A. Wahab Mohammad

Modelling the retention of ionic components for different nanofiltration membranes

Retention measurements with salt solutions of NaCl, Na2SO4, MgCl2, MgSO4 and LaCl3 were carried out for four commercial nanofiltration membranes. The retention of ionic components was analyzed by the Donnan-steric partitioning pore model (DSPM), that describes the solute transport through a membrane using the extended Nernst–Planck equation. The analysis made it possible to evaluate the membrane charge density, which showed that the charge density is not constant but depends very much on the salt and its concentration; this phenomenon was found for all membranes and is attributed to ion adsorption on the membrane material. For magnesium and lanthanum salts this could lead to a change in the sign of the membrane charge from a negative to a positive value. Theoretical calculations strengthened this finding.

A study on producing composite nanofiltration membranes with optimized properties

In this study, we attempt to produce nanofiltration membranes with varying properties through interfacial polymerization technique. The properties include pore size, effective charge density and effective membrane thickness. The ability to use NF membranes with varying properties will improve overall process efficiency as shown in our previous study. The membranes produced were characterized using permeation experiments with water, salt and uncharged solute as well as imaging using atomic force microscopy (AFM). This study has shown that through interfacial polymerization technique, the variation of reaction time as well as monomer concentrations can affect the properties of the membrane produced. Increasing the reaction time resulted in decreasing water permeabilities but based on AFM imaging, the pore size was of similar value. Increasing the monomer concentration also resulted in decreasing water permeabilities. However, based on AFM imaging the pore size differs considerably. Additional permeation experiments and data interpretation with predictive model such as DSPM model allow further understanding of the variation of membrane properties. The ability to tailor made TFC membrane with the right properties will significantly improved processing efficiency.

Understanding the steric and charge contributions in NF membranes using increasing MWCO polyamide membranes

Abstract Various studies have shown the importance of steric and charge effects in NF membranes. Most of the studies, however, were done using NF membranes of different polymeric materials. In this study we have used three membranes made of polyamide with MWCO ranging from 200–2000 to investigate the significance of steric and charge effects upon the separation performance of NF membranes. The characterization of the membranes using uncharged solutes and salt solution shows that the membrane characteristics did not follow the expected pattern based on the increasing MWCO. The rejection performance of the membranes against various categories of salts/charged organic solute was then compared to the model prediction using DSPM. Membrane BM02D was found to have a combination of high steric and charge effects, which explain why the rejections of all solutes were in the range above 80% irrespective of concentrations. For BM20D and BM05D, the pattern of rejections was quite varied and inconsistent, which made it quite difficult to assess the relative contribution of steric and charge effect between the two membranes.

A modified Donnan–steric-pore model for predicting flux and rejection of dye/NaCl mixture in nanofiltration membranes

This paper presents a modified Donnan–steric-pore model (DSPM) to predict the rejection of mixture of salts/charged organic in nanofiltration (NF) membranes, based on the extended Nernst–Planck equation with the incorporation of charge and steric effects for the transport of ions inside the membrane, and incorporation of concentration polarization effect for a mixture of charged ions/solutes. With this approach, the permeate flux can be calculated based on the concentration of ions/charged solutes at the membrane surface. The membrane performance was modeled using three parameters, namely: effective pore radius, r p; effective ratio of membrane thickness to porosity, Δx/A k; and the effective charge density, X d. Comparison of the calculation based on the model with published experimental data shows that the model can predict the tendencies and patterns of rejection and flux reduction behavior reasonably well for systems containing NaCl–dye–H2O. Effects on fluxes and NaCl rejections of system variables such as mass transfer film thickness, dye valence, dye diffusivity, and dye/salt concentration ratio were studied using this model. This model can be used as a preliminary tool to assess the rejection capability as well as the flux behavior of NF membranes towards binary solution and mixtures.

Treatment of Landfill Leachate Wastewater by Nanofiltration Membrane

Abstract Nanofiltration (NF) membrane is an alternative lower energy membrane type compared to reverse osmosis membrane. NF is suitable for rejection of ions and molecules with molecular weight greater than 200 Da. In this study leachate wastewater from a sanitary landfill site in Malaysia was filtered through a NF membrane in order to determine the rejection capability of the membrane towards pollutants such as chemical oxygen demand (COD), conductivity, nitrate, ammonia-nitrogen, and heavy metals such as Pb, Cd, Cu, Zn, Fe. The NF membrane used was HL membrane, which under the atomic force microscope (AFM) imaging, showed visible discrete pores. The overall rejections of the pollutants were more than 85% except for nitrate and ammonia nitrogen. NF can be considered an alternative for advanced filtration especially within a hybrid treatment system combining biological–physical treatment and membrane filtration.

Investigating Characteristics of Increasing Molecular Weight Cutoff Polyamide Nanofiltration Membranes Using Solutes Rejection and Atomic Force Microscopy

In this article, three nanofiltration (NF) membranes of increasing molecular weight cutoff ranging from 200 to 2000 were characterized by using solute rejection method and atomic force microscope (AFM) imaging. The membranes were all made of polyamide; thus, by using membranes made from the same polymer, it is hoped that the uncertainty imposed by the polymeric materials is eliminated and a better understanding of the relationship between the membrane characteristics and its separation performance is gained. Three approaches were used to fit the solute rejection data: characterization using information provided by the manufacturer, characterization using limiting rejection data, and characterization using the full rejection data. The characterization based on the information by the manufacturer was found to be quite misleading especially for larger pore size membranes. The method based on solute rejection data shows that the characteristics of the membranes were within that expected for NF membranes. It was possible to explain some of the membrane rejection performance based on the characteristics obtained. However, the result from AFM study shows the existence of wide pore size distribution of the membranes. This may be the reason why there have been some inconsistencies and non-uniformity in the membranes performance.

Polyethersulfone nanofiltration membrane incorporated with silicon dioxide prepared by phase inversion method for xylitol purification

Xylitol purity is essential for a high value product obtained from biomass fermentation. Common biomass fermentation from sugar cane bagasse, corncobs or rice husk source in the presence of yeast produces xylitol mixture (containing xylose, arabinose), thus, various methods have been used for the purification such as crystallization and adsorption. However, membrane technique is of interest due to the operational simplicity and flexibility, relatively high selectivity and permeability for the transport of specific components. Nanofiltration (NF) membrane is targeted for the membrane application based on the ranges of molecular weight of the mixture components that fall in NF (between 200 to 2000 g/mol). In this paper, a new and efficient NF membrane used for purifying xylitol was synthesized from polyethersulfone (PES) and PES incorporated with silicon dioxide (SiO2) nanoparticles (NP) of 5 wt.% via phase inversion technique. These membranes have been characterized for their chemical, physical and morphological properties and their performances have been evaluated in the dead end filtration to obtain the pure water flux and filtration performance using xylitol mixture. EDX showed the presence of SiO2 NP on the membrane for PES/SiO2 membrane but none in PES membrane. The membrane permeation properties improved also when SiO2 has been incorporated to the PES membrane. The hydrophilicity of the PES/SiO2 membrane measured by contact angle improved from 79.7±0.65° to 59.1±0.15° for PES/SiO2 and PES membranes, respectively. The water flux has enhanced for PES/SiO2 membrane from 24.56 to 59.14 L/m2·h measured at 4 bar. Therefore, in terms of flux and contact angle, the synthesized membrane of PES/SiO2 was found to be more effective compared to pure PES membrane.