35886612

7/27/2019 35886612

http://slidepdf.com/reader/full/35886612 1/9

ENVIRONMENTAL ENGINEERING SCIENCEVolume 25, Number 10, 2008

© Mary Ann Liebert, Inc.DOI: 10.1089/ees.2007.0218

Advanced Oxidation of Direct Red (DR 28) by Fenton Treatment

Filiz Ay, Ebru Cokay Catalkaya, Fikret Kargi*

Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey.

Received: August 13, 2007 Accepted in revised form: January 29, 2008

Abstract

Advanced oxidation of Direct Red 28 (DR 28) in aqueous solution by Fenton’s reagent using FeSO4 as sourceof Fe (II) was investigated. Effects of the dyestuff and the reagent concentrations (H2O2 and Fe (II)) on oxida-tion of the azo dye were investigated by using a Box-Behnken statistical experiment design and the surface re-sponse analysis. Degradation and mineralization (conversion to CO2 and H2O) of the azo dye by Fenton treat-ment was evaluated following total organic carbon (TOC) and color removal. Dyestuff removal increased withincreasing H2O2 and Fe (II) concentrations up to a certain level. Fe (II) had a more profound effect on dyestuff removal as compared to H2O2. Complete color removal (100%) was achieved in 5 minutes. However, mineral-ization of the dyestuff took 15 minutes and required higher doses of H2O2. Percent color removal was alwayshigher than TOC removal indicating formation of colorless organic intermediates. Optimal H2O2/Fe(II)/dyestuff ratio resulting in the maximum TOC (99.2%) and color (100%) removals was found to be1450/78/235(mg LϪ1).

Key words: advanced oxidation; Box-Behnken design; Direct Red 28; Fenton treatment; reagent concentrations

1455

Introduction

EFFLUENTS OF TEXTILE and dye industries are highly coloredwith significant amounts of auxiliary chemicals. Direct

discharge of textile effluents introduces intensive color andtoxicity to aquatic environments, causing serious environ-mental problems (Pierce, 1994). The azo dyes, characterized

by having an azo group consisting of two nitrogen atoms(NϭN), are the largest class of dyes used in the textile in-dustry. Different types of azo dyes were reported in litera-ture such as direct, acidic, basic, reactive, disperse, metalcomplexed, mordant, and sulfur dyes (Yang and Xu, 1996).The azo dyes are usually the most problematic pollutants of textile effluents since more than 15% of the textile dyes endup in the effluents during dyeing operation (Park and Choi,2003).

Due to the complex aromatic structure and stability of these dyes, conventional biological treatment methods arenot very effective for degradation (Dai et al., 1995). A num-

ber of physical, chemical, and biological methods and theircombinations were reported in literature for the treatment of textile effluents (Kapdan and Kargi, 2002a,b; Kargi andOzmihci, 2005, 2006). Among these methods, the advanced

oxidation processes are more effective and capable of min-eralizing a wide range of organic pollutants. Fenton reagent

was used for degradation of refractory organic contaminantssuch as chlorophenols (Barbeni et al., 1987; Potter and Roth,1993), chlorobenzene (Sedlak and Andren, 1991), nitrophe-nols (Kang et al., 1999), and dyestuffs (Kuo, 1992; Solozhenkoet al., 1995). Fenton treatment was reported to completely de-colorize the textile industry dyes in rather short reactiontimes (Meric et al., 2004; Neamtu et al., 2001).

The oxidation power of Fenton reagent is due to the gen-eration of hydroxyl radical (OH•) during the iron catalyzeddecomposition of hydrogen peroxide in acid medium. Thehydroxyl radicals with high oxidation potential (2.8 V) com-pletely destroys the pollutants in Fenton treatment. Thedegradation of pollutants can be considerably improved byusing UV radiation due to the generation of additional hy-

droxyl radicals. The photo-Fenton treatment was also usedfor degradation of pollutants (Kang et al., 2000; Pignatello,1992). For economic and effective color and TOC removals

by the Fenton and photo-Fenton treatment the optimal dosesof the reagents need to be determined. Most of the literaturestudies on Fenton ragent treatment of dyestuffs report de-colorization efficiencies, but not TOC removal or mineral-ization. Therefore, the major objective of this study is to in-vestigate the effects of reagent concentrations and todetermine the optimal levels maximizing the color and TOCremovals (mineralization) by the Fenton treatment of DirectRed 28 containing aqueous solution. The effects of initial

*Corresponding author: Department of Environmental Engineering,Dokuz Eylul University, Buca, Izmir, Turkey. Phone: ϩ90 2324127109;Fax: ϩ90 2324531143; E-mail: [email protected]

7/27/2019 35886612


dyestuff, Fe (II) and H2O2 concentrations on oxidation of thedyestuff (DR 28) were investigated by using a Box-Behnkenstatistical experiment design and surface response method-ology. Optimal values of the operating parameters maxi-mizing TOC (mineralization) and color (degradation) re-

movals were determined.

Design of Experiments

The classical approach of changing one variable at a timeto study the effects of variables on the response is a time-consuming method particularly for multivariable systemsand also when more than one response is considered. Sta-tistical design of experiments reduces the number of exper-iments to be performed, considers interactions among thevariables, and can be used for optimization of the operatingparameters in multivariable systems. Response surfacemethodology (RSM) is used when only several significantfactors are involved in optimization. Different types of RSM

designs include 3-level factorial design, central compositedesign (CCD) (Box and Wilson, 1951; Boza et al., 2000), Box-Behnken design (Singh et al., 1995), and D-optimal design(Sanchez-Lafuente et al., 2002).

A modified central composite experimental design knownas the Box-Behnken design is an independent, rotatable qua-dratic design with no embedded factorial or fractional fac-torial points where the variable combinations are at the mid-points of the edges of the variable space and at the center.Among all the RSM designs, the Box-Behnken design re-quires fewer runs than the others (e.g, 15 runs for a 3-factorexperimental design). By careful design and analysis of ex-periments, the Box-Behnken design allows calculations of theresponse function at intermediate levels which were not ex-

perimentally studied and enables estimation of the system

performance at any experimental point with different combinations of the variables (Hamed and Sakr, 2001).

Materials and Methods

Chemicals The azo dye (Direct red 28, DR 28) was used in the ex-

perimental studies since it is a widely used textile dyestuff in the Turkish textile industry and also is more resistant todegradation as compared to the other azo dyes. Direct Red28 (Congo red) is the sodium salt of benzidinediazo-bis-1-naphtylamine-4-sulfonic acid (formula: C32H22N6Na2O6S2;molecular weight: 696.66 g mol21) and is a secondary diazodye. Congo red is water-soluble salt, yielding a red colloidalsolution; its solubility is better in organic solvents such asethanol. Characteristics of the DR 28 are presented in Table1. Ferrous (FeSO4 и 7H2O), used as source of Fe (II), was an-alytical grade and purchased from Merck Co. (Germany).Hydrogen peroxide solution (30%, w wϪ1) in stable form,H2SO4 (98%), and NaOH were all provided from Merck(Germany). Concentrated stock solution of Fe (II) (5000 mgLϪ1) was prepared for further dilution to obtain solutions of desired concentrations. Fe (II) stock solution was stored inthe dark to prevent oxidation of Fe (II). The pH of aqueoussolutions was adjusted using either sodium hydroxide or sul-furic acid. All other chemicals were of analytical grade andused without any previous purification. Water for chemicalsolutions was purified using a Mili-Q system (milipore fil-tration).

Experimental system

A jar test apparatus consisting of four beakers of 2 liters

each were used as the experimental system. The beakers

AY ET AL.1456

TABLE 1. CHARACTERISTICS OF DIRECT RED (DR 28) AZO DYE

Direct Red 28

Color index num. 22120Synonyms Kongo RedMolecular Formula C32H24N6O6S2

Mol. Weight (g molϪ 696.671) max (nm) 497Purity (%) ϳ85%

TABLE 2. BOX-BEHNKEN STATISTICAL EXPERIMENT DESIGN VARIABLES

Coded variable level

Low Center High

Variable Symbol Ϫ1 0 ϩ1

Dye dose (mg LϪ1) X1 10 130 250Hydrogen peroxide dose H2O2, (mg LϪ1) X2 100 1050 2000Ferrous ion dose Fe (II), (mg LϪ1) X3 0 50 100

7/27/2019 35886612


were filled with 1 liter of the dyestuff solution and were me-chanically mixed at 150 rpm using mixing motors and blades.The beakers were open to the atmosphere at room temper-ature (23–25°C). The Fe (II) and H2O2 solutions were addedto the dyestuff solution at the beginning of the batch exper-iments in desired concentrations.

Analytical methods

Fenton’s reagent experiments were carried out at roomtemperature (23–25°C) using different dyestuff (DR 28), hy-drogen peroxide, and ferrous ion doses at pH 3 which is the

most suitable pH for Fenton treatment (Hsueh et al., 2005;Kim et al., 2004; Lin and Peng, 1995). Temperature changesduring reactions were negligible. Predetermined amounts of oxidants (H2O2 and Fe (II)) were injected into the agitatedreactors (150 rpm) containing dye solution at the beginningof each experiment. The iron salt was mixed well with aque-ous dye solution before the addition of hydrogen peroxidesolution. Samples withdrawn from the reactor at certain timeintervals were analyzed immediately to avoid further reac-tions. Samples (10 ml) of raw and treated dyestuff solutionswere analyzed for color and TOC contents after centrifuga-tion at 8000 rpm. pH and conductivity levels were alsorecorded.

A pH meter (WTW Scientific, Germany) was used to

monitor pH. A spectrophotometer of Novaspec II (Phar-macia Biotech.) was used to measure the absorbance. Ab-sorbance measurements were performed at 497 nm, themaximum of absorbance of DR 28. A DOHRMAN DC 190TOC Analyzer (USA) was used to determine the total or-ganic carbon (TOC) content of the samples. For the TOCmeasurements, potassium phthalate solution was used ascalibration standards with the concentrations between 0and 25 mg LϪ1.

Results and Discussion

Box-Behnken statistical experiment design and the re-sponse surface methodology (RSM) (Charles and Kennneth,

1999) were used to investigate the effects of the three inde-pendent variables on the response function and to determinethe optimal conditions maximizing the percent removals of dyestuff and TOC. The optimization procedure involvesstudying the response of the statistically designed combina-tions, estimating the coefficients by fitting the experimentaldata to the response functions, predicting the response of thefitted model, and checking the adequacy of the model. Theindependent variables were the dose of dyestuff (X1), hy-drogen peroxide (X2), and ferrous ion (X3). The low, center,and high levels of each variable are designated asϪ1, 0, andϩ1, respectively, as shown in Table 2. Initial pH was kept

constant at pH ϭ 3, which varied slightly between 3 and 3.5

ADVANCED OXIDATION OF DIRECT RED BY FENTON TREATMENT 1457

TABLE 3. BOX-BEHNKEN EXPERIMENTAL RESULTS AT PRE-DETERMINED EXPERIMENTAL POINTS

Actual and coded levels of variables

X 1 Dye, X 2 H 2O2, X 3 Fe (II),Run No (mg LϪ1) (mg LϪ1) (mg LϪ1) Color TOC

1 Ϫ1 (10) Ϫ1 (100) 0 (50) 99.14 58.412 1 (250) Ϫ1 (100) 0 (50) 92.00 65.00

3 Ϫ1 (10) 1 (2000) 0 (50) 86.99 37.264 1 (250) 1 (2000) 0 (50) 92.40 71.025 Ϫ1 (10) 0 (1050) Ϫ1 (0) 55.86 12.506 1 (250) 0 (1050) Ϫ1 (0) 11.60 2.467 Ϫ1 (10) 0 (1050) 1 (100) 90.32 37.438 1 (250) 0 (1050) 1 (100) 99.13 94.749 0 (130) Ϫ1 (100) Ϫ1 (0) 20.35 15.4010 0 (130) 1 (2000) Ϫ1 (0) 28.81 12.0111 0 (130) Ϫ1 (100) 1 (100) 99.52 75.0012 0 (130) 1 (2000) 1 (100) 98.57 70.0013 0 (130) 0 (1050) 0 (50) 99.00 86.7414 0 (130) 0 (1050) 0 (50) 99.37 93.8815 0 (130) 0 (1050) 0 (50) 99.00 91.52

Experimental percentremovals

TABLE 4. OBSERVED AND PREDICTED PERCENT

REMOVALS FOR RESPONSE FUNCTIONS

Predicted percentremovals (%)

Y 1 Y 2 Y 1 Y 2Run No Color TOC Color TOC

1 100.00 55.84 99.14 58.41

2 85.38 63.30 92.00 65.003 93.61 43.78 86.99 37.264 90.59 76.60 92.40 71.025 48.28 8.19 55.86 12.506 12.45 0.00 11.60 2.467 89.47 40.80 90.32 37.438 100.00 99.05 99.13 94.749 26.12 25.28 20.35 15.4010 29.77 9.80 28.81 12.0111 98.56 75.37 99.52 75.0012 92.79 66.10 98.57 70.0013 99.12 90.71 99.00 86.7414 99.12 90.71 99.37 93.8815 99.12 90.71 99.00 91.52

Observed percentremovals (%)

7/27/2019 35886612


during the reaction period. Preliminary experiments at pH

3, 4, and 5 resulted in insignificant differences (1–3%) in per-cent dyestuff removal by the Fenton reagent. For this reasonpH was not considered as a variable, but kept constant atpH 3 in all experiments since this was the recommended pHfor Fenton reagent treatment (Hsueh et al., 2005; Kim et al.,2004; Lin and Peng, 1995).

The dependent variables (or objective functions) were thepercent color (Y1) and TOC (Y2) removals. The values of theindependent variables and the experimental results at eachexperimental point are presented in Table 3. The center point(0, 0, 0) was repeated three times and nearly the same resultswere obtained, indicating the reproducibility of the data. Ob-served and predicted values of percent color and TOC re-movals are compared in Table 4.

The regression model

The application of RSM offers an empirical relationship between the response function and the independent vari-ables. The mathematical relationship between the response

function (Y) and the independent variables (X) can be ap-

proximated by a quadratic polynomial equation, as follows:Yϭ b0 ϩ b1X1 ϩ b2X2 ϩ b3X 3 ϩ b12X1X2

ϩ b13X1X3 ϩ b23 X2X3 ϩ b11X12ϩ b22X2

2ϩ b33X3

2 (1)

The coefficients of the response functions for different de-pendent variables were determined correlating the experi-mental data with the response functions by using a Stat-Easeregression program. Different response functions withthe determined coefficients are presented by Equations (2)and (3).

The results of analysis of variance (ANOVA) are also pre-sented in Tables 5 and 6, indicating the fact that that the pre-dictability of the model is at a 95% confidence interval. Re-

sponse function predictions were in good agreement withthe experimental data, with a coefficient of determination(R2) of larger than 0.97. Furthermore, the computed F valuewas much greater than that of the tabular F0.01 (14, 14) valueof 3.70, suggesting that the treatment was highly significant.P values of less than 0.05 for any factor in the ANOVA test

AY ET AL.1458

TABLE 5. ANOVA TEST FOR RESPONSE FUNCTION Y1 (% COLOR REMOVAL)

Source Sum of squares Df Mean Square F ratio P value

Model 14116.98 9 1568.55 28.08 0.0009X1 (Dye) 172.79 1 172.79 3.09 0.1389X2 (H2O2) 2.25 1 2.25 0.040 0.8489X3 (Fe (II)) 9174.71 1 9174.71 164.24 Ͻ0.0001X1X2 39.38 1 39.38 0.70 0.4394

X1X3 704.11 1 704.11 12.60 0.0164X2X3 22.14 1 22.14 0.40 0.5567X1

2 15.33 1 15.33 0.27 0.6227X2

2 73.21 1 73.21 1.31 0.3041X3

2 3986.37 1 3986.37 71.36 0.0004Residual 279.31 5 55.86Lack of Fit 279.22 3 93.07 2039.58 0.0005Pure Error 0.091 2 0.046Total (corr) 14396.29 14

R-squaredϭ 0.9806; R-squared (adjusted for df) ϭ 0.9457; standard error of estimate ϭ 7.47.

TABLE 6. ANOVA TEST FOR THE RESPONSE FUNCTION Y2 (% TOC REMOVAL)

Source Sum of squares Df Mean Square F ratio P value

Model 15582.55 9 1731.39 96.83 Ͻ0.0001X1 (Dye) 885.99 1 885.99 49.55 0.009

X2 (H2O2) 21.75 1 21.75 1.22 0.3203X3 (Fe (II)) 7302.36 1 7302.36 408.39 Ͻ0.0001X1X2 184.55 1 184.55 10.32 0.0237X1X3 1252.45 1 1252.45 70.04 0.0004X2X3 35.64 1 35.64 1.99 0.2171X1

2 1174.53 1 1174.53 65.69 0.0005X2

2 825.84 1 825.84 46.19 0.0011X3

2 4584.78 1 4584.78 256.41 Ͻ0.0001Total error 89.40 5 17.88Lack of Fit 62.94 3 20.98 1.59 0.4093Pure Error 26.47 2 13.23Total (corr) 15671.95 14

R-squaredϭ 0.9943; R-squared (adjusted for df) ϭ 0.9840; standard error of estimate ϭ 4.23.

7/27/2019 35886612


indicated a significant effect of the corresponding variableon the response.

Y1 ϭ 45.72 Ϫ 0.14 X1 ϩ 8.7 10Ϫ3 X2 ϩ 1.75 X3

ϩ 2.75 10Ϫ5 X1 X2 ϩ 2.21 10Ϫ3 X1X3 Ϫ 4.95 10Ϫ5

X2 X3 Ϫ 1.41 10Ϫ4 X12Ϫ 4.93 10Ϫ6 X2

2Ϫ 0.013 X3

2 (2)

Y2 ϭ 0.486 ϩ 0.2 X1 ϩ 0.028 X2 ϩ 1.70 X3 ϩ 5.96 10Ϫ5 X1X2

ϩ 2.95 10Ϫ3 X1X3 Ϫ 6.284 10Ϫ5 X2X3

Ϫ 1.238 10Ϫ3 X12Ϫ 1.657 10Ϫ5 X2

2Ϫ 0.014 X3

2 (3)

From the response function coefficients it can be said thatthe dyestuff concentration adversely affects percent color re-moval and Fe (II) concentration has more profound effect oncolor removal as compared to the H2O2 dose. TOC removalincreases with dyestuff concentration and is also more pro-foundly affected from the Fe (II) doses as compared to H2O2.

Color removal: Degradation of dyestuff

Response functions with determined coefficients were

used to estimate variations of response functions with theindependent variables under different conditions. Figure 1shows the effect of initial H2O2 concentration on percentcolor removal at different dyestuff concentrations after 5minutes of reaction time when Fe (II) was 30 mg LϪ1. Per-cent color (dyestuff) removal increased with increasing ini-tial hydrogen peroxide concentration at all dyestuff concen-trations. However, color removals decreased with increasingH2O2 concentrations above 1000 mg LϪ1 at dyestuff concen-trations below 200 mg LϪ1 due to hydroxyl radical scaveng-ing effect of high peroxide doses. Previous studies have re-ported that increases in H2O2 concentration improved thedegradation of organic compounds in Fenton reactions upto a certain limit due to additional HO• formation (Emilio

et al., 2002; Nogueira and Guimaraes, 2000). However, ad-verse effects were also observed when excess concentrationsof H2O2 were present (Ghaly et al., 2001; Torrades et al., 2003).The accepted explanation is the scavenging of HO• by H2O2

and consequent formation of the less reactive radical HO2•,

as presented by the following equations:

OH•ϩH2O2ǞH2OϩHO2

• (4)

OH•ϩHO2

•ǞH2OϩO2 (5)

At a dyestuff dose of 10 mg LϪ1, the optimal H2O2/ Fe(II)/dyestuff ratio yielding the highest color removal (100%)was 545/50/10 mg LϪ1, while at a high dyestuff dose of 250mg LϪ1 this ratio was 655/65/250 mg LϪ1 yielding 100%color removal. Complete color (dyestuff) removal at highdyestuff concentrations requires high H2O2 and Fe (II) doses.

Effects of Fe (II) and dyestuff concentrations on percentcolor removal by the Fenton treatments are depicted in Fig.2 at a H2O2 concentration of 1000 mg LϪ1. Percent color re-

moval increased with increasing Fe (II) concentrations at alldyestuff concentrations up to 60 mg LϪ1 and leveled off forFe (II) concentrations between 60 and 100 mg LϪ1. Furtherincreases in Fe (II) concentrations above 60 mg LϪ1 resultedin insignificant changes in percent color removal, especiallyfor dyestuff doses below 100 mg LϪ1, probably due to ad-verse effects of high Fe (II) doses. Optimal Fe (II) concentra-tion was nearly 50 mg LϪ1 for dyestuff concentrations below100 mg LϪ1 and 60 mg LϪ1 for dyestuff doses above 100 mgLϪ1. Percent color removals were 32.3, 99.0, and 100% withan initial dyestuff dose of 130 mg LϪ1 and Fe (II) doses of 0,50, and 100 mg LϪ1, respectively, at a H2O2 dose of 1000 mgLϪ1 indicating the fact that Fe (II) doses of above 50 mg LϪ1

did not improve the extent of color removal under the spec-

ified conditions. From the comparison of Figs. 1 and 2, it can be said that Fe (II) doses had more profound effects on per-cent color removal as compared to H2O2.

These results are in agreement with the literature reports,where a beneficial effect of increasing Fe (II) was observedin degradation of dyestuffs (Lodha and Chaudhari, 2007).However, high iron concentrations can also adversely affectdyestuff oxidation by scavenging OH•. Strict pH control isrequired to avoid precipitation of iron hydroxides which hin-ders penetration of light and therefore reduces the rate of degradation (Nogueira and Guimaraes, 2000). Complete re-moval of color was accomplished at a hydrogen peroxide


50

0 500

250

200

150

100

50

10

Dye

1000 1500

Fe (⌱⌱) ϭ 30 mg L 1

Hydrogen Peroxide Concentration (mg L 1)

2000

60

70

C o l o r R e m o v a l ( % ) 80

90

00 20

250

200

150

100

50

10Dye

40 60 80

H2O2 ϭ 1000 mg L 1

Ferrous Ion Concentration (mg L 1)

100

40

20

60

C o l o r

R e m o v a l ( % )

80

100

FIG. 2. Influence of Fe (II) concentration on DR 28 decol-orization efficiency using different dye concentrations atconstant peroxide dose of 1000 mg LϪ1.

FIG. 1. Influence of H2O2 concentration on DR 28 decol-orization efficiency using different dye concentrations atconstant Fe (II) dose of 30 mg LϪ1.

7/27/2019 35886612


dose of 450 mg LϪ1 and Fe (II) concentrations above 60 mgLϪ1 after 5 minutes reaction time when the dyestuff dose was250 mg LϪ1. Fe (II) doses lower than 60 mg LϪ1 did not re-sult in complete dyestuff degradation at high dyestuff con-centrations.

Apparently the use of high oxidant (H2O2) and catalyst(Fe(II)) doses inhibited the removal of color for low dyestuff concentrations due to formation of hydroxyl radical sca-

vengers. The ANOVA analysis indicated that all three vari-ables dyestuff, H2O2 and Fe (II) doses and the interactions(X3, X1, X3, X3) were significant and played important rolesin decolorization by the Fenton treatment.

Total organic carbon (TOC) removal:

Mineralization of dyestuff

Decolorization of the dyestuff does not always result incomplete mineralization to CO2 and H2O. In some cases, col-orless reaction intermediates may be formed during thedegradation of dyestuffs. The colorless reaction intermedi-ates may be more toxic than the parent compounds. There-fore, it is important to know the degree of mineralization or

total organic carbon (TOC) removal during decolorization of azo dyes by the Fenton treatment. In our study, completemineralization of the dyestuff was achieved after 15 minutesof reaction time while decolorization was realized in 5 min-utes. This difference indicated formation of some colorlessintermediates during the oxidation reaction, which required15 minutes for complete mineralization. The difference be-tween percent color and TOC removals is a measure of for-mation of colorless organic intermediates which contributeto TOC, but not color measurements. The reaction schemecan be summarized as follows:

Dyestuff ϩH2O2 ϩ Fe (II) l colorless intermediates

ϩ nitrate ϩ sulfatel CO2 ϩH2O (6)

The first reaction is for color removal and the second is forTOC removal or mineralization. In decolorization reactions,azo groups were removed from the dyestuff and some col-orless organic intermediates were formed which were par-

tially degraded further to CO2 and H2O for mineralizationor TOC removal.

Figure 3 depicts variation of percent TOC removal (min-eralization) with H2O2 doses at different dyestuff concen-trations (10–250 mg LϪ1) at a constant Fe (II) dose of 60 mgLϪ1. Percent TOC removal increased with H2O2 doses up to1000 mg LϪ1, indicating limitations by H2O2 concentrationat low peroxide doses. Further increases in H2O2 doses re-sulted in decreases in TOC removal due to hydroxyl radicalscavenging effect of high H2O2 doses. Percent TOC removalor mineralization steadily increased with increasing dyestuff concentrations up to 200 mg LϪ1. The reason for this is lowlevels of colorless intermediate formation at high dyestuff doses and high degree of mineralization at low intermedi-

ate (or high dyestuff) concentrations. Decrease in percentTOC removal for dyestuff concentrations above 200 mg LϪ1

is due to limitations by the peroxide and Fe (II) doses whichwere probably below the required levels. The optimalH2O2/Fe/dystuff ratio yielding the highest TOC removal(99%) was 1000/60/200 mg LϪ1.

Initial dyestuff concentration was one of the most impor-tant parameters affecting the percent TOC removal by theFenton treatment. Figure 4 depicts variations of percent TOCremoval with Fe (II) concentration at different dyestuff dosesand constant H2O2 dose of 1000 mg LϪ1. TOC removal wasprofoundly affected by the Fe (II) concentration, as seen bythe high coefficient of Fe (II) dose (X3) in Equation (3). Per-cent mineralization (TOC removal) increased with increas-

ing Fe (II) doses up to nearly 60 mg LϪ1 due to limitations by the Fe (II) ions at low doses and then decreased with fur-ther increases in Fe (II) due to radical scavenging effects of high Fe (II) doses. The optimal Fe (II) dose yielding the high-est TOC removal was nearly 60 mg LϪ1 under the specifiedexperimental conditions. Percent TOC removal increasedwith increasing dyestuff concentrations up to 200 mg LϪ1

and decreased with further increases in dyestuff doses. HighTOC removals at high dyestuff doses is due to low levels of colorless intermediate formation yielding high mineraliza-tion efficiencies as described by Equation (6). When dyestuff concentration was 130 mg LϪ1, percent TOC removals were

AY ET AL.1460

40

0 500

250

200150

100

50

10

Dye

1000 1500

Fe (⌱⌱) ϭ 60 mg L 1

Hydrogen Peroxide Concentration (mg L 1)

2000

60 T O C R e

m o v a l ( % )

80

100

00 20

250

200

150 100

50

10

Dye

40 60 80

H2O2 ϭ 1000 mg L 1

Ferrous Ion Concentration (mg L 1)

100

40

20

60

T O C R e m o v a l ( % )

80

100

FIG. 3. Influence of H2O2 concentration on TOC removalefficiency using different dye concentrations at constant Fe(II) dose of 60 mg LϪ1.

FIG. 4. Influence of Fe (II) concentration on TOC removalefficiency using different dye concentrations at constant per-oxide dose of 1000 mg LϪ1.

7/27/2019 35886612


25.5, 95.4, and 85.9%, respectively, at Fe (II) doses of 0, 60,and 100 mg LϪ1 at a hydrogen peroxide dose of 1000 mg LϪ1,yielding optimal a Fe (II) dose of 60 mg LϪ1 under the spec-ified conditions. At a dyestuff dose of 10 mg LϪ1, the opti-mal H2O2/Fe(II)/dyestuff ratio yielding the highest TOC re-moval (65%) was 740/60/10 mg LϪ1, while at a high dyestuff dose of 250 mg LϪ1 this ratio was 1125/85/250 mg LϪ1, yield-ing 100% TOC removal. High H2O2 and Fe (II) doses should

be used at high dyestuff concentrations for complete miner-alization.

The ANOVA analysis indicated that all three variablesdyestuff, H2O2 and Fe (II) doses and independent variableinteractions (X1, X3, X2X3, X1

2, X12, X3

2) played importantroles for the mineralization of dye or TOC removal.

In general, decolorization (dyestuff removal) took placefaster (5 minutes) and required lower H2O2 and Fe (II) dosessince functional groups on the dyestuff were removed moreeasily as compared to TOC removal (mineralization). Ap-parently, some colorless soluble organic intermediates wereformed during Fenton treatment, which contributed to TOCcontent of the final solution. TOC removal or mineralizationwas realized when the colorless intermediates were de-graded to CO2 and H2O, as described by the second reactionin Equation (6). Color removal at high dyestuff concentra-tions was low, yielding low colorless intermediate forma-tions resulting in low mineralization efficiencies at low in-

termediate concentrations. The difference between thepercent color and TOC removals is a measure of colorless in-termediate formation. Unlike the Fe (II) dose, color removalwas not affected from the H2O2 dose significantly. Decol-orization does not take place by oxidation, but only by re-moval of azo groups. TOC removals were more profoundlyaffected by the oxidant (H2O2) and the catalyst (Fe (II)) dosessince mineralization involves oxidation of the colorless in-termediates. Low H2O2 doses may be satisfactory for decol-orization, but not for complete mineralization. For an initialdyestuff concentration of 250 mg LϪ1, only 450 mg LϪ1 H2O2

is required for complete decolorization, whereas completemineralization requires 1125 mg LϪ1 H2O2 while Fe (II) doserequirement is 60 mg LϪ1 for both cases.

The optimal dye, H2O2 and Fe (II) doses resulting in thehighest TOC and color removals were determined by usingan optimization program and the results are presented inTable 7. Oxidant and catalyst requirements are different formaximum color and TOC removals since the reaction mech-anisms are different. Maximum color removal (100%) andmineralization efficiency (98%) were obtained with a H2O2

/Fe (II)/dyestuff ratio of 1450/78/235 mg LϪ1.

Conclusions

This study has demonstrated that the response surfacemethodology and the Box-Behnken statistical experiment de-

sign can provide statistically reliable results for advanced ox-idation of dyestuffs by the Fenton treatment and also for de-termination of optimum conditions, maximizing the dyestuff removal. Predictions obtained from the response functionswere in good agreement with the experimental results, in-dicating the reliability of the methodology used. The surfaceresponse methodology also provided a better understandingof the role of the Fe (II) and H2O2 concentration on the degra-dation of the dye for a large range of concentrations. Inde-pendent variables and their interactions were found to be ef-fective in TOC and color removals by the Fenton treatment.

High color and TOC removals indicated effective removalof azo groups from the dyestuff and mineralization. Percentcolor removals were higher than TOC removals, indicatingformation of colorless intermediates. Functional groups im-parting color were removed rather fast in 5 minutes, yield-ing colorless intermediates. Complete mineralization or ox-idation of the intermediates to CO2 and H2O took nearly 15minutes. At a constant dyestuff concentration percent, colorremoval increased with increasing H2O2 and Fe (II) concen-trations up to a certain level above which color removal de-creased due to scavenging effects of H2O2 and Fe (II) on hy-droxyl radicals. Fe (II) doses affected percent dyestuff andTOC removals more profoundly as compared to the perox-ide. Optimal peroxide and Fe (II) doses were determined fora given dyestuff concentration. Maximum color removal

(100%) and mineralization efficiency (98%) were obtainedwith a H2O2/Fe (II)/dyestuff ratio of 1450/78/235 mg LϪ1.The optimal concentrations determined for each response(mineralization and decolorization) were somewhat differ-ent since decolorization (removal of functional groups) andcomplete mineralization to CO2 and H2O had different re-action mechanisms. TOC removal required higher H2O2 andFe (II) doses as compared to decolorization since completemineralization required effective oxidation of the interme-diates formed by the decolorization reaction.

Author Disclosure Statement

The authors declare that no competing financial interestexist.

References

Barbeni, M., Minero C., and Pellizzetti, L. (1987). Chemicaldegradation of chlorophenols with Fenton’s reagent(Fe2ϩ/H2O2). Chemosphere 16, 2225–22237.

Box, G.E.P., and Wilson, K.B. (1951). On the experimental at-tainment of optimum multifactorial conditions. Royal Statis-tics Society 13, 1–12.

Boza, A., De la Cruz, Y., Jordan, G., Jauregui-Haza, U., Aleman,A., and Caraballo, I. (2000). Statistical optimization of a sus-tained-release matrix tablet of lobenzarit disodium. Drug Dev.Ind. Pharm. 26, 1303–1307.


TABLE 7. OPTIMUM LEVELS OF THE VARIABLES MAXIMIZING THE COLOR AND TOC REMOVALS BY THE FENTON TREATMENT

Dyestuff H 2O2 Fe (II)Response (X 1) mg LϪ1 (X 2) mg LϪ1 (X 3) mg LϪ1 Efficiency (Y) %

Color removal: Dye Degradation 235 340 65 100.0TOC removal: Mineralization 235 1720 80 95.6

7/27/2019 35886612


Charles, R.H., and Kennneth, V.T. (1999). Fundamental conceptsin the design of experiments. Oxford: University Press.

Dai, S., Zhuang, Y., and Chen, L. (1995). Study on the relation-ship between structure of synthetic organic chemicals andtheir biodegradability. Environ. Chem. 14, 354–367.

Emilio, C.A., Jardim, W.F., Litter, M.L., and Mansilla, H.D. (2002).EDTA destruction using the solar ferrioxalate advanced oxida-tion technology (AOT): Comparison with solar photo-Fentontreatment. J. Photochem. Photobiol. A: Chem. 151, 121–127.

Ghaly, M.Y., Haertel, G., Mayer, R., and Haseneder, R. (2001). Pho-tochemical oxidation of p-chlorophenol by UV/H2O2 and photo-Fenton process. A comparative study. Waste Manage. 21, 41–47.

Hamed, E., and Sakr, A. (2001). Application of multiple responseoptimization technique to extended release formulations de-sign. J. Control Release 73, 329–338.

Hsueh, C.L., Huang, Y.H., Wang, C.C., and Chen, C.Y. (2005).Degradation of azo dyes using low iron concentration of Fen-ton and Fenton-like system. Chemosphere 58, 1409–1414.

Kang, S.F., Liao, C.H., and Po, S.T. (2000). Decolorization of tex-tile wastewater by photo-Fenton oxidation technology.Chemosphere 41, 1287–1297.

Kang, S.F., Wang, T.H., and Lin, Y.H. (1999). Decolorization anddegradation of 2,4-dinitrophenol by Fenton’s reagent. J. Env-

iron. Sci. Health A 34, 935–950.Kapdan, I. K., and Kargi, F. (2002a). Simultaneous biodegrada-

tion and adsorption of textile dyestuff in an activated sludgeunit. Process Biochem. 37, 973–981.

Kapdan, I. K., and Kargi, F. (2002b). Biological decolorization of textile dyestuff containing wastewater by Coriolus versicolor in arotating biological contactor. Enzyme Microb. Technol. 30, 195–199.

Kargi, F., and Ozmihci. S. (2005). Comparison of adsorption per-formances of powdered activated sludge and powdered acti-vated carbon for removal of turquoise blue dyestuff. ProcessBiochem. 40, 2539–2544.

Kargi, F., and Ozmihcio, S. (2006). Utilization of powdered wastesludge (PWS) for removal of textile dyestuffs from wastewater

by adsorption. J. Environ. Manage. 81, 307–314.Kim, T.H., Park, C.,Yang, J., and Kim, S. (2004). Comparison of

disperse and reactive dye removals by chemical coagulationand Fenton oxidation. J. Hazard. Mater. B 112, 95–103.

Kuo, W.G. (1992). Decolorizing dye wastewater with Fenton’sreagent. Water Res. 26, 881–889.

Lin, S.H., and Peng, C.F. (1995). Treatment of textile wastewater by Fenton’s reagent. J. Environ. Sci. Health A 30, 89–101.

Lodha, B., and Chaudhari, S. (2007). Optimization of Fenton-bi-ological treatment scheme for the treatment of aqueous dyesolutions. J. Hazard. Mater. 148, 459.

Meric, S., Kaptan, D., and Olmez, T. (2004). Color and COD re-moval from wastewater containing Reactive Black 5 usingFenton’s oxidation process. Chemosphere 54, 435–441.

Neamtu, M., Yedilery, A., Siminiceanu, I., and Kettrup, A. (2001).Oxidation of commercial reactive azo dye aqueous solutions

by the photo-Fenton and Fenton-like processes. J. Photochem.Photobiol. A: Chem. 141, 247–254.

Nogueira, R.F.P., and Guimaraes, J.R. (2000). Photodegradationof dichloroacetic acid and 2,4-dichlorophenol by ferriox-alate/H2O2 system. Water Res. 34, 895–901.

Park, H., and Choi, W. (2003). Visible light and Fe (III)-mediateddegradation of Acid Orange in the absence of H2O2. J. Pho-tochem. Photobiol. A: Chemistry 159, 241–247.

Pierce, J. (1994). Colour in textile effluents the origins of prob-lem. J . Soc. Dyers Color 110, 131–133.

Pignatello, J.J. (1992). Dark and photo-assisted Fe (III) catalyzeddegradation of chlorophenoxy herbicides by hydrogen per-oxide. Environ. Sci. Technol. 26, 944–951.

Potter, F.J., and Roth, J.A. (1993). Oxidation of chlorinated phe-nols using Fenton’s reagent. Hazard Waste Hazard Matter 10,

151–159.Sanchez-Lafuente, C., Furlanetto, S., and Fernandez-Arevalo, M.

(2002). Didanosine extended-release matrix tablets: optimiza-tion of formulation variables using statistical experimental de-sign. Int. J. Pharm. 237, 107–118.

Sedlak, D.L., and Andren, A.W. (1991). Oxidation of chlorobenzene with Fenton’s reagent. Environ. Sci. Technol.25, 777–783.

Singh, S.K., Dodge, J., Durrani, M.J., and Khan, M.A. (1995). Op-timization and characterization of controlled release pelletscoated with an experimental latex: I. Anionic drug. Int. J.Pharm. 125, 243–255.

Solozhenko, E.G., Soboleva, N.M., and Goncharuk, V.V. (1995).Decolorization of azo dye solutions by Fenton’s oxidation.Wa-ter Res. 29, 2206–2210.

Torrades, F., Perez, M., Mansilla, H.D., and Peral, J. (2003). Ex-perimental design of Fenton and photo-Fenton reactions forthe treatment of cellulose bleaching effluents. Chemosphere 53,1211–1220.

Yang, Y., and Xu, L. (1996). Reusing hydrolyzed reactive dyebathfor nylon and wool dyeing. Am. Dyestuff Rep. 3, 27–34.

AY ET AL.1462

7/27/2019 35886612


35886612

Documents