Chemosphere 72 (2008) 1816–1822Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere Technical Note Photocatalytic and combined anaerobic–photocatalytic treatment of textile dyes F. Harrelkas a,b, A. Paulo c, M.M. Alves c, L. El Khadir b, O. Zahraa d, M.N. Pons a, F.P. van der Zee c,* a Laboratoire des Sciences du Génie Chimique, CNRS, Nancy University, INPL, 1 Rue Grandville, BP 20451, 54001 Nancy Cedex, France b Laboratoire d’Automatique et d’Etudes des Procédés, Université Cadi Ayyad, Faculté des Sciences Semlalia, Avenue Prince Mly Abdellah, BP 511, 40000 Marrakech, Morocco c IBB – Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal d Département de Chimie-Physique des Réactions, UMR 7630-CNRS, Nancy University, INPL, 1 Rue Grandville, BP 20451, 54001 Nancy Cedex, France a r t i c l e i n f o a b s t r a c t Article history: A photocatalytic process based on immobilized titanium dioxide was used to treat crude solutions of azo, Received 1 February 2008 anthraquinone and phthalocyanine textile dyes. In addition, the process was applied to the treat autox- Received in revised form 13 May 2008 idized chemically reduced azo dyes, i.e. representatives of recalcitrant dye residues after biological Accepted 16 May 2008 sequential anaerobic–aerobic treatment. Photocatalysis was able to remove more than 90% color from Available online 27 June 2008 crude as well as autoxidized chemically reduced dye solutions. UV-absorbance and COD were also removed but to a lower extent (50% in average). The end products of photocatalytic treatment were Keywords: not toxic toward methanogenic bacteria. The results demonstrate that photocatalysis can be used as a Anthraquinone dyes Autoxidation pre- or post-treatment method to biological anaerobic treatment of dye-containing textile wastewater. Azo dyes Ó 2008 Elsevier Ltd. All rights reserved. COD removal Phthalocyanine dyes Titanium dioxide 1. Introduction AOPs are based on the use of the hydroxyl radical as primary oxidant of organic pollutants. These treatments can lead to com- The textile-processing industry is putting a severe burden on plete mineralization of organic molecules into CO2 and water the environment, through the release of heavily polluted wastewa- (Legrini et al., 1993), with the hetero-atoms being transformed ters. Biological treatment methods are favored as they are consid- into chloride (Chen et al., 1995), sulfate (Kato et al., 2005), ammo- ered environment-friendly and relatively cheap. The most logical nium (Hidaka et al., 1995), etc. Systems such as UV-hydrogen per- biological strategy is sequential anaerobic–aerobic treatment oxide (Aleboyeh et al., 2005; Baldrian et al., 2006), ozonation (Field et al., 1995). The anaerobic phase is important for reductive (Farré et al., 2005; Liu et al., 2007) and photo-Fenton (Ruppert cleavage (decolorization) of azo dyes, as well as for (partial) decol- et al., 1993) have been extensively described in literature and orization of other types of dyes such as anthraquinone, phthalocy- have demonstrated their efﬁciency. More recently, techniques anine, and triphenylmethane dyes (Delee et al., 1998). The such as photocatalysis (Ollis, 2000), sonolysis (Drijvers et al., consecutive aerobic phase would serve to biomineralize aromatic 1999; Minero et al., 2008) and c-radiolysis (Getoff, 1996; LaVerne amines from azo dye cleavage (Pinheiro et al., 2004), as well as et al., 2007) have shown promising prospects. Solar photocatalysis to remove some of the other types of dyes by adsorption and bio- is especially attractive as it is based on a fully renewable and degradation (Easton, 1995). However, there are some limitations: cheap energy source (Malato et al., 2002). Titanium dioxide is a it is not certain that all aromatic amines can be degraded, and stable and non-toxic semi-conductor, which is widely used in so- the complete removal of other types of dyes is questionable (Van lar photocatalysis. However, the UV radiation that can be ab- der Zee and Villaverde, 2005). Due to these limitations, more and sorbed by TiO2 represents only 5% of the solar spectrum. This more research is focusing on combining biological treatment of limits the overall yield of the process. In order to improve this dye-containing wastewaters with other techniques, such as coagu- yield, combinations with other AOPs have been suggested (Zhang lation-ﬂocculation, adsorption on solids (activated carbon, natural et al., 2008; Neelavannan and Ahmed Basha, 2008). For the treat- products such as agro wastes), and most importantly advanced ment of various types of wastewater, including dye-containing oxidation processes (AOPs). textile wastewater, a combination of AOPs with biological pro- cesses as pre-treatment and/or polishing step have been sug- gested (Bousselmi et al., 2002; Bahnemann, 2004). Anaerobic * Corresponding author. Tel.: +351 253 604 400x5413; fax: +351 253 678 986. bioprocesses are particularly attractive: their energy input is min- E-mail address: [email protected]
(F.P. van der Zee). imal as no aeration is required. 0045-6535/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2008.05.026 —SO 3 ) and reactive groups (typically triazinyl or vinyl sulfonyl).8 Reactive Green K5BL phth Structure unknownb chromophore: 658 24.0 structures) Reactive Blue KBL anth Structure unknownb chromophore: 591 10. as a post-treatment method for the degradation of autoxidized re- duced azo dyes.9 Acid Orange 12 azo 486 48. The sample to be treated was stored in a reservoir (vol- Table 1 Characteristics of dyes Name Typea Structure kmax (nm) e (l g1 cm1) Acid Orange 10 azo 480 42. Pont-Evêque. we report the results of photocatalysis with the prior to use by heating the solutions at 80 °C for 1 h after adjusting use of immobilized TiO2. The aluminium surface was inactivated by coating it with 2. Samaro.5 Reactive Violet K2LR azo Structure unknownb chromophore: R1–[email protected]
–R2 (R1 and R2 are aromatic ring structures) 549 12. / Chemosphere 72 (2008) 1816–1822 1817 In this paper. The solution to be treated ﬂowed as a thin ﬁlm from the top of the Solutions of Acid Orange dyes from Sigma–Aldrich and reactive chamber over a non-woven fabric made of cellulose ﬁbers on dyes (commercial name: Drimarene) dyes from Clariant (Mutenz.7 Reactive Orange KGL azo Structure unknownb chromophore: R1–[email protected]
–R2 (R1 and R2 are aromatic ring structures) 398 16. Reactive dyes were hydrolyzed solution. . The photocatalytic reactor (Fig. all reactive dyes were hydrolyzed prior to use. France).5 Reactive Blue K2LR azo (form) Structure unknownb chromophore: (R1–R3 are aromatic ring 614 16. 3. –OH. Harrelkas et al..1 a Dye type: azo = azo dye.2 Reactive Black 5 azo 595 22. substituted with auxochromes (typically –NH2. both as a way to treat crude dyes.e. France). representative persistent constituents of bio. and the pH to 10 using 2 N NaOH. Photocatalysis experiments logically treated dye-containing wastewater. each dye is characterized by its wavelength corresponding (gift from Ahlstrom. Materials and methods minium plate with a working area of 30 30 cm2 (Alinsaﬁ et al. as well as sheet covered the reacting chamber to avoid evaporation of the by its absorption coefﬁcient (e). F. As shown in and Snowtex 50 SiO2 (20 g m2) have been ﬁxed by compression Table 1. form = formazan dye. which Tiona PC500 TiO2 (18 g m2).1. i. Villeurbanne. A transparent glass to the maximum band of UV–visible absorption (kmax). Dyes a thin layer of PTFE (PTFE AL. b Reactive dyes of unknown structure are all composed of the chromophore (as shown). UOP 2000 zeolite (2 g m2) Switzerland) were prepared using de-ionized water. phth = phthalocyanine dye. 2007). anth = anthraquinone dye. 1) consisted of a 37° slanted alu- 2. ume given in Table 2) and was continuously circulated in the sys. FeCl2 4H2O (2). propionate and butyrate at a 1:1:1 COD-based ratio) try using a SECOMAM (Domont. c Listed data represent average values of duplicates/triplicates. CaCl2 (10). / Chemosphere 72 (2008) 1816–1822 front view side view lamp support catalyst support pump feeding from lamps pump catalyst support glass cover to reservoir reservoir Fig.05). %Biol. NiCl2 6H2O (0. form = formazan dye. The 4. After each experimental run. Greenish yellow y Dark red 9 –d –d Acid Orange 12 azo 87 n. Slightly yellowish y Dark brown 13 462 6. Harrelkas et al. buffered at a pH 7. it was veriﬁed bottles sealed with butyl rubber stoppers. kmax (%) New kmax (nm) e (l g1 cm1) %Chem.3 ± 0.a. anth = anthraquinone dye. b Dye type: azo = azo dye. Biological decolorization in anaerobic bioassays using vfa-fed anaerobic granular sludge.41).a. Essen. The lights were posi- 5. Non- tem by a peristaltic pump at a constant ﬂow rate of 200 ml min1. H3BO3 tion (50 mg l1). trated dye solutions (5 g l1) and 100 mg of the hydrogenation cat- alyst 10% palladium on barium sulfate (Sigma–Aldrich).049). low absorbance over entire UV–vis area. the Chemical dye reduction was achieved by bubbling hydrogen at photoreactor was rinsed with de-ionized water under UV low ﬂow through 70 ml glass bottles containing 50 ml of concen- irradiation. Acid Orange 10 azo 91 n. Anaerobic biological dye reduction reaction was allowed to continue during the night (14 h). In Anaerobic biological reduction was performed in 160 ml glass case no substantial decolorization had taken place. Visual observation indicates near to complete color removal. by two UV lamps emitting light with a wavelength around 365 nm (F15T8. (0.164). BLB 15W. Light was turned on at the begin- ning of each experiment. d No peak.038).05). Germany). CuCl2 2H2O (0. The medium was the range 200–800 nm for experiments run in France and a JASCO . NaSeO3 5H2O (0. The substrate was composed of a NaOH-neutralized mixture of volatile fatty The reactions were monitored by UV–visible spectrophotome- acids (acetate.05).6 Reactive Violet K2LR azo 99 91 y 5 –c 3. The headspace was 6. Artiﬁcial irradiation was provided tration of 200 mg l1 with a syringe from 5 g l1 stock solutions.092). MnCl2 2H2O (0. dyes were added to a ﬁnal concen- to ensure sufﬁcient oxygenation.2 by addition of NaHCO3 (5 g l1). Table 2 Chemical and biological dye decolorization and autoxidation of reduced dye solutions upon exposure to oxygen Compound Chemical/biological decolorizationa Autoxidation b Name Type Color removal at kmaxc Residual color y/n Color %Abs at orig.2 Reactive Blue K2LR form 96f 100 y 3 –c 2. Analytical procedures ﬁlled with a mixture of N2 and CO2 (ratio 80%/20%). Schematic presentation of the photocatalytic reactor. (NH4)6Mo7O24 4H2O (0. France) Anthelie Light device in representing a total COD concentration of 2 g l1.5 Reactive Orange KGL azo 96 92 y Violet 5 540 1. nutrient medium with (in mg l1): NH4Cl (160).1 Reactive Blue KBL anth 94f 7 Bright yellow n – – – Reactive Green K5BL phth 35f 0 n – – – a Chemical decolorization by H2 using Pd as catalyst. f Slow reaction: value represents chemical color removal of a diluted dye solution (50 mg l1).8 g VSS l1. Duke. acclimated anaerobic granular sludge from a brewery wastewater thereby permitting optimal distribution of the liquid over the cat. CoCl2 6H2O (2). MgSO4 6H2O (100). which was mostly sufﬁcient to decolorize concentrated dye solutions. ZnCl2 (0. phth = phthalocyanine dye.3 Reactive Black 5 azo (79)e (85)e Slightly brownish y Blue 20 602 4. all reactive dyes were hydrolyzed prior to further treatment.1818 F. 1. After alytic support. e Real values are higher since autoxidation could not be prevented. by repeating the procedure using a much more diluted dye solu- KH2PO4 3H2O (328). AlCl3 (0. The reservoir was open to air pre-incubation for 24 h at 30 °C. data range less ± 5%. treatment plant was added to a concentration of 0. PTFE tubing was used. containing 50 ml of a whether any reductive decolorization reaction could be achieved. Chemical dye reduction tioned in parallel to the reactor. d Dye concentration from which the reduced dye originates. Autoxidation reactions are fast and irrevers- slower than the azo dyes.4) 10 Acid Orange 12 azo 50 180 486 93 ? 99 (5. / Chemosphere 72 (2008) 1816–1822 1819 V-560 device for experiments run in Portugal. h) Acid Orange 10 azo 50 180 480 92 ? 92 (3. mimic. phth = phthalocyanine dye. 1999). but still rather alike.. explains the decolorization of the solution.. possibly a result of tivity were measured by using.0) 59 ? 65 (3. The reaction may be a relatively small change of the molecule azo dyes. 2003). yield- orized by overnight bubbling with H2 with Pd as catalyst was ing colored compounds with a kmax distinct from that of the mostly sufﬁcient to achieve this reduction in concentrated original dye. Pearce et al.3) ? 72 (29.6) 227 25 ? 61 (6. the phthalocyanine dye Reactive plied to dye solutions and to autoxidized (chemically) reduced dye Table 3 Removal of color. USA) (Method 8000).1) 240 67 ? 89 (5. Harrelkas et al. 2006). Lee et al. red. reversible decolorization is common for this type of CH4-COD.a. but it may also involve aromatic ring opening or dimerization none dye Reactive Blue KBL could be decolorized chemically. are the results with (Chrompack Haysep Q column on a Chrompack 9001 gas chro. the anthraquinone dye could be decolorized by hydrogen but was hardly affected by anaerobic biological treatment.a. a PHM 220 pH.0) 248 50 ? 58 (3. tion of azo and formazan dyes is very similar to chemical azo dye Methane production was monitored by gas chromatography reduction. Table 3 summarizes the results of photocatalytic treatment ap- mazan and anthraquinone dyes. Table 2 lists the color removal efﬁciencies obtained ascorbic acid.1) autox. However. Colorado. no biological decol- matograph). Acid Orange aa 50d 180 –e 235 59 ? 72 (3. In fact. France). e Reduced compound has only a faint color and there is no absorbance peak in the visual area. as it has been demonstrated that most anthraquinone dyes studied are at The color removal percentages listed in Table 2 for chemical least partly biologically decolorized under anaerobic conditions reduction with hydrogen show that all dyes were at least partly (Dos Santos et al. respectively to avoid color shifts due to pH changes after 12–16 days of incubation. 2001.1) 230 21 ? 59 (5. data not determined by using the manometric OxitopÒ method (WTW Mea... Reactive aa 50d 500 389 48 225 74 64 Orange KGL Reactive Violet K2LR azo 50 500 549 95 219 72 53 autox. COD was measured Green K5BL was hardly decolorized and the same applied for an- on a Hach 2400 (Loveland. the fate of dyes in anaerobic biological treat- For the spectrometric assessment of chemically or biologically ment systems.5) Black 5 Reactive Orange KGL azo 50 500 389 96 225 52 48 autox. Germany).e.6) 19 ? 50 (6. Especially aromatic amines with ortho-substituted (5 g l1) azo dye solutions. Results and discussion anaerobic stability is not typical for anthraquinone dyes. red. respectively. samples were diluted in a phosphate buffer (10. the azo bond is cleaved hydroxyl groups.0) 10 Autox. a series of dye-amended batch vials was incubated reduced. c n. h) (%) (tend. All reduced azo dye solu- decolorized. Lee et al. which indicates the property hydroperoxyl radicals. the color removal was not more than 35%. UV and COD during photochemical treatment of dye solutions and autoxidized (chemically) reduced dye solutions Compound Initial amount of dye Color removal UV-removal COD-removal Namea Typeb Initial conc..0) n. All of the azo dyes tested were near-completely decol. which requires oxygen for the production of hydroxyl and with diluted solutions (50 mg l1). 1996. shown).. Acid Orange aa 61d 550 –e 235 90 (30.’ stands for autoxidized chemically reduced. albeit (Kudlich et al. near-complete decolorization was achieved ing. b Compound type: azo = azo dye. This apparent 7.c Acid Orange 10 azo 61 550 480 100 (29. 2006). F. The pH and the conduc.1) autox.86 g l1 with anaerobic granular sludge and the decolorization was fol- NaHPO4 2H2O. red. anth = anthraquinone dye. are susceptible to autoxidation. Acid Orange aa 50d 180 450 75 ? 96 (6.1) 28 ? 28 (5. It is seen that biological decoloriza- and to prevent autoxidation of aromatic amines. Also two of the non.38 g l1 Na2HPO4 H2O) containing 200 mg l1 lowed in time. It was found that even in diluted dye solutions (50 mg l1).c ? n. = Not available (COD measurements failed).3) 248 96 (29.5) 260 75 ? 90 (4. Less similar. which include a large fraction of the constituent yielding colorless amines (Stolz. adsorption rather than reductive transformation. Concentrated solutions (5 g l1) of these ible and cannot be avoided when anaerobic reduction is followed dyes were only decolorized for 20–25% during overnight bubbling by either aerobic biological treatment or by photocatalytic polish- with H2. In order to verify whether chemical dye reduction is suitable to Villeurbanne. BOD was other phthalocyanine dye tested (Reactive Green K4GN. red. 5. i. of dyes (Nigam et al. red. red. aa = aromatic amines (reduced azo dyes).a. Weilheim. Reactive aa 99d 180 593 83 ? 100 (4. meter and a CDM 210 conductimeter (Radiometer Analytical SAS. poor chemical vs. which aromatic amines from azo dyes. The methane concentration was expressed in terms orization. In contrast. in a fast way. surement Systems. for. Reactive aa 50d 500 –e 219 84 62 Violet K2LR Reactive Blue K2LR form 50 500 614 97 278 85 62 Reactive Blue KBL anth 50 500 591 99 278 85 52 Reactive Green K5BL phth 50 500 658 98 224 83 68 a ‘autox.1) 49 ? 68 (5. . red. In contrast to azo.5) 69 ? 70 (4.6) 12 Reactive Black 5 azo 99 180 595 97 ? 100 (5.3) Autox. 2005. all reactive dyes were hydrolyzed prior to use.4) ? 70 (30. the phthalocyanine dye. h) (nm) (%) (tend. In azo dyes. form = formazan dye. the formazan dye Reactive Blue K2LR and the anthraqui. Volume kmax t=2h ? t = tend % k t=2h ? t = tend % t=2h ? t = tend % (mg l1) (ml) (nm) (%) (tend. of these dyes to be reductively decolorized. tions were observed to autoxidize upon exposure to oxygen. UV and COD decrease (b and d) during photocatalytic treatment of Acid Orange 12 and autoxidized chemically reduced Acid Orange 10. the opposite trend was observed with 2 Acid Orange 12 vs.. it is not possible to predict whether this observa- tion represents a general trend or merely an exception. However. there is usually some UV-absorbance left. 3. UV–visible spectra of Reactive Blue KBL (a) and Reactive Green K5BL 133) by TiO2/UV suggested that the removal of this type of dyes is (b) before (thick line) and after (thin line) photocatalysis. a wave- a length in the UV range was chosen corresponding to a peak or a 4 shoulder in the spectrum at t = 0. as autoxidation reactions are complex (Kud- lich et al. Even b if the color is removed. UV–vis spectra (a and c) and color.5 h 60 COD (mg l-1) t = 5. The COD removal observed for Reactive Black 5 is much lower than the value given Absorbance (cm-1) 1 by Arslan and Balcioğlu (1999) but an exact comparison is difﬁcult as the reactor setup and the type of TiO2 were different. UV-absorbance is generally associated with aromatic rings. UV-absorbance and COD with all of the com- pounds tested. 2001). Color removal is much faster than COD 2 removal.1820 F.e. 2 and 3. its autoxidized reduced analogue. In 3 general. the removal of UV-absorbance and COD was higher with autoxidized reduced azo dyes than with untreated azo dyes. 5 either the original dye or the autoxidized reduced dye. Color removal was always higher than UV-absor- 3 bance removal. which is not the case for COD removal. For each compound. Photocatalytic treatment led to removal of color. / Chemosphere 72 (2008) 1816–1822 80 a t=0 b 486 nm 3 t=1h 240 nm Absorbance (cm-1) t = 3. Harrelkas et al. The relatively low color removal observed with autoxidized re- 0 duced azo dyes reﬂects the low initial color of these samples. 1997. its autoxidized reduced analogue. 0 200 300 400 500 600 700 800 An interesting result was obtained with photocatalytic treat- ment of the phthalocyanine dye Reactive Green K5BL. 1999). The apparent recalcitrance of autoxidized reduced Acid Orange 12 to photocata- lytic oxidation may be related to the fact that its naphthalene- based amine (i. the structure prone to autoxidation) has less sub- 1 stituents than the naphthalene-based amines from the other azo dyes tested. the color removal being generally close to its end value after 2 h. due to adsorption to the catalyst surface rather than to oxidative .1 h COD 2 40 1 20 0 0 4 80 c t=0 d 235 nm t=1h COD Absorbance (cm-1) 3 60 t=2h COD (mg l-1) t=3h 2 40 1 20 0 0 200 300 400 500 600 0 1 2 3 4 5 wavelength (nm) time (h) Fig. respectively. Prevot et al. This trend was most obvious with Reactive Black 5 vs. which are more difﬁcult to open (Theurich et al. Previous re- wavelength (nm) search to the treatment of a phthalocyanine dye (Turquoise Blue G Fig. 2. However.. solutions.. Examples are shown in Figs. method for decolorization of biorecalcitrant dyes (e. G. Stopka. In shorter assays with other wastewater (surfactants. M..54 and 3. 51% (Reactive Black 5) and 48% (autoxidized reduced Reactive Black 5). been shown toxic towards microbial activity. Van Lier. Pichat. K.. G. 2007. Biotechnol.. Bisschops. Serpone. In: Proceedings of the International have been detected in photocatalytic treatment (Tanaka et al. England. Alinsaﬁ. C. M. 2000).. W. UV-absorbance Therefore.M. Ayllon. 1995. S. No BOD was detected after photocatalysis of the original study. I.. Bahnemann. No real improvement of the color removal was ob. J. ment of Reactive Green K5BL (Fig. Zhao. formation of recalcitrant peroxide. In contrast to these ﬁnd... J.. Ghrabi. Sonochem. azo. phthalocyanine dyes. J. Stams. (55 °C) and mesophilic (30 °C) anaerobic treatments. Evaluation of the UV and COD data shows that. salts.3 treatment. E... 43. L.. F. In: Cooper.J. it is obvious that com- logue.. Chem. tion and detoxiﬁcation of dye-containing wastewater. Zayani.A. Solar photocatalytic treatment of textile wastewater – possibilities and the case of natural anaerobic reduction while phenolic compounds limitations in the Tunisian context. contaminants in water. 67. E. Franch. O’Neill. Evenou.. D.. F. 1999. respectively. H.. Appl.A. 1127–1133. Anaerobic treatment of dyes after photocatalysis. Pelizzetti. Vogelpohl. Photocatalytic water treatment: solar energy applications. P. Conclusions Field. phthalocya- The residual UV-absorbance after photocatalytic treatment may nine and anthraquinone dyes) and dye residues (e.. Cervantes.. aromatic amines from azo dyes) after biological treatment. Pinheiro. Degradation of some biorecalcitrant pesticides by homogeneous and heterogeneous photocatalytic ozonation. H... 439–445. This result is encouraging as aqueous mixture of trichloroethylene and chlorobenzene. Degradation of commercial reactive dyestuffs by creased from 0 to 0.g. I. The pressed in the dye-containing bottles as it deviated less than 5% transformation and toxicity of anthraquinone dyes during thermophilic from the blank. the results of the present study show a complete change of catalysis may be a feasible pre-treatment method for decoloriza- the shape of the UV–visible spectrum during photocatalytic treat.R. The BOD/COD ratio of Acid Orange 10 in.. Schraa. N. and as it was clear that the UV-absorbance mainly de. Chem. 66. dyes of known structure (for end times see Table 3). 2005.. J. Pons. anaerobic biodegradation tests were performed with four reactive Delee. H. Sonolysis of an alytic process was already very large. indicates its feasibility as a post-treatment the dye. ability to decolorize dyes of distinct chemical classes (i. D. A. A 91. I. since prolonged treatment (30 h) does not and 30. Ultrason. In order to check whether the by-products of a photocatalytic Chen. Int. J. 1995.. Domenech. Bahnemann. textile efﬂuents: a review. Phys.. Biotechnol. 581–593. 445–459. M.P. F. Its art. 2005. Bradford.A. pp... Bottero.Y. matic substances such as the dyes used in the present work are dif. These observations from the Portuguese Fundação para Ciência e a Tecnologia (SFRH/ are in agreement with the results reported by Hidaka et al.. for anaerobic degradation and photocatalytic degradation of aro- 258–264.. As adsorption of the dye The ability of photocatalysis to decolorize autoxidized solutions would only lower the absorbance but not alter the shape of the of chemically reduced azo dyes. A. Peral. Gabriel.. A. dye or the autoxidized reduced dye. Radiat. P. Dyes Pigments 43.R.N... 8. H. Formation of NHþ 4 and NO3 ions for the photocatalyzed anthraquinone.. Zahraa..J. The dye maker’s view. Kato. S. J.. J. 3b). M. Benhammou. M. 345– served (less than 5%) but the decolorization yield of the photocat. A.. Benes. 2). V. 323–335. respectively) yielded a residual absorbance at k = 205 nm plete mineralization does not occur.. Hruby. 2005.. G.E. (Ed.g. A.. J. A.J. Dyes Pigments 74. are probably also easily degraded by photocatalysis. D. under mesophilic and thermophilic conditions (Dos Santos et al. J.. P. generally. Arslan.. ferent: aromatic amines have been reported as intermediates in Weidemeyer. Nerud. BOD determination. 95–108. 179–186.I.. who reported that the ﬁnal ratio between ammonia (a compound without UV-absorbance) and nitrate after photocatalytic treatment References of Acid Orange 10 was higher than ﬁve.. Drijvers. / Chemosphere 72 (2008) 1816–1822 1821 degradation (Arslan and Balcioğlu. 143–148.. Farré. representing the three most mineralization of nitrogendashcontaining cationic.. 73. Leeuw. The relatively easy aerobically Sol. Harrelkas et al. Photobiol. J.. F. Society of Dyers and Colourists... Bousselmi.75 mM1.. Bouchy. was partially supported by VOLUBILIS (Project MA/02/49) and PES- creased with increasing reaction time (Fig. 9–21. F. . Decolorization of synthetic dyes by hydrogen peroxide with heterogeneous catalysis by mixed iron oxides. Aleboyeh. L. Zahraa. BPD/18748/2004). 353. O. 115. J.Y. Balcioğlu.. Lee et al. Colour in Dyehouse Efﬂuent. Hidaka. this result clearly points at oxidative transformation of anthraquinone dyes. Symposium on Environmental Pollution Control Waste Management.). A.U. M. indicates that photo- ings. of 2. Ghozzi. 1999.. creases. Photobiol.. 69% (autoxidized reduced Acid Acknowledgements Orange 12). L. Geissen. 47. evaluation of the residual UV-absorbance can give an and COD.A. However. Hufschmidt. these percent- ages were 39% (Acid Orange 12). 145–152. 2006). indication about the end products of photocatalytic oxidation of more than 50% mineralization can be achieved during two h of the N in azo and amino groups. A 85.. nondashionic and abundant types of textile dyes)... J. result in complete removal of UV and COD. Nguyen Thi Kim. The aerobic biodegradability of Acid Orange 10 was assessed by Yaacoubi. van der Zee received a grant that nitrate was not the main reaction product. etc). M. Anton. Sep. Technol. Photochem. Hawkes. Chemosphere 58. Technol.. F.. biodegradable substances produced by reduction and autoxidation Baldrian. A.. van Langenhove.B.M. Enhanced biodegradation of aromatic pollutants in cocultures of anaerobic and aerobic bacterial consortia. It is probable that ammo- nium was the main end product of photocatalytic degradation of Aleboyeh. F. N.e. N-containing organics cannot be excluded. 1998.. Treatment of textile industry wastewater by supported photocatalysis. Dussaud from Alstrohm. H. autoxidized be due to a recalcitrant organic fraction or to inorganic compounds.M. 1999). 804–812.. Photochem. Easton.70 mM1 N. Bray. Purif. as well as chemically reduced spectrum. which corresponds to 29% Further experiments will be needed to monitor the end prod- and 42% of the absorbance that can be expected in case of complete ucts and to assess the effect of other known constituents of textile oxidation of compounds’ N to nitrate. Photodegradation of surfactants XIV.. 2002. Malato.. The two long-term assays (29. some anthraquinone dyes have been found toxic to methanogens 6. Especially nitrate and nitrite have a high absorption coefﬁcient in In addition to removing color.. 2004. Kinetics of oxidative decolourisation of Acid Orange 7 in water by ultraviolet radiation in the presence of hydrogen the dyes’ azo and amino groups. albeit at lower rates and to a lower extent. Y.B. M. A. 47–77. 1996.4 h for Acid Orange 10 and its autoxidized reduced ana. Ennabli.. However. 1995.. Photocatalysis leads to a high extent of color removal of both Getoff. The pathway 2006. This work than 100%. D. Adsorption properties of TiO2 related to the photocatalytic degradation of organic treatment could be toxic to an anaerobic digestion consortium. Abdulkarim.J. pp. Moussa. Radiation-induced degradation of water pollutants – state of the crude dye solutions and (autoxidized) reduced dye solutions. Dos Santos.. Nohara. K. Merhautova. J. (1995). X. Thomas.. Energy 77. starch. As these percentages were substantially lower The authors wish to thank J.. heterogenous and homogenous advanced oxidation processes: a comparative idation. The methane production was not sup.14 after chemical reduction followed by autox. Catal. including structures that have amphoteric surfactants.. 2005.. it can be concluded SOA (Project 10807XH) programs. A. photocatalytic treatment also de- the UV region: for instance nitrate’s e (205 nm) = 8. Nejmeddine. 1995.. O. B – Environ. P. 115–121. Matsuzawa. 2005. 1–15..J. Heisler. Shi. E.. I. 671–698... Intermediat. Y. pilot-plant scale: an overview. Microbiol. C. Mater.T. 179–196.. Ultrason. Qu. 405–411. Minero. Sonochem. Augugliaro.. Stolz. Pavlostathis. J. V. A.D. 2003... G. J. Y.. Sep. Thomas. F.I. decolorization of textile efﬂuent containing azo... 1997. Sano.W. C. The photo-Fenton reaction – an effective Legrini. Vogel. 971– reactive anthraquinone and phthalocyanine dyes under various oxidation– 976. Blanco. Appl. 121–139. 370–375.. Catal.. Biotechnol.. M.. II C. L. Richter. Catal. Rev. Biological decolorization of aqueous solutions containing TiO2 suspensions. H. H. Technol. Pramauro... 1993. 23. Bauer. Liang. Microbial process for the Sonophotoelectrocatalytic degradation of azo dye on TiO2 nanotube electrode.. Banat.F.. Y. M. Radiat. Water Environ.. A.. O. Cheng. D.. Pearce. Photochem. 2008. Y. Nigam. E. 2004. diazo and reactive dyes. Ollis. / Chemosphere 72 (2008) 1816–1822 Kato. D. 109–115. 2007.. F. reduction conditions.. Res. L.. G. reduction: status review with emphasis on direct UV spectrophotometric 896–901. 308–316. 2000. Hisanaga.M. Araos. Technol. 56. 31. Process Biochem. Acad. P. 78. A. B – Environ. Bahnemann.. ... Palmisano. Tanaka. M. Baiocchi... P. G. 15..H. Guthrie.. Brussino. 34.. Appl. Savarino.. Appl.. 327–333. L. Marci. Combined anaerobic–aerobic treatment of azo Neelavannan.R. G. Photobiol. Dyes Pigments 58. K. Photocatalysis with solar energy at a commercial azo dyes. Singh. treatment. E..T. 1996. Purif. 77.B. 2006. The removal of colour from textile Kudlich.. 39. Photocatalytic degradation of Acid Blue 80 in Lee. Jin. Touraud. 61. Sci. Padermpole. Li. Photocatalytic degradation of Malato. Harrelkas et al.. Y. C. 1999. Zhang. V. 69–80. G. O. Liu.. A 73. H. T.A. A. Sci. Ruppert.J.R. A. Yuan. reactions of different aromatic o-aminohydroxynaphthalenes that are formed Pinheiro. Pellizzari. Ehamed. Chem.. 76. R. I. Sci. 2000. 2008. R.. Villaverde. Aromatic amines from azo dye during the anaerobic reduction of sulfonated azo dyes. Marchant. 435–442. Vione.. 2001. Phys. Hazard. Z. 1993.. Lloyd.. Van der Zee. Photochemical processes for water photochemical wastewater treatment process. C. 2007.1822 F.H. Braun.. S.. Takeuchi. J. degradation of textile washwater. S.. P... 144. J. 156–169. B – Environ.. Ahmed Basha. Vidal. Enhancement of Photocatalytic degradation of naphthalene and anthracene: GC–MS analysis of dye sonochemical degradation by some inorganic anions present in natural the degradation pathway.J. Ding.. Alhakimi. Dyes Pigments 61. S. Res. Autoxidation wastewater using whole bacterial cells: a review.. Knackmuss. D. Fang. 57. C. detection in textile industry wastewaters.. Oliveros..M. Radical yields in the radiolysis of cyclic Prevot. Electrochemical-assisted photocatalytic dyes – a short review of bioreactor studies. R.C. Li. J.. G. water by Fe-0/granular activated carbon system in the presence of ultrasound. waters. titanium dioxide. J.. 37. K. 247–274.M. 1272–1274. H... 33.. M.G. Environ.. Environ.P.. Hetheridge. Catal. Rajab. Chem. Water Res. 2002. Maurino.... 2005. D.. B – Environ. S.. K. S.S. J. 93. Appl.G. 168–174. H. Enomoto. LaVerne. 75–78. 2001. M.E.. 180–186. Hirano.N. K. Degradation of azo dye Acid Orange 7 in Stolz.. R. Technol. M.. 35. Iwata... compounds. Photocatalytic puriﬁcation and remediation of contaminated air Photocatalytic degradation of gaseous sulfur compounds by silver-deposited and water.. Pelizzetti.. C. 1425–1440. T.. E. Basic and applied aspects in the microbial degradation of azo dyes.. Matthews. Water Res. J. Chem.. Theurich. 2008.