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Journal of Hazardous Materials 175 (2010) 802–808

Contents lists available at ScienceDirect

Journal of Hazardous Materials

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ecolourization and detoxification of textile industry wastewater by theaccase-mediator system

im Khlifia, Lassad Belbahria, Steve Woodwarda, Mariem Ellouza, Abdelhafidh Dhouiba,ami Sayadia, Tahar Mechichia,b,∗

Laboratoire des Bioprocédés, Pôle d’Excellence Régionale AUF, (PER-LBP) Centre de Biotechnologie de Sfax, BP: «1177», 3018 Sfax, TunisiePresent address: Ecole Nationale d’Ingénieurs de Sfax, BP 1173, 3038 Sfax, Tunisia

r t i c l e i n f o

rticle history:eceived 30 January 2009eceived in revised form 20 October 2009ccepted 21 October 2009vailable online 30 October 2009

a b s t r a c t

Decolourization and detoxification of a textile industry effluent by laccase from Trametes trogii in thepresence and the absence of laccase mediators was investigated. Laccase alone was not able to decolourizethe effluent efficiently even at the highest enzyme concentration tested: less than 10% decolourizationwas obtained with 9 U/mL reaction mixture. To enhance effluent decolourization, several potential laccasemediators were tested at concentrations ranging from 0 to 1 mM. Most potential mediators enhanced

eywords:accaseextile industryyeastewater

decolourization of the effluent, with 1-hydroxybenzotriazol (HBT) being the most effective. The effect ofseveral physico-chemical parameters that could influence enzyme activity, such as pH, temperature anddye concentration was tested. Optimal decolourization occurred with 20% effluent at pH 5, a temperatureof 50 ◦C, and in the presence of 1 mM HBT.

The toxicities of crude, laccase–HBT treated and laccase–acetosyringone treated effluent were eval-assa

ent r

ediator uated using the Microtox

laccase–HBT treated efflu

. Introduction

Effluents produced by textile industries are often stronglyoloured and their disposal into receiving waters causes environ-ental damage, including significant impacts on the photosyn-

hetic activity of aquatic plants due to reduced light penetration.hese wastewaters may also be toxic to aquatic organisms due tohe presence of, for example, metals, or chlorides, and breakdownroducts of dyes [1,2]. High concentrations of such dyes can causeater borne diseases and increase the biological oxygen demand

BOD) of receiving waters [3]. Worldwide, approximately 10–15%f the total dyes used in various textile processes and in otherndustries are discharged into wastewater causing extensive pol-ution [4,5]. Treatment of industrial effluents containing aromaticompounds is necessary, therefore, prior to final discharge to thenvironment.

Wastewaters from textile dying process are usually treated byhysical- or chemical-processes, which include physical–chemical

occulation combined with flotation, electro-flotation floccu-

ation with Fe(II)/Ca(OH)2, membrane-filtration, electrokineticoagulation, electrochemical destruction, irradiation, precipitation,zonation, or the Katox method involving the use of activated car-

∗ Corresponding author. Tel.: +216 74 274 088; fax: +216 74 275 615.E-mail address: tahar.mechichi@enis.rnu.tn (T. Mechichi).

304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.jhazmat.2009.10.079

y. Only laccase–acetosyringone treated effluent was not toxic; crude andetained toxicity.

© 2009 Elsevier B.V. All rights reserved.

bon and air mixtures [6]. However, these technologies are usuallyinefficient in the removal of colour, costly and difficult to adapt toa wide range of dye wastewaters [6].

In recent years, a number of studies have focused on the abili-ties of certain microorganisms to biodegrade and biosorb dyes inwastewaters. Many fungi and bacteria are used in the develop-ment of biological processes for the treatment of textile effluents[7,8].

Several combined anaerobic and aerobic microbial treatmentsmay enhance the degradation of textile dyes [9]. Under anaerobicconditions, however, azo-reductases usually cleave azo dyes intothe corresponding amines, many of which are mutagenic and/orcarcinogenic [10,11]. In contrast, anthraquinone dyes are largelyresistant to bacterial decolourization [12].

Fungi have long been recognised for their abilities to produce avariety of extracellular proteins and for a capacity to adapt to severeenvironmental constraints [13,14]. White-rot fungi can degrade awide range of recalcitrant compounds such as xenobiotics, ligninand dyestuffs via the extracellular lignolytic enzyme system. Tram-etes trogii has received little research attention to date, althoughit is an exceptional laccase producer [15] and its ability to degrade

high priority pollutants such as polychlorinated biphenyls, polyaro-matic dyes and polycyclic aromatic compounds was demonstratedrecently [16,17].

Laccases (benzenediol: oxygen oxidoreductases, EC 1.10.3.2)are multi-copper oxidases that catalyse the one-electron oxida-

dous Materials 175 (2010) 802–808 803

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Table 1Characteristics of effluents from the textile factory Ksar Helal in Tunisia.

Characteristics Values

pH 12Maximum absorbance (�max) 600 nmChemical oxygen demand COD 1 g/LBiochemical oxygen demand BOD5 0.030 g/LTotal solids (TS) 5.810 g/LVolatile solids (VS) 2.050 g/LSuspended solids (SS) 0.115 g/LVolatile suspended solids (VSS) 0.112 g/L

where Absorbancet0 is the absorbance at 600 nm of the reaction

R. Khlifi et al. / Journal of Hazar

ion of substituted phenols, anilines, and aromatic thiols to theorresponding radicals with the concomitant reduction of molec-lar oxygen to water. The enzymes are produced by plants andungi, including white-rot basidiomycetes responsible for ligninegradation in nature [18,19], although recently some bacterial lac-ases were described and fully characterized [20]. These enzymesredominantly attack phenolic moieties in the lignin polymeratalysing a one-electron oxidation via phenoxy radicals [21].

Laccases are of great interest to the pulp and paper industry22], in textile dye decolourization [23] and in the food industryor processing beverages, sugar beet pectin gelation and baking24]. Laccase-catalysed reactions are strongly dependent on redoxotential, temperature and reaction medium [25]. However, the

ow-redox potentials of laccases (450–800 mV) compared to thosef lignolytic peroxidases (>1 V) only allow direct degradation ofow-redox-potential phenolic compounds and not oxidation of the

ost recalcitrant aromatic compounds, such different industrialyes [26]. Nevertheless, insights into lignin degradation by somehite-rot fungi that produce only laccase suggested new applica-

ions involving enzyme mediators. In the presence of a suitableedox mediator laccases are also able to oxidize non-phenolic struc-ures [27,28].

The aim of the work reported here was to test the ability ofrude laccase from the white-rot fungus T. trogii to decolourize andetoxify dye effluent from the textile industry, and the abilitiesf different redox mediators to influence the oxidative reactionsatalysed by laccase during decolourization of the effluent.

. Material and methods

.1. Chemicals

2,6-Dimethoxyphenol (DMP), 1-hydroxybenzotriazole (HBT),yringaldehyde, syringate, vanillin, vanillate, acetosyringone, m-,- and p-coumarate were obtained from Sigma–Aldrich or Fluka.

.2. Fungal isolate, media and culture conditions

T. trogii, was selected for this study for its ability to decolourizendustrial effluent from textile dyeing and to produce a high titre ofaccase [29]. The fungus was isolated from decaying Acacia wood,orthwest Tunisia and selected for the capability to oxidize ABTS

n solid medium and to decolorize Poly R478. It was and identifieds T. trogii and preserved under reference CTM 50156 in the cultureollection of the Centre de Biotechnologie de Sfax [29]. The fungusas also deposited in German Collection of Microorganisms andell Cultures under reference DSM 17 786. For short term preser-ation, the fungus was grown at 30 ◦C on 2% malt extract agar inetri dishes and stored at 4 ◦C.

For laccase production, T. trogii was cultured in a mediumontaining (g/L): glucose, 10; peptone, 5; yeast extract, 1; ammo-ium tartrate, 2; KH2PO4, 1; MgSO4·7H2O, 0.5; KCl, 0.5; tracelements solution, 1 mL. Trace elements were added to giveg/L): B4O7Na2·10H2O, 0.1; CuSO4·5H2O, 0.01; FeSO4·7H2O, 0.05;

nSO4·7H2O; 0.01; ZnSO4·7H2O, 0.07; (NH4)6Mo7O24·4H2O, 0.01.he solution was adjusted to pH 5.5 prior to autoclaving. Aliquots3 mL) of homogenized mycelium in sterile medium prepared usingn Ultra-turrax homogenizer were used to inoculate 300 mL cultureedium in 1000-mL Erlenmeyer flasks. Cultures were incubated

t 30 ◦C on a rotary shaker (160 rpm). Production of laccase was

timulated by adding 300 �M of CuSO4 to the basal medium afterdays incubation [30]. Culture broth was collected at the time ofaximum laccase production (10 d), filtered, and clarified by cen-

rifugation at 7000 × g for 15 min. The resulting clear filtrate wasecanted into dialysis tubing (10 kDa cutoff) and covered by an

Total nitrogen (Ntotal) 0.056 g/LAmmoniacal Nitrogen (Nammoniacal) 0.014 g/LInhibition of bioluminescence IB (%) 98

excess of polyethylene glycol 8000 (PEG 8000). The procedure wasrepeated until the volume of enzyme preparation in the dialysistubing decreased from 1000 to 50 mL. The concentrated enzymewas then poured in a smaller size dialysis tube and dialysed against10 mM acetate buffer pH 5. The experiments were performed withthis concentrated clear filtrate.

2.3. Determination of laccase activity and properties

Laccase activity was measured by monitoring the increasein absorbance at 469 nm (ε469nm = 27 500 M−1 cm−1) of a reac-tion mixture containing 10 mM 2,6-dimethoxyphenol in 100 mMacetate buffer, pH 5 [31]. Enzymatic reactions were carried outat room temperature (22–25 ◦C). One unit of enzyme activity wasdefined as the amount of enzyme oxidizing 1 �mol of substrate permin.

Partial characterization of the laccase in the crude preparation,showed an optimal pH at approximately 4. Activity was stable inthe crude extract at room temperature, pH 7 for 24 h; more than50% activity was retained at pH 5. The laccase in the crude extractwas also stable for 24 h at 50 ◦C; over 90% activity was lost at 60 ◦C,however [30].

2.4. Effluent used

Industrial effluent was supplied by a textile factory (Ksar Helal,Tunisia) that utilises different dyes and other chemicals includingdetergents, salts and surfactants. The amounts of these chemicalsin the effluents depend on the type of process that generates thewaste. Effluent characteristics are summarized in Table 1.

2.5. Decolourization tests

Decolourization of effluent was examined using the crude T.trogii laccase preparation. Unless otherwise indicated, all experi-ments were performed in 3-mL disposable cuvettes in a 2 mL finalreaction volume. The reaction mixture contained 100 mM acetatebuffer pH 5, 20% effluent, and laccase with or without a laccasemediator. The reaction was initiated by the addition of laccase andincubated in the dark at 30 ◦C. Decolourization of effluent was fol-lowed by measuring the absorbance at 600 nm at 1 h intervals.Decolourization was defined as:

Decolourization (%) = 100 × Absorbancet0 − Absorbancetf

Absorbancet0

mixture before incubation with the enzyme and Absorbancetf isabsorbance at 600 nm after incubation.

Controls used heat killed enzyme solution whereas blanks con-tained all components of the reaction mixture except the colouredeffluent. All experiments were performed in duplicate.

8 rdous Materials 175 (2010) 802–808

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.6. Effect of laccase mediators on effluent decolourization

The effect of phenolic compounds as laccase mediators onffluent decolourization was tested with 1-hydroxybenzotriazole,yringaldehyde, vanillin, acetosyringone, syringate, vanillate, o-,- and m-coumarate. All compounds were used at concentrationsanging from 0 to 1 mM in the reaction mixture, along with 20%rude effluent in 100 mM acetate buffer pH 5. The reaction was ini-iated by the addition of 5 U/mL laccase and further incubated for8 h in the dark at 30 ◦C.

.7. Effect of effluent and enzyme concentration onecolourization by laccase–HBT system

The effect of effluent concentration at 5, 10, 20, 30, 40 or 50% inhe reaction mixture, along with 5 U/mL laccase and 1 mM HBT in00 mM acetate buffer pH 5 on decolourization was studied in an

nitial experiment. The effect of enzyme concentration was testedt different levels of activity: 1, 2, 5, 7 or 9 U/mL with an effluentoncentration of 20%. Controls contained heat killed enzymes.

.8. Effect of pH, temperature on effluent decolourization byaccase–HBT system

To study the effect of pH on effluent decolourization, the reac-ion mixture containing 20% wastewater was incubated at 30 ◦C inhe presence of 5 U/mL crude laccase and 1 mM HBT at differentH values using 100 mM acetate buffer for pH 4 and 5 and 100 mMhosphate buffer for pH 6, 7 and 8. The effect of temperature wasxamined by incubating 20% effluent in 100 mM acetate buffer pH, 1 mM HBT and in the presence of 5 U/mL laccase at 30, 40, 50nd 60 ◦C. For each pH and temperature value a reaction mixtureithout enzyme was prepared under the same conditions to detectossible colour changes not due to enzyme activity. Controls con-ained heat killed enzymes whereas blanks used all components ofhe reaction mixture except the coloured effluent.

.9. Effect of metal ions on effluent decolourization byaccase–HBT system

In order to determine the effect of metal ions on the decolour-zation of effluent, 10 mM of CoCl2, MnCl2, FeCl2, MgSO4, Na2SeO4,a2MoO4, Na2WO4, CdCl2, CuCl2 and NiCl2 were added to the

eaction mixture, which consisted of acetate buffer 100 mM pH, effluent (20%) and 5 U/mL of crude laccase. The mixture was

ncubated at 30 ◦C for 6 h.

.10. Effect of laccase inhibitors on effluent decolourization byhe laccase–HBT system

The effects of different concentrations of several laccasenhibitors on effluent decolourization by the laccase–HBT system

ere tested. The laccase inhibitors l-cysteine, sodium dodecylsul-ate (SDS), NaBr, NaN3 and EDTA were tested at concentrations of.1, 1 and 10 mM. The reaction mixture comprised 100 mM acetateuffer pH 5, 20% effluent, 1 mM HBT and 5 U/mL of crude laccase andas incubated at 30 ◦C for 6 h. The inhibition rate was calculatedsing the formula:

= 100(ACT − AIT)ACT

here I: inhibition (in %), AIT: absorbance in inhibition test after 6 h,nd ACT: absorbance in control test after 6 h. Controls containedeat killed enzymes whereas blanks used all components of theeaction mixture except the coloured effluent.

Fig. 1. Effect of T. trogii laccase concentration on the decolourization of textile fac-tory effluent. Enzyme concentrations (U/mL): 1 (�), 2 (�) 5 (�) 7 (×) 9 (�).

2.11. Microtoxicity assay

A microtoxicity test based on inhibition of the bioluminescenceof Vibrio fischeri LCK480 using the LUMIStox system (Dr. LangeGmbH, Düsseldorf, Germany), was used according to ISO 11348-2[32]. Bacterial luminescence was measured before sample addi-tion (10 min reading), and after 15 min or 30 min incubation time,respectively. The decrease in bioluminescence, indicating toxicityof the test substance, was measured after 15 min contact time withsamples. According to the manufacturer description of the LUMIS-tox, there should not be large differences when exposure times of5, 15 and 30 min are chosen. But when different substances are tobe evaluated, it should be tested using the same incubation time inorder to compare the results. Inhibition of bioluminescence (IB) wasachieved by mixing 0.5 mL of effluent (non-treated, treated withlaccase, with laccase–acetosyringone or laccase–HBT) and 0.5 mLluminescent bacterial suspension. After 15 min exposure at 15 ◦C,the decrease in light emission was measured. The toxicity of dif-ferent concentrations of HBT (0.0925, 0.185, 0.375, 0.75, 1.5 and3 mM) was also tested. Toxicity is expressed as the percentage inhi-bition of bioluminescence (% IB) relative to a non-contaminatedreference. A positive control (7.5% NaCl) was included for eachtest.

3. Results and discussion

3.1. Decolourization of effluent by crude laccase

The degradation ability of crude laccase obtained from Cu-induced cultures of T. trogii was assessed by incubating effluentwith laccase concentrations from 1 to 9 U/mL. The reaction mixturewas incubated at 30 ◦C and decolourization followed by measuringabsorbance at 600 nm at 3 h intervals. Low colour removal (10%)was obtained after 9 h incubation at 30 ◦C using 9 U/mL laccase(Fig. 1). These results concur with previous studies which demon-strated that decolourization of dye-containing effluents by crudelaccase was limited [23]. Industrial effluents may be complex sub-strates, containing not only dyes but also salts, sometimes at veryhigh ionic strength, and extreme pH values, chelating agents, pre-cursors, by-products, and surfactants [23].

3.2. Effect of laccase mediators on effluent decolourization

Of the 9 compounds (m-, o- and p-coumarate, syringate, vanil-late, vanillin, syringaldehyde, acetosyringone and HBT) screenedas mediators in the decolourization of effluent by T. trogii crudelaccase at different concentrations, HBT produced the strongest

R. Khlifi et al. / Journal of Hazardous Materials 175 (2010) 802–808 805

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ig. 2. Effect of laccase mediators on the decolourization of textile factory effluent-coumarate, o-coum: o-coumarate, acetosyr: acetosyringone, syr A: syringic acid,

ecolourization rate, >50% in 8 h (Fig. 2). Decolourization of efflu-nt increased with HBT concentration. These results corroboratehose of Soares et al. [33], in which higher HBT concentrations (upo 0.15%) led to higher decolourization rates of the lignin analogueye Remazol Brilliant Blue R by a commercial laccase; concentra-ions above this value were inhibitory to the enzyme. In contrast,n the current work, the rate of decolourization in the presence of-coumaric acid was inversely proportional to the mediator con-entration. For the other mediators, small increases in the ratef decolourization of the textile effluent by T. trogii crude lac-ase were observed. At high mediator concentrations, however,ecolourization rates decreased. This inhibition of decolouriza-ion could be due to toxicity at the high radical concentrationsrising during laccase oxidation of the mediators (m-coumarate,cetosyringone, syringate, vanillate and syringaldehyde). The effi-iency of laccase-mediator systems in the decolourization reactionepends principally on the mediator concentrations and laccasectivity used [35]. The feasibility of the laccase-mediator systems iniotransformation reactions depends on redox reversibility of theadical–substrate reaction, as well as on the balance between thetability and reactivity of the mediator radical which, in addition,hould not inhibit enzyme activity [36].

.3. Effect of effluent concentration on decolourization by theaccase–HBT system

Effluent concentration affected the efficiency of colour removal.he laccase–HBT system (5 U/mL; 3 mM) tested here decolourizedhe effluent by 81%, 70% 65% and 58% at effluent concentrations of%, 10%, 20% and 30%, respectively, over a 6 h incubation periodFig. 3). At effluent concentrations of 40–50%, however, 40–42%olour removal was obtained. The behaviour observed here wasndicative of laccase oxidation of substrates where the rate ofubstrate oxidation increased with substrate concentration untilaturation. Colour removal efficiency also decreased with increas-ng concentrations of cotton bleaching effluent [37]. Young andu [34] also reported that high dye concentrations decreasedecolourization rates.

.4. Effect of pH and temperature on effluent decolourization byhe laccase–HBT system

Decolourization of effluent occurred at pH 4, 5, and 6, with an

ptimum at pH 5 (Fig. 4a). No decolourization was observed at pH, although slow decolourization occurred at pH 7. These results

ndicate that the pH optimum for this laccase was substrate depen-ent, as purified laccases showed optimum pH values, estimated

n 100 mM tartrate buffer, at 2.5 and 3 for oxidation of DMP [30];

ude T. trogii laccase. HBT: 1-hdroxybenzotriazole, p-coum: p-coumarate, m-coum:: vanillic acid, van: vanillin, syr Adh: syringaldehyde.

however the laccases were stable only at neutral pH values. Enzymeactivity at higher pH is decreased by the binding of a hydroxideanion to the T2/T3 coppers of laccase, interrupting internal elec-tron transfer from the T1 to the T2/T3 centers [38]. The stabilityof fungal laccases is generally higher at acidic pH [39], althoughexceptions occur [40,41]. The redox potential of HBT is approxi-mately 1100 mV at pH 4 [42]. In addition, Xu et al. [42] reportedthat there was no substantial protonation or deprotonation of HBTat pHs ranging between 4 and 9. In this pH range, therefore, theredox potential of HBT does not significantly depend on pH. Thehigh and fairly constant value of E0 suggests that over a wide rangeof pHs, the reaction between T. versicolor laccase and HBT wouldbe the least favorable compared to reactions of laccase with theother mediators. Additionally, in the pH range from 4 to 10, HBTgenerates a very unstable nitroxyl radical, –N(O•)−, which decaysrapidly into species that are no longer functional as mediators[42,43]. This process would also limit the effectiveness of HBT asa mediator.

The optimal temperature for effluent decolourization was 50 ◦C(Fig. 4b). T. trogii laccase was stable for 24 h at 50 ◦C, but lost 90%activity at 60 ◦C [30]. Temperature profiles of laccase activity usu-ally do not differ from other extracellular lignolytic enzymes, withoptima of 50–70 ◦C [44]. However, a few enzymes with optimabelow 35 ◦C have been described, such as the laccase from Gano-derma lucidum which has highest activity at 25 ◦C [45]. This laccase

Fig. 3. Effect of textile factory effluent concentration on decolourization by the T.trogii laccase–HBT system. Effluent concentration (%): 5 (�), 10 (×), 20 (�), 30 (�),40 (♦) and 50 (�).

806 R. Khlifi et al. / Journal of Hazardous

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ig. 4. Effect of pH and temperature on textile factory effluent decolourization byhe T. trogii laccase–HBT system. (a) pH values: 4 (�), 5 (�),6 (�),7 (♦), and 8 (×). (b)emperature values (◦C): 30 (�), 40 (�), 50 (�) and 60 (×).

.5. Effect of metal ions on effluent decolourization by theaccase–HBT system

Effluent decolourization was unaffected by the metal ions Mo2+,g2+, Se2+ and W2+ following 6 h of incubation at 30 ◦C (Fig. 5). In

he presence of Cd2+, Co2+, Ni2+, Fe2+, Cu2+ and Mn2+, however, pre-ipitation of the effluent was observed. Chemical reactions between

ig. 5. Decolourization of textile factory by T. trogii laccase–HBT system in the pres-nce of metal ions. (P) Precipitation of effluent occurred.

Materials 175 (2010) 802–808

the metal ions, HBT and the compounds in the effluent, such as dyes,may explain this effect.

Effluent from textile dyeing facilities contains metals used indye production technologies or in the dye molecules. A previousstudy on the interaction of metals with T. trogii laccase indicatedthat metal ions did not affect laccase stability when used at con-centrations of 1–10 mM [30]. However, Rodríguez Couto et al. [46]showed that when the concentration of metal ions was increasedto 10 mM, stability of crude laccase from T. hirsuta decreased withall metals assayed, and was particularly affected by Fe2+.

3.6. Effect of laccase inhibitors on effluent decolourization by thelaccase–HBT system

Incubation of effluent in the laccase–HBT system plus EDTA,SDS or NaBr at concentrations of up to 10 mM resulted in slightinhibition of decolourization (Fig. 6). In the presence of NaN3and l-cysteine, however, decolourization was strongly inhib-ited at 10 mM, but at 0.1 or 1 mM these compounds had littleeffect.

Laccase inhibitors, such as EDTA, sodium azide, l-cysteine, SDS,and sodium bromide usually inhibit enzyme activity through theformation of complexes with the laccase copper ions, thus, modi-fying the laccase active site. Several sulfhydryl organic compoundshave been described previously as laccase inhibitors: e.g. dithio-threitol, thioglycolic acid, cysteine and diethyldithiocarbamic acid[47]. Inhibition by these compounds may be due to the pres-ence of copper in the catalytic centre of the laccase. In contrastto the effect of NaN3, these compounds do not decrease oxy-gen consumption by laccase during catalysis. Moreover, theseinhibitors are not laccase specific and their application to phenolox-idases originates from results obtained with other metalloenzymes[44].

3.7. Evaluation of the toxicity of the raw and treated effluent

Both the raw and the laccase–HBT treated effluent were toxic,completely inhibiting the bioluminescence of V. fischeri (Inhibitionof Bioluminescence (IB) > 80%; Fig. 7). Textile effluent can be of highcomplexity, containing a mixture of auxiliaries, salts, surfactants,degradation products and unknown components of refractory pol-lutants. The high toxicity of effluent to the luminescent bacteria

may due to unknown reaction products produced during the dye-ing processes. Inhibition of V. fischeri bioluminescence remainedeven in effluents diluted 4-fold. However, inhibition of biolumines-cence decreased to less than 20% when acetosyringone was presentin the reaction mixture. Joutti et al. [48] suggested that samples

Fig. 6. Effect of laccase inhibitors on textile factory decolourization by the T. trogiilaccase–HBT system.

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ig. 7. Toxicity evaluation of treated and untreated textile factory effluent. (A) Efflu-nt treated with laccase–acetosyringone, (B) effluent treated with laccase alone,C) effluent treated with laccase–HBT, and (D) untreated effluent. IB: inhibition ofioluminescence.

ith an IB lower than 20% should not be considered toxic. It cane concluded, therefore, that treatment of textile industry effluentith the laccase–acetosyringone system reduced the toxicity of raw

ffluent and, based on the parameters suggested by Joutti et al. [48],ven detoxified it. These observations suggest that the productsrom acetosyringone oxidation of textile effluents are not toxic to V.scheri and appear to contribute to the considerable detoxificationf the effluent.

We conclude from this work that simple decolourization of tex-ile industry effluents does not necessarily result in detoxification,s the products from use of the most effective synthetic media-or tested here, HBT, is still toxic. The use of the natural mediatorcetosyringone may be a solution to this problem of toxicity. Its difficult, however, to judge the quality of results obtained. Theioluminescence test can be used as pre-toxicity screening testo obtain information on overall toxicity of different samples andhemicals from textile dyeing industry.

cknowledgements

The present research study was supported by the MESRST ofunisia under Contract Program of the Bioprocesses Laboratory andUF, (PER-LBP).

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[3] O. Tunay, I. Kabdasli, G.D. Eremektar, D. Orhan, Color removal from textilewastewater, Water Sci. Technol. 34 (1996) 9–16.

[4] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Remediation of dyes in textileeffluents: a critical review on current treatment technologies with a proposedalternative, Bioresour. Technol. 77 (2001) 247–255.

[5] H. Keharia, D. Madamvar, Bioremediation concept for treatment of dye con-taining wastewater: a review, Indian J. Exp. Biol. 41 (2003) 1068–1075.

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