Comparative Evaluation of Various Advanced Oxidation Processes for the Treatment of Textile Industry Effluents

3 (1), 2009, 149 - 160

©BEYKENT UNIVERSITY

Comparative Evaluation of Various Advanced

Oxidation Processes for the Treatment of Textile

Industry Effluents

Selda YIGIT, Aslı COBAN, Goksel DEMIR

Bahcesehir University, Faculty of Engineering, Environmental Engineering Department, 34349, Besiktas-Istanbul/Turkey

selda.yigit@ bahcesehir.edu.tr asli.coban@bahcesehir.edu.tr goksel.demir@bahcesehir.edu.tr

Received: 16.02.2009, Revised: 20.02.2009, Accepted: 23.02.2009

Abstract

Treatment of textile industry effluents is extremely difficult due to their high content of color and recalcitrant organic compounds. However, advanced oxidation is a reasonable treatment alternative for this type of wastewater. In this paper, applicability of advanced oxidation processes on textile industry effluents was discussed and it is based on five major types of advanced oxidation. These processes are Fenton-Photo Fenton, O3/H2O2, O3/UV,

H2O2/UV and TiO2 photocatalysis (TiO2/UV). As a result of this literature

review, Fenton - Photo Fenton process is concluded to be favorable than other advanced oxidation processes because of its efficiency and operation simplicity. Nonetheless, all of these processes are suitable for textile wastewater treatment with various advantages and disadvantages on the treatment.

Keywords: Fenton, Photo-fenton, , O/H2O2, O^UV, H2O2/UV, TiO2/UV,

textile wastewater

Özet

Tekstil endüstrisi atıksularının arıtımı, yoğun renk ve kararlı organik bileşik içeriklerinden dolayı oldukça zordur. Fakat, ileri oksidasyon metotları bu tip atıksular için uygun bir arıtım alternatifidir. Bu makalede, ileri oksidasyon proseslerinin tekstil endüstrisi atıksuyu arıtımı için uygulanabilirliği tartışılmış ve özellikle 5 temel ileri oksidasyon yöntemi baz alınmıştır. Bunlar Fenton-Foto Fenton O3/H2O2, O3/UV, H2O2/UV ve TiO2/UV prosesleridir. Literatür

araştırmaları sonucunda, bütün bu proseslerin tekstil atıksuları için uygulanabilir olması ve hepsinin bazı farklı avantajları ve dezavantajları olmasına karşın Fenton-Foto Fenton prosesi verim ve işletim kolaylığı açısından diğer proseslerden daha ön plana çıkmıştır.

1. Introduction

The textile industry is one of the major and fastest developing industrial sectors in the world. This industry produces large quantities of effluent with varying composition depending on the type of processes employed [13]. Among all industrial sectors, textile industry wastewater is rated as the most polluting one with respect to volume and effluent composition. The wastewater generated by different production steps ( e.g. desizing, scouring, washing, dyeing, bleaching, mercerizing, etc.) has high pH and temperature (Table 1). It also contains high concentration of organic matter, colors, toxic substances, inhibitory compounds, surfactants, chlorinated compounds, salts and alkalinity (Table 2) [28].

Table 1. Major Pollutant Types in Textile Wastewaters and Their Origin [11]

Pollutants Major chemical t y p e s

Main p r o c e s s of origin Organic lo.nl S t a r c h e s , e n z y m e s , f a t s , D e s i z i n g g r e a s e s . w a x e s , s u r f a c t a n t s S c o u r i n g W a s h i n g A c e t i c a c i d D y e i n g Colour D y e s , s c o u r e d w o o l i m p u r i t i e s D y e i n g S c o u r i n g Nutrients (N.P) A m m o n i u m s a l t s , u r e a , p h o s p h a t e -b a s e d -b u f f e r s a n d s e q u e s t r a n t s D y e i n g

pH and salt effects N a O H , m i n e r a l / o r g a n i c a c i d s , S c o u r i n g s o d i u m c h l o r i d e , s i l i c a t e , s u l p h a t e , D e s i z i n g c a r b o n a t e B l e a c h i n g M e r c e r i s i n g D y e i n g N e u t r a l i s a t i o n Sulphur S u l p h a t e , s u l p h i d e a n d h y d r o s u l p h i t e s a l t s , s u l p h u r i c a c i d D y e i n g Toxicants H e a v y m e t a l s , r e d u c i n g a g e n t s , D e s i z i n g o x i d i z i n g a g e n t s , b i o c i d e s , B l e a c h i n g q u a t e r n a r y a m m o n i u m s a l t s D y e i n g F i n i s h i n g Refractory organics S u r f a c t a n t s , d y e s , r e s i n s , S c o u r i n g s y n t h e t i c s i z e s , c h l o r i n a t e d D e s i z i n g o r g a n i c c o m p o u n d s , c a r r i e r o r g a n i c B l e a c h i n g s o l v e n t s D y e i n g W a s h i n g F i n i s h i n g

Various physical, chemical and biological methods are used in the treatment of textile industry wastewater. Biological degradation of different dyestuffs of

textile industry has been widely studied both aerobic and anaerobic cultures [7]. Nevertheless, the degradation of such compounds is generally very slow. On the other hand, chemical treatment systems are usually more effective with respect to biological processes in the treatment of textile wastewater. Advanced oxidation is a potential alternative method that is used in the treatment of textile industry wastewater for many years, to decolorize and reduce recalcitrant organics from textile dyeing and finishing effluents [4]. Advanced oxidation processes with homogeny and heterogenic advanced oxidation processes are used efficiently in the removal of color, COD and TOC [8, 20].

Ozonation and UV irradiation which compose the basis of advanced oxidation, are capable of treating the wastewater in their single use. However, when they are coupled with other processes (such as O3/UV, O3/H2O2), the efficiencies of the treatment increase significantly. Therefore, these heterogenic oxidation processes have become important recently. The most known and efficient advanced oxidation processes are the heterogenic oxidation methods such as Fenton-Photo fenton, O3/H2O2, O3/UV, H2O2/UV and TiO2

photocatalysis(TiO2/UV) with various advantages and disadvantages.

Table 2. The characteristics of the composite textile industry [2]

Parameters

Values

pH

7.0-9.0

Biochemical Oxygen Demand (mg/L)

80-6,000

Chemical Oxygen Demand (mg/L)

150-12,000

Total Suspended Solids (mg/L)

15-8,000

Total Dissolved Solids (mg/L)

2,900-3,100

Chloride (mg/L)

1,000-1,600

Total Kjehdahl Nitrogen(mg/L)

70-80

Colour(Pt-Co)

50-2,500

This study aims to demonstrate the advantages, disadvantages and applicability to the industry of the advanced oxidation processes for the treatment of textile industry effluents while giving brief important process descriptions. In the caption of this work the following Advanced Oxidation Process (AOP) technologies will be discussed;

• Fenton and Photo-fenton Processes • Hydrogen Peroxide/Ozone (O3/H2O2)

• Ozone/Ultraviolet Irradiation (O3/UV)

• Hydrogen Peroxide/Ultraviolet Irradiation (H2O2/UV)

2. Processes

2.1. Fenton and Photo-Fenton Processes

Fenton process employs iron ions (Fe2+) and hydrogen peroxide (H2O2), which

produce hydroxyl radicals (OH.). When hydrogen peroxide and Fe2+ ions are

added to an aqueous solution containing organic compounds in a strong acidic medium, the reactions will occur as follows [14, 34]:

H2

O2 + Fe2+ ^ Fe3+ + OH- + OH • (Eq.1)

O H • + R H ^ H2O + R • RH : Organic matter (Eq.2)

R • + Fe3+ ^ R + + Fe2+ (Eq.3)

R + + H2O ^ R O H + H + (Eq.4)

This is a very simple way of producing OH' radicals, neither special reactants nor special apparatus are being required. This reactant is an attractive oxidative system for wastewater treatment due to the fact that iron is very abundant and non toxic element and also hydrogen peroxide is easy to handle and environmentally safe.

Another advanced oxidation method is Photo-Fenton process that has become significant in recent years. In this process, first Fe2+ and H2O2 reacts to produce

OH' radicals which is very powerful chemical oxidant.

Fe2 + + H2O2 ^ Fe3+ + OH- + O H (Eq.5)

application of UV irradiation wastewater as follows [9];

Fe3+ + H

O + hv ^ Fe2+ + H + + OH • (Eq.6)

Photo-Fenton process oxidizes organic matter in very short time to harmless end products and the complete oxidation takes approximately 2.5-5 minutes. [9] In contrary, when oxidation take places with only Fenton reagent or only UV/H2O2 processes, the complete degradation time will be longer up to 120

minutes.

As a result, when we compare Fenton and Photo-Fenton reactions with the same H 2 O 2 and Fe2+ dosages, in Photo-Fenton reactions with more OH.

radicals formation is observed and it is favored the treatment of organic matter. The use of zero-valent iron in a Fenton-type process for the degradation of pollutants, like dyes, has become attracted significant interest recently. Under acidic conditions, the corrosion of the metal generates ferrous iron and leads to Fenton reactions. The process is called as Advanced Fenton Process (AFP),

because it has several advantages over the conventional system. First, using iron powder instead of iron salts results in prevention of unnecessary loading of aquatic system with counter anions [18]. Other important advantage is that the concentration of ferrous and ferric ions in wastewater, which is treated by AFP, is significantly lower in comparison to classic Fenton's process [21]. In addition to these, the sludge production in AFP process is quietly less than the classic process [34].

For alkaline solutions, the fenton oxidation process is not applicable, because when pH is greater than 8, Fe (II) ion begins to form flocks and precipitates. Also, H 2 O 2 is unstable and may decompose to oxygen and water, and it loses

its oxidation ability. Nearly all of the studies show that pH between 2-3 is most effective in the degradation reactions. According to Acarbabacan et al., the highest removal, by Fenton Process can be obtained at the pH value of 3. When worked with the pH values of 6 and 9, continuously pH adjustment was needed.

In literature, there are many studies about color and COD removal from wastewater using Fenton process. Lin and Lou reported the optimum conditions for this process as pH=3 at 30oC, the ratio of FeSO4/H2O2 is 1/5 and they have obtained high color and COD removal at the end of the 120 minutes treatment period. Another study is performed by Kang et al, where they noted that with very low concentrations of H2O2 and iron salts they reached 90% color removal at the end of the 5 min reaction time. However, they also noted that to provide high COD removal rates, large amounts of H 2 O 2 and iron salts

were needed for treatment. In addition, Fenton process is also has a capacity to treat strongly persistent organic compounds as reported by Tanircan et al. and it needs only very small amount of Fe2+ ions for this purpose.

As a result, Fenton and Photo Fenton reactions were compared, with the same

H 2 O 2 and Fe+2 dosages, Photo-Fenton reactions is more efficient in the treatment due to its ability to form more OH' radicals [9]. Furthermore the reaction time of Photo-Fenton process is more shorter than fenton process's. It can be decreased with the optimization of operational conditions [32].

2.2. Hydrogen Peroxide/Ozone

Simultaneous application of H 2 O 2 and O 3 to wastewater accelerates the

decomposition of ozone and enhances production of the hydroxyl radical. The mechanism of hydroxyl radicals production in O3/H2O2 process is as follows [4, 33]:

H

O

(Eq.7)

U H+

HO -+ O

^ O

+ HO

HO

-+O

'+O

'

HO

•«• H

+ O2 •

O 2 • + O3 ^ O 2 + O3^ (Eq.11)

O3 + H H O 3

ho

'^ HO •+ O

2O3 + H

O

^ 2HO• + 3O

Rosenfeldt et al. (2006) tested two advanced oxidation processes (H2O2/UV,

H2O2/O3) at different test conditions and they reported that H2O2/O3 process is

a more energy efficient technology for production of OH' radical. When a large amount of contaminant oxidation is required, their results indicate that at low peroxide levels, and high OH' radical exposure, the UV process can be comparable or less energy intensive than the H2O2/O3 processes. However, in

most situations, the ozone process will require less energy to produce OH' radicals.

The addition of both hydrogen peroxide and ozone to wastewater accelerates the decomposition of ozone and enhances production of the hydroxyl radical. Arslan et al. (1999) documented that H2O2/O3 treatment of synthetic dyehouse

wastewater highly depended on the pH of the effluent. According to Arslan et al. (1999), ozone absorption increased with increasing pH value. 74 % ozone absorption noted at pH=11.5, however at the same H2O2 dose and pH=2.5

ozone absorption was 11 %. At pH values greater than 10.5, additional efforts in order to promote OH' radical formation by the addition of H 2 O 2 is quite difficult [4].

Also, Arslan et al. (1999) reported the presence of an optimum oxidant dose of only around 1mM H2O2 for highest decolorization rate and maximum

dissolved organic carbon (DOC) and UV254nm removals at a pH value of 7.5. In

addition that they were indicated that beyond certain hydrogen peroxide concentration there is no further enhancement of the treatment performance [4].

2.3. Ozone/Ultraviolet Irradiation (O3/UV)

Ozonation can not completely oxidize most organic matter into CO2 and H2O, however UV photolysis of O 3 in water yielded H 2 O 2 , which in turn reacted with UV radiation or O3 to form OH radicals. The use of UV irradiation to

produce hydroxyl radicals with ozone occurs by the following reaction [15]:

O3 + hv + ^ H2O2 + O2 (X<300nm) (Eq.15)

H2

O2 + hv ^ 2OH• (Eq.16)

2O3 + H

O2 ^ 2 O H • + 3O2 (Eq.17)

As the above reactions illustrate, photolysis of ozone generates hydrogen peroxide and, thus O3/UV process involves all of the organic destruction mechanism present in H2O2/O3 and H2O2/UV advanced oxidation processes.

For highly colored textile industry effluents, O3/UV process is not an efficient method, because UV light is highly absorbed by dyes and quite low amount of OH. radical can be produced to decompose dyes, although ozone can be

photodecomposed into OH. radicals to improve the degradation of organics.

For this reason, the same color removal efficiencies could be expected using

O3 and O3/UV [27].

In general, ozone itself absorbs UV light, competing with organic compounds for UV energy. However, O3/UV treatment reported to be more effective

compared to ozone alone in terms of COD removal [5]. They indicated that using O3/UV process, high COD removal would be provided under basic conditions such as a pH value of 9.

2.4. Hydrogen Peroxide/Ultraviolet Irradiation (H

O

/UV)

Hydrogen peroxide is a powerful chemical oxidant. Photolysis of aqueous H 2 O 2 provides a powerful means for complete or partial oxidation of organic pollutants in aqueous media. Photolysis of one mole H 2 O 2 under UV-irradiation produces two moles of OH. radicals:

H

0

OH• (X<300nm) (Eq.18)

For heavily polluted effluents, high UV doses and H 2 O 2 concentrations are required, so this reduces the feasibility of the process for practical use. On the other side, H2O2 at excessively high doses also acts as a radical scavenger;

H2

O2 + 2 OH * ^ HO

* + H 2

O (Eq.19)

H2

O2 + 2 OH * ^ H 2

O + O

* + H + (Eq.20)

The efficiency of UV/H2O2 oxidation process was mainly affected by the H2O2

effluent. The optimum H 2 O 2 concentration in the UV-light assisted H 2 O 2 process for decolorization rate of effluent was 50 times higher than that for H2O2/O3 process. [4] For this reason, the H2O2/UV process is more effective in

the degradation of organic compounds than ozonation and H2O2/O3 treatment,

whereas O 3 alone or combined with H 2 O 2 destroys the chromophore groups of dye molecules more rapidly.

Oxidation of the textile wastewaters with hydrogen peroxide alone has been reported ineffective both in acidic and basic conditions, [22] however under UV irradiation, H 2 O 2 are photolyzed to form hydroxyl radicals (2OH.) which

react with refractory organic contaminants [10]. The optimum H2O2 dose for

the H2O2 /UV process is nearly 25-50 times higher than for the H2O2/O3

process. Maximum decolorization rate reached was 0.106 min-1 for the

H2O2/UV process. UV catalyzed H 2 O 2 process was suitable for the effective

removal of color more quickly [4]. Moreover, the H2O2/UV process is more

sensitive to the scavenger role of carbonate at higher pH values, on the other hand temperature do not have a significant effect on color removal [3].

2.5. Photocatalysis (TiO2/UV)

Among advanced oxidation processes, TiO2 photocatalysis has a great potential for the removal of organic pollutants from wastewaters, however there is no full scale application of photocatalysis process because of its low oxidation rate. The hydroxyl radical is mainly responsible for the degradation of organic matters in photocatalysis reaction. The reaction mechanism is as follows [35, 25]:

When TiO2 suspensions are irradiated, electrons are excited from the valence band to the conduction one, generating positive holes and electrons:

TiO2 + hv ^ e

First step of oxygen reduction; the oxidation state of oxygens passes from 0 to -1/2:

O2 + e O 2 ( E q . 2 2 )

Neutralization of OH- groups by photoholes that produces OH. radicals:

( H2O O H ++ OH-) + hv ^ H ++ OH' (Eq.23)

Oxidation of the organic reactant via successive attacks by O H radicals:

R + O H R ' + H

Direct oxidation by reaction with holes:

R + h+ ^ R+ ^ degradation products (Eq.25)

The advantage of using TiO2 as photocatalyst lies in its capability to degrade toxic organic compounds, to reduce metallic ions, to improve the

in solution or in solid mixtures . Its basic efficiency can be enhanced by doping.

As discussed by Pekakis et al. (2006), TiO2 photocatalysis has received

considerable attention for water and wastewater treatment [23, 24]. Photocatalysis with TiO2 is an emerging wastewater treatment technology that

has many significant advantages. Some of these advantages are the lack of mass transfer limitations, operation at ambient conditions and the possible use of solar irradiation. The catalyst is commercially available in different crystalline forms and particle characteristics, non-toxic and photochemically stable. This process can achieve decolorization and reduce significantly the organic load of textile industry effluents [17, 24]. However, most of the studies reported in the literature deal with synthetic textile effluents or solutions of specific textile dyes and there are only very few literature reports studying for real textile wastewater degradation by photocatalysis [6, 12, 26].

Intensive researches are carried out worldwide to obtain modified TiO2 with broader absorption spectrum and characterized by higher quantum yield. In spite of the important efforts dedicated for the study of photocatalytic processes, there are no indications in the literature for their application on the industrial scale [3].

3. Conclusions

For preserving natural ecosystems and human well-being, natural ecosystems and environmental flows need to become an internal part of land and water management planning, decision-making and implementation processes. In this situation, limited availability of high quality water supplies is forcing the implementation of in process water saving measures and advanced wastewater treatment for water recycling. In the same time, decreasing availability of high quality water supplies is leading to use some different processes to save water and treat wastewater using advanced wastewater treatment for water recycling. Advanced oxidation processes represent a powerful mean for the removal of refractory organic pollutants and color from wastewater. By combining ozone, hydrogen peroxide and UV, different advanced oxidation process techniques have been developed that allows solving the specific problems with the most appropriate technique.

In this paper, Fenton or Photo-Fenton process was found favorable than other advanced oxidation processes because of its efficiency and operation simplicity. The use of zero-valent iron powder instead of iron salts in a Fenton-type process for the degradation of pollutants can be suggested as an emerging alternative due to its advantages over the classic Fenton system such as quietly less sludge production than conventional process. However, all the processes that are discussed in this paper, have different abilities to treat textile industry effluents with varying removal efficiencies.

References

[1] Acarbabacan, S., Vergili, I., Kaya, Y., Demir, G., Barlas, H.; Removal of color from textile wastewater containing azodyes by Fenton's reagent, Fresenius Environmental Bulletin (2002), 840-843.

[2] Al-Kdasi, A., Idris, A., Saed, K., and Guan, C.T.; Treatment of textile wastewater by advanced oxidation processes, A review, Global Nest, the Int J. (2004), 6,3, 222-230.

[3] Andreazzi, R., Caprio, V., Insola, A., and Manotta, R.; Advanced oxidation processes (AOP) for water purification and recovery, Catalysis Today (1999), 53, 51-59.

[4] Arslan, I., Bakicioglu, I.A., and Tuhkanen,T.; Advanced oxidation of synthetic dyehouse effluent by O3, H2O2/O3 and H2O2/UV processes, Env.Tech.(1999),20, 921-931.

[5] Azbar, N., Yonar, T. and Kestioglu, K.; Comparison of various advanced oxidation processes and chemical treatment methods for COD and color removal from a polyester and acetate fiber dying effluent, Chemosphere (2004), 55, 35-43.

[6] Balcioglu, I.A. and Arslan, I.; Application of photocatalytic oxidation treatment to pretreated and new effluents from Kraft bleaching process and textile industry, Environ. Pollut. (1998), 103,261.

[7] Bali,U. and Karagözlü, B.; Performance comparison of Fenton process, ferric coagulation and H2O2/pyridine/Cu(II) system for decolorization of removal turquoise blue G-133, Dyes and Pigments (2007), 74, 73-80.

[8] Chen, G.H., Lei, L.C., Hu, X.J. and Yoe, P.L.; Kinetic study into the wet air oxidation of printing and dying wastewater, Sep. Purif. Technology (2003), 31, 1, 71-76.

[9] Cokay, E. and Sengul, F.; Treatment of toxic pollutants by advanced oxidation processes, DEU Engineering Faculty, Science and Engineering Journal (2006), 8, 2, 1-9.

[10] Crittenden, J.C., Hu, S., Hand, D.W. and Green, S.A.; A kinetic model for H2O2/UV process in a completely mixed batch reactor, Water Research (1999), 33, 2315-2328.

[11] Delee, W., O'Neill, C., Hawkes, F.R., and Pinheino, H.M.; Anaerobic treatment of textile effluents: A review, J. Chem. Technol. Biotechnol. (1998), 73, 323-325.

[12] De Manaes, S.G., Freine, R.S. and Duran, N.; Degradation and toxicity reduction of textile effluent by combined photocatalytic and ozonation processes, Chemosphere (2000), 40,369.

[13] EPA, Textile processing industry EPA-625/778-002, US. Environmental Protection Agency, Washington (1978).

[14] Gonder, Z.B. and Barlas, H.; Removal of color and COD from coloured wastewater using Fenton Process, MBGAK(2005), Istanbul.

[15] Gong, J., Liu, Y., Sun, X.; O3 and UV/O3 oxidation of organic constituents of biotreated municipal wastewater, Water Research (2008), 42, 1238-1244.

[16] Kang, S., Liao, C. and Chen, M.; Preoxidation and coagulation of textile wastewater by the Fenton Process, Chemosphere (2002), 46, 923-928.

[17] Konstantinou, I.K. and Albanis, T.A.; TiO2-assisted photocatalytic degradation of azodyes in aqueous solution: Kinetic and mechanistic investigations, a review, Appl. Catal. B: Environ. (2004), 49,1-4.

[18] Kusic, H., Bozic, A.L., Koprivanac, N.; Fenton type processes for minimization of organic content in coloured wastewaters. Part I: Process optimization, Dyes and Pigments (2007), 74, 380-387.

[19] Lin, S.H. and Lou, L.C.; Fenton process for treatment of desizing wastewater, Water Research (1997), 31, 2050-2056.

[20] Lin, S.H., and Lai, C.L.; Kinetic characteristics of textile wastewater ozonation influidized and fixed activated carbon beds, Water Research (2000), 34, 3, 763-772. [21] Lucking, F., Koser, H., Jank, M. and Ritter, A.; Iron powder, graphite and activated carbon as catalysts for the oxidation of 4-chlorophenol with hydrogen peroxide in aqueous solution, Water Research (1998), 2607-2617.

[22] Olcay, T., Isik, K., Gulen, E., and Derin, O.; Color removal from textile wastewaters, Water Science and Technology (1996), 34, 9-11.

[23] Oppenlander, T.; Photochemical Purification of water and air, Wiley-VCH, Weinheim, Germany (2003).

[24] Parsons, S.; Advanced oxidation processes for water and wastewater treatment, IWA Publishing, Cornwell, UK (2004).

[25] Pekakis, A.P., Xekoukoulatakis, N.P. and Mantzavinos, D.; Treatment of textile dyehouse wastewater by TiO2 photocatalysis, Water Research (2006), 40, 1276-1286. [26] Penalta-Zamara, P., De Manaes, S.G., Pellegrini, R., Freine, Jr. M., Reyes, J., Mansilla, H. and Duran, N.; Evaluation of ZnO, TiO2 and supported ZnO on the photoassisted remediation of black liquor, cellulose and textile mill effluents, Chemosphere (1998), 36, 2119.

[27] Perkowski, J. and Kos, L.; Decolouration of model dyehouse wastewater with advanced oxidation processes, Fibres and Textiles in Eastern Europe, 11, 67-71. [28] Rodriguez, M., Sarria, V., Esplugas, C., Pulgarin, C.; Photo-fenton treatment of a biorecalcitrant wastewater generated in textile activities: biodegradability of the photo treated solution, Journal of photochemistry and photobiology, A: Chemistry (2002), 151, 129-135.

[29] Rosenfeldt, E.J., Linden, K.G., Canonica, S., Gunten, U.; Comparison of the efficiency of OH radical formation during ozonation and the advanced oxidation processes O3/H2O2 and UV/H2O2, Water Research (2006), 40, 3695-3704. [30] Sheng H.L. and Chi M.L.; Treatment of textile waste effluents by ozonation and chemical coagulation, Water Research (1993), 27, 1743 - 1748.

[31] Tanircan, N., Barlas, H., Demir, G., Bayat, C.; Advanced chemical oxidation of monolinuron by using Fenton's reagent and H2O2/UV system,Proceedings for 1st

inernational workshop on environmental quality and environmental engineering in the middle east region, (1998), Konya-Turkey.

[32] Yang, M., Hu, J., Ito, K.; Characteristics of Fe2+/H2O2/UV oxidation process, Environ. Technol. (1998), 19, 183-191.

[33] Ying-hui, Y., Jun, M., Yan-Jun, H.; Degradation of 2,4-dichlorophenoxyacetic acid in water by ozone-hydrogen peroxide process, Jpurnal of Environmental Sciences(2006), 1043-1049.

[34] Zhang, H., Zhang, J., Zhang, C., Liu, F., Zhang, D.; degradation of C.I. Acid orange 7 by the advanced fenton process in combination with ultrasonic irradiation, Ultrasonics Sonochemistry (2008).

[35] Zou, L. and Zhu, B.; The synergistic effect of ozonation and photocatalysison color removal from reused water, Journal of Photochemistry and Photobiology, A:Chemistry (2008), 196, 24-32.