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ELSEVIER Desalination 157 (2003) 73-80
DESALINATION
www.elsevier.com/locate/desal
Combination of physico-chemical treatment and nanofiltration to reuse wastewater of a printing, dyeing and finishing textile
industry
A. Bes-Pifi*, J.A. Mendoza-Roca, M.I. Alcaina-Miranda, A. Iborra-Clar, M.I. Iborra-Clar
Department of Chemical and Nuclear Engineering, Universidad Politdcnica of Valencia, Camino de Vera s/n, 46071 Valencia, Spain
Tel. + 34 (96) 3879633; Fax + 34 (96) 3877639; email: [email protected]
Received 23 December 2002; accepted 30 December 2002
Abstract
The main goal of this work was to study the feasibility of the combination of physico-chemical treatment with nanofiltration to reuse wastewater of a printing, dyeing and finishing textile industry. For the physico-chemical treatment two coagulants (one containing Al 3+ and another containing Fe 2+) were compared by carrying out jar-tests using different chemical concentrations and pH values. After that, nanofiltration experiments with physico-chemically treated wastewater were performed at different operating pressures and cross-flow velocities. The results showed that the COD and conductivity of the nanofiltration permeates were lower than 100 mg/L and 1000 gS/cm respectively.
Keywords: Phisico-chemical treatment; Nanofiltration; Wastewater reuse
1. I n t r o d u c t i o n
Due to high water consumption in the textile industry it is essential to study its reuse. Previous experiments of the research group with waste- water o f a textile plmat that mainly manufactures
*Corresponding author.
socks, stockings and panties proved that the combination of physico-chemical treatment and membrane technologies could produce water for reuse in the factory [1]. In this case, an attempt is made to apply these technologies to the effluent of another textile plant, optimizing the operating conditions of the membrane process.
Presented at the European Conference on Desalination and the Environment: Fresh Water for All, Malta, 4-8 May 2003. European Desalination Socie~, International Water Association.
0011-9164/03/$ See front matter © 2003 Elsevier Science B.V. All rights reserved PII: S0011-9164(03)00385-0
74 A. Bes-Pid et al. / Desalination 157 (2003) 73-80
Many processes have been studied to treat textile wastewaters. Biological treatment by activated sludge offers high efficiencies in COD removal but it does not eliminate completely the colour fi'om the water [2]. Chelnicat oxidation by ozone, or a combination of UV-radiation and ozone and H~O 2, are of great interest but their costs are very high to treat raw textile wastewater. Thus, these techniques should be applied in combination with conventional treatments [3,4].
Jar-tests are a valuable tool in wastewater treatment to evaluate tile efficiency of the physico- chemical treatment [5]. The optimum operating conditions (pH, chemical concentrations) are determined by means of these experiments. According to the double layer theory, electrical repulsion forces prevent from colloids aggre- gation. Ill order to achieve an effective agglo- meration, the COlnpression of the thickness of the electrical double layer or a charge reduction of the particles have to be carried out. This implies the zeta potential reduction [6]. In this way the colloids can be settled.
Additional treatments like membrane tech- niques could be necessary according to the envi- ronmental laws for tile disposal of treated water or for its reuse in a textile plant.
The possible approaches for the membrane purification treatment are nanofiltration or reverse osmosis, since ultrafiltration membranes can hardly remove COD and conductivity, having only a slight effect on colour [7,8]. Nanofiltration does not reach the retentions of reverse osmosis, but the permeate quality is good enough for its reuse in rinse processes (COD <100 mg/L and conduc- tivity <1000 gS/cm).
In this work, the combination of the physico- chemical treatment with nanofiltration to reuse wastewater of a printing, dyeing and finishing textile industry is proposed.
2. Objectives
The objectives of this work were tile following:
• Evaluation of the efficiency of two coagulants in the physico-chemical treatment for waste- water of a printing, dyeing and finishing textile plant.
• Study of the water quality after treating the wastewater with a combination of physico- chemical treatment and nanofiltration mem- branes.
• Selection of the membrane according to the salts and COD retention and permeate flow rate.
• Optimization of the best operating conditions for nanofiltration process (feed pressure and cross flow velocity).
3. Material and methods
This work was carried out in three steps. The first step consisted in the characterization of the wastewater samples. The next step was a physico- chemical treatment by means of jar-tests to reduce COD. Once the best efficiencies were obtained, the clarified water was treated with nanofiltration membranes in a laboratory plant to improve the quality of the physico-chemically treated waste- water.
3.1. Wastewater characterizat ion
The parameters analysed were COD, BODs, pH, and conductivity. COD was determined with Spectroquant Nova 60 from Merck and BOD 5 with the Oxitop system from WTW.
3.2. Jar-teals
Physico-chemical experiments were carried out ill a multiple stirrer Jar-Test apparatus from Selecta. The chemicals used in the jar-tests were tile commercial products DK-FER 505-1 from Acideka S.A. and UPAX-33 from Kemira S.A. The general procedure consisted in introducing 900 mL of the sample in the jars, the coagulant was added and rapidly mixed (180 rpm) during 3 rain. After that, the paddles were withdrawn so
A. Bes-Pi6 et al. / Desalination 157 (2003) 73-80 75
that the particles could settle. The influence of coagulants concentration and pH values were studied. The coagulant concentrations are referred to Fe 2+ and AI20 3 for DK-FER 505-1 and UPAX- 33, respectively. The pH of the samples was changed by addition of HCl 0.1 N and NaOH 0.1 and 0.5 N.
pH values were selected in the alkaline range, since in this medium the coagulants drive to the formation of positively charged metal hidroxy complexes that specifically adsorb onto colloids.
In all tests COD, turbidity, pH and conductivity of the clarified water and the sludge volume after 30 rain sedimentation (V3o) were measured.
3.3. Experhnents with membranes
Experiments were carried out using a labora- tory nanofiltration (NF) plant. The configuration of the plant can be observed in Fig. 1. NF module is plane and its effect ive membrane area is 0.012 m 2. The tested NF membranes are described in Table 1.
For each membrane, experiments with three different transmembrane pressures (0.10, 0.15 and 0.20 MPa), and three different feed flow rates (0.2, 0.3 and 0.4 m3/h) at 25°C were performed. The cross flow velocities related to these flow rates
2 3 14
7 @
[ 8
11
13
12
Fig. 1. Scheme of NF laboratory plant. 1, feed tank; 2, thermometer; 3, stirring; 4, heat exchanger; 5, regulation valve; 6, filtration system; 7, feed pump; 8, security valve; 9-9', manometer; 10, NF module; 11, penneate stream; 12, regulation valve; 13, speed control; 14, rejection stream.
Table 1 Tested NF membranes
Membrane NaC1 MgSO 4 retention, retention, % %
Permeability, L/m2h bar*
Dow NF-90 85-95 >97 0.481 Osmonics Desal - - 98 3.863 DL-5 Osmonics Desal - - 96 3.562 DK-5
*Experimental values
are 1.11, 1.66 and 2.22 m/s respectively. The series of experiments were carried out using an experimental design obtained from Statgraphics Plus 4.0.
The operating time of the plant was established according to the steady state conditions. It was about 8 I1 in all cases. The permeate fluxes Jl, (L/m2h) and salt retentions RmL, v (%) were determined. In addition, at the end of each experiment, COD was analysed.
4. Results
Table 2 shows the average values of the measured parameters of the textile wastewater. These values are typical for textile effluents. Conductivity and COD are quite important and they have to be reduced to produce water with enough quality to be reused.
Figs. 2 and 3 show the COD obtained after jar-tests on varying the DK-FER 505-1 and UPAX-33 concentrations. In Fig. 2 it can be
Table 2 Wastewater characterization
Parameter Feedwater
T, °C 20 pH 12.0 Conductivity, mS/cm 4.53 BODs, mg/L 490 COD, mg/L 1630
76 A. Bes-Pid et al. / Desalination 157 (2003) 73-80
1600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
rm O o
1200
800
400
0 500 600 700 8 00
DK-FER 505-1 coagulant (mg/L)
Fig. 2. Influence of DK-FER 505-1 concentration on COD of treated water.
1600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1200 d ~ :::
: I"" !1
E 800
© , : t) 400
:!:<:
0 ............. ~--- --~--- --7---
200 300 400 500
UPAX-33 coagulant (mg/L)
Fig. 3. Influence of UPAX-33 concentration on COD of treated water.
observed that DK-FER 505-1 concentrations of 500 mg/L and 600 mg/L produced only a slight COD reduction. This occurred because of the in- sufficient reduction in the zeta potential of the waste- water. The maximum COD removal yield (72.5%) was reached with a concentration of 700 mg/L. Higher coagulant concentrations did not improve the efficiency. In Fig. 3, for UPAX-33 the selected coagulant concentration was 300 mg/L. For this value the COD of the clarified water was 680 mg/L (i.e. 58.0% removal).
Fig. 4 and Fig. 5 show the COD obtained after jar-test for different wastewater pH values. In Fig. 4 it can be observed that the COD removal slightly increased with wastewater pH, reaching
1000 .........................................................................................................................................................................
d
v db O O
800
600
400
20O
0
9 10 11 12
pH
Fig. 4. Influence ofwastewater pH on COD &treated water using 700 mg/L of DK-FER 505-1.
a COD removal of 70.5% at pH 12 (the raw waste- water pH).
In Fig. 5 it is shown that the best yield was reached at pH 11.0 (COD removal of 66.0%). The other tested pH did not improve the COD efficiency.
Thus, experiments showed that DK-FER 505-1 coagulant provided the best results for the physico- chemical treatment of this textile wastewater. The optimum operating conditions were: pH = 12.0 and Cve2+ = 700 mg/L. In Table 3 the characteri-zation of the clarified water after the test at these conditions can be observed. It is important to emphasize that a total colour removal was accomplished.
1000 .......................................................................................................................................................................
3
E E) 0 0
800
600
400
200
0
10.0 10.5 11,0
pH
11.4
Fig. 5. Influence ofwastewater pH on COD &treated water using 300 mg/L of UPAX-33.
,4. Bes-Pid et al. / Desalination 157 (2003) 73-80 77
Table 3 Clarified water characterization (Jar-test conditions: C~2+ = 700 rag/L; pH = 12)
pH 6.14 Conductivity, mS cm-' 3.80 Turbidity, NTU 4.7 V3o, mL/L 260 COD, mg/L 448
Nanofiltration experiments were made using wastewater treated with DK-FER 505-1 as feed water.
in Table 4 salts rejections (RS~Lr) and permeate fluxes (@) at the steady state conditions for the tested membranes can be observed.
Figs. 6-8 show the standardized Pareto charts for permeate flux of the membranes tested. These Pareto cimrts display a frequency histogram where the length of each bar is proportional to the estimated effect and interactions of the feed flow rate (B) and feed pressure (A) on permeate flux. The cross line indicates the significance.of each parameter.
For NF-90 it can be observed that feed pressure and feed flow rate were significant variables. Feed pressure variations produced an important increase on permeate flux, while the influence of the feed f low rate was substantially lower. However, it can be seen that only feed pressure
AB
BB
AA
0 2 4 6 8 0
Standardized effect
Fig. 6. Standardized Pareto chart for permeate flux of NF-90.
i . . . . i . . . . i . . . . i . . . . i . . . . i
B:Q
BB
AA
AB i , , . , i , . . , i . . . , i , , , . J . . . . i
0 1 2 3 4 5
Standardized effect
Fig. 7. Standardized Pareto chart for permeate flux of DK-5.
Table 4 Salt rejections and permeate fluxes at the steady state conditions in the different experiments
Operating conditions NF-90 DL-5 DK-5
Feed pressure, Feed flow rate, RsAz,7; Jp, Rs::,'r, J:,, bar L/h % L/m2h % L/m2h
RS'ALT~ Jl', % k/m2h
10 200 83.0 2.8 28.2 25.6 42.8 2 1.6 10 300 77.0 2.5 34.7 25.7 35.0 18.4 l 0 400 72.3 2.0 30.3 21.8 37.0 16.9 l 5 200 85.2 5.3 33.1 40.1 43.3 29.2 15 300 78.6 5.5 38.0 42.7 42.5 28.1 15 400 83.8 4.8 36.1 37.7 39.7 26.3 20 200 87.8 8.7 35.14 5 1.3 55.0 45.2 20 300 86.2 7.6 48.39 67.8 60.9 55.8 20 400 85,2 7.5 40.27 52.0 44.8 34.5
78 A. Bes-Pi~ et aL / Desalination 157 (2003) 73-80
A:P
BB
AB
B:Q
AA
B 0
0 2 4 6 8
Standardized effect
1(
¢-q
Q (L/h) 400
118-10
m6-8
114-6
D 2-4
20
~ar)
Fig. 8. Standardized Pareto chart for permeate flux of DL-5.
Fig. 9. Influence of feed pressure and feed flow rate on permeate flux in NF-90.
influenced significantly on permeate flux for DL-5 and DK-5.
In order to illustrate the obtained results, a response surface graph was plotted if both feed pressure (P) and feed flow rate (Q) were signifi- cant variables (Fig. 9). If only the feed pressure was significant, a graph showing the evolution of this variable was performed (Fig. 10).
Fig. 9 shows the increase of the permeate fluxes with the feed pressure. No influence of the feed flow rate was observed at 10 and 15 bar. However, at 20 bar a slight influence was noticed. Thus, the highest permeate flux was achieved at 20 bar and 200 L/h.
In Fig. 10 the permeate fluxes vs. tile feed pres- sure have been represented for DL-5 and DK-5. The permeate flux values correspond with the average values calculated for the tested feed flow rate. As it can be expected, the highest feed pres- sure, tile highest permeate flux.
Similarly, the obtained salts rejection values have been studied using the same types of graphs. Figs. 11-13 show the standardized Pareto charts for retention salts of the membranes tested. In all cases salts retentious did no depend on the feed flow rate.
Similarly, the obtained salts rejections values have been studied using the same types of graphs.
80.
r - c,l
E J v
n - -3
60,
40
20
0
• D L - 5 x D K - 5
5 11 ~ 20 25
P (bar)
Fig. 10. Influence of feed pressure on permeate flux in DL-5 and DK-5.
Figs. 11-13 show the standardized Pareto charts for retention salts of the membranes tested. In all cases salts retentions did no depend on the feed flow rate.
As can be seen in Fig. 14, the higher feed pres- sure, the higher salts retentions. The highest salts retentions were obtained with NF-90. DL-5 and DK-5 yielded very similar values for each tested pressure.
Table 5 summarizes the results o f the permeate analysis. By means of DK-5 and NF-90, it was possible to produce water with sufficient quality to be reused in the textile plant. The low permeate COD values (50 mg/L) can be highlighted.
A. Bes-Pid et al. / Desalination 157 (2003) 73-80 79
I : : : ~ u
AB
I i i i i I i i • , i . . . . i . . . . i , , ! i I
0 1 2 3 4 5
Standardized effect
Fig. 11. Standardized Pareto chart for retention salts of NF-90 membrane.
I
AB
0 1 2 3 4
Standardized effect
Fig. 12, Standardized Pareto chart for retention salts of DL-5.
i . . . . i . . . . i . . . . g . . . . i
A A
AB i , , , , i . . . . ~ , , 1 1 I i i i i
0 1 2 3 4
Standardized effect
Fig. 13. Standardized Pareto chart for retention salts of DK-5.
1 0 0
v
co
rl,"
80
60
4 0
20
• DL-5 ~DK-5 , NF-90
. . . . . . . . . . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . r . . . . . . . . . . . . . . . . . . . . . T . . . . . . . . . . . .
5 10 15 20 25
P (bar)
Fig. 14. Influence of feed pressure on salts rejection in tested membranes,
Table 5 Analysis of permeate streams at the best operating conditions for each membrane
Membrane Selection of operating conditions Variables
Feed pressure, Feed flow rate, Flux, RsAt.v: bar L/h L/mZh %
Effluent analysis
Conductivity, COD, m S/cm rng/L
NF-90 20 200 8-10 85-90 Desal DL-5 20 200-400 60-80 45-50 Desal DK-5 20 200-400 5 0 4 0 55-65
0.46 48 1.90-2.09 98 1.33-1.71 50
80 A. Bes-Pid et al. / Desalination 157 (2003) 73-80
5. Conclusions
By means o f a physico-chemical treatment using the coagulant DK-FER 505-1 at pH 12 and with a concentration CFe2+ : 700 mg/L, COD of a textile effluent can be reduced to values lower than 500 mg/L (72.5% COD removal efficiency). With UPAX-33 worse efficiencies were achieved.
Nanof i l t r a t i on o f the p h y s i c o - c h e m i c a l l y treated wastewater produced a permeate with a COD lower than 100 mg/L for the three tested membranes. ',
Salts rejection and permeate flux rates were dependent basically on feed pressure. However, for the feed f low rate range that was studied, no influence was found on the studied variables.
Though the permeate flux rates of NF-90 were lower than for the other membranes, this was the selected membrane, since the salts rejections were substantially higher than for the other membranes.
Prior to an industrial operation, the manage- ment o f the retentate stream has to be deeply studied.
Acknowledgment
We thank Colortex 1967 S.L. for its support in the investigation project.
References
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[2] M. Crespi Rosell and J.A. Huertas Ldpez, Indutria textil: depuracidn biol6gica o fisicoquimica?, Revista de la lndustria Textil, 233 (1995) 42--61.
[3] G. Ciardelli, G. Campanelli and A. Botino, Ozone treatment of textile wastewater for reuse, Wat. Sci. Technol., 44(5) (2001) 61~57.
[4] S Baig and RA. Liechti, Ozone treatment for bio- refractory COD removal, Wat. Sci. Technol., 43 (200l) 197-204.
[5] O.O. Hart, G.R. Groves, C.A. Buckley and B. South- worth, A guide for the planning, design and implemen- tation of wastewater treatment plants in the textile industry. Part I: Closed loop treatment/recycle system for textile sizing/desizing effluents. Pretoria, 1983.
[6] Y.H. Kim, Coagulants and Flocculants. Theory and Practice, 1995.
[7] M. Marcucci, G. Nosenzo, G. Capanelli, 1. 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.
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