The effect of NaCl and glucose concentration on retentions for nanofiltration membranes processing concentrated solutions

Characteristics of polycyclic aromatic hydrocarbons (PAHs) removal by nanofiltration with and without coexisting organics

Polycyclic aromatic hydrocarbons (PAHs) are contaminants of great concern owing to their persistence, toxicity, and bioaccumulation in aquatic environments. In this study, nanofiltration (NF) was used to investigate the removal of naphthalene (NAP) and phenanthrene (PHE) using three membranes of NF270, NF90, and DK. Subsequently, we examined the effects of coexisting organics on PAHs removal. Based on the results, DK was determined to be the optimal membrane for removing PAHs by comparing the membrane flux and pollutant rejection. The membrane flux reached 34.32 L/m2·h, and the NAP and PHE rejections were 92.21% and 97.85%, respectively, at transmembrane pressure (TMP) of 5 bar using DK. Coexisting organics decreased the membrane fluxes of NF270 and DK in the following order: protein > glucose > humic acid. The NAP and PHE rejections were obviously improved using NF270 in the following order: humic acid > protein > glucose. The PHE rejection was slightly improved using DK. A low concentration of organics could reduce the NAP rejection using DK; however, the NAP rejection could be restored at high concentrations of organics, except for humic acid. Coexisting organics could cause severe membrane fouling. The order of the effect of different coexisting organics on membrane fouling was protein > humic acid > glucose. The total investment and operating costs were about 1.47 and 0.187 million dollars, respectively, for treating PAHs solution using DK when the feed flow was 300 m3/d.

Quantifying uncertainty in nanofiltration transport models for enhanced metals recovery

To decarbonize our global energy system, sustainably harvesting metals from diverse sourcewaters is essential. Membrane-based processes have recently shown great promise in meeting these needs by achieving high metal ion selectivities with relatively low water and energy use. An example is nanofiltration, which harnesses steric, dielectric, and Donnan exclusion mechanisms to perform size- and charge-based fractionation of metal ions. To further optimize nanofiltration systems, multicomponent models are needed; however, conventional methods necessitate large amounts of data for model calibration, introduce substantial uncertainty into the characterization process, and often yield poor results when extrapolated. In this work, we develop a new computational architecture to alleviate these concerns. Specifically, we develop a framework that: (1) reduces the data requirement for model calibration to only charged species measurements; (2) eliminates uncertainty propagation problems present in conventional characterization processes; (3) enables exploration of pH optimization for enhancing metal ion selectivities; and (4) enables uncertainty quantification to assess the sensitivity of partition coefficients and ion driving forces to learned pore size distributions. Our framework captures eight independent datasets comprising over 500 measurements to within ±15%. Our studies also suggest that the expectation-maximization algorithm can effectively learn pore size distributions and that optimizing pH can improve metal ion selectivities by a factor of 3-10×. Our findings also reveal that image charges appear to play a less pronounced role in dielectric exclusion under the studied conditions and that ion driving forces are more sensitive to pore size distributions than partition coefficients.

Influence of pH and NaCl on the rejection of glycine and triglycine in binary solutions for desalination with diananofiltration

Nanofiltration can be used as the last step in the purification of the biomolecules that are present in many industrial by-products, such as biological protein hydrolysates. The present study explored the variation in glycine and triglycine rejections in binary solutions with NaCl at different feed pHs with two nanofiltration membranes: MPF-36 and Desal 5DK with molecular weight cut-offs of 1000 and 200 g mol^-1, respectively. First, water permeability coefficient showed a n-shaped curve with feed pH, which was more evident for the MPF-36 membrane. Second, membrane performance with single solutions was studied and the experimental data were fitted with the Donnan steric pore model with dielectric exclusion (DSPM-DE) to explain the variations of solute rejection with feed pHs. Glucose rejection was assessed to estimate the membrane pore radius of the MPF-36 membrane, and a pH dependence was observed. For a tight membrane (Desal 5DK), glucose rejection was close to unity and the membrane pore radius was estimated from the glycine rejection in the feed pH range from 3.7 to 8.4. Glycine and triglycine rejections showed a pH-dependence with a u-shaped curve, even for the zwitterion species. In binary solutions, glycine and triglycine rejections decreased with NaCl concentration, especially in the MPF-36 membrane. Triglycine rejection was always higher than NaCl rejection and it was estimated that triglycine can be desalted using a continuous diananofiltration the Desal 5DK membrane.

Dealcoholization of Unfiltered and Filtered Lager Beer by Hollow Fiber Polyelectrolyte Multilayer Nanofiltration Membranes-The Effect of Ion Rejection

Membrane-based beverage dealcoholization is a successful process for producing low- and non-alcoholic beer and represents a fast-growing industry. Polyamide NF and RO membranes are commonly applied for this process. Polyelectrolyte multilayer (PEM) NF membranes are emerging as industrially relevant species, and their unique properties (usually hollow fiber geometry, high and tunable selectivity, low fouling) underlines the importance of testing them in the food industry as well. To test PEM NF membranes for beer dealcoholization at a small pilot scale, we dealcoholized filtered and unfiltered lager beer with the tightest available commercial polyelectrolyte multilayer NF membrane (NX Filtration dNF40), which has a MWCO = 400 Da, which is quite high for these purposes. Dealcoholization is possible with a reasonable flux (10 L/m²h) at low pressures (5-8.6 bar) with a real extract loss of 15-18% and an alcohol passage of ~100%. Inorganic salt passage is high (which is typical for PEM NF membranes), which greatly affected beer flavor. During the dealcoholization process, the membrane underwent changes which substantially increased its salt rejection values (MgSO₄ passage decreased fourfold) while permeance loss was minimal (less than 10%). According to our sensory evaluation, the process yielded an acceptable tasting beer which could be greatly enhanced by the addition of the lost salts and glycerol.

Prediction of single salt rejection in PES/CMS based membranes

This study explains the modeling of synthesized membranes using the Donnan Steric Pore model (DSPM) based on the Extended Nernst Planck Equation (ENP). Conventionally, structural parameters required to predict the performance of the membranes were determined through tedious experimentation, which in this study are found using a new MATLAB technique. A MATLAB program is used to determine the unknown structural parameters such as effective charge density (X_d), effective pore radius (r_p), and effective membrane thickness to porosity ratio (Δx/A_k) by using the single solute rejection and permeation data. It was found that the model predicted the rejection of studied membranes accurately, with the E5C1 membrane exceeding the others (E5, E5C5) for rejection of single and divalent salt's aqueous solutions. The rejection of 100 ppm aqueous solution of NaCl for E5C1 was around 60%, whereas, for an aqueous solution of 100 ppm, CaCl₂ rejection reached up to 80% at 10 bar feed pressure. The trend of salt rejection for all three membranes was found to be in the following order: E5C1 > E5C5 > E5, confirming that their structural parameters-controlled ion transport in these membranes. The structural parameters, such as effective pore radius, effective membrane thickness to porosity ratio, and effective charge density for the best performing membrane, i.e., E5C1, were determined to be 0.5 nm, 16 μm, and -6.04 mol/m^3,respectively. Finally, it can be asserted that this method can be used to predict the real performance of membranes by significantly reducing the number of experiments previously required for the predictive modeling of nanofiltration-type membranes.

H2O2-Triggered Rapid Deposition of Poly(caffeic acid) Coatings: A Mechanism-Based Entry to Versatile and High-Efficient Molecular Separation

Plant-derived polyphenol coating offers a promising route to fabricate functional surfaces for different substrate materials. However, almost all of the deposition approaches are time-consuming and involve inefficient processes, and the mechanisms behind the coating deposition are rarely understood. Herein, we report a rational methodology to achieve the rapid deposition of poly(caffeic acid) (PCA) by using H₂O₂ as a trigger under the assistance of copper sulfate (CuSO₄). The comparative monomer structure of PCA oxidation polymerization has illustrated a significant distinction in the reaction path for PCA coating deposition which has never been reported before. Until now, the unprecedented fast velocity for polyphenol coating has been obtained, and the PCA coating exhibits excellent homogeneity, spatiotemporal tunability, and firm stability. Moreover, three different types of filtration membranes, poly(vinylidene fluoride) microfiltration membrane (PVDF MF membrane), poly(ether sulfone) (PES) ultrafiltration (UF) hollow fiber membrane, and PCA-coated PES nanofiltration (NF) membrane, are all successfully dip-coated using H₂O₂-triggered PCA coating. Without synthetic complexities and intricate procedures, the formation of hydrophilic and homogeneous PCA aggregates on the surface and/or inside pore walls resulted in various membranes. The as-prepared PCA-coated PVDF MF membrane demonstrates excellent oil/water separation efficiency of less than 150 ppm and a flux recovery rate of approximately 90% even after five cycles. By one-step co-deposition of PCA and poly(2-ethyl-2-oxazoline) (PEtOx) on the PES UF membrane surface, hydrophilicity and biofouling resistance are implemented for efficient protein filtration. The PES NF membrane formed by the PCA layer exhibits high mono-/divalent ion selectivity and excellent chlorine resistance. Overall, these results represent a rapid and sustainable approach to tailor PCA coatings for versatile liquid separation processes.

Simulation of Human Small Intestinal Digestion of Starch Using an In Vitro System Based on a Dialysis Membrane Process

This work deepens our understanding of starch digestion and the consequent absorption of hydrolytic products generated in the human small intestine. Gelatinized starch dispersions were digested with α-amylase in an in vitro intestinal digestion system (i-IDS) based on a dialysis membrane process. This study innovates with respect to the existing literature, because it considers the impact of simultaneous digestion and absorption processes occurring during the intestinal digestion of starchy foods and adopts phenomenological models that deal in a more realistic manner with the behavior found in the small intestine. Operating the i-IDS at different flow/dialysate flow ratios resulted in distinct generation and transfer curves of reducing sugars mass. This indicates that the operating conditions affected the mass transfer by diffusion and convection. However, the transfer process was also affected by membrane fouling, a dynamic phenomenon that occurred in the i-IDS. The experimental results were extrapolated to the human small intestine, where the times reached to transfer the hydrolytic products ranged between 30 and 64 min, according to the flow ratio used. We consider that the i-IDS is a versatile system that can be used for assessing and/or comparing digestion and absorption behaviors of different starch-based food matrices as found in the human small intestine, but the formation and interpretation of membrane fouling requires further studies for a better understanding at physiological level. In addition, further studies with the i-IDS are required if food matrices based on fat, proteins or more complex carbohydrates are of interest for testing. Moreover, a next improvement step of the i-IDS must include the simulation of some physiological events (e.g., electrolytes addition, enzyme activities, bile, dilution and pH) occurring in the human small intestine, in order to improve the comparison with in vivo data.

Assessment of Layer-By-Layer Modified Nanofiltration Membrane Stability in Phosphoric Acid

Nanofiltration (NF) can enable P recovery from waste streams via retaining multivalent impurities from spent pickling acid. However, with the currently available membranes, an economically feasible process is impossible. Layer-by-layer modified NF membranes are a promising solution for the recovery of P from acidic leachate. LbL membranes show a high level of versatility in terms of fine tuning for ion retention, which is necessary to achieve sufficient phosphorus yields. However, the stability of layer-by-layer modified membranes during phosphoric acid (H₃PO₄) filtration needs to be further investigated. In our study, we show that a polyethersulfone hollow fiber membrane modified with four or eight bi-layers was stable during immersing and filtering of a 15% H₃PO₄ solution. A sulfonated polyethersulfone (sPES)-based hollow fiber LbL membrane was only stable during filtration. Thus, we show the importance of applying real process conditions to evaluate membranes. Another important aspect is the influence of the high ionic strength of the feed solution on the membrane. We show that a high ionic strength led to a decrease in Mg retention, which could be increased to 85% by adjusting the process parameters.

Nanofiltration of Succinic Acid in Strong Alkaline Conditions

Nanofiltration is considered to be an appropriate separation technique in the production of bio-based materials. For the utilization of process streams from the viscose-fiber production, understanding the separation behavior of organic compounds in highly alkaline solutions is necessary. Experiments with succinic acid in sodium hydroxide (NaOH) solutions with varying concentrations up to 5 mol L-1 were performed with the NP030 membrane from Microdyn Nadir. Furthermore, experiments with aqueous disodium succinate and solutions of sodium sulfate in sodium hydroxide were carried out. The influence of concentration ratios and temperature was studied. The Spiegler and Kedem model as well as the Pusch model were applied to fit the experimental data. Additionally, scanning electron microscopy (SEM) and infrared (ATR-IR) measurements were performed to validate the chemical and thermomechanical stability of the membrane. The succinic acid retention varies with its degree of dissociation. In a fully dissociated form, the NaOH concentration shows no impact on the retention. In contrast, the retention of sulfate decreases with increasing NaOH concentration.

Robust Coatings via Catechol-Amine Codeposition: Mechanism, Kinetics, and Application

Bioinspired polyphenol/polyamine codeposition has been demonstrated by the competence for surface modification; however, the reaction processes including mechanism and kinetics remain superficially understood. In this work, the catechol (CA)-amine reaction has been thoroughly investigated by using CA and two amines m-phenylenediamine and piperazine. We verify that both primary and secondary amines are prone to link with CA through Michael addition to form polyphenol/polyamine oligomers under aerobic and mild-alkaline conditions. Molecular simulations indicate that the Michael addition products are dominant for both aromatic and aliphatic amines with CA, which supports the durable chem- and phystability of the codeposited coatings. The aggregation kinetics of polyphenol/polyamine is provided for the first time, and the formed aggregates show high-adhesive properties, which can be deposited as the skin layers for high-performance nanofiltration membranes.

Dual-Charged Hollow Fiber Membranes for Low-Pressure Nanofiltration Based on Polyelectrolyte Complexes: One-Step Fabrication with Tailored Functionalities

A new nanofiltration (NF) hollow fiber membrane is developed by using two oppositely charged polyelectrolytes coagulating into a polyelectrolyte complex (PEC) onto polyether sulfone base polymer. The particular membrane architecture emerges during a single-step procedure, allowing setting both the porous negatively charged support of the hollow fiber and the separation layer containing also the positive polyelectrolyte (PEI/PDADMAC) through a single layer dry-jet wet spinning process. The novelty is two-pronged: the composition of the hollow fiber membrane itself and its fabrication procedure (one-step fabrication of membranes employing polyelectrolytes). These result in highly permeable hollow fiber membranes with a stable separation layer and performance at par with the membranes reported in literature obtained by multistep processes. More importantly, the membranes are obtained through a simple, very fast (one-step), and less expensive procedure. The best performance among these newly obtained hollow-fiber membranes is achieved by PD5% hollow fiber (MWCO of 300 Da), which showed 7.6 L/m(2)·h·bar permeability and ∼90% rejection of MgCl2, MgSO4, and Na2SO4 at 2 bar pressure. Thus, the resulting membranes not only have the advantages of the hollow-fiber configuration, but perform very well at extremely low pressures (the lowest reported in the literature). The broad impact of the results presented in this Article lies in the potential to dramatically reduce both the fabrication (duration and complexity) and the price and desalination costs of highly performing NF hollow fiber membranes. These might result in interesting potential applications and open new directions toward designing efficient functional NF hollow fibers for water desalination.