~ ) Chemosphere, Vol. 38, No. 4, pp. 835-852, 1999 Pergamon © 1998 Elsevier Science Ltd. All rights reserved

0045-6535/99/$ - see front matter P lh S0045-6535(98)00227-6

DEGRADATION OF REACTIVE DYES I. A COMPARATIVE STUDY OF OZONATION,

ENZYMATIC AND PHOTOCHEMICAL PROCESSES•

Patrieio Peralta-Zamora*, Airton Kunz**, Sandra Gomes de Moraes**, Ronaldo Pelegrini**,

Patrieia de Campos Molelro , Juan Reyes and Nelson Duran .

*Departamento de Quimica, Universidade Federal do Paran~.

C.P. 19081, CEP 81531-990, Curitiba, Brazil. (zamora@quimica.ufpr.br)

**Biological Chemistry Laboratory, Chemical Institute, Universidade Estadual de Campinas.

C.P. 6154, CEP 13083-970, Campinas, Brazil.

(Received in USA 8 April 1998; accepted 18 June 1998)

ABSTRACT

The environmental problems associated with textile activities are represented mainly by the

extensive use of organic dyes. A great number of these compounds are recalcitrant and shown

carcinogenic or mutagenic character. In this work three processes were studied for degradation of an

anthraquinone dye (C.I. reactive blue-19). The ozonation process leads to complete decolorization with a

very short reaction time; however, effective mineralization of the dye was not observed. The enzymatic

process promotes quick deeolorization of the dye; nevertheless, maximum decolorization degrees of about

30% are insignificant in relation to the decolorization degree achieved by the other processes. The best

results were found for the photocatalytical process. The use of ZnO or TiO2 as photocatalysts, permits

total decolorization and mineralization of the dye with reaction times of about 60 rain.

(© 1998 Elsevier Science Ltd. All rights reserved

Keywords: anthraquinone dye, degradation, heterogeneous photocatalysis, lignin peroxidase, ozonation.

INTRODUCTION

At the present time, textile activities are in constant expansion showing a high pollutant potential.

A medium textile mill shows a polluting potential of 7000 persons (in relation to hydraulic charge), or

20,000 persons (in relation to organic charge). Moreover, textile effluents show an extremely variable

composition with a high shock potential to the receptor body [1 ]. In Brazil, the textile industry utilises 20

T/year of dyes. About 20% of them are lost in the effluents, which are firstly treated by activated sludge

systems and afterwards discharged in to receptor bodies [2,3]. 835

836

The more complex environmental problems associated with the textile industry are due to wide

utilisation of carcinogenic or mutagenic reactive dyes, which are resistant to microbial degradation [4].

Some reactive dyes are either toxic or can be modified biologically to toxic or carcinogenic compounds

[5].

The nonbiodegradability of textile wastewater is due to its high content of dyestuffs, surfactants

and additives. There are no universally useful methods available for treatment of dye wastes, probably

because of the complex and very varied chemical structures of these compounds [5]. The most popular

treatments to eliminate toxic compounds from the wastes are flocculation, adsorption and biotreatment

[61.

The efficiency of advanced oxidation processes for degradation of recalcitrant compounds has

been extensively documented [7-11]. Photochemical processes are used to degrade toxic organic

compounds to CO2 and H20 without the use of additional chemical oxidants, because the degradation is

assisted by high concentrations of hydroxyl radicals generated in the process. The application of

photocatalytic procedures for remediation of textile effluents has been less studied, but recently several

papers on environmental photochemistry with isolated dyes have been published [12-14]. An efficient

decolorization process which combine chemical coprecipitation with Fe(OH)3 and photochemical

treatment was recently published [15].

The use of ozone in textile effluent treatment appears as a very attractive alternative with

considerable application potential. Ozone is a powerful oxidising agent (E ° = 2,08 V), when compared

with other well known oxidising agents such as H202 (E ° = 1,78 V), and can react with several class of

compounds through direct or indirect reactions [16]. The chromophor groups generally are organic

compounds with conjugated double bonds that can be broken by ozone (directly or indirectly) forming

smaller molecules, which decrease the effluent colour. The ability of ozone to degrade dyes has been

demonstrated [ 17-20].

The lignin-degrading system of white rot fungus, Phanerochaete chrysosporium, is able to

degrade a wide range of structurally diverse organic pollutants [21,22]. Decolorization of several azo,

triphenylmethane, heterocyclic and polymeric dyes by lignin peroxidase from P. chrysosporium has been

reported [22-25]. In these works significant degrees of degradation were observed, which confirm the

great potential of the enzymatic process for degradation of this kind of compounds.

In this work, a comparative study of reactive dye degradation (anthraquinone dye: C.I. reactive

blue-19) by using photochemical, enzymatic and ozonation processes was carried out.

837

MATERIALS AND METHODS

Reagents

The anthraquinone dye C.I. reactive blue-19 (Figure 1) was purchased from a textile mill located

in Americana (SAo Paulo, Brazil). Solutions of this dye were prepared with distilled water in

concentrations of 30 mg L q.

O NH2

~ ~ SO3Na

. SO~CH~CH~OSO~Na

0 NH - ~

F i g u r e 1 - Chemical structure of reactive blue-19.

Titanium dioxide (anatase, Degusa P-25) and Zinc oxide (Merck) were used without any pre-

treatment.

Ozone was generated from pure oxygen using an OZOCAV ZT-2 (Inter Ozone Ingenieria

Ecol6gica, Santiago-Chile) equipment. The produced ozone was determinated spectrophotometrically at

258 nm, passing the gas phase containing the mixture of oxygen and ozone through a flow cell [26].

Lignin peroxidase was produced by P. chrysosporium BKMF-1767. The basic medium was the

same reported by Haapala and Linko [27]. For the immobilised P. chrysosporium cultures, 1 mL of spore

suspension (approx. 1.56 x 107 spores mL 1) was inoculated into 250-mL Erlenmeyer flasks containing

75 mL of the carbon-limited medium and 1.7 g of nylon-web cubes as carrier. After a 4-day growth period

at 37 °C and 150 rpm agitation, 25 mL medium was decanted off, and veratryl alcohol and Tween 80 were

added to give final concentrations of 2.5 mM and 0.13%, respectively. The flask was flushed for 25 min

with pure oxygen each day. At the 8th day, and after ultra-filtration and dialysis, a maximum activity of

214 U L -I for LiP was obtained. The lignin peroxidase activity was evaluated using veratryl alcohol

according Tien and Kirk [28].

Photochemical treatment

300 mL of aqueous dye solution (pH: 7.0) and 100 mg of TiO2 (or ZnO) were placed in a 400 mL

reactor equipped with water refrigeration, magnetic stirrer and a inner quartz device for a 125 W Philips

lamp (without the glass cover). The suspension was bubbled with oxygen (through a sintered glass placed

838

in the bottom of the reactor) at flows of about 100 mL min l . For analytical control samples were taken at

convenient times and centrifuged at 3500 rpm.

Ozonization of dye solutions

The aqueous dye solutions were submitted to ozonization at pH 7 and room temperature, using a

tubular reactor of 500 mL with a sinterized glass dispersor, that releases the gas from the bottom to the top

of the reactor. The ozonized sample volumes were 300 mL, the oxygen flow was adjusted to 15

(_+1) L h l , obtaining an ozone production of 0.14 g h "l.

Enzymatic treatment

300 ~tL of aqueous dye solution, 360 ~tL of 50 mM tartarate buffer (pH: 3.0), 100/xL of 40 mM

veratryl alcohol, 200 ~tL of aqueous lignin peroxidase solution (214 U L 1) and 60 ~tL of 0.4 mM

hydrogen peroxide were placed in a quartz spectrophotometric cell at 25 °C. The absorbance of the

mixture was registered between 700 and 450 nm with intervals of 30 s.

Analytical control

The efficiency of the processes was evaluated by monitoring dye decolorization at 590 nm, which

corresponds to the maximum absorption wavelength (with a Hitachi U-2000 spectrophotometer) and the

total organic carbon reduction (measured with a TOC-5000 Shimadzu Total Organic Analyser).

Chromatographic determinations were performed with a Varian HPLC (model 9050), using an

ODS Hypersil (4 mm x 100 cm) column and UV-Vis detector 0~: 254 nm). The mobile phase was

composed of 5.0 x 10 -4 mol L "l H2SO4 and acetonitrile (80:20 v/v).

RESULTS AND DISCUSSIONS

Photochemical process

By using ZnO and applying a standard heterogeneous photocatalytical procedure it was observed

an important degree of dye degradation for a short treatment time. Moreover, this degradation involves

chemical forms that absorb not only in the visible region (Figure 2B), but also in the near ultra violet

region (Figure 2A), which indicates the occurrence of drastic transformations of the dye by the

photochemical process. By chromatographic analysis (Figure 3), the presence of some impurities and

hydrolysed forms of the dye were initially confirmed [29]. By application of the photochemical process

the composition of the sample was significantly changed, with appearance of some peaks at high retention

839

times. For longer treatment times (30 min), the chromatographic analysis showed only two small

remaining peaks, which attest the substantial degradation of the dye.

The photochemical dye degradation by using TiO2 (Figures 4 and 5) was very similar that for ZnO.

A rapid degradation was observed in both the visible and the ultra violet regions, and almost total

chromatographic peak removal was observed for treatment times of about 15 rain.

w 0 z < rn n," O o9 m <

I 2,0,

1,5

1,0

0,5

A

0,C 200

B l a n k

250 300 350 400 450

W A V E L E N G T H (nm)

0,35

0,30

0,25

Blank

w 0 Z 0,20 < m

¢'Y 0,15 0 O9 m • ~ O,lO

0,05 - /

0,00 45O

840

I J I , I , 7 - - ' - - - , - -

500 550 600 650 700

W A V E L E N G T H (nm)

B

Figure 2 - Photochemical degradation of reactive blue-19 by using ZnO.

841

~ 1500~0

10030~

,~]0000

0 I I I 2

Z 15(X)~0

~o ,1l 2

q I I I I 18 8 10 12

RETENTION TIME

Blank

I q I I I I I 4 6 8 10 12

F~-II~'qTION TIf,/E

7.5 min

S

:j ~ q

OI I , 2

,I 2 4

t @ 8 10

RETENTION TIME

2.5 min

i I I 6 8 10

F:ErB~I3q TIME

30 min

,i 12

L, 12

Figure 3 - Illustration of the photochemical reduction of the chromatographic

peaks of reactive blue- 19 by using ZnO.

842

I

2,0 Blank

z 1,5 rY 1,0 0 09 m

oo' , ' , , , '

200 250 300 350 4oo 450

WAVELNGTH (nm)

A

0,35

0,30

0,25

UJ 0 Z 0,20

0,15 O O9 ~O

0,10

0,05

0,00 450

Blank

I I = I i I J 1 I

500 550 600 650 700

W A V E L E N G T H (nm)

B

F i g u r e 4 - Photochemical degradation of reactive blue-19 by using TiO2.

843

~0~04

01~ i I 2

Z

2

I ,, i i i

4 i!1 $ to

I~'ENTION TIME

Blank

I t I i 4 B 8 to 12

FEIB~CIN'nlVE

7.5 min

12 14 2

~nnnnn

i

i i i i 4 8 8 I0

RErI~411CN TIME

2.5 min

I , 12

i i i I i i t 4 6 8 10 12

FEIENI1ON'nI~

15 min

F i g u r e 5 - Illustration of the photochemical reduction of the chromatographic peaks

of reactive blue-19 by using TiO2

The photochemical decolorization kinetics for both catalysts and the effect of several experimental

conditions are presented in Figure 6. With the use of the two catalysed systems similar decolorization

kinetics were observed. Almost total decolorization was reached for times lower than 20 min, without any

significant effect of the adsorption process (Figure 6A).

When UV-light was applied only in the presence of oxygen (without the photocatalyst) significant

decolorization degrees were still observed. Naturally, with a slower kinetics than with the photocatalised

system (Figure 6B). When the irradiation process was performed in the presence of nitrogen the

decolorization kinetics were very slow, which attest to the importance of oxygen in this process. When

only oxygen was applied to the system, decolorization was not observed. As a function of these results,

844

we can suppose that the decolorization process in the uncatalysed system is due to reactions that involve

active species derived from photochemical reactions of oxygen. In order to understand this result, studies

on this direction are at present time in progress.

Ozonation process

The degradation of the dye by ozonation was very fast when the visible region was monitored

(Figure 7B). Almost total decolorization was observed for a reaction time lower than 5 rain (Figura 7C).

Nevertheless, in the ultraviolet region substantial degradation was not observed (Figure 7A), which

suggests that in the ozonation procedure the degradation process involves only slight modification of the

dye.

The chromatographic analysis (Figure 8) confirmed this conjecture. At initial ozonafion times

significant modifications were observed; however at the end of the process, when the decolodzation is

almost complete, the existence of significant remaining peaks attest that the degradation process was

incomplete.

845

0,30-

E 0,25. ~t -! '~ 0,20 -

0,15 -

Zm< 0,10

0,05 1

O,OOJ

0

- - • - - Photochemical treatment with ZnO --t3-- Adsorption on ZnO - - ° - - Photochemical treatment with TiO 2

- -0- - Adsorption on TiO 2

20 40 60 80 100 120

T I M E (rain)

A

0,30. , i x A- -A •

V" E 025 . \ ~ ° ~ t-- •

t.(3 0,20 - I.-- • < -\ (,.) 0,15 - Z

O - - -e- - Only irradiation (with nitrogen) O0 --&-- Only oxygen m 0,05 - <

o,oo - ~ , ,

0 20 40 60 80 100 120

T I M E (min)

B

Figu re 6 - Summary o f the photochemica l degradation o f reactive blue-19.

2,0

0,0 200

1,5

Z

n," 1,0 O ~0 ¢:0 <~

0,5

, , , ~ , i 250 300 350 400 450

WAVELNGTH (nm)

846

A

0,35

0.30

0,25 LU ~Z 0,20

) 0.15

o.10 ;

Blank

0.05o0 ~ ~ -

0'450 500 550 600 650 700 W A V E L E N G T H (nm)

o,3o -

E 0,25 -

0,20 - ,<

Z~ 0 , 1 5 -

QC 0,10 - 0

m 0,05 -

0.00

TIME (min)

C

Figure 7 - Degradation of reactive blue-19 by ozonation.

847

~oooq

I I i 2 4 12

300O00

2~X]OC

20OOOC

10000C

50300

i i i i 6 8 10

RETENnON riME

l soooooq

B lank

I L i I i i i i i 4 6 8 10 12

RETENnON riME

3.0 min

so~oq

01

30OOOOO

t 2

[~ i I i 8 8 10 12

I~ 'ENnON "RIVE

1.0 min

I i , ,1 , ,

2 4 6 8 10

RETENTION TIME

4.0 min

Figure 8 - Illustration of the reduction of the chromatographic peaks of reactive

blue- 19 by ozonation.

Enzymatic process

Unfortunately, the execution of the dye degradation study by lignin peroxidase, in the same

conditions of the previous experiments, was impossible. That is, the amount of enzyme solution necessary

to produce significant decolorization in 300 mL of dye solutions was so high that the study was not viable.

Only for comparative study, the efficiency of the system on the decolorization of the dye was study with

small volumes of reagents, directly in the spectrophotometric cell. The results show that even under these

conditions the decolorization of the dye is a very slow process, reaching a maximum decolorization of

about 30% for a reaction time of 150 s (Figure 9A). Increasing the amount of enzyme, the shape of the

decolorization curve was not substantially modified (Figure 9B).

848

0,50

0,45

0.40

0,35 W (_) 0,30 z raft3 0,25 n- O o,2o ~o m < 0,15

0,10

0,05

0,00 450

Blank

I i I I = I t

500 550 600 650 700

WAVELENGTH (nm)

A

E c o o3

I - < LD (D Z < m n, 0 cO c0 <

0,5

0,4 •

0,3 '

0,2.

0'1 1

0,0 0

- - " - - 200 p.L o f LiP l

- - e - - 400 p,L o f LiP I ~ i ~ i ~ a i •

- ~ o o - o • •

i u u u

0 100 150 200 250

T IME (s)

Figure 9 - Degradation of reactive blue-19 by lignin peroxidase.

Several works attest to the degradation of reactive dyes by using P. chrysosporium and lignin

peroxidase isolated from them. Usually, decolorization degrees of about 50 % are obtained for treatment

of 24 h or 20 min, using the fungi or the purified enzyme, respectively [22-25]. In view of these facts, the

849

achievement of close decolorization ratios for treatments of about 3 min are very satisfactory and suggest

the interesting potential of the enzymatic process for this purpose.

Mineralization study

To evaluate the effective mineralization of the dye by application of the remediation processes,

determinations of total organic carbon content (TOC) were carried out. The results (Table 1) indicate that

the photochemical process, performed with both ZnO and TiO2 photocatalysts, lead to complete

mineralization for treatment times of 120 and 60 min, respectively.

The UV-light/oxygen system shows a considerable TOC reduction (50%), an interesting result

which represents an attractive new alternative for treatment of this kind of compounds. The fact that TOC

reductions were not observed for the UV-light/nitrogen system confirms the important role of the oxygen

and suggests the existence of mechanisms that directly involve its participation.

In spite of the fact that the ozonation process promotes the total decolorization of the dye, the

results of TOC determinations indicate that the process leads only to small modification of the substrate,

and not to real degradation or mineralization.

Table 1 - TOC evolution by application of the studied processes.

TOTAL ORGANIC CARBON CONTENT (mg L a)

TREATMENT PHOTOCHEMICAL UV LIGHT OZONATION

TIME (rain) ZnO TiO2 02 N2

11.42 _+0.8 11.42 -+0.8 l 1.42 -+0.8 11.42 -+0.8 0

1

2

3

5

10

30

60

120

10.22 11.13

5.50 11.30

3.40 1.67

0.15 O 0

12.96 10.58

5.30 10.59

0.29

11.42 _+0.8

11.00

12.59

11.24

FINAL REMARKS

Three processes were studied for degradation of an anthraquinone dye. The results are very

promising, because each process shows specific attributes that can be explored for the implementation of

remediation procedures.

850

The ozonation process leads to complete decolorization with a very short reaction time (typically,

5 min). However, effective degradation of the dye was not observed.

The enzymatic process promotes quick decolorization of the dye; nevertheless, maximum

decolorization degrees of about 30% are insignificant in view of the arduous work involved in the enzyme

production process. It may be that the use of immobilised forms will convert the enzymatic process into a

feasible possibility for this purpose.

The best results were found for the photocatalytical process. The use of ZnO or Ti02 permits total

decolorization and mineralization of the dye with reaction times of about 60 min.

Acknowledgement: Support from FAPESP, FINEP, CNPq, CAPES and FAEP are acknowledged.

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