2003_i.arslan-alaton_the effect of pre-ozonation on the biocompatibility of reactive dye...

8/10/2019 2003_I.arslan-Alaton_The Effect of Pre-ozonation on the Biocompatibility of Reactive Dye Hydrolysates

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The effect of pre-ozonation on the biocompatibility of

reactive dye hydrolysates

Idil Arslan-Alaton *

Faculty of Civil Engineering, Department of Environmental Engineering, Istanbul Technical University,

34469 Maslak, Istanbul 80626, Turkey

Received 26 August 2002; received in revised form 18 February 2003; accepted 18 February 2003

Abstract

Pre-ozonation of 14 different reactive dyestuff hydrolysates at alkaline pH was investigated to assess possible re-

lationships between ozone transfer efficiency, first order decolourization kinetics, release of initially complexed heavy

metals and relative changes in the biodegradability of the partially oxidized dye waste samples. Biocompatibility of the

raw (untreated) and ozonated dye hydrolysates was comparatively tracked through specific oxygen uptake rate mea-

surements from which the respirometric inhibition of biological activated sludge imparted by raw and ozonated reactive

dye wastewater with respect to synthetic domestic wastewater was determined. It could be demonstrated that pre-

liminary ozonation of reactive azo dyes increases their biological compatibility more significantly than formazan copper

complex, copper complex azo and phythalocyanine dyes as a consequence of heavy metal release associated with the

cleavage of associated chromophoric groupings right at the initial stages of pre-ozonation.

2003 Elsevier Science Ltd. All rights reserved.

Keywords: Dyehouse effluent; Reactive dye hydrolysates; Ozonation; Biodegradability; Respirometric activity inhibition; Specific

oxygen uptake rate

1. Introduction

Textile industry dyes are intentionally designed to

remain photolytically, chemically and biochemically

stable and thus are usually not amenable to biodegra-

dation (Pagga and Brown, 1986). Reactive dyes are ofparticular interest to the environmental engineer and

scientist due to the following reasons: First, reactive dyes

represent an integral market share (almost 45% of all

textile dyes produced annually are belonging to the fiber

reactive class) as a consequence of an intensive use of

cellulose and viscoserayon fibers. Second, these dyes

have very poor fixation rates (typically not exceeding

75%) ending up in highly coloured dye-bath effluents

whose treatment is inadequate in conventional waste-

water treatment plants (Easton, 1995). Third, the reac-

tive dyeing process is of special concern, where in the

average 10 times more water is consumed for the prep-

aration, dyeing, washing and rinsing stages than fordyeing with other dye types (acid, disperse dyes etc.).

Consequently reactive dyes are found in the wastewater

at higher concentrations than other dye classes and

mainly in their spent, hydrolysed form (Easton, 1995).

Due to their high water solubility and low molecular

weight, they rather poorly adsorb on biomass or acti-

vated carbon, pass through the aerobic treatment sys-

tem and may impart toxicity under anoxic (reductive)

conditions if converted to their corresponding aro-

matic amino forms or other biotoxic metabolites (Reife

et al., 1998). Although advanced destructive treat-

ment methods such as ozonation, photochemical or

Chemosphere 51 (2003) 825833

www.elsevier.com/locate/chemosphere

* Tel.: +90-212-285-65-76; fax: +90-212-285-65-87.

E-mail address: [email protected](I. Arslan-Alaton).

0045-6535/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0045-6535(03)00231-5
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photocatalytic oxidation are relatively expensive, many

European countries are forced to reduce colour in dye-

house effluent to the corresponding discharge limit value

being set by their current legislations (Gaehr et al., 1994)

using the above-mentioned processes.

Rather than complete mineralization to inorganic

salts, CO2 and water, the purpose of ozonation is topre-condition recalcitrant industrial wastes to remove

or at least to reduce their inert fraction. Ozone is also

known to be very effective in removing colour caused by

water soluble dyes, particularly fiber acid and reactive

dyes (Snider and Porter, 1974; Peralta-Zamora et al.,

1988). However, ozonation has proven to be rather in-

efficient for the reduction in chemical oxygen demand

(COD) or total organic carbon (TOC), usually not ex-

ceeding 50% and 40%, respectively, independent of the

initial dye concentration (Arslan and Balcioglu, 2000).

Therefore its application for colour removal and partial

oxidation to improve biodegradability seems to be morepromising. Ozonation reportedly produces compounds

that may elicit toxicity or mutagenicity, but most re-

searchers found less toxicity in ozonated wastewater

samples and considerable biodegradability improvement

particularly in the case of textile dyes (Perkins et al.,

1999). Important is to optimize the applied ozone dose

(ozonation time) to achieve a maximum biodegradabil-

ity of the specific pollutant that might diminish with

extended ozone exposure and higher COD reduction

(Gilbert, 1987). On the other hand, changes in biocom-

patibility and toxicity during oxidative pre-treatment

can be tracked much more accurately and fast compared

to the standard biochemical oxygen demand (BOD) test

by performing respirometric activity testing as evidenced

in former studies (Ekama et al., 1986; Carvalho et al.,

2000).

In the present work 14 representative reactive dye-

stuffs with different reactive (vinylsulphone, mono-

chlorotriazine) and chromophoric (azo, metal complex

azo, phythalocyanine, formazan and oxazine) groupings

were hydrolysed and ozonated to the point of com-

plete colour removal. In this context, possible relation-

ships between heavy metal release from chromophoric

groupings of copper complex azo and phythalocyanine

dyes and their respirometric response towards mu-nicipal activated sludge were comparatively assessed.

For this purpose specific oxygen uptake rates (SOUR

values) were determined and evaluated instead of

the more traditional BOD5/COD biodegradability in-

dex (Chun and Yizhong, 1999; Uygur and Kook, 1999).

This approach has been considered as a more realistic

method due to the fact that partially treated and even

untreated dye-bath wastewater is generally discharged

to the municipal sewer and hence the prompt response

of activated sludge is thought to be of primary impor-

tance instead of the sometimes misleading BOD5/COD

ratio.

2. Materials and method

2.1. Reactive dye hydrolysates

Fourteen reactive dyestuffs obtained as gift sam-

ples from Dystar (Bayer-Hoechst, Istanbul) were step-

wise hydrolysed with 4.5 g/l 48 Bee NaOH and soda ash(5 g/l anhydrous Na2CO3) to mimic typical exhausted

dye-bath conditions according to a procedure described

elsewhere (Arslan-Alaton and Balcioglu, 2001). The

reactive dyestuff concentration was selected as 500 mg/l

for the ozonation experiments. The above mentioned

dyes have been chosen based on their relative abun-

dance, international as well as national market share,

cost and the variety of fiber reactive (anchor) and

chromophoric groupings. Table 1 lists the physicochem-

ical properties of the reactive dyes selected for the

present study.

Here it should be noted that the dyes with amino-chlorotriazine anchor groups (Procion H-EXL dyes) do

not impart any AOX (adsorbable organic halides) in the

spent dye-bath effluent since the chloro-organic com-

ponent is converted to inorganic chloride during fixation

and hydrolysis. In addition, the colour index number

and molecular structure of most selected dyestuff prep-

arations was confidential.

2.2. Ozone reactor and ozonation procedure

The reactive dye hydrolysates were ozonated for 28

42 min (corresponding to 583875 mg/l O3 dosage) in

a semi-batch, 1 litre borosilicate glass bubble column

wherein the ozone + oxygen gas mixture was continu-

ously sparged at a rate of 3 l/min through a fritted

dispersion disc with a diameter of 5 cm. Ozone was

produced by a corona discharge PCI GL-1 model pilot

scale ozone generator with a maximum capacity of 20

g/h ozone. Teflon tubing was used for all connections

from the ozone generator to the reaction vessel. All

excess (unreacted) gaseous ozone leaving the column

was collected in two gas washing bottles connected in

series and filled with 20% KI solution, whereas two

other gas washing bottles with 2% KI solution weredirectly placed after the gas introduction line to deter-

mine and calibrate exact O3 input rates. Beforehead, the

exact ozone input of 5% corresponding to an ozonation

rate of 1250 mg/h/l was selected for the experiments.

Ozone transfer efficiency (i.e. absorbed ozone O3A, %)

was determined by measuring the input and off-gas

concentrations of each pre-ozonation experiment iodo-

metrically (IOA, 1987). The mass transfer coefficient

of ozone in the semi-batch reactor was determined

in acidic pure water by employing the indigo spectro-

photometric method (Bader and Hoignee, 1981) as 0.22

min1

.

826 I. Arslan-Alaton / Chemosphere 51 (2003) 825833


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2.3. Activated sludge inhibition tests

Biological treatment of the untreated and pre-ozo-

nated reactive dye hydrolysates was conducted in two

parallel fill-and-draw glass reactors (one for the sample,

one for the domestic effluent control) where 250 ml raw

or pre-ozonated dye hydrolysate was mixed at a ratio of

1:1 with synthetic municipal wastewater and aerated in

300 ml activated sludge for a hydraulic retention time

of 3 h. This ratio is of importance since it representsa typical concentration encountered at on-site textile

treatment plants and the entrance of publicly owned

treatment works (POTWs) close to integrated textile

factory complexes. The activated sludge obtained from

a POTW was acclimated to synthetic municipal waste-

water that has been prepared according to ISO 8192

(1986). An activated sludge mixed liquor volatile sus-

pended solids (MLVSS) concentration of about 2000

mg/l ensured that a linear dissolved oxygen (DO) profile

was obtained for at least 23 min above 2 mg/l. DO

concentration was measured hourly starting after 15 min

aeration (taken as t 0; to) throughout the biological

treatment period by a WTW Oxi Digi 2000 model oxy-

gen meter. Respiration rates obtained from slopes of

DO profiles were limited to the linear portion of the

curves that corresponded to approximately 4 min acti-

vated sludge treatment. SOURs (measured in mg O2/

mg MLVSS/h) were determined by dividing abatement

rates in DO to MLVSS values. During each run the

SOUR values of the control sample containing only the

municipal wastewater sample were also monitored in

parallel to obtain relative (percent) respirometric inhi-bition levels at pre-determined time intervals. The rela-

tive SOUR inhibition index ISOUR is defined as follows:

ISOUR% SOUR of control SOUR of sample

=SOUR of control 100 1

Biological COD removal and SOUR values obtained for

decolourized (pre-ozonated) dye-bath samples were

compared with those found for synthetic municipal

wastewater treatment under otherwise same reaction

conditions (pH 77.5, activated sludge previously

acclimated to the synthetic municipal wastewater,

Table 1

Physicochemical properties of the reactive dyes used in the present studya

Dye Brand name CI reactive Anchor group Chromophore

group

kmax (nm) Dye or metal

content (%)

1 Remazol Black RL Black 31 Vinylsulphone Azo copper

complex

570 3545% dye

2 Procion Brilliant

Red H-EGXL

Monochlorotriazi-

nyl

Azo 505 7090% dye

3 Remazol Red GWF Vinylsulphone Azo 505

4 Procion Dark Blue

H-EXL

Aminochlorotriazi-

nyl

Copper complex 595

5 Remazol Brilliant

Blue BB

Blue 220 Vinylsulphone Formazan cop-

per complex

610 4550% dye;

3.7% copper

6 Procion Red Brown

H-EXL

Aminochlorotriazi-

nyl

Azo 485

7 Remazol Golden

Yellow RNL

Orange 107 Vinylsulphone Azo 410 7080% dye

8 Procion Deep Red

H-EXL

Monnochlorotriazi-

nyl

Azo 515 4060% dye

9 Remazol Red RB Red 198 Vinysul-phone + monochlo-

rotriazinylb

Azo 500

10 Procion Brilliant

Orange H-EXL

Aminochlorotriazi-

nyl

Azo 490

11 Remazol Turquoise

Blue G133

Blue 21 Vinylsulphone Phthalocyanine

copper complex

665 2.5% copper

12 Procion Blue

H-EXL

Aminochlorotriazi-

nyl

Oxazine + azo 595 3050% dye

13 Procion Navy

H-EXL

Aminochlorotriazi-

nyl

Azo 610

14 Remazol Brilliant

Yellow 4GL

Yellow 160 Vinylsulphone Azo 405 4550% dye

a Characteristic visible absorption band of the reactive dye (hydrolysate).b Heterobifunctional reactive anchors.

I. Arslan-Alaton / Chemosphere 51 (2003) 825833 827


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treatment for 3 h via continuous aeration), developed

at a feed rate of 500 mg/l/d COD, sample volume of

500 ml, and an average F=M ratio of 0.25 mg COD/mg MLVSS/d. Siphoned effluents were taken for ulti-

mate (final) COD measurement.

2.4. Analytical procedure

The extent of partial oxidation and decolourization

was traced in terms of colour and COD removal effi-

ciency. Reduction in colour was measured at the char-

acteristic visible absorption band (at the wavelength of

dye-specific maximum absorbance) of the hydrolysed

dyestuffs using a Hach DR/2 model spectrophotometer.

Both the COD of the raw, pre-ozonated, and the si-

phoned, biologically treated supernatant as well as the

MLVSS values obtained before, during and after bio-

logical treatment were measured by the closed reflux,colorimetric method according to a procedure outlined

in Standard Methods (APHA-AWWA-WEF, 1995).

The heavy metal concentration of raw and pre-ozo-

nated dye hydrolysates was measured by atomic ab-

sorption spectrometry (Perkin Elmer Instruments). For

the determination of complexed and released heavy

metal concentration before and after pre-ozonation,

respectively, samples where acidified with 6 N HNO3:

H2SO4 solutions at a ratio of 1:1 and their copper con-

tent was measured without performing pre-digestion

method.

3. Results and discussion

3.1. Pre-ozonation of reactive dye hydrolysates

Fig. 1 displays colour abatement profiles of the se-

lected reactive dye hydrolysates as a function of pre-

ozonation time at an average ozone input rate of 1250mg/l/h. As expected, colour abatement was fast and ef-

fective for all investigated reactive dyes and in most

cases no serious delay in decolourization was observed.

It was found that the kinetics of colour degradation was

usually first order as estimated by loglinear regression

analysis of normalized absorbance time-data. Fastest

decolourization was achieved for the copper phythalo-

cyanine dye (Dye11, mass transfer limited reaction) that

was practically complete after 7 min, and slowest for

the azo dye Reactive Brilliant Orange (Dye 7, kineti-

cally limited reaction), for which decolourization was

achieved after a preliminary induction period and 42min ozonation. Closer inspection of the obtained kinetic

data indicated that ozone transfer efficiency O3A varied

in the range of 1438% for the selected treatment period

(t 2842 min) which obviously depended upon boththe reactivity of the chromophore and anchor groupings

of the studied dyestuffs. It can also be concluded that

ozone exerted different reactivities towards different re-

active dye hydrolysates, however, these differences are

not extreme due to the fact that all investigated reactive

dyes contained electron withdrawing (NH2 ) as well as

electron releasing (HSO3, NO2 ) functional groupings.

0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

1 .2

1 .4

0 5 10 15 20 25 30 35 40 45

Time (min)

Normalizedab

sorbanceatcharacteristic

visible

wavelength(A/Ao

)

1 2 3 4 5 6 7 8

9 10 11 12 13 14

Dye

Ref. Nr.

R+ {0}

Fig. 1. Colour abatement profiles obtained for pre-ozonation of the reactive dye hydrolysates. Experimental conditions: average O3input rate 1250 mg/h/l; ozonation duration 2842 min; ozonation pH 11.8 + 0.2; decolourization kinetics followed as the relative

reduction in the visible absorption band at the wavelength of dye-specific maximum absorbance.



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Obviously copper complex azo, formazan copper com-

plex azo and copper phythalocyanine type reactive

dyestuffs (dyes ref. Nr. 1, 4, 5 and 11) were degraded

appreciably faster than most mono azo and disazo types.

With regard to complete colour removal, the amount of

ozone required was 180475 mg/l or 0.360.95 mg O3/

mg reactive dye, a dose below or at the limit of specificozone doses applied for pre-ozonation of industrial ef-

fluents in common practice.

The specific COD removal rates (YCOD) based on mg

COD removed per mg of ozone absorbed and achieved

at the point of complete colour removal are listed in

Table 2 together with the obtained percent COD re-

moval efficiencies and first order decolourization rate

constants (kd values). The specific COD removal rate

YCOD achieved via partial ozonation of the hydrolysed

dyestuffs varied between 0.09 and 0.73 mg COD re-

moved/mg O3 absorbed, and no clear relationship could

be established between kd and YCOD values.On the other hand, as shown in Fig. 2, a fair corre-

lation (R2 0:82) existed between percent O3absorptionefficiency O3A and kd values. This observation indicated

that the ozone demand being associated with the ozone

absorption of the oxidation system is a clear function of

the reactivity of molecular ozone and in situ formed free

radicals (HO, HO2) with the chromophoric groupings

of dye molecules. Due to the fact that reactions were run

at alkaline pH, the dominance of non-selective, free

radical initiated reactions is expected (Staehelin and

Hoignee, 1982). However, no possible relationship could

be identified between COD reduction rates (partial oxi-

dation of dyes and formed dye intermediates) and dec-

olourization kinetics indicating a more or less significant

selectivity that was probably imparted by the presence of

strong carbonate alkalinity surpressing ozone decom-

position to OH, HO2 and other free radicals (Arslan-

Alaton et al., 2002);

HCO3 OH ! HCO3 OH

k1 1:5 10

7 M1 s1

2

HCO3CO3 H

K1 1:0 10

8 M1 s1 3

CO23 OH ! CO3 OH

k2 4:2 10

8 M1 s1

4

Carbonate (CO3 ) and bicarbonate radicals (HCO

3) do

not react with ozone and hence retard or even com-

pletely inhibit ozone decomposition to free radicals. At

Table 2

Experimental results obtained for pre-ozonation of different reactive dye hydrolysates (Ozone input rate 1250 mg/h/l; initial dyeconcentration500 mg/l; ozonation time2842 min)

Dye nr. O3A (mgO3/mgCODo) O3A (mg/l) CODo (mg/l) COD removal (%) YCOD (DCOD/O3A) kd (min1)

1 1.12 404 361 68 0.61 0.35

2 0.58 249 432 37 0.64 0.18

3 0.90 276 307 27 0.30 0.28a4 0.82 330 405 10 0.12 0.28

5 1.10 367 335 50 0.46 0.33

6 0.60 260 432 12 0.20 0.09a

7 0.61 275 453 44 0.73 0.09a

8 0.66 295 445 14 0.21 0.11

9 0.68 308 453 22 0.32 0.30

10 0.63 180 286 30 0.48 0.07

11 1.26 475 376 31 0.25 0.52

12 0.38 206 547 10 0.27 0.14

13 0.65 287 445 29 0.45 0.15

14 0.88 271 309 8 0.09 0.16

a Only absorbance abatement profiles observed after the reactive dye-specific induction period were subjected to first order kinetic

modelling.

Correlation Factor R = 0.82

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6

O3A

(%)

Fig. 2. Relationship between percent O3 absorption efficiency

(O3A) and the first order decolourization rate constant (kd) for

pre-ozonation of the reactive dye hydrolysates. Experimental

conditions: average O3 input rate 1250 mg/h/l; ozonation

duration 2842 min; ozonation pH 11.8 0.2.



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the natural pH of reactive dye hydrolysates or spent

reactive dye-baths (pH 1112) CO3 is thought to bethe dominant radical scavenger. The role and fate of

CO3 has not yet been established. Speculatively CO3

is involved in oxidation of organic matter in alkaline

wastewater (Arslan-Alaton et al., 2002).

3.2. Biodegradability assessment

As has been mentioned previously, ozonation of re-

fractory organic pollutants in water usually produces

more oxygenated, polar products that are more or less

biodegradable or toxic than the parent compound

(Gilbert, 1987). The pre-ozonation + biotreatment com-

bination is used at some industrial wastewater treatment

facilities to improve the biocompatibility of otherwise

recalcitrant pollutants such as solvents, surfactants, dyes,

pesticides, pharmaceuticals etc. (Alvares et al., 2001). In

the case of textile industry sector the effects and effi-ciency of pre-ozonation may change dramatically and

results cannot be directly extrapolated from case efflu-

ent to case effluent. In the present study changes in the

aerobic biodegradability was assessed by relative com-

parison of SOUR data obtained for each reactive dye

hydrolysate.

Fig. 3 shows the DO profiles obtained for respiro-

metric monitoring of synthetic domestic effluent (con-

trol), control spiked with pre-ozonated and untreated

Reactive Yellow 160 hydrolysate during biotreatment

in unacclimated activated sludge. Reactive Yellow 160

(Dye 14) has been selected as a typical reactive azo dye

that has practically no biological activity according to

the safety data information obtained from the dye sup-

plier. Fig. 4 gives SOUR values obtained for synthetic

wastewater directly spiked with raw (indicated as inthe figures) and pre-ozonated reactive dye hydrolysates

during biological activated sludge treatment at t 0 (i.e.15 min after starting biological oxidation), t 1 h andfinally after 3 h of aeration. As can be seen on both

figures the signs of partial inhibition and instabilisation

of activated sludge exposed to the dyes did not appear

instantaneously but after 1 h of aeration. Fig. 4 also

implies that initial SOUR values obtained for raw as

well as ozonated reactive dye samples in unacclimated,

domestic sewage sludge are almost identical at to.

For most effluent samples not exposed to pre-ozonation,

the SOUR values decrease significantly after t 1 hbiotreatment down to endogeneous respiration rates

(SOURmin SOURendogeneous 0.006 mgO2/mg MLVSS/h), an observation that is usually evidenced only after

extended biotreatment (at least 34 h aeration) of the

control effluent (Figs. 3 and 4). Biological COD removal

was found as 76% for the control sample at the end of the

selected aeration period. Unlike in the case of untreated

samples, 1-h SOUR values obtained for the reac-

tive dye hydrolysates that were subjected to pre-ozo-

nation increased up to levels that were almost as

high as those obtained for the domestic wastewater

control for the same biotreatment period (SOURmax SOURdomestic 0.03 mg/mg/h).

0.0

2.5

5.0

7.5

10.0

0 50 100 150 200 250 300 350

Respirometric measurement time (s)

Dissolved

oxygenconcentration(mg/l)

control, t = 1 h

pre-ozonated Yellow 160, t = 1 h

pre-ozonated Yellow 160, t = 3 h

control, t = 3 h

Yellow 160, t = 1 h

Yellow 160, t = 3 h

Fig. 3. Dissolved oxygen profiles for synthetic domestic wastewater spiked with hydrolysed Yellow 160, pre-ozonated hydrolysed

Yellow 160 and the synthetic domestic wastewater control during respirometric measurements after t 1 and 3 h activated sludgetreatment. Experimental conditions: Average O3 input rate 1250 mg/h/l; pre-ozonation period 2842 min; ozonation pH11.8 0.2; selected F=M ratio 0.140.27 mg COD/mg MLVSS/d; biological activated sludge treatment duration 3 h ; p H

7.07.5.



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Fig. 5 presents the relationship established betweenthe amount of free (originally totally complexed) copper

and percent inhibition of SOUR (ISOUR) after 1-h treat-

ment with respect to control data (i.e. unacclimated,

synthetic domestic effluent). A positive correlation be-

tween percent respirometric inhibition and copper re-

lease was evident form Fig. 5. In parallel to this

observation the biological COD removal for the three

investigated copper complex dyes was rather poor that is

probably a consequence of the increased toxicity of the

pre-ozonated complexed metal containing dye hydroly-

sates and in contrast with the other pre-ozonation re-

sults. For instance,I

SOUR values decreased from 87% and

96% for raw azo dyes to only 24% and 51% for pre-

ozonated azo dyes, whereas the same parameter in-

creased slightly for the raw and pre-ozonated metal

complex azo and phythalocyanine dyes, respectively. As

has been stated in related studies and confirmed in the

present experimental work, the consequences of partial

treatment by ozonation have to be carefully examined

and optimised before ozone is applied in large-scale forthe pre-treatment of otherwise inert industrial pollutants.

Table 3 lists ISOUR values, biochemical and total COD

removal efficiencies achieved for the combined pre-ozo-

nation plus activated sludge treatment of the reactive

dye hydrolysate plus synthetic unacclimated domestic

wastewater mixture. As can be seen in Table 3, an

overall COD removal efficiency around 70% can be

achieved by the integrated treatment system instead of

2033% for direct biochemical treatment of reactive dye

hydrolysates. This treatment efficiency is close to that

one found for the domestic wastewater (control) sample.

4. Summary and conclusions

The present study emphasizes that the impact of

chemical pre-conditioning of otherwise recalcitrant

textile industry dyes prior to traditional, biological treat-

ment is of primary importance for proper textile dye

wastewater handling and has to be studied carefully. De-

termination of the respirometric activity response of

industrial pollutants towards biological activated sludge

is a useful and practical parameter for the assessment

and control of acute toxicity and microbial inhibition.

Correlation Factor

R2= 0.91

0

2 0

4 0

6 0

8 0

1 0 0

0 5 1 0 1 5 2 0 2 5

Released (free) copper (mg/l)

ISOUR

(%)

Dye 1 1

Dye 5

Dye 4

Dye 1

Fig. 5. Relationship between percent specific oxygen uptake

inhibition rate (ISOUR ) and the amount of copper release for

three metal complex azo and one phythalocynanine type hy-

drolysed reactive dye after pre-ozonation.

0

0.02

0.04

0.06

0.08

0.1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 C 1* 3* 5* 7* 10* 12* 13* 14*

Dye Ref. Nr.

SOUR(mgO2/mgMLVSS/h)

t o t = 1 h t = 3 h

Fig. 4. Specific oxygen uptake rate values for pre-ozonated, directly biotreated (dye) reactive dye hydrolysates and domestic

wastewater control (C+). Experimental conditions: average O3 input rate 1250 mg/h/l; ozonation duration2842 min; ozonationpH 11.8 0.2; selected F=M ratio 0.140.27 mg COD/mg MLVSS/d; biological activated sludge treatment duration 3 h;pH 7.07.5.



8/9

Herein it could be demonstrated that mere ozonation at

the natural, alkaline pH of reactive dye hydrolysates was

observed to be effective in partially oxidizing and com-

pletely decolourizing textile dyes at their relatively highconcentrations. Since water soluble organic dyes are

known to react aggressively via both OH radicals pro-

duced from O3 decomposition and directly via molecu-

lar O3, no retardation or inhibition of colour abatement

was observed except for two azo dyes experiencing dra-

matic induction periods as a consequence of their chro-

mophoric structure. Ozone was absorbed in the reaction

system at an approximate ratio of 0.381.26 mg O3/

mginitialCOD or 0.360.95 mgO3/mg dye). The re-

spirometric activity was appreciably enhanced from an

average of 0.006 to 0.03 mg O2/mg MLVSS/h by 2842

min pre-ozonation for all studied reactive dyes and ra-ther good correlations could be established between first

order decolourization kinetics and specific ozone ab-

sorption efficiencies (R2 0:82) as well as relative re-spirometric inhibition rates and the amount of initially

complexed copper release (R2 0:91).

Acknowledgement

The financial support of Istanbul Technical Univer-

sity Research Foundation under Project Number 2021 is

gratefully acknowledged.

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Table 3

Experimental results for biotreatment of pre-ozonated reactive dye hydrolysates (Aeration time 3 h; MLVSS 15002500 mg/l; F=Mratio 0.140.27 mg COD/mg MLVSS/d; Dye:synthetic municipal wastewater:ratio 1:1

Dye ISOUR (%) COD after biotreatment

(mg/l)

Biological COD

removal (%)

Total COD

removal (%)

1 60 103 10 72

2 66.4 128 32 70

3 24 118 33 62

4 83 107 12 74

5 71 189 14 62

6 22 143 31 67

7 51 113 17 75

8 69 194 5 56

9 51 82 61 82

10 62 84 52 71

11 64 107 51 72

12 84 161 27 71

13 80 123 40 72

14 84 100 19 68

3a

96 246 20 20b

7a 87 303 4 33b

14a 82 216 13 30b

Cc 66 67 67

a Biotreatment of the corresponding dye without pre-ozonation.b For the raw dye samples (a) the difference between percent biological and overall removal overall rates correspond to the difference

between the initial COD of the original reactive dye hydrolysate and the biochemical COD removal efficiency obtained for the 1:1

mixed dye+ municipal wastewater samples.c Synthetic municipal wastewater control.



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