Spiral Wound Nanofiltration Membrane Research Articles

Partial Removal of Sugar from Apple Juice by Nanofiltration and Discontinuous Diafiltration.

Partial removal of sugars in fruit juices without compromising their biofunctional properties represents a significant technological challenge. The current study was aimed at evaluating the separation of sugars from phenolic compounds in apple juice by using three different spiral-wound nanofiltration (NF) membranes with a molecular weight cut-off (MWCO) in the range of 200–500 Da. A combination of diafiltration and batch concentration processes was investigated to produce apple juice with reduced sugar content and improved health properties thanks to the preservation and concentration of phenolic compounds. For all selected membranes, permeate flux and recovery rate of glucose, fructose, and phenolic compounds, in both diafiltration and concentration processes, were evaluated. The concentration factor of target compounds as a function of the volume reduction factor (VRF) as well as the amount of adsorbed compound on the membrane surface from mass balance analysis were also evaluated. Among the investigated membranes a thin-film composite membrane with an MWCO of 200–300 Da provided the best results in terms of the preservation of phenolic compounds in the selected operating conditions. More than 70% of phenolic compounds were recovered in the retentate stream while the content of sugars was reduced by about 60%.

Separation of Fructose and Glucose via Nanofiltration in Presence of Fructooligosaccharides.

Fructose and glucose are commonly present together in mixtures and may need to be separated. Current separation methods for these isomers are complex and costly. Nanofiltration is a cost-effective method that has been widely used for separating carbohydrates of different sizes; however, it is not commonly used for such similar molecules. Here, we report the separation of fructose and glucose in a nanofiltration system in the presence of fructooligosaccharides (FOS). Experiments were performed using a pilot-scale filtration setup using a spiral wound nanofiltration membrane with molecular weight cutoff of 1 kDa. We observed three important factors that affected the separation: (1) separation of monosaccharides only occurred in the presence of FOS and became more effective when FOS dominated the solution; (2) better separation was achieved when the monosaccharides were mainly fructose; and (3) the presence of salt improved the separation only moderately. The rejection ratio (Rf/Rg) in a fructose/glucose mixture is 0.92. We reported a rejection ratio of 0.69, which was observed in a mixture of 50 g/L FOS with a fructose to glucose ratio of 4.43. The separation is hypothesized to occur due to selective transport in the FOS layer, resulting in a preferential binding towards fructose.

Impacts of non-uniform filament feed spacers characteristics on the hydraulic and anti-fouling performances in the spacer-filled membrane channels: Experiment and numerical simulation

Feed spacer is universally used in spiral-wound nanofiltration (NF) and reverse osmosis (RO) membrane modules. It can separate membrane sheets, create flow channels, promote turbulence and enhance mass transfer. However, it also induces increased pressure drop across the flow channel, and generates dead zones for biofilm growth at specific locations. Optimization of feed spacer geometries is highly desirable for energy saving and biofouling control. In this study, four kinds of commercial feed spacers featured with non-uniform filaments were compared in terms of hydraulic and anti-fouling performances. Computational fluid dynamics (CFD) simulations were launched to give insights into the impacts of feed spacer characteristics on the flow field. Results show that the hydraulic performance was substantially affected by the number of filament layers (single or dual layer), the non-uniformity of filament diameter and the width of thinning zones. The design of single layer feed spacer of non-uniform filaments was not recommended due to high flow resistance and poor anti-fouling performance. The feed spacer structure of alternating filament diameter contributed to reducing dead zones and alleviating membrane fouling. The thinning zones located adjacent to the filament junctions achieved better anti-fouling performance, as it disturbed the dead zones and partially washed away the deposited foulants. This study demonstrates for the first time that the characteristics of non-uniform filament feed spacer had a crucial impact on the hydraulic and anti-fouling performances, and suggests that more emphasis should be laid on number of filament layers, variation of filament diameter and width and positioning of thinning zones for the optimization of feed spacer geometries in the future.

Efficiencies and mechanisms of chemical cleaning agents for nanofiltration membranes used in produced wastewater desalination

A spiral-wound nanofiltration (NF) membrane module harvested from a full-scale produced wastewater desalination plant was examined and cleaned to explore appropriate chemical cleaning protocols. Foulant identification and cleaning efficiency and mechanisms were investigated. For total foulants, the organic components, including anionic polyacrylamide (APAM) and crude oil, accounted for a weight percentage of 86.3%, while the remaining foulants constituted the inorganic fraction, including Na, Mg, Ca, Ba, Al, Fe and Si. Short-term cleaning experiments were designed to identify effective reagents that could be used for further evaluations of their cleaning efficiencies in long-term cleaning. For citric acid and ethylenediaminetetraacetic acid tetrasodium (EDTA-4Na), the long-term cleaning efficiencies were relatively slight or even negative, while said values varied with different surfactants. Dodecyltrimethylammonium chloride (DTAC) achieved the greatest flux recovery; conversely, cetyltrimethylammonium chloride (CTAC) provided insignificant, even negative effects, on flux recovery, as well as salt rejection, of the fouled NF membranes. FTIR and zeta potential analyses of the fouled membranes indicated that all the tested surfactants were identically effective in removing the foulants from the membrane surface, but their cleaning efficiencies differed. Moreover, a strong correlation between the flux ratio (Sf) and concentration of surfactant in the permeate (Cps) was observed. Among the tested chemical reagents, DTAC yielded the highest Cps and the greatest flux recovery, with an Sf of 2.25. Considering this correlation and the characteristics of the fouled membranes and surfactants, it is proposed that DTAC molecules penetrated the membrane pores and removed the foulants that were attached to the pore walls.

Assessment and Modeling of Nanofiltration of Acid Mine Drainage

The main objective of the present investigation was to analyze, evaluate, and model the behavior in the treatment of real acid mine drainage (AMD) with commercial spiral-wound nanofiltration membranes (NF270 and NF90). Both membranes showed operational differences regarding the effect of pH, temperature, continuous operation, concentration polarization, and fouling. Both NF90 and NF270 presented a high rejection of divalent ions (∼100%); however, NF90 showed a greater fouling with AMD. Adjustment of pH in the continuous tests reduced the precipitation of aluminum, and gypsum was identified as the main compound generating a significant decrease in the permeate flow in the membrane. The Spliegler–Kedem model was used to represent rejection and permeate flows, identifying the contribution of convective and diffusive transport in both membranes with a good fit of the model. The results obtained represent important information for a future industrial application to the treatment of AMD by means of commercial N...

Nanofiltration for textile dye–water treatment: Experimental and parameter estimation studies using a spiral wound module and validation of the Spiegler–Kedem-based model

ABSTRACTThe present work deals with the study of the nanofiltration process for textile dye wastewater treatment. Effects of feed pressure, dye concentration, and feed flow rate on dye rejection and recovery for the spiral wound nanofiltration module were studied. The permeate characteristics were predicted by using the Spiegler–Kedem (SK)-based model. A finite difference numerical technique is used to discretize the transport equations and an optimization technique was used for estimation of unknown parameters (B, σ, ka, and kb) in the SK-based model. The model and the estimated parameter values were validated with experimental results for the spiral wound nanofiltration (NF) membrane module.

SEPARATION OF XYLOSE FROM GLUCOSE USING PILOT SCALE SPIRAL WOUND COMMERCIAL MEMBRANE

Xylose is an intermediate product in xylitol production and glucose interferes in the process of separation. Thus the aim of this study is to investigate the performance of pilot scale commercial spiral wound NF membrane namely Desal-5 DK, Desal-5 DL and NF90 for separation of xylose from glucose. Separation of xylose and glucose model solutions was done in a pilot scale cross-flow system, using a commercial nanofiltration (NF) membrane with molecular weight cut off (MWCO) ranging from 150 to 1000 g/mol. The model solution consists of 1:1 ratio of xylose to glucose at 10 g/L each diluted in ultrapure water. The filtration was operated in total recycled mode at 10 bar. The sugar concentration was analyzed using high performance liquid chromatography (HPLC). From this study, the pure water permeability (PWPs) of the Desal-5 DK membrane was considerably higher at 6.78 ± 0.06 than PWPs of the Desal-5 DL and NF90 membranes at 1.28 ± 0.24 and 1.33 ± 0.05, respectively. The Desal-5 DK also gave the higher xylose separation factor at 1.17 as compare to Desal-5 DL (0.81) and NF90 membranes (0.84). This indicates that membrane Desal-5 DK was the most selective membrane to separate xylose form glucose. Overall, it can be concluded that the spiral wound nanofiltration membrane offers cost-effective and easy-maintenance, which has a potential in xylose-glucose separation.

Separating xylose from glucose using spiral wound nanofiltration membrane: Effect of cross-flow parameters on sugar rejection

A solution model consisted of two different monosaccharides namely xylose and glucose were separated using a pilot scale spiral wound cross-flow system. This system was equipped by a commercial spiral wound nanofiltration (NF) membrane, Desal-5 DK, having a molecular weight cut off (MWCO) of 150-300 g mol-1. The aim of this present work is to investigate the effect of the cross-flow parameters: the trans-membrane pressure (TMP) and the feed concentration (C0) on the xylose separation from glucose. The filtration experiments were carried out in total reflux mode with different feed concentration of 2, 5, and 10 g/L at different TMP of 5,8 and 10 bar. The performances of the NF membrane were evaluated by measuring the permeate flux and sugar rejection for each experiment. All the samples were quantified using a high performance liquid chromatography equipped by a fractive index detector. The experimental results indicated an increase in pressure from 5 to 10 bar which was a notable increase to the permeate fluxes from 2.66 × 10-3 to 4.14 × 10-3L m-2s-1. Meanwhile, an increase in the C0 increases the xylose rejection. At TMP of 10 bar and C0 of 5 g/L, the observed xylose rejection and glucose rejection were measured at 67.19% and 91.82%, respectively. The lower rejection in xylose than glucose suggested that larger glucose molecule were not able to easily pass through the membrane compared to the smaller xylose molecule. The results of this phenomena proved that NF with spiral wound configuration has the potential to separate xylose from glucose, which is valuable to the purification of xylose in xylose production as an alternative to chromatographic processes.

Recovery of bioactive compounds from artichoke brines by nanofiltration

In this work a membrane-based process for the fractionation of artichoke brines was investigated in order to separate flavonoids and caffeoylquinic acids from salt compounds. Therefore, the performance of different spiral-wound nanofiltration (NF) membranes in the treatment of clarified artichoke brines was evaluated in terms of productivity and selectivity towards bioactive compounds in selected operating conditions. Membranes with different polymeric material (polyethersulphone, polyammide) and molecular weight cut-off (MWCO) (from 200 to 1000Da) were tested. NF membranes of 200Da produced better results in terms of recovery and concentration of compounds of interest. A better separation of salt compounds from caffeoylquinic acid derivatives was reached by using Filmtec-Dow NF 200 and Desal DL membranes. For these membranes a low rejection towards dry residue (between 14% and 18%) was observed, while rejections towards total caffeoylquinic acids, flavonoids and cynarin were higher than 92%.According to the obtained results the NF permeate, enriched in salt compounds, can be reused in the working cycle for the preparation of new acidulated brines through the adjustment of the standard salt concentration; the concentrated stream, enriched in phenolic compounds, is a good source of possible ingredients to functionalize foodstuffs.

Predicting the Rejection of Major Seawater Ions by Spiral-Wound Nanofiltration Membranes.

Seawater nanofiltration (SWNF) generates a softened permeate stream and a retentate stream in which the multivalent ions accumulate, offering opportunities for practical utilization of both streams. This study presents an approach to simulation of SWNF including all major seawater ions (Na(+), Cl(-), Ca(2+), Mg(2+), and SO4(2-)) based on the Nernst-Planck equation, and uses it for permeate and retentate streams composition prediction. The number of degrees of freedom in the system was reduced by assuming a very high ionic permeability for Na(+), which only weakly affected the other parameters in the system. Two alternatives were examined to analyze the importance of concentration dependence of ion permeabilities: The assumption of constant ion permeabilities resulted in a reasonable fit with experimental data. However, for the permeate composition the overall fit was significantly improved (P < 0.0001) when the permeabilities of Ca(2+) and Mg(2+) were allowed to depend on the ratio of their total concentration to Na(+). This type of dependence emphasizes the strong interaction of divalent ions with the membrane and its effect on the membrane fixed charge through screening or charge reversal. When this effect was included, model predictions closely matched the experimental results obtained, corroborating the phenomenological approach proposed in this study.

In-situ biofilm characterization in membrane systems using Optical Coherence Tomography: Formation, structure, detachment and impact of flux change

Biofouling causes performance loss in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane operation for process and drinking water production. The development of biofilm formation, structure and detachment was studied in-situ, non-destructively with Optical Coherence Tomography (OCT) in direct relation with the hydraulic biofilm resistance and membrane performance parameters: transmembrane pressure drop (TMP) and feed-channel pressure drop (FCP). The objective was to evaluate the suitability of OCT for biofouling studies, applying a membrane biofouling test cell operated at constant crossflow velocity (0.1 m s−1) and permeate flux (20 L m−2h−1).In time, the biofilm thickness on the membrane increased continuously causing a decline in membrane performance. Local biofilm detachment was observed at the biofilm–membrane interface.A mature biofilm was subjected to permeate flux variation (20 to 60 to 20 L m−2h−1). An increase in permeate flux caused a decrease in biofilm thickness and an increase in biofilm resistance, indicating biofilm compaction. Restoring the original permeate flux did not completely restore the original biofilm parameters: After elevated flux operation the biofilm thickness was reduced to 75% and the hydraulic resistance increased to 116% of the original values. Therefore, after a temporarily permeate flux increase the impact of the biofilm on membrane performance was stronger. OCT imaging of the biofilm with increased permeate flux revealed that the biofilm became compacted, lost internal voids, and became more dense. Therefore, membrane performance losses were not only related to biofilm thickness but also to the internal biofilm structure, e.g. caused by changes in pressure.Optical Coherence Tomography proved to be a suitable tool for quantitative in-situ biofilm thickness and morphology studies which can be carried out non-destructively and in real-time in transparent membrane biofouling monitors.

Spacer geometry and particle deposition in spiral wound membrane feed channels

Deposition of microspheres mimicking bacterial cells was studied experimentally and with a numerical model in feed spacer membrane channels, as used in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane systems. In-situ microscopic observations in membrane fouling simulators revealed formation of specific particle deposition patterns for different diamond and ladder feed spacer orientations. A three-dimensional numerical model combining fluid flow with a Lagrangian approach for particle trajectory calculations could describe very well the in-situ observations on particle deposition in flow cells. Feed spacer geometry, positioning and cross-flow velocity sensitively influenced the particle transport and deposition patterns. The deposition patterns were not influenced by permeate production. This combined experimental-modeling approach could be used for feed spacer geometry optimization studies for reduced (bio)fouling.

Development and testing of a transparent membrane biofouling monitor

A modified version of the membrane fouling simulator (MFS) was developed for assessment of (i) hydraulic biofilm resistance, (ii) performance parameters feed-channel pressure drop and transmembrane pressure drop, and (iii) in situ spatial visual and optical observations of the biofilm in the transparent monitor, e.g. using optical coherence tomography. The flow channel height equals the feed spacer thickness enabling operation with and without feed spacer. The effective membrane surface area was enlarged from 80 to 200 cm2 by increasing the monitor width compared to the standard MFS, resulting in larger biomass amounts for analysis. By use of a microfiltration membrane (pore size 0.05 μm) in the monitor salt concentration polarization is avoided, allowing operation at low pressures enabling accurate measurement of the intrinsic hydraulic biofilm resistance. Validation tests on e.g. hydrodynamic behavior, flow field distribution, and reproducibility showed that the small-sized monitor was a representative tool for membranes used in practice under the same operating conditions, such as spiral-wound nanofiltration and reverse osmosis membranes. Monitor studies with and without feed spacer use at a flux of 20 L m−2 h−1 and a cross-flow velocity of 0.1 m s−1 clearly showed the suitability of the monitor to determine hydraulic biofilm resistance and for controlled biofouling studies.

Threshold flux measurements of a nanofiltration membrane module by critical flux data conversion

Recently, for some membrane separation processes, the concept of threshold flux was introduced in substitution of the critical one. The new concept applies to all systems which trigger fouling formation from start of operation, even at very low operating conditions, and in particular to the purification of olive mill wastewater streams by membranes.The operation of a spiral-wound nanofiltration membrane module used to purify different pretreated olive mill wastewater streams and how pretreatments affect the threshold flux values and the threshold flux fitting parameters will be discussed.

Recovery of phenolic compounds from orange press liquor by nanofiltration

This research was undertaken in order to evaluate the potential of a nanofiltration (NF) process for the separation and concentration of phenolic compounds from press liquors obtained by pigmented orange peels. Four different spiral-wound NF membranes, characterised by different molecular weight cut-off (MWCO) (250, 300, 400 and 1000Da) and polymeric material (polyamide, polypiperazine amide and polyethersulphone), were investigated. The rejection of the investigated membranes towards anthocyanins, flavonoids and sugars was evaluated in order to identify a suitable membrane to separate phenolic compounds from sugars. The performance of the investigated NF membranes was also evaluated in terms of permeate flux and antifouling performance.The obtained results indicated a reduction of the average rejection towards sugars by increasing the MWCO of the selected membranes, while the rejection towards anthocyanins remained higher than 89% for all the NF membranes investigated. The NFPES10 membrane showed the lowest average rejection towards sugar compounds and high rejections towards anthocyanins (89.2%) and flavonoids (70%). Permeate flux values at lower transmembrane pressures were also favourably high compared to the other NF membranes.

Modeling the permeate flux and rejection of nanofiltration membrane separation with high concentration uncharged aqueous solutions

In this paper, the influence of feed concentration on the performance of nanofiltration membrane separation under high concentration (0.1–0.98mol/L) of aqueous glucose is investigated using a commercial spiral-wound nanofiltration membrane. The results of the experiments show that the permeate volume flux and observed rejection at certain operating pressures are influenced seriously by concentration. In this work, the influence of concentration is studied generally based on the solution-diffusion model, from which the concentration polarization boundary resistance Rcp and mass transfer coefficient k as functions of concentrations are obtained for high concentrations. Using these relationships, the observed rejection Ro can be predicted in the case of high concentration. The good agreements between the predicted and experimental values indicate that the models proposed and modified in this work could be used to describe the behavior of nanofiltration membrane separation in a wider range of uncharged aqueous solution concentration.

The Ability of a Nanofiltration Membrane to Remove Hardness and Ions from Diluted Seawater

In this work, the ability of a commercial spiral-wound nanofiltration membrane to remove hardness and ions from diluted seawater was studied. Experiments were carried out in the pressure range of 4–10 bar. Analyses of the samples, and permeates at different pressures, were performed and the effects of the trans-membrane pressure on the permeate flux were investigated. The results show that this nanofiltration membrane is capable of retaining 96–98% of the total hardness, 79–89% of the electrical conductivity and 79–89% of the total dissolved solid (TDS). Our results are in good agreement with those reported by the manufacturing company.

A pilot-plant test on desalination of soy sauce by nanofiltration

A pilot-plant test on desalination of soy sauce was performed with spiral-wound nanofiltration (NF) membrane modules. NF270 was found to be the most suitable for desalination of soy sauce due to its high permeate flux, though the rejection of amino nitrogen slightly decreased with increasing operation temperature. Soy sauce permeate was further concentrated to yield light-color soy sauce by Desal-5 DK, another membrane with higher rejection of organic matter but lower permeate flux than those of NF270. Glutamic acid and aspartic acid in soy sauce had highest retention by NF270 while glycine passed through membrane most easily. Under constant transmembrane pressure (TMP) condition, the mode that diluted soy sauce was directly concentrated to eligible product was found to be the most suitable one in terms of processing time and operation cost. Productivity for low-salt soy sauce decreased significantly in the early stage of operation and then kept constant for a long-term operation. With application of a composite cleaning agent containing alkali, surfactant and enzyme at a low concentration for a short duration, the flux of the severely fouled membrane could be completely recovered, suggesting that it could be feasible to produce low-salt soy sauce by NF technology.

Effective fouling inhibition by critical flux based optimization methods on a NF membrane module for olive mill wastewater treatment

The operation of a spiral-wound nanofiltration membrane module used continuously for three years in order to purify different pretreated olive mill wastewater streams will be discussed. The membrane module was for the first time used at the beginning of year 2006 on a batch pilot scale plant for critical flux studies and wastewater treatment in our laboratories. The olive mill wastewater is a waste stream produced by the olive oil mill factories, characterized by very high organic matter load and polyphenols concentration. Without fouling inhibition at all, nanofiltration membranes will reach zero-flux conditions within days. This is not the case of this nanofiltration membrane module, which was successfully operated continuously for three years during our laboratory work. This result was reached by proper fouling inhibition control, relaying on both critical flux measurements and the development of an optimized operation method. Moreover, supercritical operation experiments were performed on another nanofiltration module of the same model in order to validate the approach.

Water purification from pesticides by spiral wound nanofiltration membrane

An alternative ultrafiltration membrane integrity test was already developed in laboratory scale. It is based on the use of magnetic nanoparticles (Fe3O4) and measurement of magnetic susceptibility. The mean size of nanoparticles used is around 35 nm and they show a good disparity between 20 and 100 nm. In this paper, validation of this membrane integrity monitoring method was achieved by industrialscale tests. Two holes with 0.6 mm internal diameter in a module containing 10 000 fibers (35 m2 surface area) was efficiently detected by injecting 750 mL of 1.7 g.L−1 nanoparticle solution during 2s when the test was operated at low TMP (0.096 bar, corresponding to a flux of 2.2 m3.h−1). In addition, it has been demonstrated that within the detectable range, this membrane integrity test with magnetic nanoparticles has a very rapid response time. The response time depends on the permeate flux and the dead-volume of the pilot. This membrane integrity test, with the advantages of on-line operation, high detection sensitivity, detection specificity and very low influence on membrane fouling, seems to be suitable for large scale drinking water plants.