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Removal of methylene blue from aqueous solutions by poly(acrylic acid) and poly(ammonium acrylate) assisted ultrafiltration
Accepted Manuscript Removal of methylene blue from aqueous solutions by poly (acrylic acid) and poly (ammonium acrylate) assisted ultrafiltration Anouar Ben Fradj, Sofiane Ben Hamouda, Hedia Ouni, Ridha Lafi, Lassad Gzara, Amor Hafiane PII: DOI: Reference:
S1383-5866(14)00386-4 http://dx.doi.org/10.1016/j.seppur.2014.06.038 SEPPUR 11838
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
20 December 2013 21 June 2014 26 June 2014
Please cite this article as: A.B. Fradj, S.B. Hamouda, H. Ouni, R. Lafi, L. Gzara, A. Hafiane, Removal of methylene blue from aqueous solutions by poly (acrylic acid) and poly (ammonium acrylate) assisted ultrafiltration, Separation and Purification Technology (2014), doi: http://dx.doi.org/10.1016/j.seppur.2014.06.038
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Removal of methylene blue from aqueous solutions by poly (acrylic acid) and poly (ammonium acrylate) assisted ultrafiltration
Anouar Ben Fradj, Sofiane Ben Hamouda, Hedia Ouni, Ridha Lafi, Lassad Gzara, Amor Hafiane*. Laboratory of Wastewater Treatment, CERTE, BP 273, Soliman 8020, Tunisia * Corresponding author. Tel.: +216 79 325 750; fax: +216 79 325 802. E-mail address: amor.hafiane @certe.rnrt.tn (A. Hafiane)
Abstract Despite the numerous works dealing with the application of Polyelectrolyte-enhanced ultrafiltration (PEUF) for the removal of micropollutants, its application for the treatment of dye effluent is very scarce. In the present study we investigated the recovery of methylene blue (MB), a phenothiazine cationic dye, by ultrafiltration with two anionic polyelectrolytes used as complexing agents. The ultrafiltration experiments were operated in batch mode with stirred cell equipped with 10,000 MWCO regenerated cellulose. Effects of operating conditions, e.g., transmembrane pressure, feed polyelectrolyte, feed dye solution, NaCl concentration, and pH on dye retention and permeate flux have been analyzed. High retention rate of dye in the order of 98% was obtained as a result of complexation between anionic polyelectrolyte and cationic dye. However the retention of the dye decreases as the salt concentration increases and pH decreases. Keywords: Poly (acrylic acid); Poly (ammonium acrylate); Methylene blue; Dye removal; Polyelectrolyte Enhanced-Ultrafiltration. 1. Introduction The textile industry plays an important role in the economical development of many countries in the world. However this activity generates various types of dyes which are toxic and even carcinogenic and this can be a serious hazard to aquatic living organisms [1]. This becomes important to regions where water resources might be scarce or sensitive to the maintenance of ecosystem. These colored wastes need to be treated before disposal in order to respect 1
guidelines and legislation for dye effluents [2]. Several techniques such as adsorption using activated carbons [3], coagulation-flocculation [4], biological treatment [5], chemical oxidation [6], advanced oxidation processes (AOPs) that use hydroxyl radicals[7,8] have been applied to remove dissolved dyes from wastewater. Among membrane methods, pressure driven processes OI, NF, UF are more suitable for the treatment of industrial effluent. Thus reverse osmosis (RO) [9], nanofiltration (NF) [10] have been considered for the treatment of dye waters from textile industry, but the major drawback of the two membrane processes is the flux decline in permeate flux due to concentration polarisation and fouling. Ultrafiltration operates at a lower pressure with a higher flux than RO and NF but it has a lower dye rejection [11]. The combination of ultrafiltration and complexation ability of water soluble polymer may overcome the low retention of UF membrane while keeping the same performance of flux. This method known as polyelectrolyte enhanced ultrafiltration (PEUF), was first proposed by Michaels in 1968 [12] and applied by Strathmann [13], Nguyen [14], and Rumeau [15] in the eighties to the removal of heavy metals from aqueous solution. In this process contaminant ions are first bound to water-soluble polymer to form a macromolecular complex and then retained and concentrated by ultrafiltration membranes. A permeate stream with a low concentration of the target ion is finally produced. PEUF has been applied for the remove of heavy metals [16, 17], anions [18, 19], and dissolved organic matter [20] from aqueous solutions. The majority of PEUF studies reported to date has focused mainly on demonstrating the effectiveness of the process on metal removal under various experimental conditions but its application to dye retention has been proposed only recently by Tan et al [21]. The authors demonstrated that cationic triphenylmethane-type dyes, malachite green (MG), brilliant green (BG) and new fuchsin (NF) could be removed effectively from aqueous solutions by ultrafiltration using Poly (sodium-4-styrenesulfonate) (PSS) as complexing agent. Our research group is involved in this research and thus Ouni et al. showed that retention of 99% of Crystal Violet [22] and of SafraninT [23] could be obtained using PAA and PANH4 respectively To gain insights on the applicability of PEUF for discoloration aqueous dye solutions, we continue to study other dye-polyelecytrolyte systems. In the present work we are interested in the removal methylene blue, a cationic dye belonging to the phenothiazine dyes, by ultrafiltration in the presence of two anionic polyelctrolytes, poly(acrylic acid) (PAA) and poly (ammonium acrylate) (PA-NH4). The retention rate and permeate flux were investigated as a function of some key parameters such as transmenbrane pressure, polyelectrolyte and NaCl concentrations and pH of the solution.
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2. Experimental 2.1. Chemicals Methylene blue chloride MB (MW= 319. 85 g.mol-1 , 97% purity) was purchased from Fluka. Two anionic polyelectrolytes: poly (acrylic acid) (PAA) (MW= 100.000 g.mol-1, 35wt. %) and poly (ammonium acrylate) (PANH4) (MW=30.000 g.mol-1,40wt. %) were used as complexing agents in this study. PAA was supplied by Sigma-Aldrich and PANH4 was synthesized in laboratory by radical polymerization of ammonium acrylate monomer [24]. The chemical structures of the three compounds are shown in Fig.1. Hydrochloric acid, sodium hydroxide were used to adjusted the pH value. Sodium chloride was used as salt model to simulated the salinity of dye solution. All the chemicals were of analytical grade and provided by SigmaAldrich. Distilled water was used for solution preparation. 2.2. UV–Visible analysis UV-Visible spectroscopy was used to analyze MB content in permeate solution (at Ȝmax=665 nm) and to determine the polyelectrolyte-dye stoichiometry. The UV-Visible spectra were acquired on aqueous MB dye solutions with a Perkin Elmer Lambda 25 spectrophotometer, with a matched pair of cuvets of 1 cm path length. The stoichiometry of polyelectrolyte – dye complex was determined using the ratio method as follows: increasing amounts of polyelectrolyte (0–6 ml, 1 mM) were added to a fixed volume of dye solution (2 ml, 0.1 mM), dye in different sets of experiments and the total volume was made up to 10 ml by adding distilled water. Absorbance measured at Am refers to the absorbance of the monomeric band and at AM refers to the absorbance of metachromatic band. The ratio Am /AM was plotted against the polyelectrolyte concentration /dye concentration ratio [P]/ [D].
2.3. Ultrafiltration process 2.3.1 UF membrane The UF membrane used was PLCC regenerated cellulose from Millipore with molecular weight cut-off (MWCO) 10kDa and effective filtration area of 15.54 cm2. Before use, the virgin membrane was soaked in deionised water during 24 h in order to eliminate preservative products and then membrane was compacted during 3 hours under 3 bar pressure. The value of water permeability determined by using Darcy law (J=Lp'P) was found to be 107.28 L.h-1 .m-2.
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2.3.2 Procedure Ultrafiltration experiments were performed using an Amicon stirred batch cell (model 8050) (Millipore) connected to a nitrogen-pressurized solution reservoir so the effective volume of the whole system is 1 liter. The schematic diagram of ultrafiltration set up is shown in Fig. 2. The experimental procedure was as follows. The stirred cell and reservoir of total volume of 1L were filled with the well mixed polyelectrolyte-dye solution at fixed pressure of 2 bars. During the UF runs the feed solution was kept stirred at 250 rpm and temperature was fixed at 25±1 C. The pH solution was adjusted at the desired level by the addition of hydrochloric acid or sodium hydroxide solutions. A permeate volume of 10 mL was collected and analyzed by UV-Visible spectrophotometer. The used membrane was immediately flushed with distilled water and the water flux was measured in order to assess the cleanness of the membrane. To evaluate the efficiency of ultrafiltration in removing dye, two parameters, permeate flux (Jv) and observed retention rate (R) are determined according to the equations (1) and (2). Except when we studied the effect of running time, the volume of permeate collected is less than 10% of initial volume, so the observed retention rate ( R=1-Cp/Ci) is nearly equal to real retention rate (R=1-Cp/Cr).
୴ ൌ ൌ ൬ͳ െ
ܸ ሺͳሻ ܵݐݔ ܥ ൰ ͲͲͳݔሺʹሻ ܥ
Where R is the retention rate of dye, Cp is the concentration dye in the permeate (mM), Ci is the initial concentration of the dye in the feed solution (mM), Jv is the permeate flux (L hг1 mг2), V is the volume of permeate (L), t is the time difference (h) and S is the membrane area (m2). 3. Results and discussion 3.1. dye-polyelctrolyte complex study 3.1.1 UV-Visible spectra of MB in presence of polyelectrolyte The UV-Visible spectra shows that maximum wavelength of methylene blue in aqueous solution (665 nm) shifted to 579 nm in the presence of PANH4 (Fig.3). The polyelectrolyte induced metachromasy resulting by the blue shift of the absorption maxima of the dye towards to shorter wavelengths. The appearance of blue shifted band was attributed to the formation of dye H-aggregates [25] which were induced by the complexes formed between 4
cationic dye and anionic polyelectrolyte [26]. As a consequence of the higher local concentration near the polyanion the dyes may self-aggregate by means of aromatic-aromatic interaction forming H-type aggregates at substantially lower dye. In a previous work we have shown that Ȝmax of MB shifted to 598 nm in presence of PAA as a result of the formation of MB-PAA complex [27]. 3.1.2. Determination of Stoichiometry of dye- polyelectrolyte complex The stoichiometry of the dye - polyelectrolyte complex was determined using the ratio method: a plot of A665 /A579 against the poly (ammonium acrylate) concentration /dye concentration ratio [P]/ [D] was made for MB-PANH4 systems as shown in Fig. 4. According to this figure, plots of A665 /A579 decreased with the increase of P/D. The stoichiometry of MB– PANH4 complex was found to be 1: 1, which indicates that the binding is at adjacent anionic sites. This stoichiometry indicates that every potential anionic site of the polymer was associated with a dye molecule [28]. The stoichiometry of MB–PAA complex reported in previous work is 2:1 indicating that the binding takes place on alternate anionic sites [27]. 3.1.3. Binding constant The binding constant of dye-polyelectrolyte complex can be determined using the following Rose-Drago equation [29]: ୈ ͳ ܥ ൌ ሺ͵ሻ െ ܭ ܮሺߝ െ ߝ ሻ ܮሺߝ െ ߝ ሻ
where A is the absorbance of the complex measured at metachromatic band using different set of solutions containing varying amounts of polyelectrolyte solution (CP) in a fixed dye concentration (CD), L is the optical path length of the solution, İD and İDP are the respective molar extinction of dye and dye bound to polyelectrolyte, Kc is the binding constant. The value of binding constant Kc was then obtained from the slope and intercept of the plot of CD.CP / (A-A0) against CP shown in Fig. 5. The value of the binding constant of MB-PAA complex is found to be 5331.59 dm3mol-1 [27] and it is higher compared to that of MBPANH4 complex which is 4536.83 dm3mol-1.
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3.2. Ultrafiltration study 3.2.1. Ultrafiltration of MB solutions as a function of operating time The MB retention in absence and in presence of polyelectrolytes is presented in Fig.6a for three dye concentrations (0.02, 0.1, 0.5 mM), using 0.4 mM of both polyelectrolytes and at fixed transmembrane pressure of 2 bar. We observed that the retention of MB is negligible in absence of polyelectrolytes and it is in the order of only 13%. Since the MB molecules are much smaller than the membrane pores the retention could be attributed to the adsorption of dye at the surface or in the pores of membrane. In the presence of polyelectrolyte the retention has been significantly increased to 99% in the case of PAA and to 98% in the case of PANH4. This confirms that complexes were formed due to binding of cationic MB molecules on anionic polymer through electrostatic interaction resulting in the enhancement of the ultrafiltration process. The variation of the permeate flux as a function of operation time, with and without polyelectrolyte, is shown in Fig.6b. The permeate flux observed during ultrafiltration of dye with polyelectrolyte is lower than that without polyelectrolyte. The flux decline during UF of polyelectrolyte solutions was caused by the accumulation of polymeric molecules at the membrane surface which leads to an increase of total filtration resistance against the solvent flux through the membrane. The flux in the presence of PANH4 was higher compared to that in presence of PAA. This may be related to the fact that molecular weight PANH4 (MW = 30.000 g.mol-1) is lower compared to that of PAA (MW = 100.000 g.mol-1). 3.2.2. Effect of polyelectrolyte concentration The effect of polyelectrolyte concentration on the MB retention and permeate flux was studied at fixed dye concentration of 0.1 mM and with polyelectrolyte concentration ranging from 0 to 1 mM. As shown in Fig.7a, when the polyelectrolyte concentration increases the decolourization increased abruptly and then reached a limit value of 99% in the case of PAA and 98% in the case of PANH4. The increasing of the concentration of polyelectrolyte increases the amount of complexed dye and as a consequence increases MB retention. When the equilibrium of complexation is attained the excess of polymer will have no effect on the retention efficiency. From the figure it is clear that 0.1mM of PANH4 and 0.2 mM of PAA are the beginning of the high retention rate. In the rest of study we choose 0.4 mM of polyelectrolyte as optimum concentration
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Tan et al. [21] found that that anionic polymer poly (sodium-4-styrenesulfonate) (PSS) enhanced the retention of new fushin (NF), a cationic triphenylmethane dye, from aqueous solutions. The retention rate increases from 4% to nearly 100% when the concentration of added PSS increases from 0 to quantity of 10 g L-1. The enhancement is primarily resulted from the formation of dye-polyelectrolyte complex through electrostatic attraction. Fig.7b describes the effect of polyelectrolyte concentration on the permeate flux, it is observed that the permeate flux decreases when polymer concentration increases from 0 to 1 mM and thereafter remain constant. The flux decreases from 171.06 to 126.32 L. hг1. mг2 in the case of PAA and from 171.06 to 143.61 L. hг1. mг2 in the case of PANH4. The decline of flux is ascribed to the effect of concentration polarisation at the membrane surface [30]: when the polyelectrolyte concentration increased more complexes entities were formed. This generates a deposited layer over the membrane surface and consequently increases the resistance against the solvent flux through the membrane. Contrary to retention values, observed flux values obtained in presence of PAA and PANH4 polyelectrolytes were much different due to the difference in their MW values (100.000 vs. 30.000). 3.2.3. Effect of transmenbrane pressure The effect of transmembrane pressure on the MB retention and permeate flux was studied with 'P ranging from 0.8 to 2.2 bars. The dye and polyelectrolyte concentrations were fixed at 0.1 and 0.4 mM respectively. According to the Fig. 8a, it is observed that the retention of MB dye remains independent of pressure. This observation indicates that the retention of dye by PEUF is solely favored by the complexation of dye molecules by polyelectrolyte [22]. From the Fig. 8b it is shown that the permeate flux increases with pressure, this is a typical behavior of driven pressure process. It should noted that reduction of permeate flux with respect to water flux is the result of additional resistance due to concentration polarisation on the membrane surface. This phenomenon is more significant in the presence of PAA than PANH4 As macromolecular solutions have a higher viscosity this may also contribute to the decreases of flux [31]. Above 2 bars we observe a beginning of the deviation from linearity. This is related to the appearance of the osmotic pressure [32]. 3.2.4. Effect of salt concentration The presence of various auxiliaries compounds such as salts, acids, alkalis in textile dye effluent generally affect the efficiency of treatment processes such as adsorption or biological. To study the effect of salinity on the efficiency of PEUF process, retention rate of 7
MB and permeate flux were monitored in presence of various concentrations of NaCl chosen as salt model. The concentration of NaCl was varied from 1 to 2000 mM, the concentration of dye and of polyelctyrolyte were maintained constant at 0.1 mM and 0.4 mM respectively. Fig. 9a shows that the retention of MB decreases upon increasing NaCl concentration up to 1000 mM for both polyelectrolytes. At NaCl concentration above 1000 mM, the retention of MB reaches constant values in the order of 18%. The addition of salt is likely to reduce electrostatic interaction between the dye molecule and polyelectrolyte and as a result the unbound dyes molecules pass through the Ultrafiltration membrane leading to a poor retention [33].In another way when NaCl concentration increases, the Na+ ions progressively replace the ions dye (MB+), but beyond 1000 mM of NaCl an equilibrium is reached between the two cationic species. Fig. 9b depicts the effect of salt concentration on the permeate flux. It can be seen that the permeate flux increased slightly with increased NaCl concentrations for both anionic polyelectrolytes. The increase of the flux is about 22% and 12% for PAA and PANH4 respectively. The same observation has been found by Ennigrou et al. [24] for the system PANH4-Cd in presence of NaNO3 salt and the increase of flux was related to the change in polyelectrolyte conformation as a result of neutralisation of anionic sites of polymer. 3.2.5. Effect of pH on MB removal The degree of ionization of the dye and of polyelectrolyte depend on the pH of solution. This may affect the stability of the complex formed and thus the retention rate of the dye. In this study the initial pH was varied from 2 to 12 by adding hydrochloric acid or sodium hydroxide when the concentrations of dye and polyelectrolyte were kept constant at 0.1 to 0.4 mM respectively. We observed from Fig. 10a, in the case of PAA a sharp increase of dye retention from 20 to 99% when pH increases from 2 to 4 followed by a plateau. In the case of PANH4 the retention rate of MB increases progressively when pH increases from 2 to 8 and thereafter remains constant at 96%. The same trends has been reported in the case of the retention of Safranin ST with PANH4 [23] and the retention of crystal violet with PAA [22]. The change of the retention as a function of the pH may be related to the variation of the charge of the dye and that of the polyelectrolyte. Indeed, according to the acid-base equilibrium of MB represented by: MBH2+ ! MB+ + H+ and to its low pKa (less than 1) [34], MB is essentially in the cationic form MB+. The carboxylic functional groups COOH of PAA are mainly in neutral form at low pH value (less than pKa=4.28) leading to a lower retention rate.The increase)in pH leads to an increase of deprotonated carboxylic groups 8
which favours the formation of dye-polyelectrolyte complex by electrostatic interaction between MB+ and PAA-.The same interpretation applies in the case of PANH4 which has pka value of 5.8 [35]. The variation of the retention of MB with the pH is comparable to that observed in the case of the retention of Cd using PANH4 [24]. This is due to the fact that interaction between dye or cadmium with polyelectrolyte is essentially electrostatic. The effect of pH on the flux permeate is also described. According to Fig. 10b, it is observed that the flux, in an opposite trend to the retention, decreased when pH increased from 2 to 4 in the case of PAA and from 2 to 8 in the case of PANH4.This can be attributed to the change of polyelectrolyte conformation from linear to globular as a result of neutralization of polymer charge by cationic dye. This polymer configuration can produce a fouling phenomenon by pore blocking and may explain the observed decrease in permeate flux [32, 36]. 4. Conclusions The study of removal of methylene blue from aqueous solutions by anionic polyelectrolyteenchanced Ultrafiltration has been performed using a bach ultrafiltration cell demonstrating the potentiality of this method. The PEUF experiments showed that high dye retention in the order of 98% could be obtained and was attributed to electrostatic interaction between MB and anionic polyelectrolytes. The decolourisation of MB solutions depends however on the ionic strength and the pH of the feed solution. In term of pH the PAA gives better retention than PANH4, but both polymers show a decrease of efficiency with NaCl concentration so in the future it is imperative to choose a polyelectrolyte which is less sensitive to salinity of effluent. This polyelecytrolyte should interact with dye by other forces than electrostatic. References [1]
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Figures captions Fig. 1: Molecular structure of (a) Methylene blue; (b) Poly (acrylic acid) and (c) Poly (ammonium acrylate). Fig. 2: Ultrafiltration set up: 1. filtration cell; 2. ultrafiltration membrane; 3. magnetic stirrer; 4. pressure source; 5.reservoir. Fig. 3: Absorption spectra of MB in presence of PANH4 at various P/D ratios. Fig.4: Stoichiometry of MB - PANH4 complex. Fig. 5: Plots of CD·CP /A – A0 against CP for both complexes MB-PAA and MB-PANH4. Fig.6: Variation of (a) retention rate and (b) permeate flux with time at different feed MB concentrations in the absence and in the presence of PAA and PANH4 and ǻP = 2 bar. Fig.7: Variation of (a) MB retention and (b) permeate flux as a function of feed polyelectrolyte concentration. Feed MB concentration is 0.1 mM, pH = 4.06 and 8.24 for MBPAA and MB-PANH4, respectively and ǻP = 2 bar. Fig.8: Effect of transmembrane pressure on (a) MB retention and (b) permeate flux at polyelectrolyte concentration of 0.4 mM. Feed MB concentration is 0.1 mM and pH = 4.06 and 8.24 for MB-PAA and MB-PANH4, respectively. Fig.9: Effect of NaCl concentration on (a) MB retention and (b) permeate flux. Concentrations of MB and polyelectrolytes are 0.1 mM and 0.4 mM, respectively, pH = 3.52 and 6.98 for MB-PAA and MB-PANH4, respectively and ǻP = 2 bar. Fig.10: Effect of pH on (a) MB retention and (b) permeate flux. Concentrations of MB and polyelectrolytes are 0.1 mM and 0.4 mM, respectively and ǻP = 2 bar.
13
Fig. 1
(a)
( CH2
COO-NH 4+
CH )n
(b)
(c)
14
Fig. 2
1 2
5
3
15
N2
4
Fig. 3
Absorbance (a.u.)
1 .0
P /D = 0 P /D = 0 .2 P /D = 0 .5 P /D = 0 .8 P /D = 1 P /D = 2 P /D = 3 P /D = 5 P /D = 1 0 P /D = 1 5 P /D = 2 0 P /D = 3 0
0 .8 0 .6 0 .4 0 .2 0 .0 400
500
600
700
W a v e le n g t h ( n m )
16
800
Fig. 4
5
A665/A579
4 3 2 1 0
0
1
2
3
P /D
17
4
5
Fig. 5
CPCD/A-A0 x 10-8
2 .8
M B - PAA M B - PANH4
2 .4 2 .0 1 .6 1 .2 1 .0
1 .5
2 .0
2 .5
C P x 10
-4
18
3 .0
3 .5
( m o l· L ) -1
4 .0
Fig. 6
100
R(%)
80
[M B ] [M B ] [M B ] [M B ] [M B ] [M B ] [M B ]
60
= = = = = = =
0 .0 2 m M ; p H = 4 .3 4 0 .1 m M ; p H = 4 .6 5 0 .5 m M ; p H = 4 .8 2 0 .0 2 m M + [P A A ]= 0 .4 m M ; p H = 3 .7 9 0 .1 m M + [P A A ]= 0 .4 m M ; p H = 4 .0 6 0 .5 m M + [P A A ]= 0 .4 m M ; p H = 4 .3 8 0 .0 2 m M + [P A N H 4 ]= 0 .4 m M ; p H = 7 .9 2
[M B ] = 0 .1 m M + [P A N H 4 ]= 0 .4 m M ; p H = 8 .2 4
40
[M B ] = 0 .5 m M + [P A N H 4 ]= 0 .4 m M ; p H = 8 .5 7
20 0 0
25
50
75
100
T im e (m in )
Fig.6a
-1 -2 J (L. h .m ) v
200 160 120 [M [M [M [M [M [M [M
80 40
B] B] B] B] B] B] B]
= = = = = = =
0 .0 2 m M ; p H = 4 .3 4 0 .1 m M ; p H = 4 .6 5 0 .5 m M ; p H = 4 .8 2 0 .0 2 m M + [P A A ]= 0 .4 m M ; p H = 3 .7 9 0 .1 m M + [P A A ]= 0 .4 m M ; p H = 4 .0 6 0 .5 m M + [P A A ]= 0 .4 m M ; p H = 4 .3 8 0 .0 2 m M + [P A N H 4]= 0 .4 m M ; p H = 7 .9 2
[M B ] = 0 .1 m M + [P A N H 4]= 0 .4 m M ; p H = 8 .2 4 [M B ] = 0 .5 m M + [P A N H 4]= 0 .4 m M ; p H = 8 .5 7
0
0
20
40
60
T im e (m in )
Fig. 6b
19
80
100
Fig. 7
100
R (P A A ) R (P A N H 4)
R(%)
80 60 40 20 0
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
P o ly e le c tr o ly te c o n c e n tr a tio n (m M )
Fig. 7a
180
J(P A A ) J(P A N H 4 )
-1 -2 J (L. h .m ) v
160 140 120 100 80
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
P o ly e le c tr o ly te c o n c e n tr a tio n (m M )
Fig. 7b
20
Fig. 8
100
R (P A A ) R (P A N H 4 )
R(%)
80 60 40 20 0
0 .8
1 .2
1 .6
2 .0
2 .4
' P (b a r )
Fig. 8a
-1 -2 J (L. h .m ) v
250 200
J ( W a te r ) J(P A A ) J(P A N H 4)
150 100 50 0 0 .0
0 .5
1 .0
1 .5
' P (b a r)
Fig. 8b
21
2 .0
2 .5
Fig. 9
R (P A A ) R (P A N H 4)
100
R(%)
80 60 40 20 0
0
500
1000
1500
2000
N a C l c o n c e n tr a tio n (m M )
Fig.9a
180
-1 -2 J (L. h .m ) v
160
J (P A A ) J (P A N H 4 )
140 120 100 80
0
500
1000
1500
N a C l c o n c e n tr a tio n (m M ) Fig. 9b
22
2000
Fig. 10
100
R(%)
80
R (P A A ) R (P A N H 4 )
60 40 20 0
2
4
6
8
10
12
14
pH
Fig. 10a
J(P A A ) J(P A N H 4 )
-1 -2 J (L. h .m ) v
160 140 120 100 80 60
2
4
6
8
pH
Fig.10b
23
10
12
14
Research Highlights -Removal of MB was performed using polyelectrolyte enhanced ultrafiltration. - Effect of anionic polyelectrolyte concentration on R% and J was evaluated. - The decolourisation of MB depends of the salt concentration and pH.
24
S1383-5866(14)00386-4 http://dx.doi.org/10.1016/j.seppur.2014.06.038 SEPPUR 11838
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
20 December 2013 21 June 2014 26 June 2014
Please cite this article as: A.B. Fradj, S.B. Hamouda, H. Ouni, R. Lafi, L. Gzara, A. Hafiane, Removal of methylene blue from aqueous solutions by poly (acrylic acid) and poly (ammonium acrylate) assisted ultrafiltration, Separation and Purification Technology (2014), doi: http://dx.doi.org/10.1016/j.seppur.2014.06.038
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Removal of methylene blue from aqueous solutions by poly (acrylic acid) and poly (ammonium acrylate) assisted ultrafiltration
Anouar Ben Fradj, Sofiane Ben Hamouda, Hedia Ouni, Ridha Lafi, Lassad Gzara, Amor Hafiane*. Laboratory of Wastewater Treatment, CERTE, BP 273, Soliman 8020, Tunisia * Corresponding author. Tel.: +216 79 325 750; fax: +216 79 325 802. E-mail address: amor.hafiane @certe.rnrt.tn (A. Hafiane)
Abstract Despite the numerous works dealing with the application of Polyelectrolyte-enhanced ultrafiltration (PEUF) for the removal of micropollutants, its application for the treatment of dye effluent is very scarce. In the present study we investigated the recovery of methylene blue (MB), a phenothiazine cationic dye, by ultrafiltration with two anionic polyelectrolytes used as complexing agents. The ultrafiltration experiments were operated in batch mode with stirred cell equipped with 10,000 MWCO regenerated cellulose. Effects of operating conditions, e.g., transmembrane pressure, feed polyelectrolyte, feed dye solution, NaCl concentration, and pH on dye retention and permeate flux have been analyzed. High retention rate of dye in the order of 98% was obtained as a result of complexation between anionic polyelectrolyte and cationic dye. However the retention of the dye decreases as the salt concentration increases and pH decreases. Keywords: Poly (acrylic acid); Poly (ammonium acrylate); Methylene blue; Dye removal; Polyelectrolyte Enhanced-Ultrafiltration. 1. Introduction The textile industry plays an important role in the economical development of many countries in the world. However this activity generates various types of dyes which are toxic and even carcinogenic and this can be a serious hazard to aquatic living organisms [1]. This becomes important to regions where water resources might be scarce or sensitive to the maintenance of ecosystem. These colored wastes need to be treated before disposal in order to respect 1
guidelines and legislation for dye effluents [2]. Several techniques such as adsorption using activated carbons [3], coagulation-flocculation [4], biological treatment [5], chemical oxidation [6], advanced oxidation processes (AOPs) that use hydroxyl radicals[7,8] have been applied to remove dissolved dyes from wastewater. Among membrane methods, pressure driven processes OI, NF, UF are more suitable for the treatment of industrial effluent. Thus reverse osmosis (RO) [9], nanofiltration (NF) [10] have been considered for the treatment of dye waters from textile industry, but the major drawback of the two membrane processes is the flux decline in permeate flux due to concentration polarisation and fouling. Ultrafiltration operates at a lower pressure with a higher flux than RO and NF but it has a lower dye rejection [11]. The combination of ultrafiltration and complexation ability of water soluble polymer may overcome the low retention of UF membrane while keeping the same performance of flux. This method known as polyelectrolyte enhanced ultrafiltration (PEUF), was first proposed by Michaels in 1968 [12] and applied by Strathmann [13], Nguyen [14], and Rumeau [15] in the eighties to the removal of heavy metals from aqueous solution. In this process contaminant ions are first bound to water-soluble polymer to form a macromolecular complex and then retained and concentrated by ultrafiltration membranes. A permeate stream with a low concentration of the target ion is finally produced. PEUF has been applied for the remove of heavy metals [16, 17], anions [18, 19], and dissolved organic matter [20] from aqueous solutions. The majority of PEUF studies reported to date has focused mainly on demonstrating the effectiveness of the process on metal removal under various experimental conditions but its application to dye retention has been proposed only recently by Tan et al [21]. The authors demonstrated that cationic triphenylmethane-type dyes, malachite green (MG), brilliant green (BG) and new fuchsin (NF) could be removed effectively from aqueous solutions by ultrafiltration using Poly (sodium-4-styrenesulfonate) (PSS) as complexing agent. Our research group is involved in this research and thus Ouni et al. showed that retention of 99% of Crystal Violet [22] and of SafraninT [23] could be obtained using PAA and PANH4 respectively To gain insights on the applicability of PEUF for discoloration aqueous dye solutions, we continue to study other dye-polyelecytrolyte systems. In the present work we are interested in the removal methylene blue, a cationic dye belonging to the phenothiazine dyes, by ultrafiltration in the presence of two anionic polyelctrolytes, poly(acrylic acid) (PAA) and poly (ammonium acrylate) (PA-NH4). The retention rate and permeate flux were investigated as a function of some key parameters such as transmenbrane pressure, polyelectrolyte and NaCl concentrations and pH of the solution.
2
2. Experimental 2.1. Chemicals Methylene blue chloride MB (MW= 319. 85 g.mol-1 , 97% purity) was purchased from Fluka. Two anionic polyelectrolytes: poly (acrylic acid) (PAA) (MW= 100.000 g.mol-1, 35wt. %) and poly (ammonium acrylate) (PANH4) (MW=30.000 g.mol-1,40wt. %) were used as complexing agents in this study. PAA was supplied by Sigma-Aldrich and PANH4 was synthesized in laboratory by radical polymerization of ammonium acrylate monomer [24]. The chemical structures of the three compounds are shown in Fig.1. Hydrochloric acid, sodium hydroxide were used to adjusted the pH value. Sodium chloride was used as salt model to simulated the salinity of dye solution. All the chemicals were of analytical grade and provided by SigmaAldrich. Distilled water was used for solution preparation. 2.2. UV–Visible analysis UV-Visible spectroscopy was used to analyze MB content in permeate solution (at Ȝmax=665 nm) and to determine the polyelectrolyte-dye stoichiometry. The UV-Visible spectra were acquired on aqueous MB dye solutions with a Perkin Elmer Lambda 25 spectrophotometer, with a matched pair of cuvets of 1 cm path length. The stoichiometry of polyelectrolyte – dye complex was determined using the ratio method as follows: increasing amounts of polyelectrolyte (0–6 ml, 1 mM) were added to a fixed volume of dye solution (2 ml, 0.1 mM), dye in different sets of experiments and the total volume was made up to 10 ml by adding distilled water. Absorbance measured at Am refers to the absorbance of the monomeric band and at AM refers to the absorbance of metachromatic band. The ratio Am /AM was plotted against the polyelectrolyte concentration /dye concentration ratio [P]/ [D].
2.3. Ultrafiltration process 2.3.1 UF membrane The UF membrane used was PLCC regenerated cellulose from Millipore with molecular weight cut-off (MWCO) 10kDa and effective filtration area of 15.54 cm2. Before use, the virgin membrane was soaked in deionised water during 24 h in order to eliminate preservative products and then membrane was compacted during 3 hours under 3 bar pressure. The value of water permeability determined by using Darcy law (J=Lp'P) was found to be 107.28 L.h-1 .m-2.
3
2.3.2 Procedure Ultrafiltration experiments were performed using an Amicon stirred batch cell (model 8050) (Millipore) connected to a nitrogen-pressurized solution reservoir so the effective volume of the whole system is 1 liter. The schematic diagram of ultrafiltration set up is shown in Fig. 2. The experimental procedure was as follows. The stirred cell and reservoir of total volume of 1L were filled with the well mixed polyelectrolyte-dye solution at fixed pressure of 2 bars. During the UF runs the feed solution was kept stirred at 250 rpm and temperature was fixed at 25±1 C. The pH solution was adjusted at the desired level by the addition of hydrochloric acid or sodium hydroxide solutions. A permeate volume of 10 mL was collected and analyzed by UV-Visible spectrophotometer. The used membrane was immediately flushed with distilled water and the water flux was measured in order to assess the cleanness of the membrane. To evaluate the efficiency of ultrafiltration in removing dye, two parameters, permeate flux (Jv) and observed retention rate (R) are determined according to the equations (1) and (2). Except when we studied the effect of running time, the volume of permeate collected is less than 10% of initial volume, so the observed retention rate ( R=1-Cp/Ci) is nearly equal to real retention rate (R=1-Cp/Cr).
୴ ൌ ൌ ൬ͳ െ
ܸ ሺͳሻ ܵݐݔ ܥ ൰ ͲͲͳݔሺʹሻ ܥ
Where R is the retention rate of dye, Cp is the concentration dye in the permeate (mM), Ci is the initial concentration of the dye in the feed solution (mM), Jv is the permeate flux (L hг1 mг2), V is the volume of permeate (L), t is the time difference (h) and S is the membrane area (m2). 3. Results and discussion 3.1. dye-polyelctrolyte complex study 3.1.1 UV-Visible spectra of MB in presence of polyelectrolyte The UV-Visible spectra shows that maximum wavelength of methylene blue in aqueous solution (665 nm) shifted to 579 nm in the presence of PANH4 (Fig.3). The polyelectrolyte induced metachromasy resulting by the blue shift of the absorption maxima of the dye towards to shorter wavelengths. The appearance of blue shifted band was attributed to the formation of dye H-aggregates [25] which were induced by the complexes formed between 4
cationic dye and anionic polyelectrolyte [26]. As a consequence of the higher local concentration near the polyanion the dyes may self-aggregate by means of aromatic-aromatic interaction forming H-type aggregates at substantially lower dye. In a previous work we have shown that Ȝmax of MB shifted to 598 nm in presence of PAA as a result of the formation of MB-PAA complex [27]. 3.1.2. Determination of Stoichiometry of dye- polyelectrolyte complex The stoichiometry of the dye - polyelectrolyte complex was determined using the ratio method: a plot of A665 /A579 against the poly (ammonium acrylate) concentration /dye concentration ratio [P]/ [D] was made for MB-PANH4 systems as shown in Fig. 4. According to this figure, plots of A665 /A579 decreased with the increase of P/D. The stoichiometry of MB– PANH4 complex was found to be 1: 1, which indicates that the binding is at adjacent anionic sites. This stoichiometry indicates that every potential anionic site of the polymer was associated with a dye molecule [28]. The stoichiometry of MB–PAA complex reported in previous work is 2:1 indicating that the binding takes place on alternate anionic sites [27]. 3.1.3. Binding constant The binding constant of dye-polyelectrolyte complex can be determined using the following Rose-Drago equation [29]: ୈ ͳ ܥ ൌ ሺ͵ሻ െ ܭ ܮሺߝ െ ߝ ሻ ܮሺߝ െ ߝ ሻ
where A is the absorbance of the complex measured at metachromatic band using different set of solutions containing varying amounts of polyelectrolyte solution (CP) in a fixed dye concentration (CD), L is the optical path length of the solution, İD and İDP are the respective molar extinction of dye and dye bound to polyelectrolyte, Kc is the binding constant. The value of binding constant Kc was then obtained from the slope and intercept of the plot of CD.CP / (A-A0) against CP shown in Fig. 5. The value of the binding constant of MB-PAA complex is found to be 5331.59 dm3mol-1 [27] and it is higher compared to that of MBPANH4 complex which is 4536.83 dm3mol-1.
5
3.2. Ultrafiltration study 3.2.1. Ultrafiltration of MB solutions as a function of operating time The MB retention in absence and in presence of polyelectrolytes is presented in Fig.6a for three dye concentrations (0.02, 0.1, 0.5 mM), using 0.4 mM of both polyelectrolytes and at fixed transmembrane pressure of 2 bar. We observed that the retention of MB is negligible in absence of polyelectrolytes and it is in the order of only 13%. Since the MB molecules are much smaller than the membrane pores the retention could be attributed to the adsorption of dye at the surface or in the pores of membrane. In the presence of polyelectrolyte the retention has been significantly increased to 99% in the case of PAA and to 98% in the case of PANH4. This confirms that complexes were formed due to binding of cationic MB molecules on anionic polymer through electrostatic interaction resulting in the enhancement of the ultrafiltration process. The variation of the permeate flux as a function of operation time, with and without polyelectrolyte, is shown in Fig.6b. The permeate flux observed during ultrafiltration of dye with polyelectrolyte is lower than that without polyelectrolyte. The flux decline during UF of polyelectrolyte solutions was caused by the accumulation of polymeric molecules at the membrane surface which leads to an increase of total filtration resistance against the solvent flux through the membrane. The flux in the presence of PANH4 was higher compared to that in presence of PAA. This may be related to the fact that molecular weight PANH4 (MW = 30.000 g.mol-1) is lower compared to that of PAA (MW = 100.000 g.mol-1). 3.2.2. Effect of polyelectrolyte concentration The effect of polyelectrolyte concentration on the MB retention and permeate flux was studied at fixed dye concentration of 0.1 mM and with polyelectrolyte concentration ranging from 0 to 1 mM. As shown in Fig.7a, when the polyelectrolyte concentration increases the decolourization increased abruptly and then reached a limit value of 99% in the case of PAA and 98% in the case of PANH4. The increasing of the concentration of polyelectrolyte increases the amount of complexed dye and as a consequence increases MB retention. When the equilibrium of complexation is attained the excess of polymer will have no effect on the retention efficiency. From the figure it is clear that 0.1mM of PANH4 and 0.2 mM of PAA are the beginning of the high retention rate. In the rest of study we choose 0.4 mM of polyelectrolyte as optimum concentration
6
Tan et al. [21] found that that anionic polymer poly (sodium-4-styrenesulfonate) (PSS) enhanced the retention of new fushin (NF), a cationic triphenylmethane dye, from aqueous solutions. The retention rate increases from 4% to nearly 100% when the concentration of added PSS increases from 0 to quantity of 10 g L-1. The enhancement is primarily resulted from the formation of dye-polyelectrolyte complex through electrostatic attraction. Fig.7b describes the effect of polyelectrolyte concentration on the permeate flux, it is observed that the permeate flux decreases when polymer concentration increases from 0 to 1 mM and thereafter remain constant. The flux decreases from 171.06 to 126.32 L. hг1. mг2 in the case of PAA and from 171.06 to 143.61 L. hг1. mг2 in the case of PANH4. The decline of flux is ascribed to the effect of concentration polarisation at the membrane surface [30]: when the polyelectrolyte concentration increased more complexes entities were formed. This generates a deposited layer over the membrane surface and consequently increases the resistance against the solvent flux through the membrane. Contrary to retention values, observed flux values obtained in presence of PAA and PANH4 polyelectrolytes were much different due to the difference in their MW values (100.000 vs. 30.000). 3.2.3. Effect of transmenbrane pressure The effect of transmembrane pressure on the MB retention and permeate flux was studied with 'P ranging from 0.8 to 2.2 bars. The dye and polyelectrolyte concentrations were fixed at 0.1 and 0.4 mM respectively. According to the Fig. 8a, it is observed that the retention of MB dye remains independent of pressure. This observation indicates that the retention of dye by PEUF is solely favored by the complexation of dye molecules by polyelectrolyte [22]. From the Fig. 8b it is shown that the permeate flux increases with pressure, this is a typical behavior of driven pressure process. It should noted that reduction of permeate flux with respect to water flux is the result of additional resistance due to concentration polarisation on the membrane surface. This phenomenon is more significant in the presence of PAA than PANH4 As macromolecular solutions have a higher viscosity this may also contribute to the decreases of flux [31]. Above 2 bars we observe a beginning of the deviation from linearity. This is related to the appearance of the osmotic pressure [32]. 3.2.4. Effect of salt concentration The presence of various auxiliaries compounds such as salts, acids, alkalis in textile dye effluent generally affect the efficiency of treatment processes such as adsorption or biological. To study the effect of salinity on the efficiency of PEUF process, retention rate of 7
MB and permeate flux were monitored in presence of various concentrations of NaCl chosen as salt model. The concentration of NaCl was varied from 1 to 2000 mM, the concentration of dye and of polyelctyrolyte were maintained constant at 0.1 mM and 0.4 mM respectively. Fig. 9a shows that the retention of MB decreases upon increasing NaCl concentration up to 1000 mM for both polyelectrolytes. At NaCl concentration above 1000 mM, the retention of MB reaches constant values in the order of 18%. The addition of salt is likely to reduce electrostatic interaction between the dye molecule and polyelectrolyte and as a result the unbound dyes molecules pass through the Ultrafiltration membrane leading to a poor retention [33].In another way when NaCl concentration increases, the Na+ ions progressively replace the ions dye (MB+), but beyond 1000 mM of NaCl an equilibrium is reached between the two cationic species. Fig. 9b depicts the effect of salt concentration on the permeate flux. It can be seen that the permeate flux increased slightly with increased NaCl concentrations for both anionic polyelectrolytes. The increase of the flux is about 22% and 12% for PAA and PANH4 respectively. The same observation has been found by Ennigrou et al. [24] for the system PANH4-Cd in presence of NaNO3 salt and the increase of flux was related to the change in polyelectrolyte conformation as a result of neutralisation of anionic sites of polymer. 3.2.5. Effect of pH on MB removal The degree of ionization of the dye and of polyelectrolyte depend on the pH of solution. This may affect the stability of the complex formed and thus the retention rate of the dye. In this study the initial pH was varied from 2 to 12 by adding hydrochloric acid or sodium hydroxide when the concentrations of dye and polyelectrolyte were kept constant at 0.1 to 0.4 mM respectively. We observed from Fig. 10a, in the case of PAA a sharp increase of dye retention from 20 to 99% when pH increases from 2 to 4 followed by a plateau. In the case of PANH4 the retention rate of MB increases progressively when pH increases from 2 to 8 and thereafter remains constant at 96%. The same trends has been reported in the case of the retention of Safranin ST with PANH4 [23] and the retention of crystal violet with PAA [22]. The change of the retention as a function of the pH may be related to the variation of the charge of the dye and that of the polyelectrolyte. Indeed, according to the acid-base equilibrium of MB represented by: MBH2+ ! MB+ + H+ and to its low pKa (less than 1) [34], MB is essentially in the cationic form MB+. The carboxylic functional groups COOH of PAA are mainly in neutral form at low pH value (less than pKa=4.28) leading to a lower retention rate.The increase)in pH leads to an increase of deprotonated carboxylic groups 8
which favours the formation of dye-polyelectrolyte complex by electrostatic interaction between MB+ and PAA-.The same interpretation applies in the case of PANH4 which has pka value of 5.8 [35]. The variation of the retention of MB with the pH is comparable to that observed in the case of the retention of Cd using PANH4 [24]. This is due to the fact that interaction between dye or cadmium with polyelectrolyte is essentially electrostatic. The effect of pH on the flux permeate is also described. According to Fig. 10b, it is observed that the flux, in an opposite trend to the retention, decreased when pH increased from 2 to 4 in the case of PAA and from 2 to 8 in the case of PANH4.This can be attributed to the change of polyelectrolyte conformation from linear to globular as a result of neutralization of polymer charge by cationic dye. This polymer configuration can produce a fouling phenomenon by pore blocking and may explain the observed decrease in permeate flux [32, 36]. 4. Conclusions The study of removal of methylene blue from aqueous solutions by anionic polyelectrolyteenchanced Ultrafiltration has been performed using a bach ultrafiltration cell demonstrating the potentiality of this method. The PEUF experiments showed that high dye retention in the order of 98% could be obtained and was attributed to electrostatic interaction between MB and anionic polyelectrolytes. The decolourisation of MB solutions depends however on the ionic strength and the pH of the feed solution. In term of pH the PAA gives better retention than PANH4, but both polymers show a decrease of efficiency with NaCl concentration so in the future it is imperative to choose a polyelectrolyte which is less sensitive to salinity of effluent. This polyelecytrolyte should interact with dye by other forces than electrostatic. References [1]
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Figures captions Fig. 1: Molecular structure of (a) Methylene blue; (b) Poly (acrylic acid) and (c) Poly (ammonium acrylate). Fig. 2: Ultrafiltration set up: 1. filtration cell; 2. ultrafiltration membrane; 3. magnetic stirrer; 4. pressure source; 5.reservoir. Fig. 3: Absorption spectra of MB in presence of PANH4 at various P/D ratios. Fig.4: Stoichiometry of MB - PANH4 complex. Fig. 5: Plots of CD·CP /A – A0 against CP for both complexes MB-PAA and MB-PANH4. Fig.6: Variation of (a) retention rate and (b) permeate flux with time at different feed MB concentrations in the absence and in the presence of PAA and PANH4 and ǻP = 2 bar. Fig.7: Variation of (a) MB retention and (b) permeate flux as a function of feed polyelectrolyte concentration. Feed MB concentration is 0.1 mM, pH = 4.06 and 8.24 for MBPAA and MB-PANH4, respectively and ǻP = 2 bar. Fig.8: Effect of transmembrane pressure on (a) MB retention and (b) permeate flux at polyelectrolyte concentration of 0.4 mM. Feed MB concentration is 0.1 mM and pH = 4.06 and 8.24 for MB-PAA and MB-PANH4, respectively. Fig.9: Effect of NaCl concentration on (a) MB retention and (b) permeate flux. Concentrations of MB and polyelectrolytes are 0.1 mM and 0.4 mM, respectively, pH = 3.52 and 6.98 for MB-PAA and MB-PANH4, respectively and ǻP = 2 bar. Fig.10: Effect of pH on (a) MB retention and (b) permeate flux. Concentrations of MB and polyelectrolytes are 0.1 mM and 0.4 mM, respectively and ǻP = 2 bar.
13
Fig. 1
(a)
( CH2
COO-NH 4+
CH )n
(b)
(c)
14
Fig. 2
1 2
5
3
15
N2
4
Fig. 3
Absorbance (a.u.)
1 .0
P /D = 0 P /D = 0 .2 P /D = 0 .5 P /D = 0 .8 P /D = 1 P /D = 2 P /D = 3 P /D = 5 P /D = 1 0 P /D = 1 5 P /D = 2 0 P /D = 3 0
0 .8 0 .6 0 .4 0 .2 0 .0 400
500
600
700
W a v e le n g t h ( n m )
16
800
Fig. 4
5
A665/A579
4 3 2 1 0
0
1
2
3
P /D
17
4
5
Fig. 5
CPCD/A-A0 x 10-8
2 .8
M B - PAA M B - PANH4
2 .4 2 .0 1 .6 1 .2 1 .0
1 .5
2 .0
2 .5
C P x 10
-4
18
3 .0
3 .5
( m o l· L ) -1
4 .0
Fig. 6
100
R(%)
80
[M B ] [M B ] [M B ] [M B ] [M B ] [M B ] [M B ]
60
= = = = = = =
0 .0 2 m M ; p H = 4 .3 4 0 .1 m M ; p H = 4 .6 5 0 .5 m M ; p H = 4 .8 2 0 .0 2 m M + [P A A ]= 0 .4 m M ; p H = 3 .7 9 0 .1 m M + [P A A ]= 0 .4 m M ; p H = 4 .0 6 0 .5 m M + [P A A ]= 0 .4 m M ; p H = 4 .3 8 0 .0 2 m M + [P A N H 4 ]= 0 .4 m M ; p H = 7 .9 2
[M B ] = 0 .1 m M + [P A N H 4 ]= 0 .4 m M ; p H = 8 .2 4
40
[M B ] = 0 .5 m M + [P A N H 4 ]= 0 .4 m M ; p H = 8 .5 7
20 0 0
25
50
75
100
T im e (m in )
Fig.6a
-1 -2 J (L. h .m ) v
200 160 120 [M [M [M [M [M [M [M
80 40
B] B] B] B] B] B] B]
= = = = = = =
0 .0 2 m M ; p H = 4 .3 4 0 .1 m M ; p H = 4 .6 5 0 .5 m M ; p H = 4 .8 2 0 .0 2 m M + [P A A ]= 0 .4 m M ; p H = 3 .7 9 0 .1 m M + [P A A ]= 0 .4 m M ; p H = 4 .0 6 0 .5 m M + [P A A ]= 0 .4 m M ; p H = 4 .3 8 0 .0 2 m M + [P A N H 4]= 0 .4 m M ; p H = 7 .9 2
[M B ] = 0 .1 m M + [P A N H 4]= 0 .4 m M ; p H = 8 .2 4 [M B ] = 0 .5 m M + [P A N H 4]= 0 .4 m M ; p H = 8 .5 7
0
0
20
40
60
T im e (m in )
Fig. 6b
19
80
100
Fig. 7
100
R (P A A ) R (P A N H 4)
R(%)
80 60 40 20 0
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
P o ly e le c tr o ly te c o n c e n tr a tio n (m M )
Fig. 7a
180
J(P A A ) J(P A N H 4 )
-1 -2 J (L. h .m ) v
160 140 120 100 80
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0
P o ly e le c tr o ly te c o n c e n tr a tio n (m M )
Fig. 7b
20
Fig. 8
100
R (P A A ) R (P A N H 4 )
R(%)
80 60 40 20 0
0 .8
1 .2
1 .6
2 .0
2 .4
' P (b a r )
Fig. 8a
-1 -2 J (L. h .m ) v
250 200
J ( W a te r ) J(P A A ) J(P A N H 4)
150 100 50 0 0 .0
0 .5
1 .0
1 .5
' P (b a r)
Fig. 8b
21
2 .0
2 .5
Fig. 9
R (P A A ) R (P A N H 4)
100
R(%)
80 60 40 20 0
0
500
1000
1500
2000
N a C l c o n c e n tr a tio n (m M )
Fig.9a
180
-1 -2 J (L. h .m ) v
160
J (P A A ) J (P A N H 4 )
140 120 100 80
0
500
1000
1500
N a C l c o n c e n tr a tio n (m M ) Fig. 9b
22
2000
Fig. 10
100
R(%)
80
R (P A A ) R (P A N H 4 )
60 40 20 0
2
4
6
8
10
12
14
pH
Fig. 10a
J(P A A ) J(P A N H 4 )
-1 -2 J (L. h .m ) v
160 140 120 100 80 60
2
4
6
8
pH
Fig.10b
23
10
12
14
Research Highlights -Removal of MB was performed using polyelectrolyte enhanced ultrafiltration. - Effect of anionic polyelectrolyte concentration on R% and J was evaluated. - The decolourisation of MB depends of the salt concentration and pH.
24