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Integrated cleaning of coloured waste water by ceramic NF membranes
Separation and Purification Technology 25 (2001) 509– 512 www.elsevier.com/locate/seppur
Integrated cleaning of coloured waste water by ceramic NF membranes I. Voigt a,*, M. Stahn a, St. Wo¨hner a, A. Junghans b, J. Rost b, W. Voigt b a
b
Hermsdorfer Institut fu¨r Technische Keramik e.V., 07629 Hermsdorf, Germany Andreas Junghans — Spezialfabrik fu¨r Edelstahlbearbeitung und Sonderanfertigungen, Frankenberg, Germany
Abstract New TiO2 –NF membranes with a mean pore size of 0.9 nm and a cut-off of 450 D were tested in decolouring of textile waste water. A pilot plant with a membrane area of 5.1 m2 was integrated in the textile finishing in order to treat only the coloured parts of the waste water near the colouring and washing machines and to recycle the hot permeate as process water. The pilot plant was tested with 30 types of different coloured waste water over a period of 6 weeks to detect optimal parameters for the filtration process with a focus on high flux and low running costs. Due to the differences in the composition of the dyes a decolouring of 70 – 100% was obtained. The fluxes varied between 0.2 and 1.l m3/h, whereas the running costs were 0.50– 2.80 DM/m3 permeate, respectively. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Titania membrane; Nanofiltration; Decolouring; Dye retention; Partial desalination
1. Introduction An interesting application of nanofiltration is the cleaning of coloured waste water from textile industry. The amount of waste water in this field is very high. Although modern water saving plants are used it can reach more than 1000 m3/day. Therefore, a treatment of the whole waste water by nanofiltration is impossible. But only during the colouring process itself and the subsequent washing process dyes pollute the water. Therefore, only these partial waste water streams are to be cleaned using a NF membrane. At the same time a recycling of the hot cleaned water * Corresponding author.
might be possible saving water, waste water costs and energy. The kind and concentration of dyes depend on the type of the textile material, the composition and type of the dye and the colouring process. All these parameters are changed many times over the day. Furthermore, a lot of different additives, e.g. peroxides, are used to enhance the colouring process, the pH varies between 4 and 12 and the temperature is between 50 and 95°C. All these conditions together can be withstood only by ceramic membranes. Reliable ceramic nanofiltration membranes were not available on the market (cut-off smaller than 1000 D, sulphate retention), thus new membranes had to be developed. With the help of a modified polymer sol –gel technique the prepara-
1383-5866/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 0 1 ) 0 0 0 8 1 - 8
510
I. Voigt et al. / Separation/Purification Technology 25 (2001) 509–512
tion of microporous amorphous TiO2 membranes succeeded [1]. These membranes were intensively tested on a laboratory scale before the membrane preparation was scaled up to a production level. It could be shown that the membrane has cylindrical pores with a mean pore diameter of 0.9 nm, a cut-off of 450 D and a sulphate retention of \90% [2,3]. With the help of these membranes a pilot plant for decolouring of waste water from the textile finishing was built and tested. Optimum conditions for cleaning of hot coloured waste water have been determined with a focus on a high permeation rate and low running costs.
2. Experimental The TiO2 –NF membranes were prepared on 19-channel tubular supports with a length of 1.20 m. Seven of these tubes were combined to one module. Three of these modules with a total filtration area of 5.1 m2 were arranged in a pilot plant (Fig. 1). Special frequency controlled pumps made it possible to vary the pressure between 6 and 25 bar as well as the flow rate between 2.5 and 4.5 m/s. At the same time the energy consumption could be recorded. This pilot plant was connected to different partial waste water streams of a textile factory. A program with only five different operating parameters was established (Table 1). For each experiment the pilot plant was operated for 1 h before the flux and the energy consumption were recorded and samples were taken. The intensity of the colour was measured by VIS spectroscopy at three different wavelengths (436, 525, 620 nm), the COD and the salt retention by conductivity. At the end of such a run the experimental conditions have been changed to the next set of parameters. By this way, one type of waste water was tested per day. At the end of the day the membrane was cleaned using the commercial membrane cleaning agents Ultraperm P3/053 and P3/075 from HENKEL. Over a period of 6 weeks 30 different types of waste water (different machines, different colours) were tested to get representative results.
3. Results Fig. 1. Pilot plant with 5.1 m2 TiO2 –NF membrane connected with a washing machine of the textile finishing. Table 1 Operating parameters for the testing of the pilot plant Transmembrane pressure (bar)
6 15 25
Flow rate (m/s) 2.5
3.5
4.5
–
–
– – –
Over a period of 6 weeks the pilot plant worked very reliably. The cleaning process of the different types of waste water yielded nearly the same water flux of 1.5 m3/h (process water). The very sensitive measurement of the dye retention using VIS spectroscopy showed that the dye retention depended on the composition of the dye bath and varied between 70% and 100% (Table 2). At the same time a COD reduction of 45–80% and a salt retention of 10–80% was observed.
I. Voigt et al. / Separation/Purification Technology 25 (2001) 509–512
511
Table 2 Retention of dyes (measured by VIS spectroscopy), COD and salt (calculated from conductivity) Temperature (°C)
Waste water Blue1 Red Green Black2 Violet
of washing machines 55 65 85 70 50
Waste water Brown3 Red4 Gray
of dyeing machines 50 65 80
1 –4
pH
10.2 9.2 9.4 9.4 10.3 4.2 7.04 8.47
Retention (%) 436 nm (blue)
525 nm (green)
620 nm (red)
COD
Salt
79.0 73.0 90.8 75.4 87.8
83.6 81.5 93.6 82.1 86.6
88.3 95.5 94.2 89.9 89.8
67.1 61.0 67.2 59.5 48.2
58.8 10.7 28.6 22.2 76.9
95.5 93.7 99.4
96.8 96.3 99.5
98.3 71.6 99.7
55.0 78.9 76.9
15.4 16.1 23.5
These samples were selected for the graphs (Figs. 2–5).
Fig. 2. Flux versus transmembrane pressure at a constant velocity of 4.5 m/s for waste water 1 – 4 according to Table 2.
Fig. 3. Flux versus flow rate at a transmembrane pressure of 15 bar for waste water 1 –4 according to Table 2.
Fig. 4. Running costs versus transmembrane pressure at a flow rate of 4.5 m/s for waste water 1 – 4 according to Table 2.
During the filtration process the flux varied with the type of waste water and the transmembrane pressure between 0.2 and 1.1 m3/h (Fig. 2). The highest fluxes were observed at l5 bar. A reduction of the flow rate from 4.5 to 2.5 m/s resulted in a reduction of the flux (Fig. 3). Running costs are an important criterion of the evaluation of a membrane process. They were calculated from the power of the pumps (1 kW h= 0.17 DM). At 15 bar and a flow rate of 4.5 m/s the running costs were 0.80–1.80 DM/m3 (Fig. 4). A further reduction to 0.50–0.70 DM/m3 was reached by reducing the flow rate to 2.5 m/s (Fig. 5). This is approximately half of the waste water costs.
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I. Voigt et al. / Separation/Purification Technology 25 (2001) 509–512
possible to recycle the hot permeate for washing processes. That would result in an additional positive cost effect. From the composition of the dyeing bath the components will be detected which are responsible for the residual colouring of some permeates. It will be investigated if a further reduction of the pore size of the membrane can remove the dyes completely.
Acknowledgements Fig. 5. Running costs versus flow rate at a transmembrane pressure of 15 bar for waste water 1 – 4 according Table 2.
The authors thank the Federal Ministry of Education, Science, Research and Technology (BMBF) for financial support (FKZ 0l RV9637).
4. Conclusions The investigation of 30 types of coloured waste water over a period of 6 weeks showed that it is possible to clean coloured waste water from textile industry with the help of TiO2 – NF membranes. After this first testing period long-term experiments will be carried out in order to check the stability of the flux. It will be shown that it is
References [1] I. Voigt, G. Fischer, P. Puhlfu¨ rss, D. Seifert, in: Proceedings of the Fifth International Conference on Inorganic Membranes, Nagoya, 22 – 26 July, 1998 pp. 42 – 45. [2] R. Weber, H. Chmiel, G. Fischer, I. Voigt, in: preprints of 7. Aachener Membrankolloquium, Aachen, 7 – 9 March, 1999 pp. 241 – 246. [3] R. Weber, M. Morbe´ , P. Puhlfu¨ rss, I. Voigt, Journal of Membrane Science, 174 (2000) 123 – 133.
Integrated cleaning of coloured waste water by ceramic NF membranes I. Voigt a,*, M. Stahn a, St. Wo¨hner a, A. Junghans b, J. Rost b, W. Voigt b a
b
Hermsdorfer Institut fu¨r Technische Keramik e.V., 07629 Hermsdorf, Germany Andreas Junghans — Spezialfabrik fu¨r Edelstahlbearbeitung und Sonderanfertigungen, Frankenberg, Germany
Abstract New TiO2 –NF membranes with a mean pore size of 0.9 nm and a cut-off of 450 D were tested in decolouring of textile waste water. A pilot plant with a membrane area of 5.1 m2 was integrated in the textile finishing in order to treat only the coloured parts of the waste water near the colouring and washing machines and to recycle the hot permeate as process water. The pilot plant was tested with 30 types of different coloured waste water over a period of 6 weeks to detect optimal parameters for the filtration process with a focus on high flux and low running costs. Due to the differences in the composition of the dyes a decolouring of 70 – 100% was obtained. The fluxes varied between 0.2 and 1.l m3/h, whereas the running costs were 0.50– 2.80 DM/m3 permeate, respectively. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Titania membrane; Nanofiltration; Decolouring; Dye retention; Partial desalination
1. Introduction An interesting application of nanofiltration is the cleaning of coloured waste water from textile industry. The amount of waste water in this field is very high. Although modern water saving plants are used it can reach more than 1000 m3/day. Therefore, a treatment of the whole waste water by nanofiltration is impossible. But only during the colouring process itself and the subsequent washing process dyes pollute the water. Therefore, only these partial waste water streams are to be cleaned using a NF membrane. At the same time a recycling of the hot cleaned water * Corresponding author.
might be possible saving water, waste water costs and energy. The kind and concentration of dyes depend on the type of the textile material, the composition and type of the dye and the colouring process. All these parameters are changed many times over the day. Furthermore, a lot of different additives, e.g. peroxides, are used to enhance the colouring process, the pH varies between 4 and 12 and the temperature is between 50 and 95°C. All these conditions together can be withstood only by ceramic membranes. Reliable ceramic nanofiltration membranes were not available on the market (cut-off smaller than 1000 D, sulphate retention), thus new membranes had to be developed. With the help of a modified polymer sol –gel technique the prepara-
1383-5866/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 0 1 ) 0 0 0 8 1 - 8
510
I. Voigt et al. / Separation/Purification Technology 25 (2001) 509–512
tion of microporous amorphous TiO2 membranes succeeded [1]. These membranes were intensively tested on a laboratory scale before the membrane preparation was scaled up to a production level. It could be shown that the membrane has cylindrical pores with a mean pore diameter of 0.9 nm, a cut-off of 450 D and a sulphate retention of \90% [2,3]. With the help of these membranes a pilot plant for decolouring of waste water from the textile finishing was built and tested. Optimum conditions for cleaning of hot coloured waste water have been determined with a focus on a high permeation rate and low running costs.
2. Experimental The TiO2 –NF membranes were prepared on 19-channel tubular supports with a length of 1.20 m. Seven of these tubes were combined to one module. Three of these modules with a total filtration area of 5.1 m2 were arranged in a pilot plant (Fig. 1). Special frequency controlled pumps made it possible to vary the pressure between 6 and 25 bar as well as the flow rate between 2.5 and 4.5 m/s. At the same time the energy consumption could be recorded. This pilot plant was connected to different partial waste water streams of a textile factory. A program with only five different operating parameters was established (Table 1). For each experiment the pilot plant was operated for 1 h before the flux and the energy consumption were recorded and samples were taken. The intensity of the colour was measured by VIS spectroscopy at three different wavelengths (436, 525, 620 nm), the COD and the salt retention by conductivity. At the end of such a run the experimental conditions have been changed to the next set of parameters. By this way, one type of waste water was tested per day. At the end of the day the membrane was cleaned using the commercial membrane cleaning agents Ultraperm P3/053 and P3/075 from HENKEL. Over a period of 6 weeks 30 different types of waste water (different machines, different colours) were tested to get representative results.
3. Results Fig. 1. Pilot plant with 5.1 m2 TiO2 –NF membrane connected with a washing machine of the textile finishing. Table 1 Operating parameters for the testing of the pilot plant Transmembrane pressure (bar)
6 15 25
Flow rate (m/s) 2.5
3.5
4.5
–
–
– – –
Over a period of 6 weeks the pilot plant worked very reliably. The cleaning process of the different types of waste water yielded nearly the same water flux of 1.5 m3/h (process water). The very sensitive measurement of the dye retention using VIS spectroscopy showed that the dye retention depended on the composition of the dye bath and varied between 70% and 100% (Table 2). At the same time a COD reduction of 45–80% and a salt retention of 10–80% was observed.
I. Voigt et al. / Separation/Purification Technology 25 (2001) 509–512
511
Table 2 Retention of dyes (measured by VIS spectroscopy), COD and salt (calculated from conductivity) Temperature (°C)
Waste water Blue1 Red Green Black2 Violet
of washing machines 55 65 85 70 50
Waste water Brown3 Red4 Gray
of dyeing machines 50 65 80
1 –4
pH
10.2 9.2 9.4 9.4 10.3 4.2 7.04 8.47
Retention (%) 436 nm (blue)
525 nm (green)
620 nm (red)
COD
Salt
79.0 73.0 90.8 75.4 87.8
83.6 81.5 93.6 82.1 86.6
88.3 95.5 94.2 89.9 89.8
67.1 61.0 67.2 59.5 48.2
58.8 10.7 28.6 22.2 76.9
95.5 93.7 99.4
96.8 96.3 99.5
98.3 71.6 99.7
55.0 78.9 76.9
15.4 16.1 23.5
These samples were selected for the graphs (Figs. 2–5).
Fig. 2. Flux versus transmembrane pressure at a constant velocity of 4.5 m/s for waste water 1 – 4 according to Table 2.
Fig. 3. Flux versus flow rate at a transmembrane pressure of 15 bar for waste water 1 –4 according to Table 2.
Fig. 4. Running costs versus transmembrane pressure at a flow rate of 4.5 m/s for waste water 1 – 4 according to Table 2.
During the filtration process the flux varied with the type of waste water and the transmembrane pressure between 0.2 and 1.1 m3/h (Fig. 2). The highest fluxes were observed at l5 bar. A reduction of the flow rate from 4.5 to 2.5 m/s resulted in a reduction of the flux (Fig. 3). Running costs are an important criterion of the evaluation of a membrane process. They were calculated from the power of the pumps (1 kW h= 0.17 DM). At 15 bar and a flow rate of 4.5 m/s the running costs were 0.80–1.80 DM/m3 (Fig. 4). A further reduction to 0.50–0.70 DM/m3 was reached by reducing the flow rate to 2.5 m/s (Fig. 5). This is approximately half of the waste water costs.
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I. Voigt et al. / Separation/Purification Technology 25 (2001) 509–512
possible to recycle the hot permeate for washing processes. That would result in an additional positive cost effect. From the composition of the dyeing bath the components will be detected which are responsible for the residual colouring of some permeates. It will be investigated if a further reduction of the pore size of the membrane can remove the dyes completely.
Acknowledgements Fig. 5. Running costs versus flow rate at a transmembrane pressure of 15 bar for waste water 1 – 4 according Table 2.
The authors thank the Federal Ministry of Education, Science, Research and Technology (BMBF) for financial support (FKZ 0l RV9637).
4. Conclusions The investigation of 30 types of coloured waste water over a period of 6 weeks showed that it is possible to clean coloured waste water from textile industry with the help of TiO2 – NF membranes. After this first testing period long-term experiments will be carried out in order to check the stability of the flux. It will be shown that it is
References [1] I. Voigt, G. Fischer, P. Puhlfu¨ rss, D. Seifert, in: Proceedings of the Fifth International Conference on Inorganic Membranes, Nagoya, 22 – 26 July, 1998 pp. 42 – 45. [2] R. Weber, H. Chmiel, G. Fischer, I. Voigt, in: preprints of 7. Aachener Membrankolloquium, Aachen, 7 – 9 March, 1999 pp. 241 – 246. [3] R. Weber, M. Morbe´ , P. Puhlfu¨ rss, I. Voigt, Journal of Membrane Science, 174 (2000) 123 – 133.