Separation Science and Technology Volume 48, Issue 4, 2013

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1 Separation Science and Technology Volume 48, Issue 4, 2013 Effect of Hydrodynamic Operations, Salinity, and Heavy Metals on HA Removal by Microfiltration Ceramic Tubular Membrane DOI: / M. W. Hakami a, C. Tizaoui a, V. Kochkodan a & N. Hilal ab* pages Publishing models and article dates explained Received: 21 Oct 2011 Accepted: 6 Jul 2012 Accepted author version posted online: 25 Sep 2012 Published online: 01 Feb 2013 Article Views: 20 1

2 Effect of hydrodynamic operations, salinity, and heavy metals on HA removal by microfiltration ceramic tubular membrane M.W. Hakami 1, C. Tizaoui 1, V. Kochkodan 1, N. Hilal 1,2 1 The Centre for Water Advanced Technologies and Environmental Research (CWATER), College of Engineering, Swansea University, Swansea SA2 8PP, UK 2 Masdar Institute of Science and Technology, Abu Dhabi, UAE Abstract The removal of humic acids (HA) using ceramic tubular microfiltration membrane operated under various conditions including trans-membrane pressures, cross flow velocities, humic acids concentrations in the presence of different heavy metals and high NaCl content ( mg/l). It was found that HA retention increases sharply in the presence of heavy metals ions and at high salinity levels, while trans-membrane pressure has a little effect on HA retention. It was also shown that the effect of solution environmental on HA retention should reflect alterations in solute charge, and in an extent of aggregation HA macromolecules. The fouling by HA was found to be a critical factor in microfiltration with ceramic membrane. Fouling was more severe at high concentrations of NaCl and heavy metals in the feed due to the tighter packing of the HA aggregates in the fouling layer formed on the membrane surface. These results provide important insights into ceramic membrane fouling with HA at high salinity conditions relevant to treatment of brackish and seawater. Keywords: microfiltration; ceramic membranes; humic acids; fouling, salinity Introduction Over the last two decades, the water and wastewater industry has faced many challenges including energy price volatility, climate change regulation, asset capital costs and strategic resource considerations [1]. Efficient and economic methods of treatment are currently sought by water and wastewater industry. Microfiltration has been widely applied in drinking water treatment for the removal of particles, turbidity, and microorganisms from surface water and groundwater as an alternative to conventional water treatment processes such as coagulation, sedimentation and sand filtration. Microfiltration could provide a number of advantages including superior water quality, easier control of operation, lower maintenance, and reduced sludge production [2]. The particular interest is in microfiltration 2

3 removal of suspended and colloidal particles to meet the more strict obligations of the surface water treatment rule and disinfectants/disinfection by-products regulations [3]. Another application of microfiltration is pre-treatment brackish or seawater prior to reverse osmosis or nanofiltration to remove particulates which may cause severe fouling in downstream processes [4]. Nevertheless, one of the main factors limiting the use of microfiltration for water treatment is membrane fouling, the irreversible loss of system productivity over time. Naturally occurring organic matter (NOM) which is a ubiquitous constituent in natural waters has been identified as a dominant foulant in membrane treatment both surface and ground water [5]. Accumulation of NOM on the membrane surface causes flux decline that leads to a sharp drop of membrane productivity and to increase the cost of water treatment [6,7]. A main fraction of NOM presented in surface waters composes of humic substances (humic and fulvic acids), which comprise over 50% of the dissolved organic carbon, and are responsible for the colour of natural water [8]. It was indicated that different mechanisms may cause membrane fouling with humic substances such as adsorption, pore blocking and cake deposition on the membrane surface [7]. Usually humic acids (HA) have a greater effect on membrane performance (irreversible fouling) than fulvic acid (FA) [9]. The possible reason for this is that HA macromolecules are more hydrophobic with higher molecular weight and therefore are more prone to fouling of the membrane surface. HA posses both aromatic and aliphatic components and contain three main functional groups: carboxylic acids (COOH), phenolic alcohols (OH), and methoxy carbonyls (C=O) [10]. Schafer et al. observed that HA contributed in 78% of the flux decline compared to 15% for FA [11]. Yuan and Zydney [12] showed that deposition of HA aggregates on the membrane surface was mainly responsible for the fouling of 0.16 µm polyethersulphone and 0.22 µm polyvinilidene fluoride microfiltration membranes. Previous studies showed that both solution environment and operating parameters such as trans-membrane pressure (TMP) and cross-flow velocity (CFV) have considerable effect of membrane fouling [7,13]. For instance, it was found that membrane fouling with HA increased with increasing of ionic strength, decreasing ph of solution and with addition of Ca +2 ions due to aggregation of HA macromolecules [14]. The ionic strength of the feed solution may affect HA fouling because of reduction of electrostatic repulsion between the negatively charged HA macromolecules and the negatively charged polymeric membrane [12]. On the other hand the hydrodynamics of crossflow membrane filtration, particularly 3

4 CFV, was observed to be capable of reducing membrane fouling at high CFV values due to dragging of transported solute off the membrane surface [7]. However, it should be noted that a majority of investigations on HA fouling during microfiltration were performed with polymeric membranes [5-7,11-14]. Furthermore, concentration of added electrolyte (typically NaCl) while studying an effect of ionic strength on membrane fouling did not exceed 100 ml/l [2,12]. On the other hand experimental studies on HA fouling of ceramic microfiltration membranes are rather limited [15,16]. In particular Nystrom et al. [15] showed a rapid decline in flux during HA filtration through 1.9 mm pore diameter ceramic membranes made of aluminium and silica oxides: the flux for a 10 mg/l HA solution decreased by 50% after only 5 minutes of filtration at 2 bar, while the flux for a 100 mg/l HA solution decreased by more than 90% within 5 minutes. A sharp flux decline was attributed to electrostatic interactions between the negatively charged HA and the positively charged inorganic membrane, resulting in blockage of the membrane pores. To the best of the authors knowledge, detailed analysis of different operation conditions on ceramic membrane fouling with HA have not been performed. The objective of this study is to investigate the effect of solution environmental on HA removal during microfiltration through 0.5 µm ceramic membrane under a wide range of operating parameters such as TMP, CFV, various content of HA in the presence of heavy metals and NaCl concentrations of mg/l. The investigation of membrane fouling at high salinity conditions may be of special interest when microfiltration is used as a pre-treatment stage to nanofiltration or reverse osmosis desalination of brackish or seawaters. these conditions. Materials and Method Experimental Apparatus A bench scale membrane rig was developed to carry out the microfiltration experiments (Figure 1). The filtration rig is composed of a stainless steel jacketed feed/ recirculation tank with volume of 500 ml, a positive displacement gear pump (SS316/PEEK model), a rotameter, valves and a tubular membrane housing that hosts the single layer tubular membrane. The tangential flow rate through the membrane was provided by the pump for the filtration of HA solution. The volumetric feed flowrate through the module is controlled by adjusting the speed setting on the pump (variable speed controller) and adjusting the regulation valve. The flowrate for filtration experiments were in the range of L/min at pressures up to 2.0 bars. The overall membrane filtration area is 4

5 6.28 cm m A constant room temperature (22 ± 2 C) was used in all the experiments. The amount of permeate collected as function of time was measured by a digital balance (XB 3200C, Precisa) interfaced to a PC through a user-friendly software (Education Program, Version 3.02, Percisa). Materials Tubular ceramic membranes made of alumina (70%), zirconia (25%) and yttria (5%) from Sterilox Technologies International Ltd were used in this study. A nominal pore size of the membrane according to manufactures is 0.5µm. HA used in this study were purchased from Aldrich Chemicals, UK. Although Aldrich s HA are not well reprecent for aqueous systems, we decided to examine the retention and fouling behaviour of these compounds becouse of their great content of high molecular weight components [17] and also taking into account a relatively large average pore size of 0.5 µm of used ceramic membranes. NaCl was purchased from Fisher Scientific- UK with purity higher than 99.5%. The heavy metals salts used were copper (II) nitrate >97.0% purity, cadmium nitrate >99.0% purity, iron (III) nitrate 97% purity, nickel (II) nitrate 98% purity and zinc nitrate >98.0% purity. All these reagents were obtained from Sigma-Aldrich, UK g of Cu(NO 3 ) 2, g of Zn(NO 3 ) 2, g of Cd(NO 3 ) 2, g of Ni(NO 3 ) 2, g of Pb(NO 3 ) 2, and Fe(NO 3 ) 3 were dissolve in 200 ml of deionized water to make a stock solution of 1g/L total metals concentration. The heavy metals used in the study are the main species of many technological streams and waster waters in industry. The heavy metals stock solution was used within a week of preparation. A basic solution of ph>9 was needed for the preparation of 1g/L stock HA solution mg/l HA solutions were prepared from the stock solution by dilution with deionized water and were used within a week of preparation. HA solutions of various salinity and heavy metals content were obtained by addition of appropriate amounts of solid NaCl or the stock solution of heavy metals. The ph of solutions was adjusted to 7 by 0.1M NaOH or HNO 3 immediately before the experiments. ph values were measured with Jenway 3540 ph meter. Feed solutions were stirred at 400 rpm for 1 hour using a magnetic stirrer before filtration experiments. The membrane flux (J) was calculated by measuring the time needed to collect 400 ml of permeate using the following equation: 5

6 J V At where J represents flux (m 3 /m 2 s), V is volume of permeate (m 3 ), A is the effective membrane area (m 2 ) and t is the time taken to collect the permeate (sec). The concentration of HA in probes was analyzed using a UV-spectrophotometer (UVmini-1240, Shimadzo) at a wavelength of 254 nm. NaCl or heavy metals have no effect on evaluation of HA concentration. HA retention was measured using the equation [18]; R C % (1 C p b ) *100 where R is retention, C p and C b are permeate and bulk concentrations (mg/l), respectively. All filtration experiments were provided in triplicate. After a filtration test, the ceramic membrane was cleaned by soaking; first in citric acid (2%) for a minimum of 2 hours and then in sodium hypochlorite (3000 ppm) for a minimum of 2 hours. Afterwards, the membrane was rinsed with MilliQ water and stored in MilliQ water until the next experiment. Before starting a new test the ceramic membrane was characterised with MilliQ water at TMP of 1 bar to verify flux. A new measurement with the membrane was only started if the flux had not changed. All glassware used was soaked in 2M NaOH or in citric acid (2%) for 24 h and then rinsed with water to remove any organic contamination or heavy metals, respectively. Results and discussion Effect of trans-membrane pressure (TMP) The effect of trans-membrane pressure (TMP) on rejection and permeate flux during microfiltration of HA solutions of various concentration was studied. As seen in Figure 3 the TMP practically has no effect on the HA rejection, except for HA concentration of 40 mg/l at TMP value of 1.5 bar when a slightly higher retention was found. Figure 4 shows that a sharp flux decline was observed during initial period of filtration (first sec) with a 6

7 shallow flux decrease during next sec of filtration until the quasi-steady flux values were reached (an insert to Figure 4). The flux decline during microfiltration may be explained by penetration and adsorption of HA macromolecules into porous structure of the ceramic membrane, with following formation of chain-like adsorbed bridges from HA macromolecules into the pores or even deposition of a cake layer from HA aggregates on the membrane surface, that may reduce pore size or plug the pores. The possibility of realization such scenarios was previously shown elsewhere [2,7,12]. These processes most likely accelerate at high HA concentrations and operating pressures; for example increase the HA retention at high HA concentration of 40 mg/l at TMP value of 1.5 bars (Figure 3). Nevertheless, as shown in Figure 4 the quasi-steady flux increases with operating pressure and it means that the flux gain due to applying of higher operating pressure overcomes the flux drop caused by pore plugging/blockade with adsorbed and deposited HA macromolecules. According to obtained data the highest quasi-steady flux was obtained at TMP of 2 bar. Effect of Cross Flow Velocity This section shows the effect of CFV on HA rejection, permeate flux and fouling. As seen in Figure 5 at CFV value of 9.55 m/s the membrane retection of HA is practically the same (about 20%) for HA concentrations of 10 and 20 mg/l. However, the retention increased to 37 and 68% when HA feed concentration raised to 30 and 40 mg/l, respectively. These findings may be explained by larger pore blocking with HA macromolecules or even cake layer formation from HA aggregates on the membrane surface with increasing of HA concentration in the feed. The fouled membrane had a definite brown colour caused by the presence of a HA deposit on the membrane surface. The physical cleaning of membrane by wiping with paper towels removed to a great extent the brown deposit and restored the water flux of the membrane to nearly 65% of its initial (clean) value. This increase in flux indicated that the membrane fouling occurred both on the membrane surface and throughout its porous structure. When CFV increased to 14.3 m/s at feed HA concentrations of 30 and 40 mg/l HA retention values were lowered to about 30% comparing with those at CFV value of 9.6 m/s. Such retention decline is rather unexpected especially taking into account decrease in the fluxes with increase of CFV values (Figure 6) and the reason for this should be investigated. At high CFV value of 19.1 m/s HA retention increased for all used concentrations of HA comparing with the retention at CFV value of 14.3 m/s. These findings may be explained by 7

8 the reduction of concentration polarisation near the membrane surface with increasing CFV leading to higher values of HA retention. As was shown [7], an increase in the turbulence flow facilitates causing physical scouring effect at the membrane surface through forcing the back-transport of solute away from the membrane surface into the bulk solution. On the other hand, as seen in Figure 6 the permeate flux decreases with increasing CFV. The insert upper right box shows the initial flux values were 4.1, 3.9 and 3.5 m 3 /m 2 s, while the quasi-steady flux values (the lower right box) were 0.30, 0.25 and 0.19 m 3 /m 2 s for CFV values of 9.6, 14.3 and 19.1 m/l, respectively. The flux decline with an increase of CFV value was most likely due to more essential pore plugging with smaller HA aggregates which have been generated at higher cross-flow velocity due to aggregates classification. It was shown previously that increasing CFV with increment pump speed generates finer colloidal particles which can form a denser cake layer on the membrane surface [19]. Effect of Humic Acid Concentration The effect of HA concentrations on the rejection and permeate fluxes are shown in Figures 7 and 8. As seen in Figure 7 the retention decrease when feed HA concentration increases. This finding may be explained by the increase of concentration polarization at the membrane surface due to accumulation HA species (both macromolecules and aggregates) that reduce HA retention. For example, at TMP of 1.0 bar HA retention decreased from 40.9 to 31.7 and then to 25.8% when HA concentration increased from 10 to 20 and 30 mg/l, respectively. For TMP of 1.5 bars, the retentions were 37.5, 33.8, 30.0 and 28.6% for feed HA concentrations of 10, 20, 30, and 40 mg/l, respectively, while for TMP value of 2.0 bar the retentions were 38.1, 38.0, 30.5 and 31.4% for HA content of 10, 20, 30, and 40 mg/l. An increase of HA retention at TMP of 2.0 bar compared with retention at TMP of 1.5 bar could be due to the formation of a cake layer from HA aggregates on the membrane surface. As seen in Figure 8 permeate fluxes declined more rapidly within the first 50 sec of filtration that could be explained by pore plugging with HA aggregates and the fluxes also decreased slightly with an increase of HA content in the feed: the quasi-steady fluxes were 0.21, 0.18, 0.16 and 0.13 m 3 /m 2 s for HA concentration of 10, 20, 30, and 40 mg/l, respectively. These results agree with those reported previously [11, 12] and may be explained by an increase of a rate of pore blocking and formation of cake layer from HA aggregates on the membrane surface with an increase of HA content in the feed. 8

9 Salinity Effect A range of salinity of m/l used in this study corresponds to typical salt content for natural brackish water and seawater. Figure 9 shows that HA retentions increased when NaCl concentration in the feed solution raised from to and then to mg/l. For example, for HA concentration of 10 mg/l the solute retentions were 24.8, 58.5, and 65.2% for NaCl concentrations of 10000, 25000, and mg/l, respectively. These findings may be explained as follows: The acidic functional group (primary carboxylic groups) gives HA macromolecules a net negative charge at neutral ph causing both intra- and intermolecular electrostatic repulsion. The magnitude of the repulsion depends on ionic strength of the solution (salinity) which determines the extent of electrolyte shielding. This would accelerate in the presence of high salt concentration aggregation of HA due to the reduction in the intermolecular electrostatic repulsion and the increase of hydrophobisity of the humic species [20]. The HA aggregates deposit on the membrane surface by the convective flow. The increase in HA retention at high ionic strength is likely due to formation of more tightly packed, less permeable HA deposits which is caused by the increased electrostatic schielding between the HA aggregates at high salt concentrations. As seen in Figure 10, a very large flux decline was observed during HA microfiltration and the flux decline increase with an increase of feed salinity. For example fluxes of 6.1 x 10-4, 4.4 x 10-4, and 3.9 x 10-4 m 3 /m 2 s were found for NaCl concentrations of , and mg/l, respectively. It may be assumed that several different mechanisms affect membrane fouling during HA microfiltration at these conditions. An initial sharp drop of water flux may be caused by deposition of HA aggregates on the membrane surface. Additionally the flux decline with an increase of feed NaCl concentration may also be due to enhancing of HA adsorption on the membrane surface as a result of reduction in the electrostatic repulsion between the negatively charged HA and negatively charged ceramic membrane. As was shown previously alumina based ceramic membranes have negative zeta potential at ph=7 [21]. As seen in an insert to Figure 10, the quasi-steady fluxes at filtration time of 400 sec also depends on feed salinity: the values of 1.27 x 10-4, 1.05 x 10-4, and 3.62 x 10-4 m 3 /m 2 s were found for NaCl concentrations of , and mg/l, respectively. The decrease in quasi-steady flux values with salinity may be explained by an increase in the thickness of HA layer deposited on the membrane surface due to reduction in electrostatic 9

10 reduction between HA macromolecules in the feed and those already deposited on the membrane. Effect of Heavy Metals Figures 11 and 12 show an effect of the addition of heavy metals on retention and flux decline during HA microfiltration. As seen in Figure 11, HA retention increased with a raise of heavy metals content in the feed. For example, the retentions at HA concentration of 10 mg/l were 24.8, 50.5, and 88.2% for heavy metals concentrations of 0; 5; and 10 mg/l, while for the same heavy metals contents at HA concentration of 40 mg/l HA retentions were 20.6, 25.4, and 55.1% respectively. An increase of HA retention with an increase of metal ions concentration may be explained by facilitating of HA aggregation in the presence of polyvalent metal ions due to the diminution in the intermolecular electrostatic repulsion and an increase of hydrophobisity of the humic species. This assumption agrees with previously reported studies which showed that addition of metals cations accelerate the HA aggregation and coagulation by reducing electrostating repulsion and enhancing the strength of hydrophobic interactions between the negatively charged HA macromolecules [22-24]. Figure 12 shows that a sharp flux decline was observed during microfiltration likely because of deposition of HA aggregates on the membrane surface. It should be noted that the permeate flux increased with increasing the concentration of heavy metals in the feed. This finding may be explained by the increase of the size of HA aggregates, which are created in the solution. Obviously, at high heavy metal content, the large HA aggregates are formed and as a result a more open and less dense cake layer from HA aggregates deposited on the membrane surface. Conclusions The effect of solution environmental on HA removal during microfiltration through 0.5 µm ceramic membrane under a wide range of operating parameters such as TMP, CFV, various content of HA in the presence of heavy metals and NaCl concentrations of mg/l was investigated in this study. It was shown that TMP has no effect on the HA retention, while an increase in HA retention and a sharp flux decline were observed with increasing HA content in the feed solution due to pore blocking with HA macromolecules or even cake layer formation from HA aggregates on the membrane surface. It was found that an increase in CFV values results in higher HA retentions due to reduction of concentration polarisation near the membrane surface. It was also noted that the effect of solution environmental on HA retention should reflect alterations in solute charge and in an extent of 10

11 aggregation HA macromolecules. Severe fouling of ceramic membranes was found in the presence of heavy metals and at high NaCl content due to acceleration of HA aggregation and their deposition on the membrane surface. The obtained results on HA removal by microfiltration ceramic membrane at highly salinity conditions may be of special interest for application of microfiltration as a pre-treatment stage to nanofiltration or reverse osmosis desalination of brackish or seawaters. References 1. Palmer, S.J. (2010) Future challenges to asset investment in the UK water industry: the wastewater asset investment risk mitigation offered by minimising principal operating cost risks. Water and Climate Change, 01(1): p Yuan, W. and A.L. Zydney (1999) Humic acid fouling during microfiltration. Journal of Membrane Science, 157(1): p EPA. Water: Microbial & Disinfection Byproducts Rules 2006 Last updated on Monday, April 19, 2010; Available from: 4. Vial, D. and G. Doussau (2003)The use of microfiltration membranes for seawater pretreatment prior to reverse osmosis membranes. Desalination, 153 (1 3): p Kaiya, Y.; et al. (1996) Study on fouling materials in the membrane treatment process for potable water. Desalination, 106(1-3): p Yuan, W. and A.L. Zydney (1999) Effects of solution environment on humic acid fouling during microfiltration. Desalination, 122(1): p Zularisam, A.W.; A.F. Ismail; and R. Salim (2006) Behaviours of natural organic matter in membrane filtration for surface water treatment -- a review. Desalination, 194(1-3): p Hedges, J.I. (1986) Organic Geochemistry of Natural Waters : E. M. Thurman. Martinus Nijhoff/Dr. W. Junk Publishers, 1985, 497 p., $ Geochimica et Cosmochimica Acta, 50(9): p Aoustin, E.; et al. (2001) Ultrafiltration of natural organic matter. Separation and Purification Technology, 22-23: p Stevenson, F.J. (1994) Humus chemistry: genesis, composition, reactions, WILEY: New Yourk. p Schäfer, A.I.; et al. (2000) Microfiltration of colloids and natural organic matter. Journal of Membrane Science, 171(2): p

12 12. Yuan, W. and A.L. Zydney (1999) Effects of solution environment on humic acid fouling during microfiltration. Desalination, 122(1): p Hilal, N.; et al. (2005) Methods Employed for Control of Fouling in MF and UF Membranes: A Comprehensive Review. Separation Science and Technology, 40(10): p Jones, K.L. and C.R. O'Melia (2000) Protein and humic acid adsorption onto hydrophilic membrane surfaces: effects of ph and ionic strength. Journal of Membrane Science, 165(1): p Nyström, M.; Ruohomäki, K.; and Kaipia L. (1996) Humic acid as a fouling agent in filtration. Desalination, 106(1-3): p Hofs, B.; Ogier, J.; Vries, D.; Beerendonk, E. F.; Cornelissen E. R. (2011) Comparison of ceramic and polymeric membrane permeability and fouling using surface water. Separation and Purification Technology 79: p Chin, Y.-P.;Aiken, G.; and O'Loughlin, E. (1994) Molecular Weight, Polydispersity, and Spectroscopic Properties of Aquatic Humic Substances. Environmental Science & Technology, 28(11): p Pradanos, P.; Arribas, J.I.; and Hernandez, A. (1995) Mass transfer coefficient and retention of PEGs in low pressure cross-flow ultrafiltration through asymmetric membranes. Membrane Science, 99: p Thomas, H.; Judd, S.; Murrer, J. (2000) Fouling characteristics of membrane filtration in membrane bioreactors. Membr. Technol., 122: p Wershaw, R.L; Thorn, K.A.; Pinckney, D.J.; MacCarthy, P.; Rice, J.A.; Hemong, H.F. Application of a membrane model to the secondary structure of humic materials in peat, in: C.H. Fuchsman (Ed.), Peat and Water, Elsevier, New York, 1986, p Zhaoa, Y.; Xing, W.; Xub, N.; Wong, F.-S. (2005) Effects of inorganic electrolytes on zeta potentials of ceramic microfiltration membranes Separation and Purification Technology 42: p Manahan, S.E. Interactions of hazardous-waste chemicals with humic substances, in: I.H. Suffet, P. MacCarthy (Eds.) Aquatic Humic Substances: Influence on Fate and Treatment of Pollutants, ACS, Washington, DC, 1989, p Engerbretson, R.R.; Wandruszka, R.V. (1998) Kinetic aspects of cation-enhanced aggregation in aqueous humic acids, Environ. Sci. Technol 32: P Hilal, N.; et al. (2008) Effects of heavy metals and polyelectrolytes in humic substance coagulation under saline conditions. Desalination, 220(1-3): p

13 List of Figures Figure 1 shows a sketch diagram of experimental assembly Figure 2. Influence of TMP on HA rejection at feed flow rate of 1.0 L/min at various HA concentrations. Figure 3. TMP effect on flux at FR 1.5 L /min and 10 mg/l HA. The inserted graph shows the flux values at filtration time 270 sec for the three different TMP values. Figure 4. An effect of CFV on HA retention at TMP of 1.5 bars Figure 5. CFV effect on flux at P 1.5 bars and 10 mg/l HA. The inserted graphs show the initial flux and the quasi-state flux values at filtration time 210 sec for the three different CFV values. Figure 6. An effect of concentration on HA retention at FR 1.5 L/min Figure 7. Effect of HA concentration on flux at FR 1.5 L/ min and P 1.5 bars. The inserted graph shows the flux values at filtration time 260 sec for various HA concentration values. Figure 8. Effect of salinity on HA retention at FR 1.5 L/min and P 1.5 bars Figure 9. Effect of salinity on flux at HA concentration of 10 mg/l, flow rate of 1.5 L/min, and TMP of 1.5 bars. The inserted graphs show the initial flux values and the quasi state flux values at filtration time 400 sec for various HA concentrations. Figure 10. Effect of heavy metals on HA retention during filtration of HA solutions in the presence of of mg/l NaCl, at flow rate of 1.5 L/min, and TMP of 1.5 bars. Figure 11. Effect of heavy metals on flux at HA concentration of 10 mg/l, NaCl of mg/l, flow rate of 1.5 L/min, and TMP of 1.5 bars. Inserted figures show the initial and quasi-state fluxes. 13

14 B A P L C K D E F J M Time wieght G On/Off gm H I Q W R T Y U I O P [ S D F G H J K L Z X C V B N M,. Figure 1 shows a sketch diagram of experimental assembly (A) The tubular membrane module with membrane fitted inside. (B) A hose to recover permeate. (C) Pressure control valve. (D) Recycle line. (E) Jacketed process vessel (F) Pressure and safety valve (G) Digital balance. (H) Drain valve (I) Re-circulation pump (J) Flow control valve (K) Flowmeter (L) Pressure gauge (M) Personal computer 14

15 80 10 mg/l HA 20 mg/l HA 30 mg/l HA 40 mg/l HA % R obs TMP [bar] Figure 2. Influence of TMP on HA rejection at feed flow rate of 1.0 L/min at various HA concentrations. 15

16 J [m 3 / m 2.s] J [m 3 / m 2.s] 1.2 P = 1.0 bar P = 1.5 bar P = 2.0 bar Time [s] P = 1.0 bar P = 1.5 bar P = 2.0 bar Time [s] Figure 3. TMP effect on flux at FR 1.5 L /min and 10 mg/l HA. The inserted graph shows the flux values at filtration time 270 sec for the three different TMP values. 16

17 % Robs mg/l HA 20 mg/l HA 30 mg/l HA 40 mg/l HA Crossflow Velocity [m/s] Figure 4. An effect of CFV on HA retention at TMP of 1.5 bars 17

18 J [m 3 / m 2.s] J [m 3 / m 2.s] J [m 3 / m 2.s] 0.45 CFV 9.55 m/s CFV m/s CFV m/s Time [s] Initial Flux Time [s] Times[s] Figure 5. CFV effect on flux at P 1.5 bars and 10 mg/l HA. The inserted graphs show the initial flux and the quasi-state flux values at filtration time 210 sec for the three different CFV values. 18

19 45 P =1.0 bar P =1.5 bar P = 2.0 bars % R obs HA Conc. [mg/l] Figure 6. An effect of concentration on HA retention at FR 1.5 L/min 19

20 J [m 3 / m 2.s] J [m 3 / m 2.s] 1 HA 10 mg/l HA 20 mg/l HA 30 mg/l HA 40 mg/l Time [s] Time [sec] Figure 7. Effect of HA concentration on flux at FR 1.5 L/ min and P 1.5 bars. The inserted graph shows the flux values at filtration time 260 sec for various HA concentration values. 20

21 70 NaCl mg/l NaCl mg/l NaCl mg/l %R obs HA Conc. [mg/l] Figure 8. Effect of salinity on HA retention at FR 1.5 L/min and P 1.5 bars 21

22 J x 10-4 [m 3 /m 2.s] J x 10-4 [m 3 /m 2.s] J x 10-4 [m 3 /m 2.s] 8 7 Initial Flux 1.5 Quasi State Time [s] Time [s] Time [s] NaCl mg/l NaCl mg/l NaCl mg/l Figure 9. Effect of salinity on flux at HA concentration of 10 mg/l, flow rate of 1.5 L/min, and TMP of 1.5 bars. The inserted graphs show the initial flux values and the quasi state flux values at filtration time 400 sec for various HA concentrations. 22

23 Figure 10. Effect of heavy metals on HA retention during filtration of HA solutions in the presence of of mg/l NaCl, at flow rate of 1.5 L/min, and TMP of 1.5 bars. 23

24 J x 10-5 [m 3 /m 2.s] J x 10-5 [m 3 /m 2.s] J x 10-5 [m 3 /m 2.s] Quasi-state flux Initial Flux Time [s] Time [s] Time [s] 0 mg/l H. Metals 5 mg/l H. Metals 10 mg/l H. Metals Figure 11. Effect of heavy metals on flux at HA concentration of 10 mg/l, NaCl of mg/l, flow rate of 1.5 L/min, and TMP of 1.5 bars. Inserted figures show the initial and quasi-state fluxes. 24