DK Membrane Research Articles

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.

Optimization and modeling of diananofiltration process for the detoxification of ligno-cellulosic hydrolysates - Study at pre-industrial scale

In order to improve bioethanol production by yeast fermentation of lignocellulosic hydrolysates, sugar/inhibitor separation by nanofiltration was studied on a bench-scale unit equipped with a spiral-wound membrane. Therefore, a model solution containing 3 sugars and 4 inhibitors was treated with two previously selected membranes (NF270 from DOW Filmtec and DK from GE Osmonics). Both membranes led to high sugar rejection, especially at high permeate flux (>90% for glucose and arabinose and >85% for xylose). Although its water permeability was smaller, DK membrane was preferred for its higher transmission of the inhibitors, especially for the largest ones (vanillin and 5-hydroxymethyl furfural), ensuring a better detoxification level. Diafiltration was applied to improve sugar purity of the treated hydrolysate. With a diavolume equivalent to 1.25 times that of the feed, acetic acid concentration was divided by 5 and brought back to concentrations lower than 1gL−1. A simulation model was proposed to predict the diavolume to apply, depending on the initial concentrations. Finally, processed hydrolysates were tested for the fermentation ability with a Pichia stipitis species. Fermentation tests showed that diafiltration followed by concentration led to retentates as fermentable as an equivalent pure sugars solution.

Comparison of NF membrane fouling and cleaning by two pretreatment strategies for the advanced treatment of antibiotic production wastewater.

The nanofiltration (NF) membrane fouling characteristics and cleaning strategies were investigated and compared for treating membrane bioreactor (MBR) effluent and MBR-granular activated carbon (GAC) effluent of an antibiotic production wastewater by DK membrane. Results showed that the fouling of treating MBR effluent was more severe than that of treating MBR-GAC effluent. After filtering for 216 h, the difference of membrane flux decline was obvious between MBR effluent and MBR-GAC effluent, with 14.9% and 10.3% flux decline, respectively. Further study showed that organic fouling is the main NF membrane fouling in the advanced treatment of antibiotic production wastewater for both of the two different effluents. Soluble microbial by-product like and tyrosine-like substances were the dominant components in the foulants, whereas humic-like substances existing in the effluents had little contribution to the NF membrane fouling. A satisfactory efficiency of NF chemical cleaning could be obtained using combination of acid (HCl, pH 2.0-2.5) and alkali (NaOH + 0.3 wt% NaDS, pH 10.0-10.5). The favorable cleaning strategy is acid-alkali for treating the MBR-GAC effluent, while it is alkali-acid for treating the MBR effluent.

Ultrasound assisted extraction and nanofiltration of phenolic compounds from artichoke solid wastes

Artichoke wastes from the canning industry are rich in phenolic compounds, which can be used as food additives. This study aims to evaluate the potential of sequential process based on the use of ultrasound extraction and membrane technology for phenolic recovery. In the extraction step, solvent composition and ultrasound power were evaluated to understand their impact on phenolic content and antioxidant capacity. The highest yields were observed for extracts with higher ethanol content (50 and 75%). Therefore, these extracts were selected for concentration by nanofiltration in a tangential module, using differents membranes (NF270, DK and DL). The flux decrease and the phenolic retention were evaluated. Hermia's models and membrane surface characterization were used to investigate the fouling. The highest flux was observed for extracts with 50% of ethanol with a retention of chlorogenic acid higher than 95%. DK membrane showed to be less susceptible to fouling, although the cake formation occurred in all evaluated membranes. The most suitable process condition to obtain the highest phenolic yields was extraction with 50% ethanol and an ultrasound power of 240 W and extracts nanofiltration using DK membrane.

Fouling characteristics and cleaning strategies of NF membranes for the advanced treatment of antibiotic production wastewater.

The nanofiltration (NF) membrane fouling characteristics and cleaning strategies were investigated through a laboratory-scale NF fouling test treating membrane bioreactor (MBR) effluent and MBR-granular activated carbon (GAC) effluent of an antibiotic production wastewater by DK and NF90 membranes, respectively. Results showed that organic fouling is the main NF membrane fouling for treating both the MBR effluent and MBR-GAC effluent. Soluble microbial by-product (SMP)-like and aromatic protein-like substances were the dominant components in the foulants, whereas humic-like substances had little contribution to the NF fouling. The fouling of DK was more severe than that of NF90. However, foulants respond by UV254 were more easily to foul NF90 membrane. It could get satisfactory effect using combined cleaning of acid (HCl, pH2.0∼2.5) and alkali (NaOH + 0.3wt% NaDS, pH10.0∼10.5). The favorable cleaning strategy is "acid + alkali" for treating MBR-GAC effluent, while it is "alkali + acid" for treating MBR effluent.

Two-stage nanofiltration process for high-value chemical production from hydrolysates of lignocellulosic biomass through hydrothermal liquefaction

Two-stage nanofiltration (TSNF) process was proposed for recovering high-value chemicals, including monophenols, cyclopentenones, glucose and acetic acid, from hydrolysates of lignocellulosic biomass (rice straw) through hydrothermal liquefaction (HTL). The separation performances of three single nanofiltration (NF) processes and three TSNF processes were studied. Results showed that at the first stage of (DL+DK) TSNF process, DL membrane had high glucose rejection of 97.12%, and lower acetic acid rejection as well as lower aromatics rejections than DK membrane. At the second stage, DK membrane had rather low acetic acid rejection of 5.04% to ensure acid separation from aromatics. Unlike glucose or acetic acid, aromatics were unable to be recovered into one fraction due to scattered rejections of different aromatic compounds on NF membrane. The (DL+DK) TSNF process was proved to be a feasible way to fractionate hydrolysates into three parts: glucose concentrate, monophenols and cyclopentenones concentrate, and acetic acid permeate.

A two-step nanofiltration process for the production of phenolic-rich fractions from artichoke aqueous extracts.

Commercial nanofiltration (NF) membranes in spiral-wound configuration (NP030 from Microdyn Nadir and Desal DK from GE Water & Process Technologies) were used in a sequential design in order to produce a separated fraction of phenolic and sugar compounds from an aqueous artichoke extract. For both membranes, the effect of transmembrane pressure (TMP) on the permeation flux was evaluated. In optimized conditions of TMP, the NP030 membrane exhibited high rejections of apigenin, cynarin and chlorogenic acid (higher than 85%); on the other hand, very low rejections of fructose, glucose and sucrose (lower than 4%) were measured. Starting from an extract with a total antioxidant activity (TAA) of 5.28 mM trolox a retentate fraction with a TAA of 47.75 mM trolox was obtained. The NF permeate from the NP030 membrane was processed with the Desal DK membrane in optimized conditions of TMP producing a permeate stream free of phenolic and sugar compounds. Accordingly, as most part of phenolic compounds was removed in the first NF step, the concentration of sugar compounds in the NF retentate had much higher results than that of phenolic compounds.

Characterization of the isolated active layer of a NF membrane by electrochemical impedance spectroscopy

The dielectric and electric properties of the isolated active layer of an NF membrane were determined by electrochemical impedance spectroscopy (EIS). To our knowledge, this was the first attempt aimed at assessing the above properties from measurements performed directly on the active layer alone. Experiments were conducted with Desal DK membrane and various electrolyte solutions (KCl, KI, LiCl, NH4Cl, CaCl2 and BaCl2) at 10−2 mol m−3. The comparison of impedance spectra obtained for the whole membrane and active layer alone revealed very low contribution of the active layer to the overall membrane impedance. The dielectric constant (εp) and conductivity (κca) inside the pores of the active layer were evaluated from capacity and resistance measurements. The dielectric constant inside the pores was found to be smaller than its bulk value, irrespective of the electrolyte used. The reduction in εp was attributed only to confinement effect. It was also shown that pore conductivity exceeded the bulk conductivity. This increased conduction inside the pores could have been due to the excess of counter-ions inside the pores resulting from fixed charges on the pore walls. The present study shows that the dielectric constant inside the pores of the active layer of NF membranes can be determined independently from nano-filtration measurements and without any ambiguity, provided that EIS measurements are performed directly on the isolated active layer.

Nanofiltration of glucose: Analysis of parameters and membrane characterization

Membrane characterization and modeling of nanofiltration processes of uncharged solutes are of special interest for the food industry. In this work two commercial membranes, DK and DL, were used to concentrate glucose solutions. Membranes were characterized according hydrophobicity, thickness, porosity, and hydraulic permeability. The influence of pressure and concentration of glucose on the permeate flux and rejection were studied. Both membranes presented a great potential for the food industry due to their high rejection of glucose. The osmotic pressure model was combined with film theory and the real driven force was calculated taking into account the osmotic pressure and the concentration polarization. Both phenomena influenced the process (concentration polarization only in the most dilute solutions at low pressure) and the permeability for glucose solutions was similar to the hydraulic permeability. A mathematical model based on the Donnan-Steric Pore Model was used to determine the pore radius and the effective thickness of both membranes. As the concentration inside the pore (needed for the calculations) is difficult to measure experimentally, various alternatives were proposed. The average of the concentration at the interface and permeate best fitted the experimental data. The model was applied successfully; the maximum error was 8% within the range of concentrations (5–100g/L) for the DL membrane and 5% for the DK membrane up to 50g/L.

Rejection and modeling of arsenate by nanofiltration: Contributions of convection, diffusion and electromigration to arsenic transport

Nanofiltration (NF) membranes, DK and DL, were characterized by attenuated total reflection-Fourier transform infrared spectroscopy, surface charge titration, pore size determination and salt rejection. The results showed both membranes have amide I and carbonyl groups on their surfaces, and have the same basic structure of polyamide layer sitting on the top of a polysulfone layer. The DK membrane carries more negative charges in the entire pH range investigated. Arsenate rejections by the NF membranes were evaluated with a crossflow test setup. The effects of pH, ionic strength, operating pressure, arsenate initial concentration on the membrane performance were investigated. Mass transfer coefficients of the membranes were determined experimentally. The Donann Steric Pore Model and concentration polarization film theory were applied to calculate the arsenic rejection rate. The rejection mechanism was interpreted by calculating the contributions of convection, diffusion, and electrostatic migration to arsenic transport through the membranes. The calculated results showed that the contribution of diffusive transport dominated at low flux, and convection and electromigrative transport, especially the latter, play an increasingly important role at a high flux.

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.

Recovery of volatile fatty acids (VFA) from complex waste effluents using membranes

Waste effluents from anaerobic digesters of agricultural waste were treated with a range of membranes, including microfiltration and nanofiltration (NF), to concentrate volatile fatty acids (VFA). Microfiltration was applied successfully to produce sterile, particle-free solutions with a VFA concentration of 21.08 mM of acetic acid and 15.81 mM of butyric acid. These were further treated using a variety of NF membranes: NF270 (Dow Chemicals, USA), HL, DL, DK (Osmonics, USA) and LF10 (Nitto Denko, Japan), achieving retention ratios of up to 75%, and giving retentates of up to 53.94 mM of acetate and 28.38 mM of butyrate. DK and NF270 membranes were identified as the best candidates for VFA separation and concentration from these multicomponent effluents, both in terms of retention and permeate flux. When the effluents are adjusted to alkali conditions, the highest productivity, retention and flux were achieved at pH 7. At higher pH there was a significant reduction in flux.

Separation of three divalent cations (Cu2 +, Co2 + and Ni2 +) by NF membranes from pHs 3 to 5

Separation mechanisms for the three model divalent cations with very similar atomic weights (Cu, 63.5Da; Co, 58.9Da and Ni, 58.7Da) by two nanofiltration (NF) membranes (Nitto Denko ESNA and GE Osmonics DK) were studied in a cross flow module from pHs3 to 5. The results show that the rejection order for the two selected membranes was Ni2+>Cu2+>Co2+ from the conducted experiments, and the removal efficiency was increased as pH was decreased for all three metals. It was found that enthalpy of hydration and concentration polarization exerted the controlling effect on the membrane selective transport rather than atomic weight, Stokes radius and hydrated radius. Besides, the counterion of sulfate enhanced the removal efficiencies, but an increase of sulfate more than 0.01M reduced the removal efficiencies. Moreover, the removal efficiency of DK membrane was better than that of the ESNA membrane due to the positive charge of DK membrane at low pH.

Insights into nanofiltration of textile wastewaters for water reuse

Textile industry constitutes nowadays one the largest consumers of water, and consequently the wastewater reuse can be a profitable operation. In this study, the decontamination of pure dyes solutions (Remazol Turquoise Blue G, Remazol Yellow GR and Lanaset Blue 2R) and synthetic textile wastewaters was evaluated in a nanofiltration (NF) cross-flow cell, using polyamide NF membranes, NF90 and DK, with molecular weight cut-off between 200–400 Da and 150–300 Da, respectively. Permeate flux and the color reduction were evaluated for the different dye solutions under different temperature and pH conditions and, NaCl, wetting and dispersant concentrations. DK membrane showed the best results in terms of permeate flux for all the dye solutions tested. The highest permeate flux was achieved for higher temperatures under acidic to neutral pHs values, resulting in almost 100 % color removal for all situations.

Limitation of hardness from thermal water by means of nanofiltration

Geothermal conditions are extremely favourable in Hungary. Thermal water is accessible in 70% of the territory of the country, with a lowest temperature of 30°C. For energetic purposes, it can be utilized in two different ways: for supplying heat or generating electricity. In relation to utilization, one of the most serious problems derives from the chemical composition of thermal water. The present paper investigates the opportunities of preventing scaling by nanofiltration. Experiments were performed on a Thin Film NF DK membrane, thermostated at 50°C and at a pressure of 3.5 MPa with four different samples (from four Hungarian cities - Eger, Mezőkövesd, Bogács, Miskolc-Tapolca) using batch plant. Reproducibility of experiments was also investigated using water samples from Komárom at 50 and 60°C. The results showed that NF DK could achieve high retention of divalent ions. The results of the second phase of the experiments proved that water flux and rejections were very stable. After filtration, the scaling properties of thermal water were simulated with the help of chemical equilibrium modelling software, called Visual MINTEQ 3.0. The results of the permeate samples prove that nanofiltration is a successful process in preventing scaling of thermal water for further use.

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.

Nanofiltration process of glyphosate simulated wastewater

Nanofiltration separation of glyphosate simulated wastewater was investigated using a DK membrane. The effects of operating parameters and the addition of impurities on membrane performance were studied in detail. It was found that at 20 °C, with a glyphosate concentration of 500 mg/L and pH of 2.96, the glyphosate retention rate and the membrane permeate flux increased slightly with increasing transmembrane pressure. With an increase in operating temperature, the permeate flux increased linearly while the retention rate decreased. The permeate flux and glyphosate retention rate decreased with increasing feed concentration. Within the pH range of 3-5, the glyphosate retention rate decreases with increasing pH and reaches a minimum at the isoelectric point of the membrane, while the permeate flux reaches a maximum level at this point. In the pH range of 5-11, with the increases of pH, the glyphosate retention rate increases and the permeate flux decreases. Glyphosate retention decreases slightly with increasing NaCl and phosphite concentrations. This can be explained in terms of the shielding phenomenon.

Back-Propagation Model for Nanofiltration Process Simulation in Pesticide Wastewater Treatment

This study simulated the nanofiltration (NF) process of contamination removing by back-propagation neural network (BPNN), according to the test values of DK membrane pre-treating Imidacloprid pesticide wastewater. The real time nanofiltration (NF) separation model was presented for effective controlling of DK NF separation. The research showed the simulation precision met the application demands, with the correlation coefficient between the simulation and test rejection of COD and salt over 0.99, and absoluteness error below ±4%. In order to test the prediction of this BPNN simulation model, further NF experiments were carried out. Under the same multifactor condition, the predictions for the NF process performances were found to be in good agreement with the experimental results. This BP simulation model for NF process could be used to test the stability and effectively of NF system, and support the membrane technology well.

Application of NF-RDM (nanofiltration rotating disk membrane) module under extreme hydraulic conditions for the treatment of dairy wastewater

Dairy wastewater can be concentrated by membrane technology to produce reusable water, and the retentate with high concentration could be reutilized as feed supplement for animals or substrate for biohydrogen production. Treatment of a model dairy wastewater (diluted skim milk) by nanofiltration (NF) with a rotating disk membrane (RDM) module was investigated using a NF membrane NF270 (Dow-Filmtec). Compared with the Desal-5 DK (Ge-Osmonics) membrane studied previously, the NF270 membrane gave much higher permeate flux, but same rejection. At a high enough shear rate for reducing concentration polarization, permeate flux and solutes rejection increased while specific energy per m 3 of permeate decreased when transmembrane pressure (TMP) rose from 10 to 40 bar. Because the RDM module could produce very high shear rates, concentration of dairy wastewater by NF could be operated under extreme hydraulic conditions that combined extreme TMP with high shear rate. Process efficiency and permeate quality were improved by operating under these condition, while membrane fouling was a little higher than when operating below critical flux. A real dairy wastewater was also treated by NF270 under same hydraulic conditions, and results were very similar to those of model solution. Membrane fouling was decreased by raising pH above 9. Irreversible fouling was almost removed using a commercial cleaning agent at high shear rate in a short time. The RDM module appeared to be a suitable technology to treat dairy waste without any biological and chemical treatments. Permeate qualities were suitable for reuse or discharge in river. These results from laboratory-scale tests can be very useful in the analysis of membrane process under extreme hydraulic conditions and can serve as valuable guide for process design in industrial application.