350 JSDC VOLUME 115 NOVEMBER 1999

Decolorisation treatments of azo dye waste watersincluding dichlorotriazinyl reactive groups by usingadvanced oxidation method

Ayse Uygur and Ece Kök*

Textile Dept, Faculty of Fine Arts, University of Marmara, Istanbul, Turkey

*Chemistry Dept, Faculty of Science-Literature, University of Marmara, Istanbul, Turkey

Decolorisation treatments of azo dye waste waters, which include dichlorotriazinyl reactive groups,were investigated by using ultraviolet (UV) radiation and hydrogen peroxide at various exposuretimes. Decolorisation time decreased when UV radiation power and hydrogen peroxide concentrationincreased. Colour removal reached 98.0–99.5% by using this method. Some environmentalparameters of decolorised waste water, such as biological oxygen demand (BOD), chemical oxygendemand (COD), total organic carbon (TOC), total inorganic carbon (TIC), total carbon (TC),adsorbable organohalides (AOX), sulphate and chloride, were determined. It was concluded thatTOC, COD and AOX decreased while BOD increased and sulphate ions remained unchanged. Theseresults suggested that the dye molecules were totally destroyed and some of these decompositionproducts were removed as carbon dioxide and water to some degree.

INTRODUCTIONThe discharge of strongly coloured waste water into theenvironment is undesirable and so the effluent fromtextile processes has to be treated before release [1]. Someazo dyes, for example benzidine-based direct dyes, areeasily reduced in waste water to colourless primaryorganic amines, but these are more toxic than the originaldyes. Conventional biological treatments are insufficientfor the decolorisation of textile waste waters, so moreeffective chemical treatment methods have been in-vestigated [2]. Currently, there is no single colour removalmethod that is the optimum in terms of cost and from thepoint of view of technological, environmental andpractical considerations. The most promising methodseems to be the advanced oxidation colour removalmethod, although it is costly. Other oxidation methodsusing sodium hypochlorite, hydrogen peroxide, ozone orultraviolet (UV) radiation have been found ineffective indecolorising various types of waste water. More advancedoxidation methods, employing UV radiation together withhydrogen peroxide, or UV radiation plus ozone, havebeen found quite effective in decolourising waste waterthrough the agency of hydroxyl radicals during oxidation[3]. UV radiation plus hydrogen peroxide was suggestedas a very efficient decolorisation method for azo dyes [4],and the degree of decolorisation was improved withchemical auxiliaries in the dyebath by using this method[5]. None of the decomposition products of azo reactivedyes were found to be environmentally harmful afterdecolorisation with UV radiation plus hydrogen peroxide[6]. This method was carried out with reactive dyes, bothby batch operation and by continuous circulation. Under

similar experimental conditions, continuous operation hasbeen found to be more efficient than batch operation [7].Coloured waste water has also been decolourised byequilibrium peracetic acid or hydrogen peroxide plus UVradiation and equilibrium peracetic acid gave similarresults to that of hydrogen peroxide [8].

In the present study, waste water containing dichloro-triazinyl azo reactive dyes were decolourised by using UVradiation plus hydrogen peroxide, and some environ-mental parameters were determined to highlight proper-ties that are helpful for reuse in dyeing treatments. Thereis inadequate information reported in the literature on thissubject.

EXPERIMENTAL

DyeingThe fabric used was 153 g/m2 knitted cotton. The dyesused were as follows:– Procion Yellow MX-8G (BASF, CI Reactive Yellow 86)– Procion Red MX-8B (BASF, CI Reactive Red 11)– Procion Blue MX-2R (BASF, CI Reactive Blue 4).

Dyeing was carried out at a concentration of 2% owf on5 g fabric samples. In addition, 35 g/l sodium sulphate(anhydrous) was included in the dye liquor. Dyeing wascarried out at 30 °C and this temperature was held for 30min before adding 4 g/l soda ash, and the processcontinued for another 45 min, liquor ratio 20:1. The fabricwas then subjected to the following treatments:

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(a) Rinse, 10 min at 20 °C(b) Rinse, 10–20 min at 40–50 °C(c) Boil, with Kierolon (BASF) detergent for 30 min(d) Rinse, 10 min at 80 °C(e) Rinse, 10 min at 20 °C.

Decolorisation procedureThe waste waters produced were collected and diluted to1 l with deionised water. Following the addition ofhydrogen peroxide at various concentrations, thecoloured waste waters were put into 3.3 ml quartzcuvettes, which were then placed 10 cm from a UV lamp(Philips HPM 17, wavelength range 320–450 nm,adjustable output 550/1000/1500 W) to be decolorisedunder varying powers of UV radiation for different timeperiods. The dye concentrations in coloured anddecolorised waste waters were determined by a UV-VISspectrophotometer (Shimadzu UV 240) at the maximumabsorption wavelength of each dye.

UV radiation at a power of 1000 W was used inpreference to 1500 W for the environmental parameterdeterminations (as the UV equipment lining was notresistant to high temperatures (90 °C) for an extended timeperiod under a power of 1500 W, even though fasterdecolorisation was obtained by using 1500 W).

The environmental parameter determinations such ashydrogen peroxide [9], chemical oxygen demand (COD)and biological oxygen demand (BOD) [10] were carriedout as reported in the literature, using a Hach DR 200direct reading spectrophotometer and a YSI model 54Aoxygenmeter. Other determinations were: total organiccarbon (TOC), total carbon (TC), total inorganic carbon(TIC), all measured using a Shimadzu TOC 500 with anASI 502 automatic sample injector; bonded adsorbableorganohalides (AOX), measured with a Clinico-Syritol 12-IDC-AOX-2; and sulphate, chloride, nitrate and nitriteions, determined with a Dionex conductivity detector – allof which were carried out according to the directions inthe manual for the equipment. Since the presence ofreleased hydrogen peroxide in decolorised waste waterscould be harmful, all environmental parameter determin-ations were carried out after the removal of hydrogenperoxide.

0 6 12 180

10

20

30

40

50

Time, min

Dye

con

cn, m

g/l

0 ml/l0.5 ml/l1 ml/l5 ml/l20 ml/l

Peroxideconcn

Figure 1 Decolorisation of waste waters of Procion Blue MX-2Rreactive dye by using UV radiation of 1500 W and by varying theconcentrations of hydrogen peroxide (35%) at given time intervals

relatively low concentrations of hydrogen peroxide (35%)but decolorisation increased to 70% when higherconcentrations of hydrogen peroxide were utilised in thefirst 3 min of the experiment. Although higherconcentrations gave faster results, it was preferred todecolorise waste waters by using lower concentrations ofhydrogen peroxide with longer exposure to UV radiation,because the hydrogen peroxide released can be harmfulfor experimental determinations. Since lower peroxideconcentrations gave good results, 1 ml/l hydrogenperoxide concentration at 1000 W UV power, which wassafe for the UV equipment, and 21 min were chosen forthe experimental studies and approximately 99%decolorisation was obtained under these conditions.These results suggested that there was a total destructionof dye molecules by advanced oxidation. It is possible toexplain this by the formation of hydroxyl radicals duringUV radiation plus hydrogen peroxide reaction, whichhave a higher oxidation potential than hydrogen peroxidealone. As can be also seen in Figure 1, when thedecolorisation of waste waters was carried out by usingUV radiation alone, the extent of decolorisation obtainedwas between 5 and 22%, depending on the dyes selectedunder these conditions. Another study was also carriedout by using only hydrogen peroxide with no exposure toUV radiation and the extent of decolorisation wasbetween 1 and 19% depending on the dyes selected andthe hydrogen peroxide concentration. The extent and rateof decolorisation increased with the increasing UV power.The dye most resistant to advanced oxidativedecolorisation was Procion Yellow MX-8G.

The UV-VIS spectra of coloured and decolorised wastewaters of Procion Blue MX-2R are given in Figure 2.

As can be seen in Figure 2, dye concentration reached1–2% under the experimental conditions which suggestedthat the total destruction of the dye molecule was possibleand that the dye decomposition products were colourlessafter using an advanced oxidation method.

RESULTS AND DISCUSSION

Investigations on decolorisationThe coloured waste waters of selected dyes weredecolorised by using different powers of UV radiation andby varying the concentrations of hydrogen peroxide atvarious time intervals, in an attempt to optimise theconditions for decolorisation. The results of Procion BlueMX-2R are given in Figure 1.

As can be seen in Figure 1, approximately 50%decolorisation of waste waters was obtained by using

352 JSDC VOLUME 115 NOVEMBER 1999

200 400 600 800Wavelength, nm

Abs

orba

nce

ColouredDecolorised

Figure 2 UV-visible spectra of colored and decolorised waste watersof Procion Blue MX -2R

Environmental parameter determinations in decolorisedwaste watersThe decolorisation of waste waters for environmentalparameter determinations was carried out by using UVradiation at 1000 W plus 1 ml/l hydrogen peroxide (35%)for 21 min; the results are given in Figure 2.

The pH value of blue dye waste water decreased from10.5 to 8.55 following the advanced oxidativedecolorisation procedure. Yellow and red dyes also gavesimilar results, which were in accordance with thosereported in the literature, which indicates that the dyemolecules decompose to organic acids, aldehydes, etc.during oxidative decolorisation, resulting in a decrease inpH values [11].

Since hydrogen peroxide is an oxidising agent and ifreleased may affect the environmental parameterdeterminations, the amounts of hydrogen peroxide indecolorised waste waters were determined [9]. Initially thehydrogen peroxide added was not totally consumedduring the advanced oxidation reactions, with significantamounts remaining in solution.

Ion chromatography was used to determine theamount of sulphate, chloride, nitrite and nitrate ions indecolorised waste waters; the results are given in Table 1.The sulphate ions were not affected by advancedoxidative decolorisation, since the values are within an

experimental error of ±4%, suggesting that sodiumsulphate could be reused.

Chloride ions were also detected in the coloured wastewaters, possibly due to the sodium chloride that had beenadded to the dye formulations. The increase of chlorideions in decolorised waste waters may be explained by theconversion of chloro substituents on the dichlorotriazinerings to chloride ions during the cleavage of the dyemolecules by advanced oxidation.

Nitrite and nitrate ions were not detected in thisexperiment. Therefore it was assumed that the nitrogenatoms present in azo groups and triazine rings were notconverted but may have been released into theatmosphere as nitrogen gas during advanced oxidativedecolorisation. These results are in accordance with thedata reported in the literature concerning the oxidativedecolorisation processes [12].

Certain dyes may contain metals that may show up asfree ions after advanced oxidative decolorisation followingcleavage of the dye molecules. Although azo dyes wereused in this work, tests were carried out to detect anymetal ions released from a catalyst used or from othersources, but none was detected.

The total carbon, the total organic carbon, and the totalinorganic carbon were determined in decolorised wastewaters in order to assess the percentage of decompositionproducts that occurred due to advanced oxidation. Theresults are given in Table 2. Total carbon remainedunchanged and, while there was a 30–40% decrease oftotal organic carbon, there was 50–60% increase of totalinorganic carbon. These results showed that thedecomposition products of the dye molecules were carbondioxide and water in amounts of 30–40% and theremaining part may have decomposed to acids,aldehydes, etc. Since the pH of coloured and decolorisedwaste waters was around 9–10, the carbon dioxideproduced might have remained in solution, or a smallamount might have been absorbed from the atmosphere.

Since dichlorotriazine rings in dye moleculesdecompose to smaller molecules during advancedoxidative decolorisation and the chloro substituents maybe converted to chloride ions or to new AOX, the latterwere determined in the decolorised waste waters; theresults are given in Table 3. AOX decreased by nearly by

Table 1 Concentration of various ions in decolorised waste waters

Sulphate concn Chloride concn Nitrite/nitrate concn

Coloured Decolorised Coloured Decolorised Coloured Decolorisedwaste waste Difference waste waste Increase waste waste

Dye water (mg/l) water (mg/l) (%) water (mg/l) water (mg/l) (%) water water

Procion Yellow MX-8G 2540 2510 +1.1 13.0 16.0 23.2 0 0Procion Red MX-8B 2530 2510 +0.7 14.9 15.5 4.3 0 0Procion Blue MX-2R 2550 2570 –0.5 6.4 7.3 15.2 0 0

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Table 2 TC, TOC, TIC values in decolorised waste waters

TC TOC TIC

Coloured Decolorised Coloured Decolorised Coloured Decolorisedwaste waste Difference waste waste Decrease waste waste Increase

Dye water (mg/l) water (mg/l) (%) water (mg/l) water (mg/l) (%) water (mg/l) water (mg/l) (%)

Procion Yellow MX-8G 148 144 –2.2 98.1 70.1 28.5 47.2 74.1 57.0Procion Red MX-8B 166 157 –5.1 119 76.7 35.5 47.5 77.7 63.6Procion Blue MX-2R 112 113 +0.8 63.0 38.3 39.2 48.5 73.7 52.0

26–38% for selected dyes, pointing to the decompositionof the dye molecules and the removal of some of thedecomposition products. These results are in agreementwith those in the literature for oxidative decolorisation[11].

The coloured waste waters did not have a high BODand since these values might change because of theoccurrence of decomposition products from dyemolecules, the BOD values were determined indecolorised waste waters; the results are given in Table 5.The increase in BOD values of was approximately twicethat for coloured waste waters. These results are inagreement with those in the literature, which suggeststhat more biodegradable products are formed fromorganic compounds during advanced oxidativedecolorisation [14].

CONCLUSIONSAdvanced oxidative decolorisation has proved to be anefficient method for the removing colour from dyehouseeffluents containing azo reactive dyes. Decolorisation of98.0–99.5% was achievable under the experimentalconditions used in the present study. It was also observedthat decolorisation increased with exposure time and thepower of the UV radiation applied. Depending on thecolour of the dyes, the decrease in chemical oxygendemand (COD) was between 26–38%, and the decrease ofthe total organic carbon (TOC) was between 28–39% afteradvanced oxidative decolorisation, suggesting thedecomposition of dye molecules to carbon dioxide, waterand colourless smaller molecules. There was an obviousincrease in the biological oxygen demand (BOD) values,suggesting the production of more biodegradableproducts during advanced oxidation. These results showthat the use of advanced oxidative decolorisation isbeneficial before biological treatments. After the removalof released hydrogen peroxide and the decompositionproducts, the decolorised waste water is of a reusablequality for dyeing. Sodium sulphate present remainedunchanged and therefore of a reusable quality.

This subject needs further investigations for itsapplication to industry, including a study of thedecolorisation and the reuse of different types of textilewaste waters. It has been said that the textile dyeing andfinishing processes of the 21st century must produce zero

Table 3 AOX values in decolorised waste waters

Coloured Decolorised AOXwaste waste decrease

Dye water (µg/l) water (µg/l) (%)

Yellow 40.0 21.2 47.0Red 54.0 28.0 48.2Blue 278a 12.4 95.5a

a Since AOX value of blue dye waste water was differentfrom yellow and red dyes, it was tested three times;these results were 340, 320, 278 µg/l successively

Table 4 COD values of decolorised waste waters

Coloured Decolorised CODwaste waste decrease

Dye water (mg/l) water (mg/l) (%)

Yellow 145 104 28.4Red 145 107 26.6Blue 157 100 38.2

Table 5 BOD values of decolorised waste waters

Coloured Decolorised BODwaste waste increase

Dye water (mg/l) water (mg/l) (%)

Yellow 20 56 180Red 20 56 180Blue 25 63 152

50% for both yellow and red dyes, and by 95% for the bluedye following the advanced oxidative decolorisation. Ithas been suggested in the literature that AOX remainedunchanged after oxidative decolorisation [12]. Theseresults also demonstrate the superiority of advancedoxidative decolorisation to oxidative decolorisation.

Since smaller molecules were produced during theadvanced oxidation, the COD in decolorised waste waterswas also determined. The results of these experiments aregiven in Table 4. The decrease in COD values was between

354 JSDC VOLUME 115 NOVEMBER 1999

waste. Although it still has cost drawbacks, the mostpromising decolorisation method by this definition is anadvanced oxidative method. Hopefully furtherinvestigations into the reusability of waste water and anysodium sulphate it contains will eliminate thesedrawbacks. Our research will continue into the reuse ofdecolorised waste water containing inorganic salts, in anattempt to decrease the treatment costs.

* * *

The authors would like to thank the Research Foundationof Marmara University and the Association of TextileDyeing and Finishing Manufacturers of Turkey for theirfinancial support. Furthermore, the authors would like tothank Prof. Dr Adnan Aydin for his academic assistanceand BASF for supplying the dyes.

REFERENCES 1. S H Lin and C H Lin, Water Res., 27 (12) (1993) 1743. 2. J Watson, Text. Environment, (1991). 3. A Uygur, J.S.D.C., 113 (1997) 211. 4. S Hung-Yee and H Ching Rang, Amer. Dyestuff Rep., 84 (8) (1995)

30. 5. Y M Slokar, A Majcen-Le Marechal and T Taufer, Tekstilec, 39 (3/4)

(1996) 53. 6. A Majcen Le Marechal, Y M Slokar and T Taufer, Tekstilec, 38 (10)

(1995) 276. 7. C G Namboodri and W K Walsh, Amer. Dyestuff Rep., 85 (3) (1996)

15. 8. K Poulakis, E Bach and E Schollmeyer, Textilveredlung, 32 (3/4)

(1997) 74. 9. E Dölen, Analitik Kimya-Volumetrik Yöntemler, (1988).10. L F Clesceri, A E Greenberg and R R Trussel, Standard methods for

the examination of water and waste water (1989).11. C G Namboodri, W S Perkins and W K Walsh, Amer. Dyestuff Rep.,

83 (3) (1994) 17.12. G Schultz, H Herlinger, F U Gahr and T Lehr, Textil Praxis, 47 (11)

(1992) 1055.13. B Jones, R Sakaji and C Daughton, Water Res., 19 (1985) 1421.14. E Gilbert, Water Res., 22 (1) (1988) 123.

ERRATUM

Colour – it’ll all come out in the wash!, Geoff Bevan, J.S.D.C., 115 (May/June 1999) 151. The author has pointedout that Table 1 should be as follows:

Synthesis and application of an azo dye containing a β-sulphatoethylsulphonyl and a dimercaptotriazinylgroup: an attempt to achieve 100% fixation to cellulose, by A H M Renfrew and M Clarkson, J.S.D.C., 115(Sept 1999) 280.1. The correct forms for structures 3 and 5 should be as follows.

HN

NH

SO3Na

NH2

N N

N

SO3Na

CI

CI

3

O

O S NN N

NHHN

HN

N

O OCH3

SNaO3SO

5

S

2. In Scheme 1, the back reaction should be labelled k–2.

Table 1 Correlation between bleach fading of dyed fabrics in UK-TO and multiple machinewashes (MMW)

Cellulosics UK-TO MMW Correlation Comments

Sulphur ± after treatment Fail Fail Good Bleach sensitiveVats Pass Pass Good Low bleach sensitivityAzoics Fail Fail Good Bleach sensitiveDirects ± after treatment Good Dependent on after treatmentReactives Good Dependent on dye structure