10737529

7/27/2019 10737529

1/13

2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

MARCELDEKKER,INC. 270 MADISONAVENUE NEWYORK, NY 10016

JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH

Part AToxic/Hazardous Substances & Environmental Engineering

Vol. A38, No. 10, pp. 22412250, 2003

INDUSTRIAL WASTEWATER TREATMENT

Removal of Color and COD from a Mixture of Four

Reactive Azo Dyes Using Fenton Oxidation Process

Sureyya Meric,* Deniz Kaptan, and Olcay Tu nay

Department of Environmental Engineering,

Civil Engineering Faculty, Istanbul Technical University,

Maslak, Istanbul, Turkey

ABSTRACT

This study was designed to decolorize and to reduce COD content in a mixture of

four reactive dyes, i.e., Remazol Black 5 (RB5), Remazol Red RB (RR), Remazol

Yellow 84 (RY), Remazol Brilliant Blue (RB) using Fenton Oxidation Process

(FOP). Optimum pH, temperature, and the doses of FeSO4 and H2O2 were

determined. Experiments were conducted on the samples containing a total con-

centration of 100 mgL1 (RBRY), 200 mgL1 (RB5RR), 300 mgL1

(RB5RRRB RY), and 400 mgL1 (RRRBRY) dyes consideringtheir actual application doses in dyehouses. Optimum pH was observed as 2.5

at 30

C using 400 mg L1 FeSO4 and 800mgL1 of H2O2 resulting in more than

96% COD and 99% Pt-Co unit of color removal for the mixture of RB5 and RR.

The optimum conditions determined were 4.0 pH, 50C, and 500mgL1 FeSO4applying 1000 mg L1 H2O2 for the mixture of (RB5RRRBRY). A

100mgL1 solution of a mixture of RB and RY at equal amounts was oxidized

using 200 mgL1 FeSO4 and 300mgL1 H2O2 at 3.0 pH and 50

C.

Key Words: Color; COD removal; Fentons oxidation process; Reactive dyes;

Textile industry.

*Correspondence: Sureyya Meric, Department of Environmental Engineering, Civil

Engineering Faculty, Istanbul Technical University, Maslak 34469, Istanbul, Turkey; Fax:

0900 212 285 6882; E-mail: [email protected].

2241

DOI: 10.1081/ESE-120023371 1093-4529 (Print); 1532-4117 (Online)

Copyright & 2003 by Marcel Dekker, Inc. www.dekker.com

7/27/2019 10737529

2/13



INTRODUCTION

Wastewaters originated from the textile industry contain various pollutants

including a high content of organic matter and color problem depending on forms

of dyes, surface active materials, and textile additive materials used in the process. [1]

Reactive dyes having azo bounds are the most commonly applied (6070%)

among more than 10,000 dyes applied in textile processing industries.[2] Discharge

of azo dyes is undesirable not only for aesthetic reasons but also because many

azo dyes and their breakdown products are toxic to aquatic life[3] and exhibit muta-

genic/carcinogenic properties.[4]

Azo dyes are resistant to biodegradation under aerobic conditions[5] whereas

anaerobic color removal due to reductive NN cleavage was applied by many

researchers successfully.[2,6,7]

Many chemical processes have been used extensively for the treatment of textile

wastewaters. Most of the studies, such as chemical precipitation,

[8]

adsorptionby activated carbon[9] and use of some natural absorbents,[10] photocatalytic

oxidation,[11] ozonation,[12,13] and Fenton oxidation process[1420] have been focused

on color removal.

Fenton oxidation process (FOP) has the advantages of both oxidation and

coagulation processes. During FOP, the organic substances are reacted with

hydrogen peroxide (H2O2) in the presence of inexpensive ferrous sulphate (FeSO4)

to reduce COD content and color of wastewater. [14] FOP has been used to treat

recalcitrant/toxic wastewaters.[20,21]

The chemistry of FOP is explained. The reactions are given by Walling and Kato

as cited in Lin and Peng.[22] COD and color removal reactions are initiated by the

hydroxyl radical.

H2O2 Fe

2

! Fe

3

OH

OH 1

RH OH ! R H2O 2

R Fe3 ! R Fe2 3

Fe2 OH ! Fe3 OH 4

FOP was composed of four stages, which are: pH adjustment, oxidation reac-

tion, neutralization, and coagulation.[14] It is mentioned that for decolorization

purposes of azo dyes mineralization is not necessary because the removal of color

is associated with break down of the conjugated unsaturated bonds in molecules.[15]

In that case the dose of H2O2 must be well defined. Kuo[14] reported that at pH lower

than 3.5, H2O2 and ferrous ions are more stable resulting in a better redox systemand a more effective decolorization. However, at pH values higher than 4.0, ferrous

ions easily form ferric ions, which have a tendency to produce ferric hydroxo com-

plexes. H2O2 is unstable and easily decomposes itself in the basic solutions.

FOP was studied by many workers to remove color and COD from textile

wastewaters. Some of these studies have focused on the dyes,[14,15,19] textile addi-

tives,[20] and textile wastewater.[1618] Kuo [14] used 1167mg L1 of H2O2 and

2242 Meric, Kaptan, and Tunay

7/27/2019 10737529

3/13



500mgL1 of FeSO4 for 0.3gL1 of reactive dye solution at 50C and lower than

3.5 pH.

Kang and Chang[16] used FOP for COD and color removal from artificial textile

wastewaters and textile secondary effluents containing reactive dyes. They concluded

that the optimum pH was between 3.0 and 5.0 and the determining step for COD

and color removal was the oxidation rather than coagulation. Park et al.[18] applied

FOP to pigment wastewaters. Optimum pH and molar Fe2/H2O2 ratio were found

to be 3.0 and 0.4, respectively. Lin and Lo [17] used FOP for simulated textile dyeing

wastewater containing direct and reactive dyes. Optimum values of pH, temperature,

and molar FeSO4/H2O2 ratio were found to be 3.0, 30C, and 0.09 respectively.

These studies indicate the success of FOP in removing color and delineate the oper-

ating conditions. However application of FOP for the actual conditions is rare.

Textile dye baths contain more than one dye stuff and the mixture of dyes may

respond to oxidation in a different way than they singly exist.

The purpose of this study is to investigate the FOP applications for several dyemixtures that represent actual combinations. The investigation covered the determi-

nation of other parameters affecting the process efficiency to find out optimum

values and to make comparisons with the literature values. Effect of temperature

was also evaluated to assess the advantage of high temperature of spent baths.

MATERIALS AND METHODS

Commonly used reactive dyes Remazol Black B(RB5), Remazol Red RB (RR),

Remazol Brilliant Blue (RB), and Remazol Yellow 84 (RY) and their combinations

were used in the study.

Experimental Set-Up

Experimental study was designed for the optimization of COD and color

removal, pH, temperature, and FeSO4 and H2O2 doses. FOP was performed by

the method reported by Kuo[14] with a modification of 2 min rapid mixing (RM)

at 100 rpm first and later, 20 min slow mixing (SM) at 30 rpm followed by 30 min

for settling.[23] First, the pH of the sample was lowered to desired pH value using

1 N H2SO4. FeSO4 and H2O2 were added to the 500 mL beakers containing of 100,

200, 300, and 400 mg L1 dye solutions. After rapid and slow mixing, settling period,

the pH of the supernatant was readjusted using 1 N NaOH up to 7.5 and the super-

natant was left to settle for 2 h. During mixing, reactors were kept at constant

temperature.

Experiments were conducted on the dye solutions at 30, 40, 50, and 60Ctemperatures changing FeSO4 and H2O2 molar ratio ranging from 0.05 to 1.25.

pH was changed between 2.5 and 4.0.

The study was designed in 5 stages. In the first stage H 2O2, temperature, pH,

rapid and slow mixing were kept constant to determine optimum FeSO 4 concentra-

tion yielding maximum color and COD removals. In the second stage, using

optimum FeSO4 concentration and the same oxidation conditions, optimum H2O2

Removal of Color and COD in Azo Dyes 2243

7/27/2019 10737529

4/13



concentration was investigated. By considering the optimum doses of first and

second stages, pH, and temperature were investigated in the third, fourth stages,

respectively. The effect of the mixture time was also studied.

Analytical Measurements

COD was measured according to Standard Methods.[24] Absorbance measure-

ments were made using Pharmacia LKB-Novaspe II model spectrophotometer.

HACH-Dr-B model spectrophotometer was used for the color measurements in

APHA Pt-Co unit. The effluent was filtered by 0.45 mm Millipore membrane filter

for measuring COD, color, and absorbance at 436, 525, and 620 nm wavelengths

considering German Water Discharge Standards.[25] FeSO4 solution was prepared

daily and H2O2 (30%) solution was of analytical grade. Reactive dyes were obtained

from a dyestuff company. The solution of each dye was hydrolyzed at pH higherthan 11.5 and at 80C temperature for at least 4 h according to literature.[5] H2O2 was

destroyed before COD measurements by increasing the pH over 9 and aerating the

sample for 30 min.

RESULTS AND DISCUSSION

COD equivalents of the dyes were determined as 0.75 mg COD mg1 RB5,

2.2mgCODmg1 RR, 1.5 mgCODmg1 RB, and 1.5 mgCODmg1 RY, respec-

tively. The matrix illustration of dye mixtures including COD contents of each

one is seen in Table 1. The concentrations of the dyes were chosen taking into

account their actual uses in the textile industry.

Experimental results of FOP for defining optimum conditions are given below.According to the results of FeSO4 optimization as seen in Table 2, maximum COD

removal was obtained as (88%) using 300 mg L1 FeSO4 and 600mgL1 H2O2.

However the color removal was relatively low (>91%). The absorbance measure-

ments showed that the limits could not be provided at 436 and 525 wavelengths.

Thus the concentration of H2O2 was increased up to 800 mg L1 yielding (90%)

COD and (97%) color removal (Table 3). In this case, the absorbances were lowered

than the limits starting from the 300 mg L1 of FeSO4. pH, temperature, and slow

mixing were kept at 3.0 and 40C, respectively.

Table 1. The mixtures of the reactive dyes and their total COD contents.

Concentration of the dyes used (mg L

1

) COD of dye mixture

RB5 RR RB RY (mg L1)

Run 1 100 100 295

Run 2 100 100 50 50 445

Run 3 200 100 100 740

Run 4 50 50 150


7/27/2019 10737529

5/13



For the optimization of H2O2 concentration, 300 mg L1 of FeSO4 was chosen.

As depicted in Table 4, COD removal efficiency increased by increasing H2O2concentration from 600mg L1 (88%) to 900 mgL1 (92%). Color removal and

absorbance measurements confirmed the optimum H2O2 concentration as

800mgL1 resulting in 97% color and 90% COD removal.

To determine the optimum pH, pH was changed between 2.5 and 4.0 as shown

in Table 5. Although more than 99% color removal was obtained at all pH values,

the maximum COD removal (96%) was proved at 2.5 pH. The absorbances were

also measured lower than the limits at each pH. As seen in Table 6, optimum

temperature was found as 30C at which 96% COD and 99% color removal were

obtained.

Table 7 presents the results of optimization of slow mixing time. Color was

removed higher than 99% for all mixing times. Maximum COD removal (97%)was obtained at 10th min.

Optimum conditions determined for 100 mg L1 of RB5, 100mgL1 RR, and

200mgL1 of their mixture are summarized in Table 8. Upon the data given in Table

8, molar ratio between FeSO4 and H2O2 was determined as 0.055 for RB5, 0.11 for

RR, and 0.11 for their mixture. Although color removal was obtained (higher than

99%) at almost all conditions for each dye and their mixture. COD removal varied

Table 2. The relation between FeSO4 concentration and color and COD removals for the

mixture of RB5 and RR at 40

C, 3.0 pH, 2 min rapid mixing, 20 min slow mixing using

600mgL1 of H2O2.

FeSO4Absorbance

Color

Pt-Co

removal COD

COD

removal

(mgL1) 436 nm 525 nm 620 nm Pt-Co (%) (mg L1) (%)

100 0.31 0.230 0.082 800 85 64 78

150 0.16 0.150 0.073 460 92 60 80

200 0.10 0.066 0.012 260 94 55 81

250 0.12 0.068 0.015 350 92 42 86

300 0.20 0.067 0.016 410 93 36 88

Table 3. The relation between FeSO4 concentration and color and COD removals for themixture of RB5 and RR at 40C, 3.0 pH, 2 min rapid mixing, 20 min slow mixing using

800mgL1 of H2O2.

FeSO4Absorbance

Color

Pt-Co

removal COD

COD

removal


100 0.290 0.240 0.088 700 87 69 77

200 0.140 0.079 0.027 400 93 46 84

300 0.065 0.021 0.009 150 97 33 90

400 0.003 0.002 0.001 10 >99 15 95


7/27/2019 10737529

6/13



between 7086% for RB5, 8595% for RR, and 8096% for their mixture. Lower

COD removal efficiency of RB5 indicated that its oxidation was more difficult than

RR. In the case of the oxidation of their mixture, it was necessary to increase the

doses of FeSO4 and H2O2 more than 2 fold. However, increasing ratio of the H2O2dose (1000 mgL1 for both RB5 and RR) was lower than their individual

200mgL1 uses.[23] Optimum temperature and pH values of their mixture (30C,

Table 5. The relation between pH and color and COD removals for the mixture of RB5 and

RR at 40C, 2 min rapid mixing, 20min slow mixing using 400mg L1 of FeSO4 and800mgL1 of H2O2.

pH

AbsorbanceColor

Pt-Co

removal COD

COD

removal

436 nm 525 nm 620 nm Pt-Co (%) (mg L1) (%)

2.5 0.002 0.001 0.001 99 10 96

3.0 0.003 0.002 0.001 99 15 94

3.5 0.006 0.004 0.003 99 17 93

4.0 0.003 0.001 0.001 99 20 92

Table 6. The relation between temperature and color and COD removals for the mixture of

RB5 and RR at 3.0 pH, 2 min rapid mixing, 20 min slow mixing using 400 mg L1 of FeSO4and 800mgL1 of H2O2.

T(C)

AbsorbanceColor

Pt-Co

removal COD

COD

removal

436 nm 525 nm 620 nm Pt-Co (%) (mg L1) (%)

30 0.002 0.001 0.001 99 10 96

40 0.003 0.002 0.001 99 15 94

50 0.003 0.002 0.001 99 19 93

60 0.002 0.001 0.001 99 21 92

Table 4. The relation between H2O2 concentration and color and COD removals for the

mixture of RB5 and RR at 40

C, 3.0 pH, 2 min rapid mixing, 20 min slow mixing using

300mgL1 of FeSO4.

H2O2Absorbance

Color

Pt-Co

removal COD

COD

removal


600 0.200 0.067 0.016 410 93 36 88

700 0.140 0.040 0.011 300 95 32 89

800 0.065 0.021 0.009 150 97 30 90

900 0.012 0.004 0.002 30 99 24 92


7/27/2019 10737529

7/13



2.5 pH) were quite different from each dye (40C and 3.0 pH for RB5, 50C and 3.5

pH for RR).

Considering the methodology explained for Run 1, Runs 24 were performed

in the same context. The results of Run 2, 3, and 4 are shown together in Table 9.

Table 8. Optimum removal conditions for RB5, RR, and their mixture using FOP process.

RB5 RR RR Mixture of RB5RR

Dye concentration (mg L1) 100 100 200 200

COD removal (%) 7086 (86.4)* 95 94 96

Color removal (%) >99 >99 >99 >99

T (C) 40 50 50 30

pH 3.0 (3.5)* 3.5 3.5 2.5

FeSO4 (mgL1) 100 150 250 400

H2O2 (mgL1) 400 300 1,000 800

Molar ratio [FeSO4/H2O2] 0.055 0.11 0.055 0.11

*Maximum efficiency obtained at 3.5 pH.

Table 9. FO process results for the mixture of dyes.

Composition Run 2 Run 3 Run 4

Dye concentration (mg L1) 300 400 100

COD removal (%) 93 94 (96)* 93

Color removal (%) >99 >99 91

T(C) 50 30 50

pH 4 3 (4)* 3

FeSO4 (mgL1) 500 600 200

H2O2 (mgL1) 1,000 1,000 300

FeSO4/H2O2 molar ratio 0.11 0.13 0.15

*Maximum efficiency obtained at 4 pH.

Table 7. The relation between mixing time and color and COD removals for the mixture of

RB5 and RR at 40

C, 3.0 pH, 2 min rapid mixing, 20 min slow mixing time (SM) using

400mgL1 of FeSO4 and 800 mgL1 of H2O2.

AbsorbanceColor

Pt-Co

removal COD

COD

removal

SM (min) 436 nm 525 nm 620 nm Pt-Co (%) (mg L1) (%)

10 0.002 0.001 0.001 99 10 97

15 0.001 0.001 0.001 99 8 96

20 0.003 0.002 0.001 99 15 94

30 0.001 0.001 0.001 99 18 93


7/27/2019 10737529

8/13



As seen from the results, the presence of RB and RY in the mixture of RB5 and

RR (Run 2) changed the optimum oxidation conditions of RB5, RR, and

their mixture as depicted in Table 8. The increase of the dose of FeSO4 was

higher for Run 3 with respect to Run 2. To obtain high COD and color removals

(>90%) the doses of FeSO4 and H2O2 had to be increased up to 500600mg L1

and 1000 mg L1, respectively. However, that increase did not change the molar ratio

of Run 2 and Run 3, although to treat the mixture solution of RB and RY (Run 4)

seemed to be rather difficult with respect to the Run 1, 2, and 3.

It can be concluded from this study that 2 min rapid mixing phase served as

accelerator for formation and the consuming up the radicals in the oxidation reac-

tions resulting in the shortened total reaction time and yielding higher color and

COD removals.

It was observed that increasing the dye concentration improved the floc

structure in the coagulation phase. Increasing the concentration of FeSO4 did not

improve COD removal efficiency significantly, whereas the change of pH affectedsystem performance more effectively. Moreover, absorbance measurements were

helpful for defining the optimum process conditions.

The purpose of the study was to comparatively assess the oxidation

characteristics of a mixture of dyes via FOP. Results of this study indicated the

differences between the combination of dyes. H2O2 requirement seems to be related

to initial COD of the sample. The optimum pH range of 2.54.0 corresponds to the

pH range given for FOP.[14] FeSO4/H2O2 ratios found were also in accordance with

the literature value of 0.09.[17]

CONCLUSIONS

The removal of color and COD in the mixture of RB5, RR, RB, RY azo dyeswas studied by using FOP. A systematic approach with four stages, which are

the determination of concentrations of FeSO4 and H2O2, pH, temperature was

applied to the dye mixtures in the manner of a matrix use. The effect of mixing

time on optimum conditions of FOP was also investigated. The results obtained

from this study explain the Fenton oxidation pattern of reactive dyes in the case

of the mixed use.

FOP performed effectively to remove color and COD at high efficiency (>90%)

of the dye mixtures. It seemed that the dyes used in the mixtures were oxidized

in the sequence RR, RB5, than RB and RY since their addition to the mixtures

(Run 2 and 3) reflected different optimum oxidation conditions. The temperature did

not affect the color removal significantly. 30C may be accepted as an optimum for

the cases studied.

Increasing total dye concentration in the solution required increasing the use ofFeSO4 and H2O2 to remove color and COD content.

The optimum pH changed between 2.54.0 indicating that the addition of RB

and RY caused a shift in pH from 3.0 to 4.0. Whereas the temperature for the

mixtures varied between 30C and 50C.

More than changing FeSO4 concentration, increasing the concentration of H2O2and the change of pH affected system performance significantly.


7/27/2019 10737529

9/13



ACKNOWLEDGMENTS

This work was partially supported by a grant from the ITU Research

and Development Center (Project No. 1989) and Scientific Research Council of

Turkey (_IIC TAG-C 035). The authors gratefully thank Huseyin Selcuk for his helps.

REFERENCES

1. Grau, P. Textile industry wastewater treatment. Water Sci. Technol. 1991,

24, 97103.

2. van der Zee, F.P.; Lettinga, G.; Filed, J.A. Azo dye decolorization by anaerobic

granular sludge. Chemosphere 2001, 44, 11691176.

3. Chung, K.T.; Stevens, S.E.J. Degradation of azo dyes by environmental micro-organisms and helmints. Environ. Toxicol. Chem. 1993, 12, 21212132.

4. Chung, K.T.; Stevens, S.E.J.; Cerniglia, C.E. The reduction of azo dyes by the

intestinal microflora. Crit. Rev. Microbiol. 1992, 18, 175197.

5. Ganesh, R.; Boardman, G.D.; Michelsen, D. Fate of azo dyes in sludges. Water

Res. 1994, 28, 13671376.

6. ONeill, C.; Hawkes, F.R.; Hawkes, D.L.; Esteves, S.; Wilcox, S.J. Anaerobic-

aerobic biotreatment of simulated textile effluent containing varied ratios of

starch and azo dyes. Water Res. 2000, 34, 23552361.

7. Panswad, T.; Luangdilok, W. Decolorization of reactive dyes with different

molecular structures under different environmental conditions. Water Res.

2000, 34, 41774184.

8. Tu nay, O.; Kabdas li, I.; Orhon, D.; Eremektar, G. Color removal from textile

wastewater. Water Sci. Technol. 1996, 34, 916.9. Al-Degs, Y.; Khraisheh, M.A.M.; Allen, S.J.; Ahmad, M.N. Effect of carbon

surface chemistry on the removal of reactive dyes from textile effluent. Water

Res. 2000, 34, 927935.

10. Morais, L.C.; Freitas, O.M.; Goncalves, E.P.; Vasconcelos, L.T.; Beca, C.G.G.

Reactive dyes removal from wastewaters by adsorption on Eucalyptus Bark:

Variables that define the process. Water Res. 1999, 33, 979988.

11. So, C.M.; Cheng, M.Y.; Yu, J.C.; Wang, P.K. Degradation of azo dye Procin

Red MX-5B by photocatalytic oxidation. Chemosphere 2002, 46, 905912.

12. O lmez, T. Color removal from reactive dyebath in textile industry using ozone.

M.Sc. Thesis, 1999; Istanbul Technical University, Institute of Science and

Technology, Istanbul, Turkey (in Turkish).

13. Lin, S.H.; Lai, C.L. Kinetic characteristic of textile wastewater ozonation in

fluidized and fixed activated carbon belts. Water Res. 2000, 34, 763772.14. Kuo, W.G. Decolorizing dye wastewater with Fentons Reagent. Water Res.

2000, 26, 881886.

15. Solozhenko, E.G.; Soboleva, N.M.; Goncharuck, V.V. Decolorizing of azo dye

solutions by Fentons Oxidation. Water Res. 1995, 29, 22062210.

16. Kang, S-F.; Chang, H-M. Coagulation of textile secondary effluents with

Fentons Reagent. Water Sci. Technol. 1997, 36 (12), 215222.


7/27/2019 10737529

10/13



17. Lin, S.H.; Lo, C.C. Fenton process for treatment of desizing wastewater.

Water Res. 1997, 31, 20502056.

18. Park, T.J.; Lee, K.H.; Jung, E.J.; Kim, C.W. Removal of refractory organics

and color in pigment wastewater with Fenton Oxidation. Water Sci. Technol.

1999, 39, 189192.

19. Arslan, I.; Balcioglu, A. Degradation of Remazol Black B Dye and its simu-

lated dyebath wastewater by advanced oxidation processess in heterogenous

and homogeneous media. Color Technol. 2001, 117, 3842.

20. Kang, S-F.; Liao, C-H.; Chen, M-C. Pre-oxidation and coagulation of textile

wastewater by the Fenton Process. Chemosphere 2002, 46, 923928.

21. Gulyas, H. Processes for the removal of recalcitrant organics from industrial

wastewaters. Water Sci. Technol. 1997, 36 (23), 916.

22. Lin, S.H.; Peng, C.F. A continuous fentons process for treatment of textile

wastewater. Environ. Technol. 1995, 16, 693699.

23. Kaptan, D. Toxicity reduction in textile industry wastewater. M.Sc. Thesis,2002; Istanbul Technical University, Institute of Science and Technology,

Istanbul, Turkey (in Turkish).

24. APHA-AWWA-WPCF. Standard Methods for the Examination of Water and

Wastewater; 20th Ed.; Washington DC, USA, 1998.

25. Gahr, F.; Hermanutz, F.; Oppermann, W. OzonationAn important techni-

que to comply with new German Laws for textile wastewater. Water Sci.

Technol. 1994, 30, 255263.


7/27/2019 10737529

11/13

7/27/2019 10737529

12/13

7/27/2019 10737529

13/13

Copyright of Journal of Environmental Science & Health, Part A: Toxic/Hazardous Substances &

Environmental Engineering is the property of Taylor & Francis Ltd 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.

Documents

10737529