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Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry
DESALINATION Desalination 175 (2005) 111-119
ELSEVIER
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Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry B. Van der Bruggen a*, G. Cornelis a, C. Vandecasteele", I. Devreese b aLaboratoryfor Applied Physical Chemistry and Environmental Technology, Department of Chemical Engineering, K.U. Leuven, W. de Croylaan 46, B-3001 Heverlee, Belgium Tel. +32 (16) 32 23 40; Fax: +32 (16) 32 29 91; email: [email protected] bCentexbel-Gent, Technologiepark 7, 9052 Zwijnaarde, Belgium
Received 15 May 2004; accepted 21 September 2004
Abstract
Textile effluents usually contain high concentrations ofinorganics as well as organics, and are therefore difficult to treat. Membrane processes can be used for many of these wastewaters in the textile industry. Two typical examples are discussed: (1) the use of nanofiltration for the treatment of exhausted dye baths, in view of water recycling, and (2) the use ofultrafiltration for the removal of spin finish from waste water resulting from rinsing of textile fibres. Both applications are in principle feasible, but in practice the process is negatively influenced by membrane fouling. In the first application, fouling is assumed to be caused by (ad)sorption of organic compounds, which has a large influence because of the high concentrations used in textile dyeing. Furthermore, the high salt concentrations result in a decrease of the effective driving force because of the high osmotic pressures obtained for typical dye baths. Experimental results are discussed, and the applicability ofnanofiltration is related to the characteristics of the dye baths for different dyeing methods. In the second application, the concentration of organic compounds is relatively low, but because of the hydrophobic nature of the spin finish compounds, a significant effect of membrane fouling is expected. An improvement is suggested by using nanofiltration membranes instead of ultrafiltration membranes. Keywords: Nanofiltration; Ultrafiltration; Fouling; Wastewater regeneration
I. Introduction
It is generally accepted that membrane technology offers solutions for the wastewater *Corresponding author.
problem in the textile industry, with the possibility of water recycling [ 1,2]. In particular, nanofiltration (NF) and ultrafiltration (UF) are often suggested as good candidates [3--6] and have been tested on a pilot scale [7,8]. A membrane filtration unit can be placed at the very end of the
Presented at the Conference on Fouling and Crit&al Flux: Theory and Applications, June 16-18, 2004, Lappeenranta, Finland. Organized by Lappeenranta University of Technology.
0011-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved doi: 10.1016/j.desal.2004.09.025
112
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
wastewater treatment line, treating wastewater from various sources after traditional pretreatment and biological degradation. Although this option has proven to be feasible [9] and fits within the current situation for the vast majority of textile companies, it has a number of disadvantages. First of all, the membranes should reject relatively small organic compounds, broken down in the biological degradation step. Second, there is no option to perform the filtration at elevated temperatures, which would allow energy savings. Third, treatment of specific fractions (e.g., batches of a pronounced color) is not possible. The alternative is to treat individual waste streams from textile finishing processes such as dyeing or rinsing. This approach allows a direct recycling of treated water to the process itself, possibly even at high temperatures. Nevertheless, different aspects still need to be studied: (1) the influence of the use of regenerated water on the quality of the final textile product; (2) the environmental fate of the concentrate fraction; and (3) control of membrane fouling. All of these aspects are still unsolved questions posing important hurdles for the implementation of membrane filtration in the textile industry. This article discusses membrane fouling in two applications in the textile industry: the use of NF for removal of dyes from wastewater, and the use of UF for removal of spin finish. Spin finish is a complex mixture of various chemical components used to facilitate the spinning of textile fibres. The composition of the spin finish depends on the end use of the yam [10]. During rinsing of the yam, spin finish is removed by rinse water, resulting in a significant fraction of wastewater contaminated with spin finish. Most components of spin finish are not biodegradable; wastewater treatment should be done by using physicochemical methods such as membrane filtration. In this case, the spin finish from the production of polyamide carpet contains only anionic and nonionic surfactants.
Membrane fouling was reported for both NF of exhausted dye baths and UF of oil/water mixtures [ 11,12]. Mechanisms of fouling are still unclear, although a number of factors influencing the flux have been reported. Adsorption appears to play a key role for organic compounds with polymeric membranes [ 13-16], which might even influence rejection when very low concentrations are considered [16]; for filtration of, e.g., natural waters algogenic organic matter and particles are also important [ 17,18]. These observations lead to the conclusion that fouling is closely related to transport mechanisms. This was also confirmed by recent studies on transport characterization [19,20]. In this article membrane fouling in the case of NF and UF of textile effluents will be related to fouling mechanisms and to solute transport through the membranes.
2. Methods and materials
2.1. Nanofiltration of used dye baths Flux decline experiments were carried out in a laboratory-scale NF unit using flat-sheet membranes with an effective surface area of 59 cm2. The flow channel was rectangular with a hydraulic diameter of 4.2 mm. The total channel length was 293 mm. This set-up has been previously described in detail [21]. The membranes used were the NF70 (Filmtec), UTC-20 (Toray Ind.) and NTR 7450 (Nitto-Denko); before being used they were soaked in deionized water for 24 h and pressurized during 1 h at 20 bar. The temperature in the experiments was 25°C. Pure water fluxes were measured in the same setup using deionized water. Experiments were carried out using exhausted strong acid (SA) and metal complex (MC) dye baths used for wool dyeing. The compositions are given in Table 1. Sandolan is an acid dye with exceptionally good lightfastness and a good penetration. Lanasyn is a metal complex dye with
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
113
Table 1 Compositionof the dye baths used in the experiments
Foam reducing agent, g/l Egaliser, g/l Antimoth,g/l Wetting agent, g/1 Salt, g/l Acid, g/l Bleaching agent, g/1 Lubricant, g/1 Acid spender, g/l Dyes
Strong acid
Metal complex
0.25 0.85 0.15 0.7 7.8 2.4 1.55 1.7 -Sandolan Jaune E2 GL 133% AY17 Sandolan Rubinol E3 GSL 230% AR37
0.25 0.85 0.15 0.7 7.8 2.4 / 1.7 0.6 Lanasyn Jaune $2 GL Isolan Rot SRL (Azo-chromiumcomplex with CI Acid Red 414) Lanasyn Bleu SDNL
Bleu Alizarine 110% GS AB 45 (CI Acid Blue 45)
Lanasyn Bordeaux SD Erionyl Black MR (CI Acid Black 172) good fastness properties that is often used in combination with other dyes. Isolan Rot SRL is a red metal complex dye that contains 3.1% chromium. Erionyl Black MR is a black metal complex dye with high wet fastness and a shade shift in artificial light towards red. Alizarin Brilliant Blue GS is a red acid dye. 2.2. Filtration o f rinsing waters from the production o f polyamide carpet
Synthetic solutions were prepared with a commercial spin finish (Fasavin CA 73, Zschimmer & Schwarz) and antifoaming agent (Defoamer RKN, Lomat International). Rinsing water samples were obtained from Nelca (Lendelede, Belgium) and were filtrated within 3 days after sampling. Chemical oxygen demand (COD) of rinsing waters was determined by a standard procedure [22]. Non-ionic surfactant concentration was determined by a two-phase titration with sodiumtetracis(4-fluorophenyl)borate [23]. All determinations ofnonionic surfactants were tom-
pared with a standard series of solutions with known spin finish concentration. In the UF experiments UF-PES-10 (Osmonics) was used, which is a hydrophilic membrane with a 10 kDa cut-off. Temperature was kept constant at 50°C and transmembrane pressure at 5 bar. Rinsing waters were filtrated without prior treatment. In the NF experiments the N30F (Nadir, MWCO 400-500 Da, hydrophobic) and Desal DL 5 (Osmonies, MWCO 150 to 300 Da, hydrophilic) were used. Temperature was kept constant at 50°C and transmembrane pressure at 8 bar. Rinsing waters were filtered with a paper filter prior to NF. Static adsorption experiments were carried out with Desal DL 5 membranes and spin finish solutions for 24 h. The amount of adsorbed spin finish was measured by calculating the decrease in concentration of the spin oil solution (substracted by a blank). Contact angle measurements between these membranes and the corresponding spin finish solutions were carried out with a dropshape analysis system (Krfiss, DSA Mk2).
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B. Van der Bruggen et al. / Desalination 175 (2005) 111-119 40-
3. Results and discussion
35
3.1. Nanofiltration of exhausted dye baths Fig. 1 gives a typical curve for the water flux as a function of time (MC dye bath, NF70 membrane, 10 bar) when the permeate is recycled to the feed tank of the NF unit (constant concentration). The water flux decreased, but a stable flux was obtained after 6-10 h. When the permeate was not recycled (increasing concentration as a function of time, Fig. 2), no stable value was obtained. Two phenomena considered here might be responsible for this, i.e., the osmotic pressure and adsorption of organic compounds on the membrane material (both concentration dependent). Additionally, the increase in viscosity might also result in a lower flux. Table 2 summarizes the water fluxes through the membranes measured after stabilisation at 10 bar during 1 h. The pressure was chosen as a typical NF pressure at which the flux-pressure proportionality is still valid. The initial pure water flux was in the same order of magnitude for all three membranes, although the water flux for UTC-20 was higher than for the two other membranes. The water flux for NF70 was significantly different in both experiments, this is attributed to a difference between different membrane sheets. The difference between the initial pure water flux and the dye bath flux divided by the initial pure water flux reflects the flux decline (in %) caused by the composition of the dye bath. This flux decline is partly reversible because of the osmotic pressure of the feed mixture, and partly irreversible because of pore blocking and adsorption of organic compounds on the membrane (referred to as fouling). The osmotic pressure calculated from the composition of the feed mixture (mainly caused by) using the Van't Hoff equation is 4.1 bar; using the Pitzer model [24], which takes interactions between ions into account, the osmotic pressure is 2.7 bar. Compared to a feed pressure of 10 bar, 27% flux decline due to the osmotic
30
25.
5 20
40
15, 10, 5. 0 100
200
300
400
500
600
Time (rain)
Fig. 1. Water flux as a functionof time for nanofiltration of the MC dye bath with the NF70 (transmembrane pressure = 10 bar). ~" 100
"~ o
80
................................. • • O O
.......................
60
40
4
i
i
i
|
i
|
200
400
600
800
1000
1200
Time (rain) Fig. 2. W a t e r flux as a f u n c t i o n o f time without recycling o f the retentate to the feed ( m e m b r a n e : UTC-20, feed: M C dye bath, pressure: 10 bar).
pressure is expected for complete ion rejection. For NF70, this is a reasonable assumption; for UTC-20, a rejection of ca. 70% was measured for Na2SO4, resulting in a somewhat lower osmotic pressure difference (1.8 bar) and, consequently, 18% flux decline due to the osmotic pressure. The remaining flux loss was due to pore blocking and/or adsorption. The distinction between pore blocking and adsorption was not made in the experiments; both will be considered together as fouling. A significant effect of adsorption/pore blocking was found: flux decline values range from 26 to 46%. The effect of the osmotic pressure is fully reversible: when a feed with lower salt concen-
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B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
Table 2 Nanofiltrationof the acid dye bath (SA) and the metal complex dye bath (MC) Feed
SA SA SA MC MC MC
Membrane
NF70 UTC-20 NTR 7450 NF70 UTC-20 NTR 7450
Water flux with Water flux Flux pure water with dye bath decline
(I/m~h)
(I/m2h)
(%)
120 228 132 93 222 122
33 127 * 32 89 *
73 44 100 65 60 100
Flux difference due Water flux to pore blocking- with pure adsorption water (I/m2h)
Irreversible flux decline (%)
46 26
66 149
45 34
--
~
na
38 42
70 133
25 40
--
~
na
*No water flux obtained; t not measured; na, not applicable.
trations was applied, the osmotic pressure decreased accordingly. The interaction between organic compounds and the membrane material is thought to be mainly irreversible, although desorption of adsorbed organic material might oceur by rinsing with water. Interactions with the charged components in the dye baths are strong, which is logical because dyes are supposed to interact with textile fibres (which are also organic); components that are attached to the membrane do not desorb easily. The irreversible flux decline (in %), measured as the relative difference between the initial pure water flux and the pure water flux measured after the experiment, should therefore correspond to the fraction of flux decline caused by adsorption. For the SA bath with NF70 and for the MC bath with UTC-20, both values correspond (Table 2). For the SA bath with UTC-20, the irreversible part is larger than expected, probably because of a higher salt passage than assumed in this dye bath. For the MC bath with NF70, a rinsing (and desorption) effect might have resulted in a lower than expected irreversible flux decline. A confirmation of the effect of pore blocking/ adsorption was found with NTR 7450. Although the osmotic pressure is assumed to be low for NF
with NTR 7450 (low salt retentions), the flux decline was so pronounced that no water flux was obtained with the different dye baths. NTR 7450 has larger pores; the MWC is estimated at 600800, and the average pore size is 0.80 nm. The molecules in the dye bath are relatively large and fit well into the pores of the NTR 7450 membrane. Although the molecular structure is not known for the additives, the dyes have been found to have a size that correspond to the pore size of NTR 7450.
3.2. Ultrafiltration and nanofiltration of wastewater containing spin finish The COD and nonionic surfactant concentration of the rinsing waters (1 to 3) and of solutions with known spin finish concentrations, together with the average permeate concentrations and rejections during UF with UF-PES-10, are given in Table 3. Large differences in concentrations were found; rejections depended on the rinsing water but were usually relatively low. Thus, a large fraction of the spin finish components penetrated the membrane. In Figs. 3 and 4, water fluxes as a function of time are given for UF of real rinsing waters (containing spin finish, antifoaming agents, polyamide monomers and fibers,
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B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
Table 3 Chemical oxygen demand (COD) and nonionic surfactant concentration in feed and permeate after ultra filtration of rinsing waters and a synthetic solution. The nonionic surfactant concentrations where compared to solutions containing a known amount of spin finish
COD (mg 02/1) Feed Rinsing water 1
Nonionic surfactant (ppm)
Permeate
44
11
Rinsing water 2
1125
172
Rinsing water 3
2788
693
401
166
Spin finish, 200 ppm
Retention, %
Feed
Permeate
Retention, %
74 85 75 58
21 107 256 207
1.7 46 168 83
8 43 65 41
60%
60% x
50%
d 0
Xl *2 "3
40% 30% 0-'~3~- x l ~ x
X X )K X
X
50% • J#
40%
30%
X e,
200/6 nnIi • • • • •
:
~
•
• •
~
•
•
•
•
20%
X
10%
10%
~XXX
0% 0% 0
I
)
50
100
|
150
• 200 ppm spin finish and antifoam tt 200 ppm spin finish X 600 ppm spin finish
|
200
Time (rain)
0
X X X x
X
X
!
i
i
i
50
100
150
200
Time (min)
Fig. 3. Flux relative to the pure water flux as a function of time during ultrafiltration of riming waters from the production of polyamide carpet.
Fig. 4. Flux relative to the pure water flux as a function of time during ultrafiltration of synthetic solutions conmining only spin finish or antifoam. In all experiments, UF-PES 10 was used.
Fig. 3) and of synthetic solutions (containing only spin finish and/or antifoam, Fig. 4). The more pronounced flux decline with higher surfactant concentrations in both rinsing waters and synthetic solutions indicates adsorption o f spin finish components in membrane pores. Surfactants and especially nonionie surfactants are known to adsorb to pores o f UF membranes, thereby causing flux decline [25]. Furthermore, a large initial flux decline was observed (initial fluxes are from 20% to 50% of the pure water flux), which indicates pore blocking. However, for the rinsing waters a stable flux was not found on the time scale o f the experiments (ca. 3 h), while for synthetic spin
finish solutions with a comparable nonionic surfactant concentration a stable flux was found after ca. 1 h, with even an increasing tendency after this period. It appears that after a rapid initial adsorption o f spin finish, other components (including polyamide monomers and fibers) gradually adsorb and cause a slow flux decline. The rinsing waters contained a high load of organic contaminants, which was evident from measured COD levels (Table 3). Using UF, retention o f nonionic surfactants increases with feed concentration (Table 3). In general, monomers o f commercial surfactants are 300-650 Da in size, but surfactants are known to
117
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
form micelle aggregates above a characteristic concentration, the critical micelle concentration (cmc). Micelles are generally 3 0 - 60 kDa in size; thus, with an increasing surfactant load above the cmc, a larger fraction o f the surfactants will not pass through the UF membrane. The cmc o f spin finish surfactants was found to be between 100 and 500 ppm (results not shown), so UF o f rinsing waters from the production ofpolyamide carpets is not efficient enough. A more efficient removal o f surfactant solutions can be obtained with NF [26]. Figs. 5 and 6 10% 8% 6% O
4% 2% 0%
1
0
50
- - - -
I
i
100 Tkne (min)
I
150
200
Fig. 5. Flux relative to the pure water flux as a function of time using N30F for a 200 pprn spin finish solution.
show flux as a function of time using two NF membranes. Since both surfaetant monomers and micelles are rejected, both N30F and Desal DL 5 show substantial retentions that range from 90% to 97%, depending on surfactant load. Similar to UF-PES 10, the water flux obtained with N30F as a function o f time was not satisfactory. Due to its high cut-off (400-500 Da), which is comparable to the size o f surfactant monomers, and its relatively hydrophobic nature, a dramatic initial flux decline was observed. Especially nonionic surfactants adsorb to hydrophobic membranes causing a more pronounced flux decline than ionic surfactants [27]. A different behaviour was observed for Desal DL 5, a membrane with pores tight enough (MWCO 150-300) to impede pore penetration. During static adsorption experiments, the spin finish adsorbed on the membrane surface (Fig. 7). It has been observed with MF membranes that this can render the membrane surface more hydrophilic (the hydrophobic tail o f the surfactant interacts with the membrane, while the hydrophilic head remains available) so that the water flux increases above the initial pure water flux [27]. The contact angle o f pure water on a wet, clean Desal DL 5 membrane was 40.7 ° while a 100 ppm spin finish solution had a contact 6
120%
~5
100%
~ 80% 3
•~ 60%
•
4
40%
-~ 5
2O%
× Spinfinish200 ppm
0%
*
..................
0
1 - .............
50
~
.
.
6
.
.
.
< 1 .
1O0 Time (rrdn)
.
.
.
I
150
. . . . . .
I
200
Fig. 6. Flux relative to the pure water flux as a function of time using Desal DL 5 for three different rinsing waters and a 200 ppm spin finish solution.
o
..............
0
T .......................
r ...................
"7- .................
~. . . . . . . . . . . . . . . . . . . . .
20 40 60 80 Spin finishconcentration (pprn)
7
100
Fig. 7. Adsorbed spin finish on Desal DL 5 membranes as a function of the spin finish concentration of the corresponding solutions.
118
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
angle of 29.5 ° with a Desal DL 5 membrane to which a 100 ppm finish solution had been allowed to adsorb for 24 h. The lower contact angle indicates that the membrane surface is more hydrophilic. However, further research is required to elucidate the mechanisms o f the observed flux increase.
4. Conclusions Membrane fouling during the filtration o f textile effluents is caused by the adsorption o f organic compounds present in the wastewater. Depending on their ability to penetrate into the membrane, a significant effect can be observed. This is similar for UF and NF. A possible solution is to use tighter membranes, which might even lead to a flux increase in the specific ease o f surfactants. In NF, high salt concentrations cause a large osmotic pressure difference, which also leads to lower fluxes. Although this is not a fouling effect (it is reversible), the result in terms o f water fluxes is the same as for membrane fouling.
References [1] G. Ciardelli, L. Corsi and M. Mareueei, Membrane separation for wastewater reuse in the textile industry. Resources Cons. Recycling, 31(2) (2001) 189197. [2] C.V. Vedavyasan, Combating water shortages with innovative uses of membranes. Desalination, 132 (2000) 345-347. [3] A. Sungpet, R. Jiraratananon and P. Luangsowan, Treatment of effluents from textile-rinsing operations by thermally stable nanofiltration membranes. Desalination, 160 (2004) 75-81. [4] S. Chakraborty, M.K. Purkait, S. DasGupta, S. De, and J.K. Basu, Nanofiltration of textile plant effluent for color removal and reduction in COD. Sep. Purif. Technol., 31(2) (2003) 141-151. [5] C. Tang and V. Chen, Nanofiltration of textile wastewater for water reuse. Desalination, 143 (2002) 11-20.
[6] M. Marcucci, G. Nosenzo,G. CapanneUi, I. Ciabatti, D. Corrieri and G. Ciardelli, Treatment and reuse of textile effluents baaed on new ultrafiltration and other membrane technologies. Desalination, 138 (2001) 75-82. [7] M. Marcucci, G. Ciardelli, A. Matteucci, L. Ranieri, and M. Russo, Experimental campaigns on textile wastewater for reuse by means of different membrane processes. Desalination, 149 (2002) 137-143. [8] I. Koyuncu, E. Kural and D. Topacik, Pilot scale nanofiltration membrane separation for waste management in textile industry. Water Sci. Teehnol., 43(10) (2001) 233-240. [9] A. Bes-Pia, J.A. Mendoza-Roca, L. Roig-Alcoyer, A. Iborra-Clar, M.I. Iborra-Clar and M.I. AlcainaMiranda, Comparison between nanofiltration and ozonation of biologically treated textile wastewater for its reuse in the industry. Desalination, 157 (2003) 81-86. [10] P.E. Slade, Handbook of Fiber Finish Technology, Marcel Dekker, New York, 1998. [11] S. Chakraborty, B.C. Bag, S. DasGupta, J.K, Basu and S. De, Prediction of permeate flux and permeate concentration in nanofiltration of dye solution. Sep. Purif. Technol., 35(2) (2004) 141-152. [ 12] N.A. Ochoa, M. Masuelli and J. Marehese, Effect of hydrophilicity on fouling of an emulsified oil wastewater with PVDF/PMMA membranes. J. Membr. Sci., 226 (2003) 203-211. [13] L.D. Nghiem and A.I. Sehafer, Adsorption and transport of trace contaminant estrone in NF/RO membranes. Environ. Engn. Sci., 19(6) (2002) 441451. [14] L.D. Nghiem, A.I. Sehafer and T.D. WaRe, Adsorptive interactions between membranes and trace contaminants. Desalination, 147 (2002) 269-274. [15] S. Chang, T.D. Waite, A.I. Schafer and A.G. Fane, Adsorption of the endocrine-active compound estrone on microfiltration hollow fiber membranes. Environ. Sci. Technol., 37(14) (2003) 3158-3163. [16] K. Kimura, G. Amy, J. Drewes and Y. Watanabe, Adsorption ofhydrophobie compounds onto NF/RO membranes: an artifact leading to overestimation of rejection. J. Membr. Sci., 221 (2003) 89-101. [17] N. Her, G. Amy, H.R. Park and M. Song, Characterizing algogenic organic matter (AOM) and evaluating associated NF membrane fouling. Water Research 2004, 38 (6) 1427-1438.
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[18] M. Nystrom, A. Pihlajamaki, R. Liikanen and M. Manttari, Influence of process conditions and membrane/particle interaction in NF ofwastewaters. Desalination, 156 (2003) 379-387. [19] A.E. Yaroshchuk, Recent progress in the transport characterization ofnanofiltrationmembranes. Desalination, 149 (2002) 423--428. [20] A.E. Yaroshehuk and V. Ribitseh, The uses of nonsteady-state membrane characterization techniques for the study of transport properties of active layers of nanofiltration membranes: theory with experimental examples. Chem. Engn. J., 80 (2000) 203214. [21] B. Van der Bruggen, J. Schaep, D. Wilms and C. Vandecasteele, Influence of molecular size, polarity and charge on the retention of organic molecules by nanofiltration. J. Membr. Sci., 156 (1999) 29-41. [22] L.S. Clesceri, A.E. Greenberg and R.R. Trussel, eds., Standard Methods for the Examination of Water and Wastewater, 17th ed., American Public Health Association, 1989.
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[23] M. Tsubouchi, N. Yamasaki and K. Yanagisawa, Two-phase titration of poly(oxyethylene) nonionic surfactants with tetrakis(4-fluomphenyl)borate. Anal. Chem., 57 (1985) 783-784. [24] K.S. Pitzer, Thermodynamics of electrolytes I. Theoretical basis and general equations, J. Phys. Chem., 77 (1973) 268-277. [25] A.-S. JSnsson and B. JSnsson, The influence of nonionic and ionic surfactants on hydrophobic and hydrophilic ultrafiltration membranes. J. Membr. Sei., 56 (1991) 49-76. [26] B. Goers and G. en Wozny, Flexible design and operation of a two-step UF/NF-system for product recovery from rinsing waters in batch production. Water Sci. Teehnol., 41(10--11) (2000) 93-100. [27] M. Mietton-Peuchot, O. Ranisio and C. Peuchot, Study of behaviour of membranes in the presence of anionic or nonionic surfaetants. Filtr. Sep., 34(8) (1997) 883-886.
ELSEVIER
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Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry B. Van der Bruggen a*, G. Cornelis a, C. Vandecasteele", I. Devreese b aLaboratoryfor Applied Physical Chemistry and Environmental Technology, Department of Chemical Engineering, K.U. Leuven, W. de Croylaan 46, B-3001 Heverlee, Belgium Tel. +32 (16) 32 23 40; Fax: +32 (16) 32 29 91; email: [email protected] bCentexbel-Gent, Technologiepark 7, 9052 Zwijnaarde, Belgium
Received 15 May 2004; accepted 21 September 2004
Abstract
Textile effluents usually contain high concentrations ofinorganics as well as organics, and are therefore difficult to treat. Membrane processes can be used for many of these wastewaters in the textile industry. Two typical examples are discussed: (1) the use of nanofiltration for the treatment of exhausted dye baths, in view of water recycling, and (2) the use ofultrafiltration for the removal of spin finish from waste water resulting from rinsing of textile fibres. Both applications are in principle feasible, but in practice the process is negatively influenced by membrane fouling. In the first application, fouling is assumed to be caused by (ad)sorption of organic compounds, which has a large influence because of the high concentrations used in textile dyeing. Furthermore, the high salt concentrations result in a decrease of the effective driving force because of the high osmotic pressures obtained for typical dye baths. Experimental results are discussed, and the applicability ofnanofiltration is related to the characteristics of the dye baths for different dyeing methods. In the second application, the concentration of organic compounds is relatively low, but because of the hydrophobic nature of the spin finish compounds, a significant effect of membrane fouling is expected. An improvement is suggested by using nanofiltration membranes instead of ultrafiltration membranes. Keywords: Nanofiltration; Ultrafiltration; Fouling; Wastewater regeneration
I. Introduction
It is generally accepted that membrane technology offers solutions for the wastewater *Corresponding author.
problem in the textile industry, with the possibility of water recycling [ 1,2]. In particular, nanofiltration (NF) and ultrafiltration (UF) are often suggested as good candidates [3--6] and have been tested on a pilot scale [7,8]. A membrane filtration unit can be placed at the very end of the
Presented at the Conference on Fouling and Crit&al Flux: Theory and Applications, June 16-18, 2004, Lappeenranta, Finland. Organized by Lappeenranta University of Technology.
0011-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved doi: 10.1016/j.desal.2004.09.025
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B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
wastewater treatment line, treating wastewater from various sources after traditional pretreatment and biological degradation. Although this option has proven to be feasible [9] and fits within the current situation for the vast majority of textile companies, it has a number of disadvantages. First of all, the membranes should reject relatively small organic compounds, broken down in the biological degradation step. Second, there is no option to perform the filtration at elevated temperatures, which would allow energy savings. Third, treatment of specific fractions (e.g., batches of a pronounced color) is not possible. The alternative is to treat individual waste streams from textile finishing processes such as dyeing or rinsing. This approach allows a direct recycling of treated water to the process itself, possibly even at high temperatures. Nevertheless, different aspects still need to be studied: (1) the influence of the use of regenerated water on the quality of the final textile product; (2) the environmental fate of the concentrate fraction; and (3) control of membrane fouling. All of these aspects are still unsolved questions posing important hurdles for the implementation of membrane filtration in the textile industry. This article discusses membrane fouling in two applications in the textile industry: the use of NF for removal of dyes from wastewater, and the use of UF for removal of spin finish. Spin finish is a complex mixture of various chemical components used to facilitate the spinning of textile fibres. The composition of the spin finish depends on the end use of the yam [10]. During rinsing of the yam, spin finish is removed by rinse water, resulting in a significant fraction of wastewater contaminated with spin finish. Most components of spin finish are not biodegradable; wastewater treatment should be done by using physicochemical methods such as membrane filtration. In this case, the spin finish from the production of polyamide carpet contains only anionic and nonionic surfactants.
Membrane fouling was reported for both NF of exhausted dye baths and UF of oil/water mixtures [ 11,12]. Mechanisms of fouling are still unclear, although a number of factors influencing the flux have been reported. Adsorption appears to play a key role for organic compounds with polymeric membranes [ 13-16], which might even influence rejection when very low concentrations are considered [16]; for filtration of, e.g., natural waters algogenic organic matter and particles are also important [ 17,18]. These observations lead to the conclusion that fouling is closely related to transport mechanisms. This was also confirmed by recent studies on transport characterization [19,20]. In this article membrane fouling in the case of NF and UF of textile effluents will be related to fouling mechanisms and to solute transport through the membranes.
2. Methods and materials
2.1. Nanofiltration of used dye baths Flux decline experiments were carried out in a laboratory-scale NF unit using flat-sheet membranes with an effective surface area of 59 cm2. The flow channel was rectangular with a hydraulic diameter of 4.2 mm. The total channel length was 293 mm. This set-up has been previously described in detail [21]. The membranes used were the NF70 (Filmtec), UTC-20 (Toray Ind.) and NTR 7450 (Nitto-Denko); before being used they were soaked in deionized water for 24 h and pressurized during 1 h at 20 bar. The temperature in the experiments was 25°C. Pure water fluxes were measured in the same setup using deionized water. Experiments were carried out using exhausted strong acid (SA) and metal complex (MC) dye baths used for wool dyeing. The compositions are given in Table 1. Sandolan is an acid dye with exceptionally good lightfastness and a good penetration. Lanasyn is a metal complex dye with
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
113
Table 1 Compositionof the dye baths used in the experiments
Foam reducing agent, g/l Egaliser, g/l Antimoth,g/l Wetting agent, g/1 Salt, g/l Acid, g/l Bleaching agent, g/1 Lubricant, g/1 Acid spender, g/l Dyes
Strong acid
Metal complex
0.25 0.85 0.15 0.7 7.8 2.4 1.55 1.7 -Sandolan Jaune E2 GL 133% AY17 Sandolan Rubinol E3 GSL 230% AR37
0.25 0.85 0.15 0.7 7.8 2.4 / 1.7 0.6 Lanasyn Jaune $2 GL Isolan Rot SRL (Azo-chromiumcomplex with CI Acid Red 414) Lanasyn Bleu SDNL
Bleu Alizarine 110% GS AB 45 (CI Acid Blue 45)
Lanasyn Bordeaux SD Erionyl Black MR (CI Acid Black 172) good fastness properties that is often used in combination with other dyes. Isolan Rot SRL is a red metal complex dye that contains 3.1% chromium. Erionyl Black MR is a black metal complex dye with high wet fastness and a shade shift in artificial light towards red. Alizarin Brilliant Blue GS is a red acid dye. 2.2. Filtration o f rinsing waters from the production o f polyamide carpet
Synthetic solutions were prepared with a commercial spin finish (Fasavin CA 73, Zschimmer & Schwarz) and antifoaming agent (Defoamer RKN, Lomat International). Rinsing water samples were obtained from Nelca (Lendelede, Belgium) and were filtrated within 3 days after sampling. Chemical oxygen demand (COD) of rinsing waters was determined by a standard procedure [22]. Non-ionic surfactant concentration was determined by a two-phase titration with sodiumtetracis(4-fluorophenyl)borate [23]. All determinations ofnonionic surfactants were tom-
pared with a standard series of solutions with known spin finish concentration. In the UF experiments UF-PES-10 (Osmonics) was used, which is a hydrophilic membrane with a 10 kDa cut-off. Temperature was kept constant at 50°C and transmembrane pressure at 5 bar. Rinsing waters were filtrated without prior treatment. In the NF experiments the N30F (Nadir, MWCO 400-500 Da, hydrophobic) and Desal DL 5 (Osmonies, MWCO 150 to 300 Da, hydrophilic) were used. Temperature was kept constant at 50°C and transmembrane pressure at 8 bar. Rinsing waters were filtered with a paper filter prior to NF. Static adsorption experiments were carried out with Desal DL 5 membranes and spin finish solutions for 24 h. The amount of adsorbed spin finish was measured by calculating the decrease in concentration of the spin oil solution (substracted by a blank). Contact angle measurements between these membranes and the corresponding spin finish solutions were carried out with a dropshape analysis system (Krfiss, DSA Mk2).
114
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119 40-
3. Results and discussion
35
3.1. Nanofiltration of exhausted dye baths Fig. 1 gives a typical curve for the water flux as a function of time (MC dye bath, NF70 membrane, 10 bar) when the permeate is recycled to the feed tank of the NF unit (constant concentration). The water flux decreased, but a stable flux was obtained after 6-10 h. When the permeate was not recycled (increasing concentration as a function of time, Fig. 2), no stable value was obtained. Two phenomena considered here might be responsible for this, i.e., the osmotic pressure and adsorption of organic compounds on the membrane material (both concentration dependent). Additionally, the increase in viscosity might also result in a lower flux. Table 2 summarizes the water fluxes through the membranes measured after stabilisation at 10 bar during 1 h. The pressure was chosen as a typical NF pressure at which the flux-pressure proportionality is still valid. The initial pure water flux was in the same order of magnitude for all three membranes, although the water flux for UTC-20 was higher than for the two other membranes. The water flux for NF70 was significantly different in both experiments, this is attributed to a difference between different membrane sheets. The difference between the initial pure water flux and the dye bath flux divided by the initial pure water flux reflects the flux decline (in %) caused by the composition of the dye bath. This flux decline is partly reversible because of the osmotic pressure of the feed mixture, and partly irreversible because of pore blocking and adsorption of organic compounds on the membrane (referred to as fouling). The osmotic pressure calculated from the composition of the feed mixture (mainly caused by) using the Van't Hoff equation is 4.1 bar; using the Pitzer model [24], which takes interactions between ions into account, the osmotic pressure is 2.7 bar. Compared to a feed pressure of 10 bar, 27% flux decline due to the osmotic
30
25.
5 20
40
15, 10, 5. 0 100
200
300
400
500
600
Time (rain)
Fig. 1. Water flux as a functionof time for nanofiltration of the MC dye bath with the NF70 (transmembrane pressure = 10 bar). ~" 100
"~ o
80
................................. • • O O
.......................
60
40
4
i
i
i
|
i
|
200
400
600
800
1000
1200
Time (rain) Fig. 2. W a t e r flux as a f u n c t i o n o f time without recycling o f the retentate to the feed ( m e m b r a n e : UTC-20, feed: M C dye bath, pressure: 10 bar).
pressure is expected for complete ion rejection. For NF70, this is a reasonable assumption; for UTC-20, a rejection of ca. 70% was measured for Na2SO4, resulting in a somewhat lower osmotic pressure difference (1.8 bar) and, consequently, 18% flux decline due to the osmotic pressure. The remaining flux loss was due to pore blocking and/or adsorption. The distinction between pore blocking and adsorption was not made in the experiments; both will be considered together as fouling. A significant effect of adsorption/pore blocking was found: flux decline values range from 26 to 46%. The effect of the osmotic pressure is fully reversible: when a feed with lower salt concen-
115
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
Table 2 Nanofiltrationof the acid dye bath (SA) and the metal complex dye bath (MC) Feed
SA SA SA MC MC MC
Membrane
NF70 UTC-20 NTR 7450 NF70 UTC-20 NTR 7450
Water flux with Water flux Flux pure water with dye bath decline
(I/m~h)
(I/m2h)
(%)
120 228 132 93 222 122
33 127 * 32 89 *
73 44 100 65 60 100
Flux difference due Water flux to pore blocking- with pure adsorption water (I/m2h)
Irreversible flux decline (%)
46 26
66 149
45 34
--
~
na
38 42
70 133
25 40
--
~
na
*No water flux obtained; t not measured; na, not applicable.
trations was applied, the osmotic pressure decreased accordingly. The interaction between organic compounds and the membrane material is thought to be mainly irreversible, although desorption of adsorbed organic material might oceur by rinsing with water. Interactions with the charged components in the dye baths are strong, which is logical because dyes are supposed to interact with textile fibres (which are also organic); components that are attached to the membrane do not desorb easily. The irreversible flux decline (in %), measured as the relative difference between the initial pure water flux and the pure water flux measured after the experiment, should therefore correspond to the fraction of flux decline caused by adsorption. For the SA bath with NF70 and for the MC bath with UTC-20, both values correspond (Table 2). For the SA bath with UTC-20, the irreversible part is larger than expected, probably because of a higher salt passage than assumed in this dye bath. For the MC bath with NF70, a rinsing (and desorption) effect might have resulted in a lower than expected irreversible flux decline. A confirmation of the effect of pore blocking/ adsorption was found with NTR 7450. Although the osmotic pressure is assumed to be low for NF
with NTR 7450 (low salt retentions), the flux decline was so pronounced that no water flux was obtained with the different dye baths. NTR 7450 has larger pores; the MWC is estimated at 600800, and the average pore size is 0.80 nm. The molecules in the dye bath are relatively large and fit well into the pores of the NTR 7450 membrane. Although the molecular structure is not known for the additives, the dyes have been found to have a size that correspond to the pore size of NTR 7450.
3.2. Ultrafiltration and nanofiltration of wastewater containing spin finish The COD and nonionic surfactant concentration of the rinsing waters (1 to 3) and of solutions with known spin finish concentrations, together with the average permeate concentrations and rejections during UF with UF-PES-10, are given in Table 3. Large differences in concentrations were found; rejections depended on the rinsing water but were usually relatively low. Thus, a large fraction of the spin finish components penetrated the membrane. In Figs. 3 and 4, water fluxes as a function of time are given for UF of real rinsing waters (containing spin finish, antifoaming agents, polyamide monomers and fibers,
116
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
Table 3 Chemical oxygen demand (COD) and nonionic surfactant concentration in feed and permeate after ultra filtration of rinsing waters and a synthetic solution. The nonionic surfactant concentrations where compared to solutions containing a known amount of spin finish
COD (mg 02/1) Feed Rinsing water 1
Nonionic surfactant (ppm)
Permeate
44
11
Rinsing water 2
1125
172
Rinsing water 3
2788
693
401
166
Spin finish, 200 ppm
Retention, %
Feed
Permeate
Retention, %
74 85 75 58
21 107 256 207
1.7 46 168 83
8 43 65 41
60%
60% x
50%
d 0
Xl *2 "3
40% 30% 0-'~3~- x l ~ x
X X )K X
X
50% • J#
40%
30%
X e,
200/6 nnIi • • • • •
:
~
•
• •
~
•
•
•
•
20%
X
10%
10%
~XXX
0% 0% 0
I
)
50
100
|
150
• 200 ppm spin finish and antifoam tt 200 ppm spin finish X 600 ppm spin finish
|
200
Time (rain)
0
X X X x
X
X
!
i
i
i
50
100
150
200
Time (min)
Fig. 3. Flux relative to the pure water flux as a function of time during ultrafiltration of riming waters from the production of polyamide carpet.
Fig. 4. Flux relative to the pure water flux as a function of time during ultrafiltration of synthetic solutions conmining only spin finish or antifoam. In all experiments, UF-PES 10 was used.
Fig. 3) and of synthetic solutions (containing only spin finish and/or antifoam, Fig. 4). The more pronounced flux decline with higher surfactant concentrations in both rinsing waters and synthetic solutions indicates adsorption o f spin finish components in membrane pores. Surfactants and especially nonionie surfactants are known to adsorb to pores o f UF membranes, thereby causing flux decline [25]. Furthermore, a large initial flux decline was observed (initial fluxes are from 20% to 50% of the pure water flux), which indicates pore blocking. However, for the rinsing waters a stable flux was not found on the time scale o f the experiments (ca. 3 h), while for synthetic spin
finish solutions with a comparable nonionic surfactant concentration a stable flux was found after ca. 1 h, with even an increasing tendency after this period. It appears that after a rapid initial adsorption o f spin finish, other components (including polyamide monomers and fibers) gradually adsorb and cause a slow flux decline. The rinsing waters contained a high load of organic contaminants, which was evident from measured COD levels (Table 3). Using UF, retention o f nonionic surfactants increases with feed concentration (Table 3). In general, monomers o f commercial surfactants are 300-650 Da in size, but surfactants are known to
117
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
form micelle aggregates above a characteristic concentration, the critical micelle concentration (cmc). Micelles are generally 3 0 - 60 kDa in size; thus, with an increasing surfactant load above the cmc, a larger fraction o f the surfactants will not pass through the UF membrane. The cmc o f spin finish surfactants was found to be between 100 and 500 ppm (results not shown), so UF o f rinsing waters from the production ofpolyamide carpets is not efficient enough. A more efficient removal o f surfactant solutions can be obtained with NF [26]. Figs. 5 and 6 10% 8% 6% O
4% 2% 0%
1
0
50
- - - -
I
i
100 Tkne (min)
I
150
200
Fig. 5. Flux relative to the pure water flux as a function of time using N30F for a 200 pprn spin finish solution.
show flux as a function of time using two NF membranes. Since both surfaetant monomers and micelles are rejected, both N30F and Desal DL 5 show substantial retentions that range from 90% to 97%, depending on surfactant load. Similar to UF-PES 10, the water flux obtained with N30F as a function o f time was not satisfactory. Due to its high cut-off (400-500 Da), which is comparable to the size o f surfactant monomers, and its relatively hydrophobic nature, a dramatic initial flux decline was observed. Especially nonionic surfactants adsorb to hydrophobic membranes causing a more pronounced flux decline than ionic surfactants [27]. A different behaviour was observed for Desal DL 5, a membrane with pores tight enough (MWCO 150-300) to impede pore penetration. During static adsorption experiments, the spin finish adsorbed on the membrane surface (Fig. 7). It has been observed with MF membranes that this can render the membrane surface more hydrophilic (the hydrophobic tail o f the surfactant interacts with the membrane, while the hydrophilic head remains available) so that the water flux increases above the initial pure water flux [27]. The contact angle o f pure water on a wet, clean Desal DL 5 membrane was 40.7 ° while a 100 ppm spin finish solution had a contact 6
120%
~5
100%
~ 80% 3
•~ 60%
•
4
40%
-~ 5
2O%
× Spinfinish200 ppm
0%
*
..................
0
1 - .............
50
~
.
.
6
.
.
.
< 1 .
1O0 Time (rrdn)
.
.
.
I
150
. . . . . .
I
200
Fig. 6. Flux relative to the pure water flux as a function of time using Desal DL 5 for three different rinsing waters and a 200 ppm spin finish solution.
o
..............
0
T .......................
r ...................
"7- .................
~. . . . . . . . . . . . . . . . . . . . .
20 40 60 80 Spin finishconcentration (pprn)
7
100
Fig. 7. Adsorbed spin finish on Desal DL 5 membranes as a function of the spin finish concentration of the corresponding solutions.
118
B. Van der Bruggen et al. / Desalination 175 (2005) 111-119
angle of 29.5 ° with a Desal DL 5 membrane to which a 100 ppm finish solution had been allowed to adsorb for 24 h. The lower contact angle indicates that the membrane surface is more hydrophilic. However, further research is required to elucidate the mechanisms o f the observed flux increase.
4. Conclusions Membrane fouling during the filtration o f textile effluents is caused by the adsorption o f organic compounds present in the wastewater. Depending on their ability to penetrate into the membrane, a significant effect can be observed. This is similar for UF and NF. A possible solution is to use tighter membranes, which might even lead to a flux increase in the specific ease o f surfactants. In NF, high salt concentrations cause a large osmotic pressure difference, which also leads to lower fluxes. Although this is not a fouling effect (it is reversible), the result in terms o f water fluxes is the same as for membrane fouling.
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[6] M. Marcucci, G. Nosenzo,G. CapanneUi, I. Ciabatti, D. Corrieri and G. Ciardelli, Treatment and reuse of textile effluents baaed on new ultrafiltration and other membrane technologies. Desalination, 138 (2001) 75-82. [7] M. Marcucci, G. Ciardelli, A. Matteucci, L. Ranieri, and M. Russo, Experimental campaigns on textile wastewater for reuse by means of different membrane processes. Desalination, 149 (2002) 137-143. [8] I. Koyuncu, E. Kural and D. Topacik, Pilot scale nanofiltration membrane separation for waste management in textile industry. Water Sci. Teehnol., 43(10) (2001) 233-240. [9] A. Bes-Pia, J.A. Mendoza-Roca, L. Roig-Alcoyer, A. Iborra-Clar, M.I. Iborra-Clar and M.I. AlcainaMiranda, Comparison between nanofiltration and ozonation of biologically treated textile wastewater for its reuse in the industry. Desalination, 157 (2003) 81-86. [10] P.E. Slade, Handbook of Fiber Finish Technology, Marcel Dekker, New York, 1998. [11] S. Chakraborty, B.C. Bag, S. DasGupta, J.K, Basu and S. De, Prediction of permeate flux and permeate concentration in nanofiltration of dye solution. Sep. Purif. Technol., 35(2) (2004) 141-152. [ 12] N.A. Ochoa, M. Masuelli and J. Marehese, Effect of hydrophilicity on fouling of an emulsified oil wastewater with PVDF/PMMA membranes. J. Membr. Sci., 226 (2003) 203-211. [13] L.D. Nghiem and A.I. Sehafer, Adsorption and transport of trace contaminant estrone in NF/RO membranes. Environ. Engn. Sci., 19(6) (2002) 441451. [14] L.D. Nghiem, A.I. Sehafer and T.D. WaRe, Adsorptive interactions between membranes and trace contaminants. Desalination, 147 (2002) 269-274. [15] S. Chang, T.D. Waite, A.I. Schafer and A.G. Fane, Adsorption of the endocrine-active compound estrone on microfiltration hollow fiber membranes. Environ. Sci. Technol., 37(14) (2003) 3158-3163. [16] K. Kimura, G. Amy, J. Drewes and Y. Watanabe, Adsorption ofhydrophobie compounds onto NF/RO membranes: an artifact leading to overestimation of rejection. J. Membr. Sci., 221 (2003) 89-101. [17] N. Her, G. Amy, H.R. Park and M. Song, Characterizing algogenic organic matter (AOM) and evaluating associated NF membrane fouling. Water Research 2004, 38 (6) 1427-1438.
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[18] M. Nystrom, A. Pihlajamaki, R. Liikanen and M. Manttari, Influence of process conditions and membrane/particle interaction in NF ofwastewaters. Desalination, 156 (2003) 379-387. [19] A.E. Yaroshchuk, Recent progress in the transport characterization ofnanofiltrationmembranes. Desalination, 149 (2002) 423--428. [20] A.E. Yaroshehuk and V. Ribitseh, The uses of nonsteady-state membrane characterization techniques for the study of transport properties of active layers of nanofiltration membranes: theory with experimental examples. Chem. Engn. J., 80 (2000) 203214. [21] B. Van der Bruggen, J. Schaep, D. Wilms and C. Vandecasteele, Influence of molecular size, polarity and charge on the retention of organic molecules by nanofiltration. J. Membr. Sci., 156 (1999) 29-41. [22] L.S. Clesceri, A.E. Greenberg and R.R. Trussel, eds., Standard Methods for the Examination of Water and Wastewater, 17th ed., American Public Health Association, 1989.
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[23] M. Tsubouchi, N. Yamasaki and K. Yanagisawa, Two-phase titration of poly(oxyethylene) nonionic surfactants with tetrakis(4-fluomphenyl)borate. Anal. Chem., 57 (1985) 783-784. [24] K.S. Pitzer, Thermodynamics of electrolytes I. Theoretical basis and general equations, J. Phys. Chem., 77 (1973) 268-277. [25] A.-S. JSnsson and B. JSnsson, The influence of nonionic and ionic surfactants on hydrophobic and hydrophilic ultrafiltration membranes. J. Membr. Sei., 56 (1991) 49-76. [26] B. Goers and G. en Wozny, Flexible design and operation of a two-step UF/NF-system for product recovery from rinsing waters in batch production. Water Sci. Teehnol., 41(10--11) (2000) 93-100. [27] M. Mietton-Peuchot, O. Ranisio and C. Peuchot, Study of behaviour of membranes in the presence of anionic or nonionic surfaetants. Filtr. Sep., 34(8) (1997) 883-886.