Nanofiltration extends the range of membrane filtration

Eriksson, Peter K.

doi:10.1002/ep.3300070116

Cited by 271 publications

(92 citation statements)

References 2 publications

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“…Nanofiltration (NF) is a membrane separation process, first recognized in the late 1980's, whose performance is intermediate between that of reverse osmosis (RO) and ultrafiltration (UF), with a pore size on the order of one nanometer and a corresponding molecular weight cut-off (MWCO) of 300 − 500 Da [1].…”

Section: Introductionmentioning

confidence: 99%

Fundamentals of low-pressure nanofiltration: Membrane characterization, modeling, and understanding the multi-ionic interactions in water softening

Labban

Liu

Chong

et al. 2017

Journal of Membrane Science

148

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Recently, a novel class of low-pressure nanofiltration (NF) hollow fiber membranes, particularly suited for water softening and desalination pretreatment have been fabricated in-house using layer-by-layer (LbL) deposition with chemical crosslinking. These membranes can operate at exceedingly low pressures (2 bar), while maintaining relatively high rejections of multivalent ions. In spite of their great potential, our understanding as to what makes them superior has been limited, demanding further investigation before any large-scale implementation can be realized. In this study, the Donnan-Steric Pore Model with dielectric exclusion (DSPM-DE) is applied for the first time to these membranes to describe the membrane separation performance, and to explain the observed rejection trends, including negative rejection, and their underlying multi-ionic interactions. Experiments were conducted on a spectrum of feed chemistries, ranging from uncharged solutes to single salts, salt mixtures, and artificial seawater to characterize the membrane and accurately predict its performance. Modeling results were validated with experiments, and then used to elucidate the working principles that underlie the low-pressure softening process. An approach based on sensitivity analysis shows that the membrane pore dielectric constant, followed by the pore size, are primarily responsible for the selectively high rejections of the NF membranes to multivalent ions. Surprisingly, the softening process is found to be less sensitive to changes in membrane charge density. Our findings demonstrate that the unique ability of these membranes to exclusively separate multivalent ions from the solution, while allowing monovalent ions to permeate, is key to making this low-pressure softening process realizable.

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Section: Introductionmentioning

confidence: 99%

Fundamentals of low-pressure nanofiltration: Membrane characterization, modeling, and understanding the multi-ionic interactions in water softening

Labban

Liu

Chong

et al. 2017

Journal of Membrane Science

148

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“…NF membranes combine the advantages of a high water flux at relatively low operating pressure and high salt and organic matter rejection rate [3]. Nanofiltration has received much attention in the last decades due to its applications in textile, paper, and food industries including water desalination [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%

“…The considered electrolyte concentrations were 1 mol/m 3 and lower except the work [24] (the pressure-driven flow was not considered there). However, typical nanofiltration membranes have the pore diameter of a few nanometers and the aspect ratio of order 100-1000, while the electrolyte concentration can be as high as 1000 mol/m 3 [1][2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of electrolyte transport in nanofiltration membranes with constant surface potential/charge density

Ryzhkov

Минаков

2016

Journal of Membrane Science

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Abstract. The pressure-driven ion transport through nanofiltration membrane pores with constant surface potential or charge density is investigated theoretically. Two approaches are employed in the study. The first one is based on one-dimensional Nernst-Planck equation coupled with electroneutrality, zero current, and Donnan equilibrium conditions. This model is extended to account for interfacial effects by using a smooth approximation of step function for the volume charge density. A simplified model for the case of constant surface potential is also proposed. The second approach is based on two-dimensional Nernst-Planck, Poisson, and Navier-Stokes equations, which are solved in a high aspect ratio nanopore connecting two reservoirs with much larger diameter. The modification of equations on the basis of Slotboom transformation is employed to speed up the convergence rate. The distributions of potential, pressure, ion concentrations and fluxes due to convection, diffusion, and migration in the nanopore and reservoirs are discussed and analyzed. It is found that for constant surface charge density, the convective flux of counter-ions in the nanopore is almost completely balanced by the opposite migration flux, while for constant surface potential, the convective flux is balanced by the opposite diffusion and migration fluxes. The co-ions in the nanopore are mainly transported by diffusion. A particular attention is focused on describing the interfacial effects at the nanopore entrance/exit. Detailed comparison between one-and two-dimensional models is performed in terms of rejection, pressure drop, and membrane potential dependence on the surface potential/charge density, volume flux, electrolyte concentration, and pore radius. A good agreement between these models is found when the Debye length is smaller than the pore radius and the surface potential or charge density are sufficiently low.

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“…treatment alternative for the removal of natural organic matter (NOM), a precursor of disinfection by-products, in anticipation of more stringent regulations [3,4]. NF technology also offers a versatile approach to meeting multiple water quality objectives, such as the control of organic, inorganic, and microbial contaminants [5,6].…”

Section: Introductionmentioning

confidence: 99%

“…NF membranes are usually made of polymeric films with a molecular weight cutoff between 300 and 1000 [5]. This allows performance characteristics of both ultrafiltration and reverse osmosis, depending on molecular weight cutoff.…”

Section: Introductionmentioning

confidence: 99%

Fouling of nanofiltration membranes

1998

Membrane Technology

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The role of chemical and physical interactions in natural organic matter (NOM) fouling of nanofiltration membranes is systematically investigated. Results of fouling experiments with three humic acids demonstrate that membrane fouling increases with increasing electrolyte (NaC1) concentration, decreasing solution pH, and addition of divalent cations (Ca2+). At fixed solution ionic strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on membrane fouling. Divalent cations interact specifically with humic carboxyl functional groups and, thus, substantially reduce humic charge and the electrostatic repulsion between humic macromolecules. Reduced NOM interchain repulsion results in increased NOM deposition on the membrane surface and formation of a densely packed fouling layer. In addition to the aforementioned chemical effects, results show that NOM fouling rate increases substantially with increasing initial permeation rate. It is demonstrated that the rate of fouling is controlled by an interplay between permeation drag and electrostatic double layer repulsion; that is, NOM fouling of NF membranes involves interrelationship (coupling) between physical and chemical interactions. The addition of a strong chelating agent (EDTA) to feed water reduces NOM fouling significantly by removing free and NOM-complexed calcium ions. EDTA treatment of NOM-fouled membranes also improves the cleaning efficiency dramatically by disrupting the fouling layer structure through a ligand exchange reaction between EDTA and NOM-calcium complexes.

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Nanofiltration extends the range of membrane filtration

Cited by 271 publications

References 2 publications

Fundamentals of low-pressure nanofiltration: Membrane characterization, modeling, and understanding the multi-ionic interactions in water softening

Fundamentals of low-pressure nanofiltration: Membrane characterization, modeling, and understanding the multi-ionic interactions in water softening

Theoretical study of electrolyte transport in nanofiltration membranes with constant surface potential/charge density

Fouling of nanofiltration membranes

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