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Macromolecule adsorption in an MBR mixed liquor suspension
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RESEARCH TRENDS Prediction of permeate flux for UF in wire–rod tubularmembrane modules Predicting equations for the permeate flux of membrane ultrafiltration in wire–rod tubular modules were derived from momentum and mass balances based on the resistance-inseries model, coupled with the considerations of declinations of flow rate and transmembrane pressure along the membrane tubes. Experimental work for the ultrafiltration of dextran 500 aqueous solution was carried out in a ceramic microporous tube with a twisted wire–rod assembly. Correlation predictions are in better agreement with the experimental results than those predicted in previous works where the flow rate was simply taken with the arithmeticmean value. The effect of wire angle of inclination on the performance was also discussed. Increasing the wire angle of inclination will increase the fluid velocity in the spiral channel. Actually, the increase of fluid velocity has two conflict effects on permeation: one is decreasing the concentration polarization, which is good for ultrafiltration, while the other is reducing the transmembrane pressure which is bad for performance. It was found that the optimal wire angle of inclination for maximum average permeate flux exists between 45° and 50° in the system of present interest. H.M. Yeh, J.F. Dong, M.J. Hsieh, C.C. Yang: J. of Membrane Science 209(1) 19–26 (1 November 2002).
Macromolecule adsorption in an MBR mixed liquor suspension The aim of this study was to quantify the specific effect of adsorption on membrane fouling during filtration of a membrane bioreactor (MBR) mixed liquor suspension. Adsorption experiments were performed on welldefined protein solutions (β-lactoglobulin solutions) to provide reference results and compare them to those obtained during the filtration of MBR suspensions (raw suspension and settled suspension). Two different methods were used to quantify the role of adsorption in membrane fouling: a ‘static’ method in which membranes were immersed in the biological suspension, and a ‘dynamic’ method supposing that the resistance due to adsorption is an irreversible phenomenon that remains after filtration and back-washing. It was shown for the two types of 16
suspensions that: (i) due to limited diffusion, the dynamic method appears to be more adapted than the static method; (ii) adsorption is a rapid fouling phenomenon that induces irreversible resistance and that, in frontal mode takes place at the beginning of the operation; (iii) the adsorption phenomenon shows specific hydraulic resistance of the same order of magnitude as the clean membrane resistance; (iv) other phenomena, i.e. progressive pore clogging, can also take place though subcritical hydrodynamic conditions. S. Ognier, C. Wisniewski, A. Grasmick: J. of Membrane Science 209(1) 27–37 (1 November 2002).
UF of pulp and paper effluent Effluent arriving from the Mondi Kraft paper mill at Piet Retief, South Africa was filtered through tubular poly(ether sulphone) (PES) ultrafiltration membranes under constant pressure cross-flow conditions. The effluent that was fed into the membranes and permeate produced during filtration were characterized by UV–vis light-spectroscopy. Substances that adsorbed onto membranes during filtration caused changes to the permeability characteristics of the membranes. Changes in membrane performance were monitored by pure-water and product flux (pf ) measurements. A colorimetric staining technique was developed to determine the nature of foulants adsorbed onto the membranes. Membrane cleaning solutions were subsequently selected using information obtained from the characterization studies. In addition, the anti-fouling potential of non-covalently attached coating materials was investigated as a possible membrane pretreatment technique. Results showed that foulants present in the effluent are of phenolic and hydrophobic nature. Increasing the hydrophilic characteristics of membranes prior to filtration could reduce the amount of organic foulants that adsorbed onto the membranes. Membrane pretreatment not only reduced fouling, but also improved the effectiveness of cleaning methods. Membranes were effectively cleaned by a combination of mechanical and chemical cleaning techniques. A. Maartens, E.P. Jacobs, P. Swart: J. of Membrane Science 209(1) 81–92 (1 November 2002).
Affinity UF processes for chiral separations Affinity ultrafiltration using a large stereospecific binding agent can be used to separate enantiomeric mixtures; however, the overall yield and purification factor have generally been inadequate for commercial separations. The objective of this study was to examine the performance of a multi-stage diafiltration process for chiral separations. Data were obtained for the separation of D- and L-tryptophan using bovine serum albumin (BSA) as the affinity macroligand. Tangential flow filtration (TFF) was conducted with laboratory scale modules that are linearly scalable to industrial operation. The two-stage system gave purification factors of more than 20 at greater than 90% yield. Theoretical calculations based on a two site competitive binding model were in good agreement with the experimental data. Purificationyield diagrams were used to examine the effects of the ligand concentration, number of stages, and stage volume on the overall separation. The results clearly demonstrate that multi-stage affinity ultrafiltration processes can provide high purification factors and yield for enantiomeric separations. J. Romero, A.L. Zydney: J. of Membrane Science 209(1) 107–119 (1 November 2002).
Acrylonitrile–maleic anhydride copolymer membranes The structure and performance of acrylonitrile–maleic anhydride copolymer membranes with different molecular weights were investigated. The results showed that the water flux of the membrane decreased gradually with increasing molecular weight of the copolymer; the rejection increased only when there was an obvious increase of molecular weight. The addition of an additive (polyvinylpyrrolidone) largely decreased the water flux and rejection of the membrane when the concentration of the copolymer remained unchanged. The higher the molecular weight, the thicker were the transition layer and the wall of the support pore and the better was the anticompactness of the membrane. Z.-C. Pei, Y.-X. Pei, Q.-R. Wang: J. of Applied Polymer Science 85(12) 2521–2527 (19 September 2002).
Radiation-grafted copolymer membranes in metal recovery ET-g-PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene-ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K+, Ag+, Hg2+, Co2+, and Cu2+ in a mixed aqueous solution. The ionexchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg2+ ion content of the membrane was more than that of either the K+ or Ag+ ions. The presence of metal ions in the membranes was studied by infrared and energy-dispersive spectroscopy measurements. Scanning electron microscopy showed modification of the morphology of the surface due to the adsorption of K+ and Ag+ ions. No change was observed for the surface of the membrane that was treated with Hg2+ ions. N.M. El-Sawy, F.A. Al Sagheer: J. of Applied Polymer Science 85(13) 2692–2698 (23 September 2002).
Next month News Business activities Industry trends Commercial news New products
Features Developments and applications around the world
Research Trends The latest membrane research published in the key journals
Patents Recently published US and WO patents
Events Calendar Conferences and shows relevant to the membranes industry
Membrane Technology December 2002
27/01/2003
12:18
Page 16
RESEARCH TRENDS Prediction of permeate flux for UF in wire–rod tubularmembrane modules Predicting equations for the permeate flux of membrane ultrafiltration in wire–rod tubular modules were derived from momentum and mass balances based on the resistance-inseries model, coupled with the considerations of declinations of flow rate and transmembrane pressure along the membrane tubes. Experimental work for the ultrafiltration of dextran 500 aqueous solution was carried out in a ceramic microporous tube with a twisted wire–rod assembly. Correlation predictions are in better agreement with the experimental results than those predicted in previous works where the flow rate was simply taken with the arithmeticmean value. The effect of wire angle of inclination on the performance was also discussed. Increasing the wire angle of inclination will increase the fluid velocity in the spiral channel. Actually, the increase of fluid velocity has two conflict effects on permeation: one is decreasing the concentration polarization, which is good for ultrafiltration, while the other is reducing the transmembrane pressure which is bad for performance. It was found that the optimal wire angle of inclination for maximum average permeate flux exists between 45° and 50° in the system of present interest. H.M. Yeh, J.F. Dong, M.J. Hsieh, C.C. Yang: J. of Membrane Science 209(1) 19–26 (1 November 2002).
Macromolecule adsorption in an MBR mixed liquor suspension The aim of this study was to quantify the specific effect of adsorption on membrane fouling during filtration of a membrane bioreactor (MBR) mixed liquor suspension. Adsorption experiments were performed on welldefined protein solutions (β-lactoglobulin solutions) to provide reference results and compare them to those obtained during the filtration of MBR suspensions (raw suspension and settled suspension). Two different methods were used to quantify the role of adsorption in membrane fouling: a ‘static’ method in which membranes were immersed in the biological suspension, and a ‘dynamic’ method supposing that the resistance due to adsorption is an irreversible phenomenon that remains after filtration and back-washing. It was shown for the two types of 16
suspensions that: (i) due to limited diffusion, the dynamic method appears to be more adapted than the static method; (ii) adsorption is a rapid fouling phenomenon that induces irreversible resistance and that, in frontal mode takes place at the beginning of the operation; (iii) the adsorption phenomenon shows specific hydraulic resistance of the same order of magnitude as the clean membrane resistance; (iv) other phenomena, i.e. progressive pore clogging, can also take place though subcritical hydrodynamic conditions. S. Ognier, C. Wisniewski, A. Grasmick: J. of Membrane Science 209(1) 27–37 (1 November 2002).
UF of pulp and paper effluent Effluent arriving from the Mondi Kraft paper mill at Piet Retief, South Africa was filtered through tubular poly(ether sulphone) (PES) ultrafiltration membranes under constant pressure cross-flow conditions. The effluent that was fed into the membranes and permeate produced during filtration were characterized by UV–vis light-spectroscopy. Substances that adsorbed onto membranes during filtration caused changes to the permeability characteristics of the membranes. Changes in membrane performance were monitored by pure-water and product flux (pf ) measurements. A colorimetric staining technique was developed to determine the nature of foulants adsorbed onto the membranes. Membrane cleaning solutions were subsequently selected using information obtained from the characterization studies. In addition, the anti-fouling potential of non-covalently attached coating materials was investigated as a possible membrane pretreatment technique. Results showed that foulants present in the effluent are of phenolic and hydrophobic nature. Increasing the hydrophilic characteristics of membranes prior to filtration could reduce the amount of organic foulants that adsorbed onto the membranes. Membrane pretreatment not only reduced fouling, but also improved the effectiveness of cleaning methods. Membranes were effectively cleaned by a combination of mechanical and chemical cleaning techniques. A. Maartens, E.P. Jacobs, P. Swart: J. of Membrane Science 209(1) 81–92 (1 November 2002).
Affinity UF processes for chiral separations Affinity ultrafiltration using a large stereospecific binding agent can be used to separate enantiomeric mixtures; however, the overall yield and purification factor have generally been inadequate for commercial separations. The objective of this study was to examine the performance of a multi-stage diafiltration process for chiral separations. Data were obtained for the separation of D- and L-tryptophan using bovine serum albumin (BSA) as the affinity macroligand. Tangential flow filtration (TFF) was conducted with laboratory scale modules that are linearly scalable to industrial operation. The two-stage system gave purification factors of more than 20 at greater than 90% yield. Theoretical calculations based on a two site competitive binding model were in good agreement with the experimental data. Purificationyield diagrams were used to examine the effects of the ligand concentration, number of stages, and stage volume on the overall separation. The results clearly demonstrate that multi-stage affinity ultrafiltration processes can provide high purification factors and yield for enantiomeric separations. J. Romero, A.L. Zydney: J. of Membrane Science 209(1) 107–119 (1 November 2002).
Acrylonitrile–maleic anhydride copolymer membranes The structure and performance of acrylonitrile–maleic anhydride copolymer membranes with different molecular weights were investigated. The results showed that the water flux of the membrane decreased gradually with increasing molecular weight of the copolymer; the rejection increased only when there was an obvious increase of molecular weight. The addition of an additive (polyvinylpyrrolidone) largely decreased the water flux and rejection of the membrane when the concentration of the copolymer remained unchanged. The higher the molecular weight, the thicker were the transition layer and the wall of the support pore and the better was the anticompactness of the membrane. Z.-C. Pei, Y.-X. Pei, Q.-R. Wang: J. of Applied Polymer Science 85(12) 2521–2527 (19 September 2002).
Radiation-grafted copolymer membranes in metal recovery ET-g-PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene-ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K+, Ag+, Hg2+, Co2+, and Cu2+ in a mixed aqueous solution. The ionexchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg2+ ion content of the membrane was more than that of either the K+ or Ag+ ions. The presence of metal ions in the membranes was studied by infrared and energy-dispersive spectroscopy measurements. Scanning electron microscopy showed modification of the morphology of the surface due to the adsorption of K+ and Ag+ ions. No change was observed for the surface of the membrane that was treated with Hg2+ ions. N.M. El-Sawy, F.A. Al Sagheer: J. of Applied Polymer Science 85(13) 2692–2698 (23 September 2002).
Next month News Business activities Industry trends Commercial news New products
Features Developments and applications around the world
Research Trends The latest membrane research published in the key journals
Patents Recently published US and WO patents
Events Calendar Conferences and shows relevant to the membranes industry
Membrane Technology December 2002