In this paper, electrical properties and rejection rates of dyes on TiO2/ZnAl2O4 (50/50) ceramic ultrafiltration membranes were studied. A correlation between the ...
WATMED 2 - Marrakech 14-17 November 2005
REMOVAL OF TEXTILE DYES FROM WASTE WATER BY CERAMIC ULTRAFILTRATION MEMBRANE H. Loukilia,b, M. Persin b, S. Alami Younssia, A. Albizanea, M. Bouhriaa, N. Saffaja, A. Larbotb a
Laboratoire des Matériaux Catalyse et Environnement, Faculté des Sciences et Techniques, Mohammedia BP 146, Mohammedia 20650, Morocco b lnstitut Européen des Membranes, UMR 5635 CNRS ENSCM UMII, 1919 Route de Mende, 34293 Montpellier, Cedex 5, France Abstract The characterization of electrical surface properties of membrane materials is critical for understanding and predicting filtration performances of membranes. In this paper, electrical properties and rejection rates of dyes on TiO2/ZnAl2O4 (50/50) ceramic ultrafiltration membranes were studied. A correlation between the filtration results and the streaming potential measured through the membrane was established.
Keywords: Ceramic membrane, streaming potential, ultrafiltration, dyes, electric interactions
1. Introduction Industrial, agricultural and domestic wastes, due to the rapid development in technology and urbanization, are discharged to several receivers. Generally, this discharge is done to the nearest water sources such as rivers, lakes and seas. Control of water pollution is very important for the organisms which live in water and need water of sufficient quality. The use of different kinds of dye has been continuously increasing in industrial processes such as textile, pulp and paper, paints……. The effluents rejected by these industries contain toxic dyes, which causes many environmental problems, therefore the treatment of the coloured waste is required before its disposal [1, 2]. A variety of physico-chemical methods have been studied for the removal of colour from industrial effluents. These studies include the use of oxidizing agents [3], membrane filtration [4, 5], electrochemical [6], and adsorption [7] techniques. The advantages and disadvantages of each technique have been recently reviewed [8]. Pressure-driven membrane processes such as ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) have been considered for the treatment of dye effluents of the textile industry [9]. These methods are able to clarify the coloured wastewater and to minimize effluent discharge [10]. Despite the fact that the permeate flux produced by RO is generally low, it can be reused in dyeing processes without any further treatment. NF does not reach the rejection rate obtained with RO, but the permeate quality is generally sufficient for water reuse [4, 11]. UF treatment is not widely used by the textile industry due to the low dye rejection [12], this is why, direct recycle of filtrate is not possible without further treatment. Alves and Pinho [13] reported that UF is more suitable than reverse osmosis to decolourize the wastewaters supply by the tanning industry because the dyes are bound to fats.
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WATMED 2 - Marrakech 14-17 November 2005 In the presence of water, the ceramic membranes made of mineral oxides, will develop an electrical surface charge which is due to the amphoteric behaviour of the hydroxyl groups. The charged surface will be responsible of the rejection of salts which will be depending on the charge of the ions. The characterization of membranes surface charge is very useful to predict their filtration properties. The solute–membrane interactions at the membrane solution interface needs a previous knowledge of the zeta potential [14,15] of the porous material, it is generally evaluated from electrophoretic and streaming potential (SP) measurements. Streaming potential measurements are convenient to calculate the zeta potential by means of the Smoluchowsky relation, its value depends mainly on the concentration of the filtered salt [16]. However, the SP measurements are limited to membranes with pore diameter higher than 5 nm. The SP and the zeta potential values depend strongly on the nature of the ions and on the membrane material [17, 18]. This work presents the behaviour of organic dye solutions during filtration process performed by means of UF ceramic membranes with active layer made of TiO2-ZnAl2O4 (50-50) prepared by sol gel route.
2. Experimental 2.1. Membrane preparation The grain size of cordierite powder (ternary oxide 2MgO.2Al2O3.5SiO2) used to prepare the paste for the membrane support is in the range 0–125µm. The paste which contains organic additives is then extruded to obtain a tubular support of 10 mm outer diameter. After drying and sintering at 1275°C for consolidation, the average pore diameter of the support is 7 µm; its porosity is 40 % and its mechanical strength 15 MPa. An intermediate ZrO2 microfiltration layer [19-20] was then coated on the cordierite support before depositing the final sol-gel layer. This intermediate layer allows the ultrafiltration membrane to be maintained without infiltration into the support, it was prepared using the suspended powder technique by means of pure ZrO2 powder of 8 m2 specific area. After firing at 1100°C for 2 h, a ZrO2 layer of 0.23 µm pore diameter is obtained. The final ultrafiltration membrane was prepared by slip casting of the ZnAl2O4–TiO2 (50/50) sol in the inner part of the tubular cordierite support. The sol used was prepared after mixing the pure TiO2 sol and the pure ZnAl2O4 sol with hydroxyethyl cellulose. The coating time was 30 min. The coated :
Fig. 1. SEM micrograph of ZnAl2O4–TiO2 membrane (a) general view of the surface; (b) cross section view.
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WATMED 2 - Marrakech 14-17 November 2005
support was then dried for 24 h at room temperature, then keeps at 250°C for 2 h and finally sintered at 400°C for 2 h [19]. The ZnAl2O4–TiO2 ultrafiltration layers obtained presents a pore diameter measured by nitrogen adsorption desorption centred on 5 nm.
2.2. Filtration ®
Membrane
N2
Fig.2. Laboratory filtration pilot
The filtration experiments were carried out with a laboratory pilot already described [21]. The capacity of the tank was two liters; the working pressure was fixed between 0 and 10 bars by means of a nitrogen gas bottle. The measurements of the streaming potential SP were performed through the membrane my means of two silver wires covered with silver chloride used as reference electrodes, one is positioned in the axis of the membrane tube and the second near the opposite side of the tube (fig.2). The filtered solutions were prepared with dyes at a concentration of 40ppm. The adjustment of the pH was made with either sodium hydroxide or nitric acid. The pH values of the solution were measured by means of a radiometer pH-meter.
2.2.1. Determination of membrane permeability The average membrane permeability determined using pure distilled water is 7.96 l/h.m².bar, it remains almost constant during all the filtration experiments. 2.2.3. Filtration of dyes The filtration of different dyes was carried out to evaluate the efficiency of the ultrafiltration membranes prepared for the rejection of colour with variation of pressure and pH. Five types of dyes Dye
symbols
Acid Blue 62
AB62
molecular weight MW (g/mol) 432
Reactif Blue 19
RB19
626.55
C22H16N2Na2O11S3
Direct Blue 71
DB71
1029.86
C40H23N7Na4O13S4
Reactive Yellow 145
RY145
1026.2
C28H20ClN9Na4O16S5
Direct Yellow 106
DY106
1372
C48H66N8Na6O18S6
Compact formula C20H29N2NaO5S
Table 1: Characteristics of the dyes tested
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WATMED 2 - Marrakech 14-17 November 2005 were investigated: Acid Blue 62 (A.B.62), Reactif Blue 19 (R.B.19), Direct Blue 71 (D.B.71), reactive yellow 145 (R.Y.145) and Direct Yellow 106 (D.Y.106). The characteristics of the dyes used are gathered in table 1 and the structure of dye molecules represented in figure 3. The experimental rejection coefficient R is defined by the classical equation:
R = 1−
CP CO
where Cp and Co are respectively the solute concentration in the permeate and in the feed solution.
Direct yellow 106
Acid blue 62
reactive blue 19
Direct Blue 71
reactive yellow 145
Fig.3. Structures of dyes
3. Results and discussion 3.1. Influence of pressure When the working pressure is increasing, the flux and retention increase also. Fig. 4 shows the variation of flux and retentions vs. pressure for dye RB.19. This is the classical behaviour for ultrafiltration membranes.
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WATMED 2 - Marrakech 14-17 November 2005 3.2. Streaming potential The streaming potential (SP=∆E/∆P) which is the electric potential measured for the unit of pressure was measured in the dynamic conditions during the filtration of the different dyes my means of the membrane. Fig.5 shows that the streaming potential values depend on the pH of the filtered dye solutions; this behaviour is expected because the SP which is given by the Smoluchowsky relation (1) depends on the zeta potential, which also depends on surface charge of the membrane.
SP =
εζ µλ
(1)
30
3
27
2
100 90
1
24 80
flux SP(mV/bar)
18
retention 15
50 40
12
30
9
20
6
10
3
0
0 0
2
4
6
8
J(l/h.m²)
60
% TR
0
21
70
-1
0
2
4
6
8
10
12
-2 -3 -4 -5 -6 R.B.19
D.Y.106
pH D.B.71
A.B.62
R.Y.145
10
pressure (bar)
Fig.5. Evolution of the streaming potential measured vs. pH for different dyes (C=40 ppm, ∆P=8bar)
Fig. 4. Evolution of the rejection and flux of dye RB 19 (C=40 ppm, ∆P=8bar) vs. pressure
The variation of the surface charge of the membrane with the pH of the filtered solution can be explained by the amphoteric properties of the material used to prepare the membrane which is rather positively charged at low pH and negatively charged when the pH is increasing.
3.3. pH influence
100
100
110
retention flux
100 90
100
80
retention flux
80
80
80
2
40
40
% R
%R
50
60
60
40
40
20
20
J(l/h.m²)
60
60
J(l/h.m )
70
30 20
20 10
Acid Blue 62
Reactive Blue 19 0
0 0
2
4
6
8
10
12
pH
Fig.6. Evolution of retention and flux of reactive blue 19 (C=40ppm, ∆P=8bar) vs. pH
0
0 0
2
4
6
8
10
12
pH
Fig.7. Evolution of retention and flux of acid blue 62 (C=40ppm, ∆P=8bar) vs. pH
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WATMED 2 - Marrakech 14-17 November 2005 The pH is one of the most important factors affecting the ultrafiltration process. In order to study the influence of the pH on the ultrafiltration performance, different experiments were performed using various dye solutions for pH values adjusted from 2 to 9. The variation of the rejection rates of the dyes are reported in Figs. 6-10, they depend on the pH of the filtered solutions; this is the consequence of the electric interactions developed between the ions and the charged membrane 100
100
retention flux
100 100
retention flux
80
80
80
80
%R
% R 40
40
20
20
20
0
0
40
2
40
20
Direct Yellow 106 0 0
2
4
6
8
10
Direct Blue 71 0
12
2
J(l/h.m )
60
J(l/h.m )
60
60
60
2
0 4
6
8
10
12
pH
pH
Fig.9. Evolution of retention and flux of direct blue 71 (C=40ppm, ∆P=8bar) vs. pH
Fig.8. Evolution of retention and flux of direct yellow 106 (C=40ppm, ∆P=8bar) vs. pH
surface. The rejections of dyes R.B.19 A.B.62 (figs. 6-7), increases while increasing the pH; in this case the surface charge of the membrane becomes more and more important as the pH value increases which leads to the exclusion of the dye anion (coion) by Donnan effect. Nevertheless, the rejection of dyes D.Y.106, R.Y.145 and D.B.71 (Fig.8-10) seems constant whatever the pH range; this effect may be explained taking into account of the more important molecular weight of these three molecules (table1). These results seems proved the dominant size effect compared with the Donnan repulsion effect to explain the rejection observed for dyes D.Y.106, R.Y.145 and D.B.71. For all the filtered dyes, the flux measured is not strongly affected by the pH, particularly for the three highest molecular weight dyes. 100 100
retention flux
80
80
%R
40 40
Flux(l/h.m²)
60 60
20
20
Reactive Yellow 145 0
0 0
2
4
6
8
10
12
pH
Fig.10. Evolution of retention and flux of reactive yellow 145 (C=40ppm, ∆P=8bar) vs. pH
4. Conclusion The dye manufacturing industry produces a large amount of wastewater that is highly coloured. Ultrafiltration process by means of TiO2-ZnAl2O4 membranes is able to improve the quality of the waste and offers the possibility to recycle the dyes in the process. The efficiency of the filtration 6
WATMED 2 - Marrakech 14-17 November 2005 process will depend on the complexity of the filtered solution. In the case of the dye solutions studied, the steric and electrical interactions are the two main parameters which must considered to explain the results.
Symbols SP
Streaming potential
ξ
Zeta potential
ε
Dielectric constant
µ
Viscosity of the solution
λ
Electric conductivity of the solution
References [1]: P. Nigam, G. Atmour, I. Banat, D. Singh and R. Marchant, Physical removal of textile dyes and solid state fermentation of dye adsorbed a agricultural residues. Biores. Technol., 72 (2000) 219-226. [2]: R.M. Ribeiro, R. Bergamasco, M.L. Gimenes. Membranes synthesis for colour removal of a textile effluent. Desalination 145 (2002) 61-63. [3]: N. Ince and D. Gonenc, Treatability of a textile azo dye by UV/H202. Environ. Technol., 18 (1997) 179-185. [4]: Y. Xu and R. Lebrun, Treatment of textile dye plant effluent by nanofiltration membrane. Sep. Sci. Technol., 34 (1999) 2501-2519. [5]: K. Majewska-Nowak, Effect of flow conditions on ultrafiltration efficiency of dye solutions and textile effluents. Desalination, 71 (1989) 127-135. [6]: Z. Ding, C. Min and W. Hui, A study on the use of bipolar particles-electrode in the decolorization of dyeing effluents and its principle. Water Sci. Technol., 19 (1987) 39-44. [7]: G. Annadurai, R. Juang and D. Lee, Use of cellulose- based wastes for adsorption of dyes from aqueous solutions. J. Hazard. Mater. B92 (2002) 263-274. [8]: T. Robinson, G. McMullan, R. Marchant and P. Nigam, Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative. Biores. Technol., 77 (2001) 247-255. [9]: G. Ciardelli, L. Corsi and M. Marcucci, Membrane separation for wastewater reuse in the textile industry. Resources Conserv. Recycl., 31 (2001) 189-197. [10]: J. Sojka-Ledakowicaz, T. Koprowski, W. Mach- nowski and H. Knudsen, Membrane filtration of textile dyehouse wastewater for technological water reuse. Desalination, 119 (1998) 1-10. [11]: M. Marcucci, G. Nosenzo, G. Gapanneli, I. Ciabatti, D. Corrieri and G. Ciardelli, Treatment and reuse of textile effluents based on new ultrafiltration and other membrane technologies. Desalination, 138 (2001) 75-82. [12]: C. Tang and V. Chen, Nanofiltration of textile waste- water for water reuse. Desalination, 143 (2002) 11-20. [13]: A. Alves and M. Pinho, Ultrafiltration of colour removal of tannery dyeing wastewaters. Desalination, 130 (2000) 147-154. [14]: M. Smoluchowski, Zur theorie der elektrischen kataphorese und der oberflächenleiting, Phys. Z. 6 (1905) 529. 7
WATMED 2 - Marrakech 14-17 November 2005 [15]: C. Lettmann, D. Möckel, E. Staude, Permeation and tangential flow streaming potential measurements for electrokinetic characterization of track-etched microfiltration membranes, J. Membr. Sci. 159 (1999) 243. [16]: J.I. Calvo, A. Hernández, P. Prádanos, F. Tejerina, Charge adsorption and zeta-potential in cyclopore membranes, J. Membr. Sci. 181 (1996) 399. [17]: M. Ernst, A. Bismarck, J. Springer, M. Jakel, Zeta-potential and rejection rates of a polyethersulfone nanofiltration membrane in single salt solutions, J. Membr. Sci. 165 (2000) 251 [18]: D.B. Birns, A.L. Zydney, Buffer effects on the zeta potential of ultrafiltration membranes, J. Membr. Sci. 172 (2000) 39. [19]: N. Saffaj, S. Alami-Younssi, A. Albizane, A. Messouadi, M. Bouhria, M. Persin, M. Cretin, A. Larbot,Elaboration and characterization of TiO2- ZnAl2O4 ultrafiltration membranes deposited on cordierite support, Sep. Pur. Technol. 36 (2004) 107-114. [20]: L. Broussous, E. Prouzet, L. Beque and A. Larbot, An experimental study of hellically ceramic microfiltration membranes using bentonite suspensions; Sep. Pur. Technol., 24 (2001) 205-221. [21]: N. Saffaj, H. Loukili, S. Alami Younssi, A. Albizane, M. Bouhria, M. Persin, A. Larbot, Filtration of solution containing heavy metals and dyes by means of ultrafiltration membranes deposited on support made of Moroccan clay, Desalination 168 (2004) 301-306.
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