reduction of H₂O₂ (i.e., pH 5, 7, and 9, using a fractioned aliquot of 1,500 mg/L H₂O₂ at 40°C).

Results in Table 4 indicate a larger TOC reduction in acidic pH (pH 5) than in neutral or alkaline pH. TOC reductions of 92.0%, 72.6%, and 61.3% were obtained using the pH values of 5, 7, and 9, respectively. The reduction values of TOC are similar to the results obtained for the reductions of COD and color, confirming that there was more degradation of the dye in this pH value (pH 5) and that the UV/H₂O₂ oxidative process was effective in the degradation of organic matter.

Table 4.

Reduction of TOC Using Different PH Adjustments and [1,500 mg/L] of UV/H₂O₂ (Fractionated Aliquot) AT 40°C

Initial pH	Final pH	TOC reduction (%)
5 ± 0.1	4.2 ± 0.1	92.0 ± 1.2
7 ± 0.1	6.8 ± 0.1	72.6 ± 1.6
9 ± 0.1	8.1 ± 0.1	61.3 ± 2.1

TOC, total organic carbon.

Best conditions of the UV/H₂O₂ treatment

To perform the optimized process, we chose the treatment that used 1,500 mg/L H₂O₂/UV, pH 5, and a temperature of 40°C, because these conditions showed the best results in the reduction of COD (98.6%), color reduction (100%), reduction of TOC (92.0%), and reduction of H₂O₂ (99%).

To perform a more detailed study of the treatment, samples were taken every 10 min (6 × 250 mg/L). It can be seen from Figure 6 that a COD reduction of over 67% was achieved in the first 10 min of treatment. According to the results, it was possible to degrade more than 85% of the COD in the first 20 min of treatment, about 11% more when using aliquots of 375 mg/L of H₂O₂, also increasing to ∼91% in the middle of the treatment. In the period from 30 to 50 min, the rate of degradation decreased until it was almost constant in the 50–60-min range.

FIG. 6.

Reduction kinetics of COD and H₂O₂ during treatment of indanthrene blue dye solutions (60 mg/L) with UV/H₂O₂ (fractional rate) [1,500 mg/L] at 40°C and pH 5. Samples withdrawn and H₂O₂ injected every 10 min of treatment.

Conclusions

The H₂O₂/UV advanced oxidation process was effective in the degradation/mineralization of the indanthrene blue dye. The process removed 100% color, 98.6% COD, 92.0% TOC, and 99% H₂O₂ at pH 5 using 1,500 mg/L H₂O₂ (fractional aliquot) at 40°C. High efficiencies were also obtained by using a single aliquot of H₂O₂ under the same treatment conditions.

By optimizing the process, a rapid reduction in COD and H₂O₂ consumption was realized. After treatment for 30 min, using 1,500 mg/L H₂O₂, pH 5, and a temperature of 40°C, it was possible to reduce both the COD of the effluent by more than 91% and H₂O₂ by 99%.

Of the studied parameters, it was noticed that the concentration of H₂O₂ and the pH of the samples showed the greatest influence on the treatment efficacy. Although temperature showed little influence on the process, increased temperature was shown to contribute to the removal of both COD and color. The use of fractionated aliquots of H₂O₂ resulted in higher degradation efficiencies, demonstrating that the use of a single aliquot at the beginning of the treatment decreases the efficiency of the process, probably by the formation of hydroperoxyl radicals with a consequent decrease in •OH concentration.

Footnotes

Acknowledgments

The authors thank the National Council of Technological and Scientific Development-CNPq (grants 303630/2012-4 and 310282/2013-6), FAPITEC, and CAPES from Brazil for the scholarships and the financial support provided for this work.

Author Disclosure Statement

No competing financial interests exist.

References

Aleboyeh

, Moussa

, and Aleboyeh

(2005). The effect of operational parameters on UV/H₂O₂ decolourisation of Acid Blue 74. Dyes Pigments., 66, 129.

Alpha-standard methods for examination of water and wastewater. (2005). American Public Health Association, 21st ed. Washington DC: American Water Works Association.

Al-Qodah

, Lafi

W.K.

, Al-Anber

, Al-Shannag

, and Harahsheh

(2007). Adsorption of methylene blue by acid and heat treated diatomaceous silica. Desalination., 217, 212.

Benitez

F.J.

, Acero

J.L.

, and Real

F.J.

(2002). Degradation of carbofuran by using ozone, UV radiation and advanced oxidation processes. J. Hazard. Mater., 89, 51.

Chang

, Chung

, Chern

, and Chen

(2010). Dye decomposition kinetics by UV/H₂O₂: Initial rate analysis by effective kinetic modelling methodology. Chem. Eng. Sci., 65, 135.

Çiçek

, Özer

, and Özer

(2007). Low cost removal of reactive dyes using wheat bran. J. Hazard. Mater., 146, 408.

Cisneros

R.L.

, Espinoza

A.G.

, and Litter

M.I.

(2002). Photodegradation of an azo dye of textile industry. Chemosphere., 48, 393.

CPPA–Canadian pulp and paper association. (1975). Technical Section Standart Test Methods, H5P. Montreal: Pulp and Paper Technical Association of Canada.

Epolito

W.J.

, Lee

Y.H.

, Bottomley

L.A.

, and Pavlostathis

S.G.

(2005). Characterization of the textile anthraquinone dye reactive blue 4. Dyes Pigments., 67, 35.

10.

Fanchiang

, and Tseng

(2009). Degradation of anthraquinone dye C.I. Reactive blue 19 in aqueous solution by ozonation. Chemosphere., 77, 214.

11.

Fernandez

, Bandara

, Lopez

, Buffat

PH.

, and Kiwi

(1999). Photo-assisted Fenton degradation of non-biodegradable azo-dye (Orange II) in Fe-free solutions mediated by cation transfer membranes. Langmuir., 15, 185.

12.

Galindo

, Jacques

, and Kalt

(2001). Photochemical and photocatalytic degradation of an indigolid dye: A case study of acid blue 74 (AB74). J. Photoch. Photobio. A., 141, 47.

13.

Ghodbane

, and Hamdaoui

(2010). Decolorization of antraquinonic dye, C.I. Acid blue 25, in aqueous solution by direct UV irradiation, UV/H₂O₂ and UV/Fe(II) processes. Chem. Eng. J., 160, 226.

14.

Gogate

, and Pandit

(2004). A review of imperative technologies for wastewater treatment I: Oxidation technologies at ambient conditions. Adv. Environ. Res., 8, 501.

15.

Guarantini

C.C.I.

, and Zanoni

M.V.

(2000). Corantes têxteis: Revisão. Quim. Nova., 23, 71.

16.

Hihara

, Okada

, and Morita

(2002). Photo-oxidation and -reduction of vat dyes on water-swollen cellulose and their lightfastness on dry cellulose. Dyes Pigments., 53, 153.

17.

Lee

J.W.

, Choi

S.P.

, Thiruvenkatachari

, Shim

W.G.

, and Moon

(2006). Evaluation of the performance of adsorption and coagulation processes for the maximum removal of reactive dyes. Dyes Pigments., 69, 196.

18.

Martins

L.M.

, Silva

C.E.

, Moita Neto

J.M.

, Lima

A.S.

, and Moreira

R.F.P.M.

(2011). Application of Fenton, photo-Fenton and UV/H₂O₂ in treating synthetic textile wastewater containing the dye Black Biozol UC. Eng. Sanit. Ambient., 16, 261.

19.

Mattos

I.L.

, Shiraishi

K.A.

, Braz

A.D.

, and Fernandes

J.R.

(2003). Peróxido de hidrogênio: Importância e determinação. Quim. Nova., 26, 373.

20.

Moussavi

, and Mahmoudi

(2009). Removal of azo and anthraquinone reactive dyes from industrial wastewaters using MgO nanoparticles. J. Hazard. Mater., 168, 806.

21.

Nagel-Hassemer

M.E.

, Coral

L.A.

, Lapolli

F.R.

, and Amorim

M.T.S.P.

(2012). Processo UV/H₂O₂ como pós-tratamento para remoção de cor e polimento final em efluentes têxteis. Quim. Nova., 35, 900.

22.

Nidheesh

P.V.

, Gandhimathi

, and Ramesh

S.T.

(2013). Degradation of dyes from aqueous solution by Fenton processes: A review. Environ. Sci. Pollut. Res., 20, 2099.

23.

Novotny

, Dias

, Kapanen

, Malachova

, Vandrovcova

, Itavaara

, and Lima

(2006). Comparative use of bacterial, algal and protozoan tests to study toxicity of azo and anthraquinone dyes. Chemosphere., 63, 1436.

24.

Órfão

J.J.M.

, Silva

A.I.M.

, Pereira

J.C.V.

, Barata

S.A.

, Fonseca

I.M.

, Faria

P.C.C.

, and Pereira

M.F.R.

(2006). Adsorption of a reactive dye on chemically modified activated carbons-Influence of pH. J. Colloid Interf. Sci., 296, 480.

25.

Park

, Lee

, Kim

S.W.

, Chase

H.A.

, Lee

, and Kim

(2007). Biodegradation and biosorption for decolorization of synthetic dyes by Funalia trogii. Biochem. Eng. J., 36, 59.

26.

Parshetti

G.K.

, Telke

A.A.

, Kalyan

D.C.

, and Govindwar

S.P.

(2010). Decolorization and detoxification of sulfonated azo dye methyl orange by Kocuria rosea MTCC 1532. J. Hazard. Mater., 176, 503.

27.

Pupo

M.M.S.

, da Costa

L.S.

, Figueiredo

A.C.

, da Silva

R.S.

, Cunha

F.G.C.

, Eguiluz

K.I.B.

, and Salazar-Banda

G.R.

(2013). Photoelectrocatalytic degradation of indanthrene blue dye using Ti/Ru-based electrodes prepared by a modified pechini method. J. Braz. Chem. Soc., 24, 459.

28.

Queissada

D.D.

(2009). Isolamento e seleção de microrganismos para remediação de efluente oleoso da indústria metal-mecânica, Tese de doutorado. Lorena: Universidade de São Paulo, Departamento de Biotecnologia Industrial.

29.

Raj

C.B.C.

, and Quen

H.L.

(2005). Advanced oxidation processes for wastewater treatment: Optimization of UV/H₂O₂ process through a statistical technique. Chem. Eng. Sci., 60, 5305.

30.

Rathi

, Rajor

H.K.

, and Sharma

R.K.

(2003). Photodegradation of direct yellow-12 using UV/H₂O₂/Fe²⁺. J. Hazard. Mater., 102, 231.

31.

Rodriguez

, Peche

, Merino

J.M.

, and Camarero

L.M.

(2007). Decoloring of aqueous solutions of indigocarmine dye in an acid medium by UV/H₂O₂ advanced oxidation. Environ. Eng. Sci., 24, 363.

32.

Roessler

, and Crettenand

(2004). Direct electrochemical reduction of vat dyes in a fixed bed of graphite granules. Dyes Pigments., 63, 29.

33.

Salgado

B.C.B.

(2009). Descoloração de efluentes aquosos sintéticos e têxtil contendo corantes índigo e azo via processos Fenton e foto-assistidos (UV e UV/H₂O₂). Eng. Sanit. Ambient., 14, 1.

34.

Society of Dyers and Colourists. (1976). Color Index, 3rd ed. Yorkshire: Society of Dyers and Colourists.

35.

Sostar-Turk

, Simonic

, and Petrinic

(2005). Wastewater treatment after reactive printing. Dyes Pigments., 64, 147.

36.

Zaghbani

, Hafiane

, and Dhahbi

(2007). Separation of methylene blue from aqueous solution by micellar enhanced ultrafiltration. Sep. Purif. Technol., 55, 117.

Indanthrene Blue Dye Degradation by UV/H 2 O 2 Process: H 2 O 2 as a Single or Fractioned Aliquot?

Abstract

Abstract

Introduction

Materials and Methods

Results and Discussion

Treatment using single addition of H2O2

Effect of H2O2 concentration

Effect of pH

Effect of temperature

Pearson correlation

Treatment with fractionated aliquot of H2O2

Best conditions of the UV/H2O2 treatment

Conclusions

Footnotes

Acknowledgments

Author Disclosure Statement

References

Treatment using single addition of H₂O₂

Effect of H₂O₂ concentration

Treatment with fractionated aliquot of H₂O₂

Best conditions of the UV/H₂O₂ treatment