- Email: [email protected]
Study of the UF process as pretreatment of NF membranes for textile wastewater reuse
Desalination 200 (2006) 745–747
Study of the UF process as pretreatment of NF membranes for textile wastewater reuse S. Barredo-Damas*, M.I. Alcaina-Miranda, M.I. Iborra-Clar, A. Bes-Piá, J.A. Mendoza-Roca, A. Iborra-Clar Department of Chemical and Nuclear Engineering, Polytechnic University of Valencia, Camino de Vera s/n, 46022 Valencia, Spain Tel. +34 96 3879633 Fax +34 96 3877639; email: [email protected] Received 24 October 2005; accepted 6 March 2006
1. Introduction Textile industry is characterized by using a great variety of chemicals and by large water consumption. In this way, textile effluents contain many types of dyes, detergents, solvents and salts depending on the particular textile mill processes (dyeing, printing, finishing...) and on the raw matter. For those reasons, textile industry is one of the main sources of industrial pollution, producing effluents discharges characterized by high conductivities and chemical oxygen demand (COD) values and strong colour [1]. Physical–chemical and biological treatments are typically used in order to eliminate or reduce the concentrations of the pollutants coming from textile industries. However, this kind of treatments does not allow water reuse in any step of the productive process [2]. Membranes technologies provide an important solution in environmental fields such as pollution reduction and water reuse, recycling valuable components from the waste streams [3]. Both nanofiltraton (NF) and reverse osmosis *Corresponding author.
(RO) are good alternatives for textile wastewater treatment since high reductions in the aforementioned parameters (conductivity, COD and colour) can be reached. Nevertheless, effluents from a conventional treatment cannot be used directly as influent to nanofiltration or reverse osmosis membranes due to the high solids concentrations. Thus, it is necessary to carry out a very exhaustive pre-treatment in order to avoid fouling and membrane deterioration [4,5]. There are several techniques appropriate as pre-treatments prior to NF or RO processes, including membrane processes as MF and UF. In this way the aim of this paper is to optimise the ultrafiltration process as a pre-treatment of the final step for textile water reuse. 2. Theory and experimental The study was divided in three steps. Initially, water characterization (COD, conductivity, pH and turbidity) was carried out in order to make possible subsequent monitoring. Then, a microfiltration step was done comparing two microfilters (5 and 20 mm). The third stage consisted on the study of the ultrafiltration process.
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.497
746
S. Barredo-Damas et al. / Desalination 200 (2006) 745–747
Flux (L/m2 h)
30 25 20 15 10 5 0
0
0.4 m/sec 1 m/sec 1.6 m/sec 2.2 m/sec 10 20
30 40 Time (min)
50
60
70
Fig. 1. Evolution of permeate fluxes with the operating time (10 kD, 20 mm).
Three commercial membranes of different cut-offs were tested. The behaviour of two polymeric membranes (10 kD and 100 kD from Orelis tested in a flat-sheet module Rayflow) and an inorganic (ZrO2–TiO2) membrane (50 kD from Orelis set in a tubular module) were studied at different crossflow velocities, ranging between 0.4 and 2.2 m/sec. The operating conditions for all UF experiments were a transmembrane pressure of 1 bar and a temperature of 20°C. Both the retentate and permeate streams were returned to the feed tank. 3. Results and discussion Analysis of textile wastewater offered high COD and conductivity values ranging between 1500 and 2500 mg/L and 3 and 5 mS/cm, respectively. Fig. 1 shows the evolution of UF permeate fluxes with the operating time at different cross flow velocities. The feeding stream was the textile wastewater pre-filtered by the 20 mm filter. The membrane tested was 10 kD. In general, it can be observed that fluxes increased with the cross flow velocity. At cross flow velocities higher than 1 m/s fluxes slightly decreased over the period studied. This flux reduction was higher at a cross flow velocity of 0.4 m/s. In particular, at 2.2 m/s and 0.4 m/s the permeate
fluxes decline were 9% and 33%, respectively. This difference was due to the solid deposition onto the membrane surface at the lowest cross flow velocity. For all membranes tested, there was no influence of cross flow velocity on the COD removal efficiencies. For 10 kD membrane the COD removals were around 66%. The same behaviour was observed for the colour measurements. As expected, the COD rejections decreased with the membrane cut-off. 4. Conclusions Ultrafiltration is an appropriate technique as a pre-treatment of a NF/RO process to textile wastewater reuse. Membrane selection and operating conditions are important issues to optimize technically and economically the process. The influence of material as well as cross flow velocity on the permeate fluxes were significant. Nevertheless, these parameters hardly affected the COD and color removal efficiencies. The highest flux values were reached for 2.2 m/s for all membranes tested. It was observed that ceramic membranes produced much higher permeate fluxes rather than organic ones probably due to a variety of interacting physical–chemical and hydrodynamic factors. Acknowledgements This work was supported by the Spanish Ministerio de Educación y Ciencia (CTM2004-03130/ TECNO). References [1]
A. Bes-Piá et al., Reuse of the textile industry after its treatment with a combination of physicalchem. treatment and membrane technologies, Desalination, 149 (2002) 169–174.
S. Barredo-Damas et al. / Desalination 200 (2006) 745–747 [2]
[3]
M. Marcucci et al., Experimental campaigns on textile wastewater for reuse by means of different membrane proceses, Desalination, 149 (2002) 137–143. M. Marcucci et al., Treatment and reuse of textile effluents based on new ultrafiltration and other membrane technologies, Desalination, 138 (2001) 75–82.
[4]
[5]
747
S. Sostar-Turk et al., Wastewater treatment after reactive printing, Dyes Pigments, 64 (2005) 147–152. S. Petrov Petrov et al., Ultrafiltration purification of waters contaminated with bifunctional reactive dyes, Desalination, 154 (2003) 247–252.
Study of the UF process as pretreatment of NF membranes for textile wastewater reuse S. Barredo-Damas*, M.I. Alcaina-Miranda, M.I. Iborra-Clar, A. Bes-Piá, J.A. Mendoza-Roca, A. Iborra-Clar Department of Chemical and Nuclear Engineering, Polytechnic University of Valencia, Camino de Vera s/n, 46022 Valencia, Spain Tel. +34 96 3879633 Fax +34 96 3877639; email: [email protected] Received 24 October 2005; accepted 6 March 2006
1. Introduction Textile industry is characterized by using a great variety of chemicals and by large water consumption. In this way, textile effluents contain many types of dyes, detergents, solvents and salts depending on the particular textile mill processes (dyeing, printing, finishing...) and on the raw matter. For those reasons, textile industry is one of the main sources of industrial pollution, producing effluents discharges characterized by high conductivities and chemical oxygen demand (COD) values and strong colour [1]. Physical–chemical and biological treatments are typically used in order to eliminate or reduce the concentrations of the pollutants coming from textile industries. However, this kind of treatments does not allow water reuse in any step of the productive process [2]. Membranes technologies provide an important solution in environmental fields such as pollution reduction and water reuse, recycling valuable components from the waste streams [3]. Both nanofiltraton (NF) and reverse osmosis *Corresponding author.
(RO) are good alternatives for textile wastewater treatment since high reductions in the aforementioned parameters (conductivity, COD and colour) can be reached. Nevertheless, effluents from a conventional treatment cannot be used directly as influent to nanofiltration or reverse osmosis membranes due to the high solids concentrations. Thus, it is necessary to carry out a very exhaustive pre-treatment in order to avoid fouling and membrane deterioration [4,5]. There are several techniques appropriate as pre-treatments prior to NF or RO processes, including membrane processes as MF and UF. In this way the aim of this paper is to optimise the ultrafiltration process as a pre-treatment of the final step for textile water reuse. 2. Theory and experimental The study was divided in three steps. Initially, water characterization (COD, conductivity, pH and turbidity) was carried out in order to make possible subsequent monitoring. Then, a microfiltration step was done comparing two microfilters (5 and 20 mm). The third stage consisted on the study of the ultrafiltration process.
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.03.497
746
S. Barredo-Damas et al. / Desalination 200 (2006) 745–747
Flux (L/m2 h)
30 25 20 15 10 5 0
0
0.4 m/sec 1 m/sec 1.6 m/sec 2.2 m/sec 10 20
30 40 Time (min)
50
60
70
Fig. 1. Evolution of permeate fluxes with the operating time (10 kD, 20 mm).
Three commercial membranes of different cut-offs were tested. The behaviour of two polymeric membranes (10 kD and 100 kD from Orelis tested in a flat-sheet module Rayflow) and an inorganic (ZrO2–TiO2) membrane (50 kD from Orelis set in a tubular module) were studied at different crossflow velocities, ranging between 0.4 and 2.2 m/sec. The operating conditions for all UF experiments were a transmembrane pressure of 1 bar and a temperature of 20°C. Both the retentate and permeate streams were returned to the feed tank. 3. Results and discussion Analysis of textile wastewater offered high COD and conductivity values ranging between 1500 and 2500 mg/L and 3 and 5 mS/cm, respectively. Fig. 1 shows the evolution of UF permeate fluxes with the operating time at different cross flow velocities. The feeding stream was the textile wastewater pre-filtered by the 20 mm filter. The membrane tested was 10 kD. In general, it can be observed that fluxes increased with the cross flow velocity. At cross flow velocities higher than 1 m/s fluxes slightly decreased over the period studied. This flux reduction was higher at a cross flow velocity of 0.4 m/s. In particular, at 2.2 m/s and 0.4 m/s the permeate
fluxes decline were 9% and 33%, respectively. This difference was due to the solid deposition onto the membrane surface at the lowest cross flow velocity. For all membranes tested, there was no influence of cross flow velocity on the COD removal efficiencies. For 10 kD membrane the COD removals were around 66%. The same behaviour was observed for the colour measurements. As expected, the COD rejections decreased with the membrane cut-off. 4. Conclusions Ultrafiltration is an appropriate technique as a pre-treatment of a NF/RO process to textile wastewater reuse. Membrane selection and operating conditions are important issues to optimize technically and economically the process. The influence of material as well as cross flow velocity on the permeate fluxes were significant. Nevertheless, these parameters hardly affected the COD and color removal efficiencies. The highest flux values were reached for 2.2 m/s for all membranes tested. It was observed that ceramic membranes produced much higher permeate fluxes rather than organic ones probably due to a variety of interacting physical–chemical and hydrodynamic factors. Acknowledgements This work was supported by the Spanish Ministerio de Educación y Ciencia (CTM2004-03130/ TECNO). References [1]
A. Bes-Piá et al., Reuse of the textile industry after its treatment with a combination of physicalchem. treatment and membrane technologies, Desalination, 149 (2002) 169–174.
S. Barredo-Damas et al. / Desalination 200 (2006) 745–747 [2]
[3]
M. Marcucci et al., Experimental campaigns on textile wastewater for reuse by means of different membrane proceses, Desalination, 149 (2002) 137–143. M. Marcucci et al., Treatment and reuse of textile effluents based on new ultrafiltration and other membrane technologies, Desalination, 138 (2001) 75–82.
[4]
[5]
747
S. Sostar-Turk et al., Wastewater treatment after reactive printing, Dyes Pigments, 64 (2005) 147–152. S. Petrov Petrov et al., Ultrafiltration purification of waters contaminated with bifunctional reactive dyes, Desalination, 154 (2003) 247–252.