Preparation and Application of Chitosan - Polyethersulfone Composite Ultrafiltration Membrane for Humic Acid Removal

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1 Preparation and Application of Chitosan - Polyethersulfone Composite Ultrafiltration Membrane for Humic Acid Removal Yong Sun 1, Tianshi Wang 1, Jiasen Wang 1, Huiling Yang 1, Fuqiao Guo 1, Xinyu Wang 1, Shihao Sheng 1, Tianqi Wang 1, Li Dai 1, Yingjie Li 1 1 College of Aerospace and Civil Engineering, Harbin Engineering University, Harbin, Heilongjiang, 151, PR China ( sunyong@hrbeu.edu.cn; wangjiasen@hrbeu.edu.cn) Abstract To remove excessive humic acid from water, this paper designed a polyethersulfone ultrafiltration membrane by phase inversion. Surface modification was used to modify obtained membrane and a new type of chitosan - polyethersulfone membrane was made. This type of membrane has higher mechanical strength and hydrophilicity. Result of SEM and FTIR proved the modification of membrane was successful. Humic acid containing synthesis surface water was processed and the removal rate of composite membrane (PESCHIUF-4) was up to 97.9%. AFM analysis proved chitosan - polyethersulfone composite ultrafiltration membrane has a good antifouling property. Keywords Humic acid; Chitosan; Surface modification method; Polyethersulfone ultrafiltration membrane; Membrane fouling 1.INTRODUCE Humic acid (HA) is a main composition of humus, which is normally 1 mg/l in raw water as 5-9 % of total organic matter[1]. The excess of HA may alter water color to dark, affect the coagulation and removal efficiency of heavy metals and hinder the photodegradation of toxins algal[2, 3]. It has been proved to be the main contributor of disinfection by-product precursors like trihalomethane. Therefore, the removal of HA is very important for slight polluted water treatment[4]. Ultrafiltration membrane made from polyethersulfone (PES) is widely used in the removal of humic acid, due to their excellent chemical resistance, thermal stability and mechanical properties[5-7]. However, this low hydrophilic material combining with hydrophobic nature such as humus may cause severe fouling[5, 8]. Membrane surface modification with additive is a common technology to enhance its hydrophilicity and fouling resistance property[8-11]. Chitosan as a biopolymer extracted from the shells of shellfish attracted increasing attention because it s a hydrophilic, non-toxic, biodegradable and biocompatible material and, moreover, it exhibits antimicrobial activity[8, 12-14]. Chitosan was widely used as membrane raw material as well as additive in the field of membrane preparation for water treatment. Some researchers have studied the modification of ultrafiltration membranes with chitosan solution in order to obtain hydrophilic membranes with antifouling property. The hydrophilicity and the antifouling property of modified membranes increased with the increase of chitosan concentration[8, 13, 15]. In this work, a PES membrane was made and modified with chitosan in order to obtain a composite membrane. The effects of the additive on strength, hydrophilicity and the incorporation of additive in membrane were investigated. Its humic acid filtration performance and antifouling property was also reported. 2.MATERIAL AND METHODS 2.1 The ultrafiltration reactor A cup type ultrafilter made of organic glass with an effective volume of 3 ml (Fig. 1), a diameter of 8 mm and an effective filter area of 36.3 cm 2 was used. The filtration pressure was supplied by a nitrogen bottle, the maximum operation pressure was.25 MPa. The flux of membrane was calculated by the quality of the filtrated water obtained by on-line monitoring electronic balance.

2 1. Nitrogen gas cylinder 2. Pressure gage 3. Reducing valve 4. UF cell 5. Magnetic rotor 6. Seal rubber ring 7. Ultrafiltration membrane 8. Magnetic stirring apparatus 9. Beaker 1. Electronic balance 11. Computer Fig. 1. Schematic picture of experimental set-up. The influent water used in this study contained 1 mg/l HA, and turbidity was NTU (configured by the kaolin). The ph adjustment was conducted by NaHCO 3 and CaCl The preparation of polyethersulfone ultrafiltration membrane. In this study, raw polyethersulfone ultrafiltration membrane was prepared by phase inversion[3]. As shown in Fig. 2, we dissolved dry polyethersulfone (PES) and polyvinylpyrrolidone (PVP) in dimethyl acetamide (DMAC), accelerated by heating and vibrating. When liquid was homogeneously transparent, it was air dried in 7 for 24 hours. After standing and deaeration, the liquid was coated by a glass rod on a clean glass plate. Then the membrane was bathed by 2% dimethyl acetamide (DMAC) solution to coagulation and soaked in water for 24 hours to stabilize. Fig. 2. Schematic picture of the preparation of PES membrane[3]. 2.3 Preparation of chitosan composite ultrafiltration membrane The coating solution added into ultrafilter was made from chitosan dissolved in 2% acetic acid solution. After 3s-filtration with operating property of 2 kpa and 6 RPM, the membrane was plated. Then it was air dried in 6 for 15 min to solidify and made chitosan evenly covering on membrane surface. Under same pressure and RPM with modification, we used cured membrane to filter sodium hydroxide (4%, mass fraction) ethanol solution (5%, volume fraction) for 3 min, then we remove the instrument and wash the membrane with ethanol (5%, volume fraction) for 2 min and wash it with tap water for 12 h. After washing, we use isophthaloyl chloride to crosslink chitosan with the surface of membrane to extend the life span of the surface chitosan layer. Composite membrane was sealed in a formaldehyde solution (5%, volume fraction). Composite ultrafiltration membranes whose mass fraction of coating solution was,.1%,.2%,.3%,.4% and.5% respectively was labeled with PESCHIUF- (no chitosan), PESCHIUF-1 (.1% chitosan), PESCHIUF-2 (.2% chitosan), PESCHIUF-3 (.3% chitosan), PESCHIUF-4 (.4% chitosan) and PESCHIUF -5 (.5% chitosan). 2.4 Operating parameter calculation 1. The flux of membrane was calculated by the quality of the filtrated water obtained by on-line monitoring of electronic balance, according to Eq. (1)

3 V J At (1) Where J is membrane flux (Lm -2 h -1 ), V is volume of effluent (L), A is effective filtration area (m 2 ) and t is operating time (h). 2. Transmembrane pressure (TMP) is the operation pressure of system, the reading of piezometer. 3. The reject rate was normalized according to Eq. (2) Cp R (1 ) 1% Co (2) Where R is reject rate (%), and C p and C are the concentrations of effluent and influent. The concerned membrane characterizations consists of scanning electron microscope (SEM,Quanta2), fourier transform infrared spectroscopy (FTIR, Perkin Elmer) and atomic force microscopy (AFM-Veeco Di BioScope). 3 The performance of the membrane 3.1 The mechanical property of the membrane Tensile strength and elongation of composite membrane were determined by 3365 electronic pulling machine (2~25, 2 mm/min stretching rate). The mechanical performance of composite membrane is shown in Fig. 3. Along with the increase of the content of chitosan, tensile strength and tensile rupture elongation of composite membrane increased. The tensile strength of membrane PESCHIUF-4 increased by 51.5% than membrane PESCHIUF-, and the tensile fracture elongation of membrane PESCHIUF-4 is 1.21 times of membrane PESCHIUF-. Chitosan has high mechanical strength and good toughness. After the modification, a viscosity chitosan membrane surface layer formed and the mechanical strenghth of membrane enhanced. Tensile strength(n) Tensile strength Tensile elongation Tensile elongation(%) The concentration of coating solution(%) Fig. 3. Mechanical properties of composite membrane affected by chitosan content. 3.2 The measurement of the contact angle of the membrane A contact angle instrument (JYC-4) was used for measuring the contact angle between membrane and pure water. The contact angle of composite membranes is shown in Fig. 4. Contact angel( ) Chitosan concentration of coating solution(%) Fig. 4. Contact angle of composite membrane affected by chitosan content. With the increase of chitosan in composite membrane, the contact angle decreased. The addition of chitosan could improve the hydrophilicity of polyethersulfone membrane. Polar groups -NH 2 and OH,

belong to hydrophilic cationic polymer, are contained in the chain of chitosan. So thin chitosan layer formed on membrane surface can greatly enhance its hydrophilic and antifouling property.

5%, chitosan solution was saturated and wouldn t enhance its hydrophilicity anymore. 3.

2 MPa for 3 min[16, 17]. Then measured the pure water flux in 2 ~ 25 and under the operation pressure of.15 ~.3 MPa.

Fig. 5 shows that with the increase of operating pressure, the pure water flux of membrane increased. With the increase of the chitosan content in membrane, the pure water flux increased constantly.

4 belong to hydrophilic cationic polymer, are contained in the chain of chitosan. So thin chitosan layer formed on membrane surface can greatly enhance its hydrophilic and antifouling property. But when the concentration of chitosan in coating solution increased from.4% to.5%, the contact angle changed very little. We hold the oppinion that when the concentration of chitosan was above.5%, chitosan solution was saturated and wouldn t enhance its hydrophilicity anymore Flux of pure water In order to exclude the effect on membrane flux made by deformation, and to ensure the stability of test data, we pressed chitosan sulfone composite membrane under.2 MPa for 3 min[16, 17]. Then measured the pure water flux in 2 ~ 25 and under the operation pressure of.15 ~.3 MPa. Flux(L/m 2 h) PESCHIUF- PESCHIUF-1 PESCHIUF-2 PESCHIUF-3 PESCHIUF-4 PESCHIUF Operation pressure(mpa) Fig. 5. The membrane water flux affected by the operating pressure. Fig. 5 shows that with the increase of operating pressure, the pure water flux of membrane increased. With the increase of the chitosan content in membrane, the pure water flux increased constantly. Under the same operation properties, the flux of the membrane whose chitosan concentration of coating solution is.4% is maximum. When the chitosan content reached.5%, the membrane flux no longer increased and began to decay. Consistent with the results of contact angle measurement, the pure water flux test reveals that a moderate addition of chitosan could enhance the hydrophilicity of polyether sulfone ultrafiltration membrane. But when the concentration of the chitosan is too high, reunions may occur because of the saturation of chitosan. Reunions may accumulate on the surface of composite membrane, and caused the blockage of membrane hole and the decrease of flux. The mechanical property and hydrophilicity of membrane PESCHIUF-4 whose chitosan mass fraction in coating solution is.4% was optimal, so we further compared the properties of membrane PESCHIUF- (no chitosan) and membrane PESCHIUF-4 to measure the efficiency of modification. 3.4 Analysis of SEM As shown in Fig. 6, both structures of membrane PESCHIUF-4 and membrane PESCHIUF- have support layers similar to needle-like shape, indicating that the addition of chitosan didn t change the internal structure of membrane. And membrane hole of membrane PESCHIUF-4 is more smooth than membrane PESCHIUF-. It reveals membrane hole walls were filled by chitosan in membrane PESCHIUF-4. (1)PESCHIUF-4 (2)PESCHIUF- (1)PESCHIUF-4 (2)PESCHIUF- Fig. 6. SEM of membrane section (1kx). Fig. 7. SEM of membrane surface (1kx).

5 According to Fig. 7, holes are evenly distributed on the surface of two membranes, but holes on the surface of membrane PESCHIUF-4 are smaller. And the surface of membrane PESCHIUF-4 is more smooth. 3.5 Analysis of FT-IR The presence of chitosan in composite membrane is verified by FTIR analysis. The IR spectra of raw PES membrane, chitosan, membrane PESCHIUF-4 and membrane PESCHIUF- in range from 8 cm -1 to 4 cm -1 is shown in Fig. 8. PESCHIUF-4 Transmittance(%) PESCHIUF- PES CHITOSAN Wave number(cm -1 ) Fig. 8. IR spectra of CHITOSAN PES membrane membrane PESCHIUF- membrane PESCHIUF-4. There are amino and acetylamino groups on the chain of chitosan, so chitosan had the properties of both primary and secondary amide. In the spectra of chitosan, the peak related to primary amide can be observed at cm -1 (C=O stretching). The peak related to secondary amide can be observed at cm -1 (C-N stretching) and cm -1 (-NH 3 symmetrical bending )[18]. Comparing the IR spectra of PES membrane and membrane PESCHIUF- which was washed by acetic and sodium but not coated by chitosan, in the region 3 36 cm 1 there is a broad band related to O-H and N-H stretching, which was much less intense for membrane PESCHIUF-, probably due to the reaction of amine groups after the washing of acetic acid and sodium hydroxide solution. In spectrum of membrane PESCHIUF-4, it was observed a broadening of the band at cm 1, which is due to the overlap of the O-H stretching band present in chitosan spectrum. The broadening of the peak at cm -1 in PESCHIUF-4 spectrum was due to the overlap of the peak at 17 cm -1 in PESCHIUF- spectrum with the one at cm -1 in chitosan spectrum. Infrared spectrum and SEM analyses reveal that after series of treatment, the chitosan thin layer was successfully compounded on PES membrane. 4. Antifouling property of composite membrane to humic acid 4.1 The effect on the removal of humic acid We used humic acid containing synthetic surface water to test the antifouling property and the removal efficiency of membrane PESCHIUF- and membrane PESCHIUF-4. The experiment was under operation pressure of.1 MPa, temperature of 2 ~ 25 and operation time of 6 min. Humic acid concentration(mg/l) PESCHIUF- PESCHIUF Operation time(min) Removal rate of humic acid(1%) Fig. 9. The removal of humic acid of composite membrane. Fig. 1. The removal of tubidity of composite membrane. According to Fig. 9 and Fig. 1, membrane PESCHIUF-4 has higher reject rate of humic acid and

6 tubidity than membrane PESCHIUF-. The modification of chitosan enhanced the reject rate of humic acid and tubidity. The removal rate of humic acid at first stage of operation is unstable and is far lower than the one at stable stage. The main reason is that during start-up, membrane was uncontaminated, and membrane surface and membrane holes remained smooth, contaminants in medium size could easily went through membrane hole. As the process continues, some of the solute would stagnate on membrane surface and form a high concentration zone. When the concentration polarization reached a certain level, an covering layer would form. The covering layer could prevent particles from seeping into the pores. Membrane flux would decrease, but the removal rate would further enhanced. With the further aggravation of concentration polarization, the surface of the membrane would form a gel layer. The Removal rate reached an optimal state, but the formation of gel layer would increase the resistance of filtration and decrease the penetration rate. 4.2 Analysis of antifouling property of composite membrane Clearly shown in Fig. 11 and Fig. 12, the thickness of pollutants depositing on contaminated membrane PESCHIUF-4 is thinner than the one on membrane PESCHIUF-. The surface groove of contaminated membrane PESCHIUF- is more obvious and the surface of the contaminated membrane PESCHIUF-4 is not much fluctuation. Fig. 11 Atomic force microscopy of contaminated membrane PESCHIUF-. Fig. 12. Atomic force microscopy of contaminated membrane PESCHIUF-4. Depth curve of contaminated membrane PESCHIUF-4 was mainly distributed in 2nm ~ 3nm, and the curve of contaminated membrane PESCHIUF- was mainly distributed in 42nm ~ 55nm. Obviously

7 contaminated membrane PESCHIUF- was coarser than contaminated membrane PESCHIUF-4. It reveals that the antifouling property of membrane PESCHIUF-4 is better than membrane PESCHIUF-. 5. Conclusion In this study, a composite PES membrane modified by chitosan was made. The properties of membrane and its antifouling capacity were studied respectively. The optimal concentration of chitosan in coating solution was.4%. The observation by SEM and FTIR reveals that the composition of chitosan and membrane was successful and stable. Tensile test and contact angle measurement reveals that the mechanical strength and the hydrophilic of the composite membrane was enhanced. The removal rate of humic acid enhanced with the modification of chitosan. Using AFM technology, we confirmed that antifouling property of membrane was greatly enhanced after the coating of chitosan. Applicating composite membrane in water treatment has a broader prospect of promotion. We also found the solubility of chitosan limited the effect of coating. But with the solubility of additive increase, the stability of composite layer may decrease. This issue deserves a further discussion. Conference 1. Liu, Z.-Z. and G. Song, Harm and Removal Methods for Humic Acid in Water Resources. Jiangxi Science, (4): p Feng, Q.Y., et al., Removal of Humic Acid from Groundwater by Electrocoagulation. International Journal of Mining Science and Technology, (4): p Walker, H.W. and M.M. Bob, Stability of particle flocs upon addition of natural organic matter under quiescent conditions. Water Research, (4): p Xu, B., et al., Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters. Science of the Total Environment, (6): p Ahmad, A.L., et al., Recent development in additives modifications of polyethersulfone membrane for flux enhancement. Chemical Engineering Journal, (5): p Susanto, H. and M. Ulbricht, Characteristics, performance and stability of polyethersulfone ultrafiltration membranes prepared by phase separation method using different macromolecular additives. Journal of Membrane Science, (1 2): p Chen, Y., et al., Preparation and antibacterial property of polyethersulfone ultrafiltration hybrid membrane containing halloysite nanotubes loaded with copper ions. Chemical Engineering Journal, (6): p Boributh, S., A. Chanachai, and R. Jiraratananon, Modification of PVDF membrane by chitosan solution for reducing protein fouling. Journal of Membrane Science, (1): p La, Y.H., et al., Bifunctional hydrogel coatings for water purification membranes: Improved fouling resistance and antimicrobial activity. Journal of Membrane Science, (1 2): p Zhang, Y., et al., Surface modification of polyamide reverse osmosis membrane with sulfonated polyvinyl alcohol for antifouling. Applied Surface Science, : p Ekambaram, K. and M. Doraisamy, Surface modification of PVDF nanofiltration membrane using Carboxymethylchitosan-Zinc oxide bionanocomposite for the removal of inorganic salts and humic acid. Colloids & Surfaces A Physicochemical & Engineering Aspects, : p Krajewska, B., Membrane-based processes performed with use of chitin/chitosan materials. Separation & Purification Technology, (3): p Wang, C., F. Yang, and H. Zhang, Fabrication of non-woven composite membrane by chitosan coating for resisting the adsorption of proteins and the adhesion of bacteria. Separation & Purification Technology, (3): p Pillai, C.K.S., W. Paul, and C.P. Sharma, Chitin and chitosan polymers: Chemistry, solubility and fiber formation. Progress in Polymer Science, (7): p Ghiggi, F.F., et al., Preparation and characterization of polyethersulfone/n-phthaloyl-chitosan ultrafiltration

8 membrane with antifouling property. European Polymer Journal, 217: p Su, Y.L., et al., Preparation of antifouling ultrafiltration membranes with poly(ethylene glycol)- graft -polyacrylonitrile copolymers. Journal of Membrane Science, (1 2): p Mimoune, S. and F. Amrani, Experimental study of metal ions removal from aqueous solutions by complexation ultrafiltration. Journal of Membrane Science, (1 2): p Wu, G., Material structure characterization and applications. 22: Textbook publishing center of chemical industry press.

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