DL Membrane Research Articles

Comparative study of the removal of heavy metals by two nanofiltration membranes

This study describes the rejection of heavy metal ions (Cu(II), Cd(II), and Zn(II)) using two commercial nanofiltration membranes (DL and DK). The effect of transmembrane pressure and metal concentration on the metal rejections and permeate flux was explored. The results showed that for DL membrane the maximum rejection was obtained at ΔP = 4 bar for all studied heavy metals. The rejections of Zn, Cu, and Cd were 93, 90, and 86%, respectively, when the concentration of each heavy metal was fixed to 10−5 mol/L and were 79, 76, and 78%, respectively, when the concentration of each heavy metal was fixed to 10−3 mol/L. The rejection sequence was identical for both membranes (RCu < RZn < RCd). However, the transmembrane pressure and the metal concentration had no great effect on rejection factors in the case of DK membrane. The variation of the permeate flux vs. the transmembrane pressure after treating different mixtures containing Cu(II), Cd(II), and Zn(II) metals by nanofiltration using DL and DK membranes was studied. A deviation from the straight line representing Jv vs. ΔP of different mixtures studied compared to pure water line was observed, but it was much more important in the case of DL membrane confirming a greater sensitivity to pores clogging.

Valorization of artichoke wastewaters by integrated membrane process

In this work an integrated membrane system was developed on laboratory scale to fractionate artichoke wastewaters. In particular, a preliminary ultrafiltration (UF) step, based on the use of hollow fibre membranes, was investigated to remove suspended solids from an artichoke extract. The clarified solution was then submitted to a nanofiltration (NF) step. Two different 2.5 × 21 in. spiral-wound membranes (Desal DL and NP030) with different properties were investigated. Both membranes showed a high rejection towards the phenolic compounds analysed (chlorogenic acid, cynarin and apigenin-7-O-glucoside) and, consequently, towards the total antioxidant activity (TAA). On the other hand, the Desal DL membrane was characterized by a high rejection towards sugar compounds (glucose, fructose and sucrose) (100%) when compared with the NP030 membrane (4.02%).The performance of selected membranes in terms of permeate flux, fouling index and water permeability recovery was also evaluated.On the base of experimental results, an integrated membrane process for the fractionation of artichoke wastewaters was proposed. This conceptual process design permitted to obtain different valuable products: a retentate fraction (from the NP030 membrane) enriched in phenolic compounds suitable for nutraceutical, cosmeceutical or food application; a retentate fraction (from the Desal DL membrane), enriched in sugar compounds, of interest for food applications; a clear permeate (from the Desal DL membrane) which can be reused as process water or for membrane cleaning.

Application of the solution-diffusion model for the removal of atrazine using a nanofiltration membrane

The solution-diffusion model was used to predict the behaviour of four nanofiltration membranes, two were made of polyamide (NF-99 and NF-97) and the other two were made of polypiperazineamide (DL and DK), when used for the removal of atrazine from aqueous solutions. The mass transfer model applied is very simple and its linearization facilitates rapid calculation of the relevant parameters. The two main parameters, permeate concentration and volumetric permeate flux, are obtained from three different coefficients: water permeability, Aw, solute permeability, Bs, and osmotic pressure coefficients, Ψ. Good agreement between the experimental and the predicted atrazine concentrations was obtained for the NF-99, DL and DK membranes when the concentration was low. However, only the NF-99 membrane provided accurate values for the two main parameters in the whole range of concentrations studied, which suggests that the solution-diffusion model can only be applied to this membrane.

Removal of Higher Fatty Acid Esters from Taiwanese Rice-Spirits by Nanofiltration

The amounts of the three higher fatty acid esters (ethyl palmitate, ethyl oletate, and ethyl linolenate) in rice spirit were significantly decreased, over 65 % through nanofiltration (NF) with DK or DL membranes, compared to the 26–42 % reduction observed for an ultrafiltration membrane. The molecular weight cut-off was the main factor for the removal of the higher fatty acid esters. In addition, the rejection rates were increased with operating pressures; 60 psi was the most suitable pressure for the NF system. Not less than 80 % of higher fatty acid esters could be removed by the DK membrane under 60 psi pressure at 4 °C; only slight changes in physicochemical indices, including the ethanol concentration, flavor, and total acidity were observed for rice spirits following the NF treatment. On the other hand, the fusel alcohols in the treated-rice spirits were simultaneously decreased from 4.5 to 2.5 g/L (reaching the Chinese National Standard, below 3.3 g/L) and the product achieved a higher score in color via sensory evaluation. We anticipate a practical application of non-heat processes, such as NF, in Taiwanese rice spirits production due to the quality improvement achieved thereby.

Preparation and performance of dynamic layer-by-layer PDADMAC/PSS nanofiltration membrane

Dynamic layer-by-layer (LBL) self-assembly technology was used to prepare as few as three to five bilayers of poly(diallyl-dimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) on negatively charged polysulfone (PS) ultrafiltration (UF) membranes of 50kDa MWCO and compared with those of the static assembly membranes. The prepared dynamic assembly (PDADMAC/PSS)4 nanofiltration (NF) membrane showed a permeation flux of 60Lm−2h−1 at 1.0MPa, much higher than that of the commercial DL membrane (GE Osmonics, USA), but with a rejection of about 90% of SO42− which is relatively less than that of the DL membrane. The rejection performance showed that the dynamic–static assembly was more effective than others. Using dynamic–static assembly preparation, the rejection of (PDADMAC/PSS)3 membrane was about 90%, while the flux was about 55Lm−2h−1 at 1.0MPa. The surface morphology of the prepared LBL membranes were characterized by SEM and AFM, and no defect was found. The surface morphology of the membrane prepared by dynamic–static assembly was almost the same as the commercial membranes. The analysis of filtration resistance indicated that the deposition of the first and second bilayer was crucial during the whole preparation process.

Selective separation of seawater Mg 2+ ions for use in downstream water treatment processes

A nanofiltration-based method is presented for selectively separating soluble Mg(II) species from seawater, with the aim of using the Mg-loaded brine for either enriching desalinated water with magnesium ions or for enhancing precipitation of struvite from wastewater steams. Two 2.4″ commercial NF membranes were tested under varying operational conditions. The membrane that was chosen for further investigation (DS-5 DL, Osmonics) showed lower Cl:Mg and Na:Mg concentration ratios in the brine, and improved performance (with respect to the investigated process) at high recovery values. Since the addition of antiscalants was perceived detrimental to the downstream uses of the brine, the aquatic chemistry program PHREEQC was used to simulate the critical (highest) recovery values at which no CaSO 4 would precipitate, assuming two concentration polarization factors. To prevent CaCO 3 precipitation at the critical recovery values a theoretical calculation was performed (PHREEQC) to determine the required strong acid dosages to the raw seawater. Using the DS-5 DL membrane at 64% recovery, the attained Mg(II) concentration in the brine was 3500 mg/l. Therefore, for attaining 12.15 mg Mg/l of desalinated water the brine should be dosed to the water at a 1:288 ratio, resulting in additional concentrations of 32.5 mg SO 4 −2/l, 89.3 mg Cl −/l, 39.4 mg Na +/l, 3.3 mg Ca +2/l, and 0.01 mg B/l. The overall cost of the proposed process was estimated at 0.00098 $/m 3 product water, i.e. approximately five times lower than two assessed alternative processes and more than one order of magnitude cheaper than implementing direct dissolution of chemicals, using either MgCl 2 or MgSO 4.

Selection of membranes for purification of fructooligosaccharides

The aim of this study was to purify fructooligosaccharides (FOS) present in a mixture of sugars, containing also glucose, fructose and sucrose through, nanofiltration membranes. Four membranes were used: NP010 and NP030 (Microdyn Nadir, Germany), Desal−5 DL and Desal−5 HL (GE Water & Process Technologies). Experimental assays were performed in a dead-end cell and tangential cell filtration to select the most appropriate membrane. Then, with the membrane selected performed diafi ltration in tangential cell fi ltration up to a concentration about 80% FOS. In the dead-end filtration cell experiments the NP010, NP030, HL and DL membranes were selected, since they performed the highest retentions of FOS, and lowest retention of glucose. The results showed that NP030 membrane performed the highest differences between the retention of FOS and sucrose, where the retentions of the different saccharides were: fructooligosaccharides (Robs = 0.66), glucose (R obs = 0.18), fructose (R obs = 0.15) and sucrose (R obs = 0.24). The results clearly demonstrate the potential of diafiltration using the NP030 membrane in the purification of FOS from mixtures containing mono and disaccharides.

Removal of glyphosate in neutralization liquor from the glycine-dimethylphosphit process by nanofiltration

Nanofiltration (NF) was investigated for the removal of glyphosate in the neutralization liquor produced by the glycine-dimethylphosphit process. The Desal-5 DK membrane was chosen as the most suitable membrane for the NF process when compared to the DL and NTR7450 membranes according to retention of glyphosate and the permeate flux. The effects of applied pressure, temperature, and feed pH on the performances of the DK membrane were investigated. An applied pressure of 2 MPa was found to be optimum since a high glyphosate rejection of 95.5% was obtained with a high flux of 7.32 L/(h m 2); temperature had a slight impact on the retention of glyphosate with an increase in flux; both the minimum glyphosate retention and maximum permeate flux were achieved when the feed pH was around the isoelectric point of the DK membrane. In batch NF, the permeate flux decreased gradually but glyphosate rejection remained higher than 90%. After 8 h of NF, glyphosate recovery from the neutralization liquor reached 89.6% with an average permeate flux of around 4 L/(h m 2). Moreover, membrane surface crystallization induced by concentration polarization probably caused the flux to decline during the process of batch NF.

Application of nanofiltration models for the prediction of lactose retention using three modes of operation

The desal 5 DL membrane (Dow Chemical, USA) was used to recover lactose from whey ultrafiltration permeate. Lactose and ions rejection and permeate flux were measured using ultrafiltered sweet whey as feed solution. Three different operation modes (total recycle mode, concentration mode and continuous diafiltration mode) were considered. Lactose retention was predicted by means of the Donnan Steric Partioning model (DSPM) and the Kedem–Spiegler model (KSM). The best fit for the total recycle and concentration modes was obtained with the KSM. Moreover, the KSM predictions were worse for the CDM. These models contribute to a better understanding of the transport mechanisms involved in nanofiltration processes and to optimize the process at industrial scale. The two models can be considered as a useful tool to improve the recovery, demineralization and concentration of lactose.

Develop a Novel Method for Removing Fusel Alcohols from Rice Spirits Using Nanofiltration

The removal effect on excessive fusel alcohols from rice spirits were investigated using nanofiltration (NF) and ultrafiltration (UF). Compared to UF (GE and GH membranes), NF (DK and DL membranes) showed 10 times greater effect for fusel alcohols rejection due to molecular weight cut-off. On operating pressures, 488.95 kPa was suitable with a rejection rate attaining 44.2% for DK membrane. Only slight changes in physicochemical indices including ethanol concentration, flavor, total acidity, pH value, and soluble solid content were observed for rice-spirits after NF treatment. Moreover, rice spirits treated with the DK membrane achieved a higher score in sensory evaluation. We anticipated a practical application of the nonheat processes in rice spirits production.

Atrazine removal from aqueous solutions by nanofiltration

There is an increasing concern about the release of herbicides and other organic compounds to the environment as a result of agricultural activities, due to their high toxicity for living organisms and their difficult to be degraded. Triazines are widely used herbicides that are highly toxic and frequently appear in natural watercourses, atrazine being one of the most commonly detected herbicides in aquatic systems. The atrazine rejection coefficients and the permeate fluxes of different nanofiltration membranes (NF-99, NF-97, Desal-5-DL and Desal-5-DK) for the removal of atrazine from water solutions in different operating conditions (feed atrazine concentration, pressure and pH) are studied in this article. Atrazine rejection was greater with the NF 99 and NF 97 membranes (90–98%), while the DL and DK membranes show much lower rejections (40–50%). The highest permeate fluxes are obtained with NF-99 and DL membranes. Atrazine rejection and permeate flux show no dependence on the atrazine feed concentration, low dependence on pH and a high positive dependence on pressure (especially the permeate flux). The results are explained by taking into account different solute parameters and membrane properties that affect the nanofiltration process.

Application of membrane processes in closing of water cycle in a textile dye-house

In this study, investigations were made to close water cycle in dye-houses. At the first stage, optimum operation conditions of a membrane nanofiltration were determined. Experiments were carried out for DL membranes (Osmonics, USA). The effect of temperature, pressure and pH was investigated. Investigations were performed for different types of real wastewater produced in a laboratory-scale Pyrotec S dyeing apparatus (Roaches) for various types of reactive dyes. An over 90% dye hold-up was obtained for all dye baths. At the final stage of the experiments, dyeing processes were carried out with the use of a filtrate from nanofiltration as water applied for dyeing, rinsing and washing after dyeing. In cooperation with the Technical University of Lodz, we have managed to apply biological degradation of the concentrate, carried out in two different reactor systems.

Nanofiltration for Trace Organic Contaminant Removal: Structure, Solution, and Membrane Fouling Effects on the Rejection of Perfluorochemicals

The use of nanofiltration (NF) membranes for water recycling requires an improved understanding of the factors that govern rejection of potentially harmful organic trace contaminants. Rejections of 15 perfluorochemicals (PFCs)--5 perfluorinated sulfonates, 9 perfluorinated carboxylates, and perfluorooctane sulfonamide (FOSA)--by four nanofiltration membranes (NF270, NF200, DK, and DL) were measured. Rejections for anionic species were >95% for MW >300 g/mol. FOSA (MW = 499 g/mol), which is uncharged at the pH of deionized water (5.6), was rejected as little as 42% (DL membrane). Decreasing the pH to less than 3 decreases rejection by up to 35%, effectively increasing the MWCO of NF270 by >200 g/mol, while a 2500 mg/L NaCl equivalent increase in ionic strength reduces rejections <1%. An alginate fouling layer increases transmission, where quantifiable, by factors of 4-8. Accumulation of PFCs on membranes was measured after the completion of rejection experiments. Based on rejection kinetics and the extent of sorption, we infer that two different sorption processes are significant: charged species adsorb quickly to the membrane surface, whereas the uncharged FOSA absorbs within the membrane matrix in a much slower process.

Xylose recovery by nanofiltration from different hemicellulose hydrolyzate feeds

Xylose is an intermediate product in xylitol production. Nanofiltration could simplify and enhance this separation step conventionally done by chromatographic methods. Here different hemicellulose hydrolyzate feeds were nanofiltered to recover xylose into the permeate. Two different batches of hemicellulose hydrolyzate were prepared: the hydrolyzate as such and modified with crystalline xylose addition. Both feed solutions were diluted to a total dry solids (TDS) content of approximately 21 wt.% and the xylose contents were 48.7% and 59.1% of the TDS f (total dry solids in feed). The filtration experiments were made at 40, 50 and 60 °C in total reflux mode for approximately 30 min at each pressure of 20, 25, 30, 35 and 40 bar. In addition, a 20-h filtration was made at 50 °C and 30 bar. A DDS LabStak M20-filter was used and it was equipped with Desal-5 DK, Desal-5 DL and NF270 membranes. In short-term filtrations, the nanofiltered permeate of the original hydrolyzate had 78–82% xylose of the TDS p (total dry solids in permeate) and the modified hydrolyzate 86–88% xylose of the TDS p. Thus, considerable xylose purification was obtained. The addition of crystalline xylose into the hemicellulose hydrolyzate gave a notable increase in permeate fluxes. The 20-h filtration showed fouling and compaction effects as a flux decrease of approximately 10–25% was detected in the retention integrity test. According to the results, xylose purification from hemicellulose hydrolyzate could be enhanced by nanofiltration.

Experimental study on treatment of electroplating wastewater by nanofiltration

Nanofiltration (NF) was investigated for the treatment of an electroplating rinse wastewater containing Cu and Cr. Three NF membranes, DL, DK, and NTR-7450, were used in the experiment. Effects of pressure, temperature, and feed pH on membrane performance were investigated. With the rise of pressure, flux decline with time for DL and DK membranes was obvious. Flux of NTR-7450 membrane was stable at different pressure in the experiment. With the increase of pressure, the Cr and Cu rejections of three NF membranes increased slightly. With the rise of temperature, the permeate flux increased and rejections of Cr and Cu did not change obviously in the scope of this experiment. The change of flux with feed pH was not great generally. The permeate flux was minimum around the isoelectric points of the membranes. The Cr and Cu rejections for the feed with pH more than 7 were greater than that for the feed with pH less than 7. In the latter stage of the NF concentration process, flux decline behaviors of membranes were obvious. Stability investigation results showed that DK membrane had better stability in the raw electroplating wastewater with pH 2.32 than DL membrane.

Rejection of estrone by nanofiltration: Influence of solution chemistry

The objective of this study was to investigate the rejection of steroid hormone estrone by NF membranes as a function of feed water chemistry. Experimental results indicated that estrone rejection by NF membranes in electrolyte background solution decreased continuously during first 10 h and then stabilized. A clear pH-dependency was observed for estrone rejection. DL membrane exhibited a better performance in terms of estrone rejection at pH 10.4 because the electrostatic repulsion between the dissociated estrone molecules and highly negative-charged DL membrane reduced the proximity of estrone to the membrane surface. The presence of HA in feed solution appeared to improve both of estrone adsorption on membrane and estrone rejection. The lower the solution pH value, the higher amount of HA adsorbed on DL membrane and the greater the increment in adsorption of estrone on membrane by addition of HA. More importantly, it was found that, the presence of HA could enhance the rejection of estrone under all the pH conditions investigated in this study, with the greatest “enhancement effect” on estrone rejection at pH 4.

Comparison of the Behavior of Two Nanofiltration Membranes for Sweet Whey Demineralization

Nanofiltration is a process used to separate mineral salts from lactose, having previously removed the proteins by ultrafiltration. Both proteins and lactose can be used as raw materials to prepare a variety of products. In this paper, we studied the feasibility of demineralizing sweet whey obtained from the cheese industry of the Comunidad Valenciana (Spain) using membrane technologies. The NF200 membrane showed the highest volumetric flux and solute rejection values, whereas the DS-5 DL membrane showed the lowest values. The volumetric fluxes obtained with the NF200 and DS-5 DL membranes in these experiments with the ultra-filtered whey demonstrated significant differences between membranes. Concerning solute rejection, the highest values were obtained using the NF200 membrane. The chosen parameter to evaluate the demineralization capability was solute flux. In this way, the values obtained for chloride ion were 9.90 and 32.42 g/ (m2·h) for the NF200 and DS-5 DL membranes, respectively, with the highest demineralization rates being achieved with the DS-5 DL membrane.

Separation of xylose from glucose by nanofiltration from concentrated monosaccharide solutions

Complex separation of monosaccharides from each other is commercially carried out by chromatographic methods. The possibility of nanofiltration in a demanding separation of a pentose sugar, xylose, from a hexose sugar, glucose, is studied here. Xylose is an intermediate product in xylitol production and glucose interferes in the process. Feed solutions were made of xylose and glucose in different mass ratios and total monosaccharide concentrations. The mass ratios of xylose to glucose in solutions were 1:9, 1:1 and 9:1 and the monosaccharide concentrations of the solutions were 2, 10 and 30 wt.%. Desal-5 DK, -DL and NF270 membranes were used. Filtrations were done in total reflux mode (i.e. both permeate and retentate were recycled back to the feed tank) at 50 °C and the applied pressures were from 2 to 40 bar. The results indicate that the separation of xylose from glucose by nanofiltration is possible to a limited extent. The mass ratio of xylose to glucose in the permeate was 1.5–3.0 times higher than their ratio in the feed. The observed monosaccharide retentions depend highly on permeate flux, and retentions increase to certain reproducible level as pressure and consequently flux is increased. The observed xylose retentions were from 0 to 80% and the glucose retentions were from 10 to 90%. The effect of total monosaccharide concentration on the observed retention is smaller than the effect of flux. The largest difference between xylose and glucose retentions was detected at permeate fluxes between 5 to 30 kg m −2 h −1. The ratio of xylose to glucose in the feed had an influence on permeate flux and on xylose retentions. Xylose retentions decreased as the proportion of glucose increased in the feed. The higher the proportion of xylose in the feed the higher was the total permeate flux.

Treatment of wastewater during the production of reactive dyestuff using a spiral nanofiltration membrane system

In this study, a stage-2 spiral-wound nanofiltration (NF) system was used to further treat the permeate produced by a stage-1 tubular NF employed for treatment of dyestuff wastewater. Pilot-scale experiments were carried out to select the appropriate commercial NF membranes by investigating the TOC removal, color removal, the flux and VCR values, respectively. Compared with the Dow NF1 and Desal DL membranes, Desal DK NF membrane was selected for subsequent study. Using Desal DK NF membrane, the permeation flux could be kept at a relatively high value (>30 L.h −1.m −2) while the VCR reached 10.0. Meanwhile, the TOC values could be reduced to less than 400 ppm, which meets industrial requirements and would facilitate the subsequent bio-treatment unit. Based on the pilot-scale experiments, a full-scale system was set up, and the treatment system has been successfully implemented at a company in Thailand.

Cleaning results of new and fouled nanofiltration membrane characterized by zeta potential and permeability

In the membrane process industries, membrane cleaning is one of the most important concerns from both economical and scientific points of view. The characterisation of membrane surface by using zeta potential technique provides a more appropriate tool to study the cleaning performance and membrane integrity. The use of zeta potential technique to characterize the cleaning effect on membrane surfaces has very little precedence in literature. In this study the cleaning performance has been studied with membrane zeta potential and hydraulic permeability measurement. Virgin nanofiltration (NF) membranes provided by GE Osmonics (DK, HL and DL), as well as fouled DK membranes were used in this study. Several cleaning agents were investigated, some of them were analytical grade, such as HCl, NaOH and others were commercial grade agents that are already in use in commercial plants. Zeta potential of virgin and fouled NF membranes before and after chemical cleaning were measured and compared. The results of the zeta potential measurements with and without chemical cleaning of virgin and fouled membrane indicated that zeta potential may be used to characterise the membrane surface cleanliness and permeability. The effects of temperature, pH and the cleaning agents on membrane zeta potential were also investigated. The temperature was not found to have any significant effect on membrane zeta potential; however, the effect of pH and cleaning agents had pronounced effects on the surface charge and zeta potential. At high pH values mixed cleaning agents of mixture of trisodium phosphate, sodium tripolyphosphate and EDTA (recommended by membrane manufacturer) had a marked effect on zeta potential of HL and DL membranes compared to other cleaning agents. A DK fouled membrane was found to be almost negatively charged with no isoelectric point compared to a virgin DK membrane. At low pH, the zeta potential values of a fouled DK membrane were in close agreement with those obtained with an untreated virgin membrane after cleaning by NaOH followed by HCl. The zeta potential of all virgin membranes cleaned with SDS changed to more negative for the entire pH range compared to untreated virgin membranes. The study revealed that the SDS cleaning agent had the highest effect on surface charge for both virgin and fouled NF membranes.