Effect of varying piperazine concentration and post-modification on prepared nanofiltration membranes in selectively rejecting organic micropollutants and salts

Energy harvesting from acid mine drainage using a highly proton/ion-selective thin polyamide film

A huge chemical potential difference exists between the acid mine drainage (AMD) and the alkaline neutralization solution, which is wasted in the traditional AMD neutralization process. This study reports, for the first time, the harvest of this chemical potential energy through a controlled neutralization of AMD using H+-conductive films. Polyamide films with controllable thickness achieved much higher H+ conductance than a commercially available cation exchange membrane (CEM). Meanwhile, the optimal polyamide film had an excellent H+/Ca2+ selectivity of 63.7, over two orders of magnitude higher than that of the CEM (0.3). The combined advantages of fast proton transport and high proton/ion selectivity greatly enhanced the power generation of the AMD battery. The power density was 3.1 W m-2, which is over one order of magnitude higher than that of the commercial CEM (0.2 W m-2). Our study provides a new sustainable solution to address the environmental issues of AMD while simultaneously enabling clean energy production.

Double charge flips of polyamide membrane by ionic liquid-decoupled bulk and interfacial diffusion for on-demand nanofiltration

Fine design of surface charge properties of polyamide membranes is crucial for selective ionic and molecular sieving. Traditional membranes face limitations due to their inherent negative charge and limited charge modification range. Herein, we report a facile ionic liquid-decoupled bulk/interfacial diffusion strategy to elaborate the double charge flips of polyamide membranes, enabling on-demand transformation from inherently negative to highly positive and near-neutral charges. The key to these flips lies in the meticulous utilization of ionic liquid that decouples intertwined bulk/interfacial diffusion, enhancing interfacial while inhibiting bulk diffusion. These charge-tunable polyamide membranes can be customized for impressive separation performance, for example, profound Cl-/SO42- selectivity above 470 in sulfate recovery, ultrahigh Li+/Mg2+ selectivity up to 68 in lithium extraction, and effective divalent ion removal in pharmaceutical purification, surpassing many reported polyamide nanofiltration membranes. This advancement adds a new dimension to in the design of advanced polymer membranes via interfacial polymerization.

Polyamide nanofiltration membranes by vacuum-assisted interfacial polymerization: Broad universality of Substrate, wide window of monomer concentration and high reproducibility of performance

Vacuum assistance is used for filtering solid substances onto porous substrates to create composite membranes typically. However, the potential of this approach has rarely been assessed in facilitating the distribution of liquids within those porous substrates to fabricate composite membranes in typical interfacial polymerization. In this work, we demonstrate the advantages of vacuum-assisted interfacial polymerization (VAIP) in terms of substrate universality, monomer concentration range, and performance reproducibility in the fabrication of polyimide nanofiltration membranes. Aqueous solutions of PIP can be homogeneously distributed by vacuum filtration on diverse microfiltration substrates of polyether sulfone (PES), Nylon-66, polyvinylidene fluoride (PVDF), cellulose acetate (CA), and mixed cellulose esters (MCE), respectively. Interfacial polymerization is then performed on these substrates using different concentrations of piperazine (PIP, 0.0075-0.1000 wt%) and trimoyl chloride (TMC, 0.0112-0.1500 wt%). Remarkably, a uniform and ultra-thin polyamide layer with a thickness of 15 nm can be achieved at an exceptionally low PIP concentration of 0.0250 wt%, exhibits a rejection rate of over 98.8 % for Na2SO4 and a water permeance of 25.8 L·m-2·h-1·bar-1. The membranes with a diameter of 30 cm demonstrate reproducibility in nanofiltration performance and satisfactory long-term stability. This method offers a simple yet effective strategy for regulating the liquid distribution and optimizing interfacial polymerization in fabricating polyamide composite membranes.

Decoration of β-Cyclodextrin and Tuning Active Layer Chemistry Leading to Nanofiltration Membranes for Desalination and Wastewater Decontamination

Given the huge potential of thin film composite (TFC) nanofiltration (NF) membranes for desalination and micro-pollutant removal, two different sets of six NF membranes were synthesized. The molecular structure of the polyamide active layer was tuned by using two different cross-linkers, terephthaloyl chloride (TPC) and trimesoyl chloride (TMC), reacted with tetra-amine solution containing β-Cyclodextrin (BCD). To further tune the structure of the active layers, the time duration of interfacial polymerization (IP) was varied from 1 to 3 min. The membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA), attenuated total reflectance Fourier transform infra-red (ATR-FTIR) spectroscopy, elemental mapping and energy dispersive (EDX) analysis. The six fabricated membranes were tested for their ability to reject divalent and monovalent ions followed by rejection of micro-pollutants (pharmaceuticals). Consequently, terephthaloyl chloride turned out to be the most effective crosslinker for the fabrication of membrane active layer with tetra-amine in the presence of β-Cyclodextrin using interfacial polymerization reaction for 1 min. The membrane fabricated using TPC crosslinker (BCD-TA-TPC@PSf) showed higher % rejection for divalent ions (Na₂SO₄ = 93%; MgSO₄ = 92%; MgCl₂ = 91%; CaCl₂ = 84%) and micro-pollutants (Caffeine = 88%; Sulfamethoxazole = 90%; Amitriptyline HCl = 92%; Loperamide HCl = 94%) compared to the membrane fabricated using TMC crosslinker (BCD-TA-TMC@PSf). For the BCD-TA-TPC@PSf membrane, the flux was increased from 8 LMH (L/m².h) to 36 LMH as the transmembrane pressure was increased from 5 bar to 25 bar.

Molecular Design of the Polyamide Layer Structure of Nanofiltration Membranes by Sacrificing Hydrolyzable Groups toward Enhanced Separation Performance

Nanofiltration (NF) is an effective technology for removing trace organic contaminants (TrOCs), while the inherent trade-off effect between water permeance and solute rejections hinders its widespread application in water treatment. Herein, we propose a novel scheme of "monomers with sacrificial groups" to regulate the microstructure of the polyamide active layer via introducing a hydrolyzable ester group onto piperazine to control the diffusion and interfacial polymerization process. The achieved benefits include narrowing the pore size, improving the interpore connectivity, enhancing the microporosity, and reducing the active layer thickness, which collectively realized the simultaneous improvement of water permeance and enhancement of TrOCs rejection performance. The resulting membranes were superior to both the control and commercial membranes, especially in water-TrOCs selectivity. The effects of using the new monomers on the membrane physicochemical properties were systematically studied, and underlying mechanisms for the enhanced separation performance were further revealed by simulating the polymerization process through density functional theory calculation and measuring the trans-interface diffusion rate of monomers. This study demonstrates a novel promising NF membrane synthesis strategy by designing the structure of reaction monomers for achieving excellent rejection of TrOCs with a low energy input in water treatment.

Boosting the Performance of Nanofiltration Membranes in Removing Organic Micropollutants: Trade-Off Effect, Strategy Evaluation, and Prospective Development

In view of the high risks brought about by organic micropollutants (OMPs), nanofiltration (NF) processes have been playing a vital role in advanced water and wastewater treatment, owing to the high membrane performance in rejection of OMPs, permeation of water, and passage of mineral salts. Though numerous studies have been devoted to evaluating and technically enhancing membrane performance in removing various OMPs, the trade-off effect between water permeance and water/OMP selectivity for state-of-the-art membranes remains far from being understood. Knowledge of this effect is significant for comparing and guiding membrane development works toward cost-efficient OMP removal. In this work, we comprehensively assessed the performance of 88 NF membranes, commercialized or newly developed, based on their water permeance and OMP rejection data published in the literature. The effectiveness and underlying mechanisms of various modification methods in tailoring properties and in turn performance of the mainstream polyamide (PA) thin-film composite (TFC) membranes were quantitatively analyzed. The trade-off effect was demonstrated by the abundant data from both experimental measurements and machine learning-based prediction. On this basis, the advancement of novel membranes was benchmarked by the performance upper-bound revealed by commercial membranes and lab-made PA membranes. We also assessed the potentials of current NF membranes in selectively separating OMPs from inorganic salts and identified the future research perspectives to achieve further enhancement in OMP removal and salt/OMP selectivity of NF membranes.

NH2-CuO-MCM-41 covalently cross-linked multipurpose membrane for applications in water treatment: Removal of hazardous pollutants from water, water desalination and anti-biofouling performance

The current study was planned to fabricate a new set of membranes to target multiple application areas such as desalting, removal of micropollutants and antibiofouling performance. In-situ incorporated copper oxide to MCM-41 (CuO-MCM-41) was synthesized and amine (-NH₂) functionalized by reacting with N1-(3-trimethoxy silylpropyl) diethylenetriamine (NTSDETA) yielding NH₂-CuO-MCM-41. Different concentrations of NH₂-CuO-MCM-41 were covalently cross-linked in polyamide active layer during interfacial polymerization (IP) between N, N'-bis(3-aminopropyl)ethylenediamine and terephthaloyl chloride (TPC) on polysulfone/poly ester terephthalate (PS/PET) support. The membranes were extensively characterized by Water Contact Angle (WCA), Scanning Electron Microscopy (SEM), Fourier Transform Infra-red (FTIR) spectroscopy, Energy Dispersive X-ray (EDX) analysis, Elemental mapping and Powder X-ray Diffraction (PXRD). From among the different versions of X-CuO-MCM-41/PA@PS/PET membranes, the 0.05%-CuO-MCM-41/PA@PS/PET membrane showed best performance in terms of rejecting a variety of salts, micropollutants and antibiofouling. The 0.05%-CuO-MCM-41/PA@PS/PET showed >98% rejection of MgCl₂ and 78% rejection of caffeine with a permeate flux of 16 LMH at 25 bar. The 0.1-NH₂-CuO-MCM-41inhibited S. aureus growth by 51.7%. Hence, the current strategy of membrane fabrication proved to be highly efficient for multipurpose applications in water treatment.

Membrane technology for pesticide removal from aquatic environment: Status quo and way forward

The noxious side effects of pesticides on human health and environment have prompted the search of effective and reliable treatment techniques for pesticide removal. The removal of pesticides can be accomplished through physical, chemical and biologicals. Physical approaches such as filtration and adsorption are prevailing pesticide removal strategies on account of their effectiveness and ease of operation. Membrane-based filtration technology has been recognized as a promising water and wastewater treatment approach that can be used for a wide range of organic micropollutants including pesticides. Nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) have been increasingly explored for pesticide removal from aquatic environment owing to their versatility and high treatment efficiencies. This review looks into the remedial strategies of pesticides from aqueous environment using membrane-based processes. The potentials and applications of three prevailing membrane processes, namely NF, RO and FO for the treatment of pesticide-containing wastewater are discussed in terms of the development of advanced membranes, separation mechanisms and system design. The challenges in regards to the practical implementation of membrane-based processes for pesticide remediation are identified. The corresponding research directions and way forward are highlighted. An in depth understanding of the pesticide nature, water chemistry and the pesticide-membrane interactions is the key to achieving high pesticide removal efficiency. The integration of membrane technology and conventional removal technologies represents a new dimension and the future direction for the treatment of wastewater containing recalcitrant pesticides.

Modulating the Asymmetry of the Active Layer in Pursuit of Nanofiltration Selectivity via Differentiating Interfacial Reactions of Piperazine

Nanofiltration (NF), highly prospective for drinking water treatment, faces a challenge in simultaneously removing emerging contaminants while maintaining mineral salts, particularly divalent cations. To overcome this challenge, NF membranes possessing small pores concomitant with highly negatively charged surfaces were synthesized via a two-step fabrication strategy. The key is to generate a polyamide active layer having a loose and carboxyl group-abundant segment on top and a dense barrier segment underneath. This was achieved by restrained interfacial polymerization between trimesoyl chloride and partly protonated piperazine to form a highly depth-heterogeneous polyamide network, followed by second amidation in an organic environment to remove untethered polyamide fragments and associate malonyl chlorides with reserved amine groups to introduce more negative charges. Most importantly, on first-principle engineering the spatial architecture of the polyamide layer, amplifying asymmetric charge distribution was paired with the thinning of the vertical structure. The optimized membrane exhibits high salt/organic rejection selectivity and water permeance superior to most NF membranes reported previously. The rejections of eight emerging contaminants were in the range of 66.0-94.4%, much higher than the MgCl₂ rejection of 41.1%. This new fabrication strategy, suitable for various diacyl chlorides, along with the new membranes so produced, offers a novel option for NF in potable water systems.

Fabrication of Loose Nanofiltration Membranes with High Rejection Selectivity between Natural Organic Matter and Salts for Drinking Water Treatment

Loose nanofiltration (LNF) membranes with a molecular weight cut-off (MWCO) of about 1000 Da and high surface negative charge density have great application potential for drinking water treatment pursuing high rejection selectivity between natural organic matter (NOM) and mineral salts. This study was conducted to exploit the novel method coupling non-solvent induced phase separation (NIPS) and interfacial polymerization (IP) for the preparation of high-performance LNF membranes. A number of LNF membranes were synthesized by varying the polyethersulfone (PES) and piperazine (PIP) concentrations in the cast solution for the PES support layer preparation. Results showed that these two conditions could greatly affect the membrane water permeance, MWCO and surface charge. One LNF membrane, with a water permeance as high as 23.0 ± 1.8 L/m²/h/bar, when used for the filtration of conventional process-treated natural water, demonstrated a rejection of NOM higher than 70% and a low rejection of mineral salts at about 20%. Both the mineral salts/NOM selectivity and permselectivity were superior to the currently available LNF membranes as far as the authors know. This study demonstrated the great advantage of the NIPS-IP method for the fabrication of LNF membranes, particularly for the advanced treatment of drinking water.

Exploitation of Amine Groups Cooped up in Polyamide Nanofiltration Membranes to Achieve High Rejection of Micropollutants and High Permeance of Divalent Cations

To enhance the use of nanofiltration in the production of quality drinking water, particularly through the efficient removal of micropollutants yet still preserving essential minerals, the targeted nanofiltration membranes (NFMs) are required to have small pore dimensions coupled with a high, net-negative charge density. Herein, after the formation of a separation layer using piperazine interfacially polymerized with trimesoyl chloride, the exploitation of residual amine groups was systematically investigated by different diacyl chlorides in an organic milieu, which caused the upper part of the final separation layer to be denser and highly negatively charged. Hence, this protocol offers a novel means to fabricate NFMs simultaneously endowed with a low molecular cutoff (MWCO) of 145-238 Da and a reduced rejection of MgCl₂ (48%-80%) as well as a competitive water permeance. Those features are ideally applicable to the goal of removing small micropollutants while preserving mineral ions, as needed for the energy-efficient production of safe, quality drinking water. Furthermore, an attempt was made to correlate MWCO with MgCl₂ rejection, which provides some insights on the nexus of the electrostatic effects constrained by size exclusion. The significance of residual amine groups and the modification environment was unveiled, and this method paves a new avenue for designing functional NFMs.

Highly Selective and pH-Stable Reverse Osmosis Membranes Prepared via Layered Interfacial Polymerization

Ultrathin and smooth polyamide (PA) reverse osmosis (RO) membranes have attracted significant interest due to their potential advantages of high permeance and low fouling propensity. Although a layered interfacial polymerization (LIP) technique aided by the insertion of a polyelectrolyte interlayer has proven effective in fabricating ultrathin and uniform membranes, the RO performance and pH stability of the fabricated LIP membrane remain inadequate. In this study, a poly(piperazineamide) (PIPA) layer prepared via interfacial polymerization (IP) was employed as an interlayer to overcome the limitations of the prototype LIP method. Similar to the control polyelectrolyte-interlayered LIP membrane, the PIPA-interlayered LIP (pLIP) membrane had a much thinner (~20 nm) and smoother selective layer than the membrane fabricated via conventional IP due to the highly surface-confined and uniform LIP reaction. The pLIP membrane also exhibited RO performance exceeding that of the control LIP and conventional IP-assembled membranes, by enabling denser monomer deposition and a more confined interfacial reaction. Importantly, the chemically crosslinked PIPA interlayer endowed the pLIP membrane with higher pH stability than the control polyelectrolyte interlayer. The proposed strategy enables the fabrication of high-performance and pH-stable PA membranes using hydrophilic supports, which can be applied to other separation processes, including osmosis-driven separation and organic solvent filtration.

Covalent Organic Framework-Mediated Thin-Film Composite Polyamide Membranes toward Precise Ion Sieving

Covalent organic frameworks (COFs) have evinced a potential solution that promises for fast and efficient molecular separation due to the presence of orderly arranged pores and regulable pore apertures. Herein, the synthesized COF (TPB-DMTP-COF) with the pore aperture matching the pore size of the nanofiltration (NF) membrane was utilized to modulate the physicochemical characters of the polyamide (PA) membranes. It is demonstrated that COFs with superior polymer affinity and hydrophilicity not only circumvent the nonselective interfacial cavities but also improve the hydrophilicity of the resultant thin-film nanocomposite (TFN) membranes. Furthermore, the predeposited COF layer is able to slow down the diffusion rate toward the reaction boundary through hydrogen bonding, which is consistent with the results of molecular dynamic (MD) and dissipative particle dynamic (DPD) simulations. In this context, COF-modulated TFN membranes show a roughened and thickened surface with bubble-shaped structures in contrast to the nodular structure of original polyamide membranes. Combined with the introduced in-plane pores of COFs, the resultant TFN membranes display a significantly elevated water permeance of 35.7 L m² h^-1 bar^-1, almost 4-fold that of unmodified polyamide membranes. Furthermore, the selectivity coefficient of Cl^-/SO₄^2- for COF-modulated TFN membranes achieves a high value of 84 mainly related to the enhanced charge density, far exceeding the traditional NF membranes. This work is considered to provide a guideline of exploring hydrophilic COFs as an interlayer for constructing highly permeable membranes with precise ion-sieving ability.

The stabilization of ultrafiltration membrane blended with randomly structured amphiphilic copolymer: Micropollutants adsorption properties in filtration processes

In this study, a blend membrane consisting of polyvinylidene fluoride (PVDF) and tertiary amine containing random copolymer poly(methyl methacrylate-r-dimethylamino-2-ethyl methacrylate) (P(MMA-r-DMAEMA)) was fabricated and utilized as an adsorptive membrane for micropollutants (anionic dye and heavy metal ions) removal from aqueous solutions. Cross-linking the random copolymer by p-xylylene dichloride (XDC) produced the membrane with improved copolymer retention ratio and stability, while slightly variated physicochemical properties. Besides, the fluxes of crosslinked blend membranes dramatically increased from 0.7 ± 0.1 L/(m²h) to 118.6 ± 5.9 L/(m²h). Then the present blend membrane was carried out adsorption and filtration experiments to investigate the influence of various of operation parameters including initial solution pH value, contacting time, initial solution concentration, and recycling efficiency on micropollutants removal. The experimental results showed that the removal of the anionic dyes and heavy metal ions on this tertiary amine containing blend membrane was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of 3.5 for anionic dyes and 6.0 for metal ions, respectively. The membrane showed highly efficient capture of sunset yellow (above 99%). Meanwhile, the captured sunset yellow was recovered and concentrated with a small volume of alkaline solutions at pH 10.0, which simultaneously regenerated the membrane for its reuse. In a 3-cycle capture-recovery test, the membrane demonstrated a high sunset yellow recovery ratio and a volumetric concentration ratio as high as 400%. Our study provides an alternative strategy for functionalized membrane fabrication, micropollutants removal and recovery.

Tailored design of nanofiltration membranes for water treatment based on synthesis-property-performance relationships

Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

Toward Enhancing Desalination and Heavy Metal Removal of TFC Nanofiltration Membranes: A Cost-Effective Interface Temperature-Regulated Interfacial Polymerization

Polyamide (PA) chemistry-based nanofiltration (NF) membranes have an important role in the field of seawater desalination and wastewater reclamation. Achieving an ultrathin and defect-free active layer via precisely controlled interfacial polymerization (IP) is an effective routine to improve the separation efficiencies of NF membranes. Herein, the morphologies and chemical structures of the thin-film composite (TFC) NF membranes were accurately regulated by tailoring the interfacial reaction temperature during the IP process. This strategy was achieved by controlling the temperature (-15, 5, 20, 35, and 50°) of the oil-phase solutions. The structural compositions, morphological variations, and separation features of the fabricated NF membranes were studied in detail. In addition, the formation mechanisms of the NF membranes featuring different PAs were also proposed and discussed. The temperature-assisted IP (TAIP) method greatly changed the compositions of the resultant PA membranes. A very smooth and thin PA film was obtained for the NF membranes fabricated at a low interfacial temperature; thus, a high 19.2 L m^-2 h^-1 bar^-1 of water permeance and 97.7% of Na₂SO₄ rejection were observed. With regard to the NF membranes obtained at a high interfacial temperature, a lower water permeance and higher salt rejection with fewer membrane defects were achieved. Impressively, the high interfacial temperature-assisted NF membranes exhibited uniform coffee-ring-like surface morphologies. The special surface-featured NF membrane showed superior separation for selected heavy metals. Rejections of 93.9%, 97.9%, and 87.7% for Cu²⁺, Mn²⁺, and Cd²⁺ were observed with the optimized membrane. Three cycles of fouling tests indicated that NF membranes fabricated at low temperatures exhibited excellent antifouling behavior, whereas a high interface temperature contributed to the formation of NF membranes with high fouling tendency. This study provides an economical, facile, and universal TAIP strategy for tailoring the performances of TFC PA membranes for environmental water treatment.

Surface modification of nanofiltration membranes to improve the removal of organic micropollutants: Linking membrane characteristics to solute transmission

Surface modification of nanofiltration (NF) membranes has great potential to improve the removal of organic micropollutants (OMs) by NF membranes. This study used polydopamine (PDA) as a model coating to comprehensively link the changes in membrane properties with the changes in transmission of 34 OMs. The membrane characterization demonstrated that a thicker, denser, and more hydrophilic PDA coating can be achieved by increasing the PDA deposition time from 0.5 to 4 hours. Overall, the transmissions of target OMs were reduced by PDA-coated NF membranes compared to unmodified NF membranes. The neutral hydrophobic compounds showed lower transmissions for longer PDA coating (PDA4), while the neutral hydrophilic compounds tended to show lower transmissions for shorter PDA coating (PDA0.5). To explain this, competing effects provided by the PDA coatings are proposed including sealing defects, inducing cake-enhanced concentration polarization in the coating layer for neutral hydrophilic compounds, and weakened hydrophobic adsorption for neutral hydrophobic compounds. For charged compounds, PDA4 with the greatest negative charge among the PDA-coated membranes showed the lowest transmission. Depending on the molecular size and hydrophilicity of the compounds, the transmission of OMs by the PDA4 coating could be reduced by 70% with only a 26.4% decline in water permeance. The correlations and mechanistic insights provided by this work are highly useful for designing membranes with specific surface properties via surface modification to improve the removal of OMs without compromising water production.

Fit-for-Purpose Design of Nanofiltration Membranes for Simultaneous Nutrient Recovery and Micropollutant Removal

Domestic wastewater is a valuable reservoir of nutrients such as nitrogen and phosphorus. However, the presence of emerging micropollutants (EMPs) hinders its applications in resource recovery. In this study, we designed and fabricated a novel thin-film composite polyamide membrane, which enables highly selective nanofiltration (NF) that removes EMPs effectively while preserving valuable nutrients in the permeate. By incorporating polyethylenimine as an additional monomer to piperazine and surfactant sodium dodecyl sulfate in interfacial polymerization, we precisely tuned membrane pore size, pore size distribution, and surface charge. The resultant NF membrane achieved desirable solute-solute selectivity between EMPs (rejection rate > 75%) and nutrient N and P ions (rejection rate < 25%). By applying a modified Donnan steric pore model with dielectric exclusion, which takes membrane pore size distribution into consideration, we demonstrate the synergistic effect of membrane pore size, pore size distribution, and surface charge in regulating membrane solute-solute selectivity. Designing solute-solute selective NF membranes for fit-for-purpose wastewater treatment has great potential to improve the flexibility of membrane technologies that can convert wastewater streams to valuable water and nutrient resources.

Positively charged nanofiltration membrane synthesis, transport models, and lanthanides separation

The design and understanding of rejection mechanisms for both positively and negatively charged nanofiltration (NF) membranes are needed for the development of highly selective separation of multivalent ions. In this study, positively charged nanofiltration membranes were created via an addition of commercially available polyallylamine hydrochloride (PAH) by conventional interfacial polymerization technique. Demonstration of real increase in surface zeta potential, along with other characterization methods, confirmed the addition of weak basic functional groups from PAH. Both positively and negatively charged NF membranes were tested for evaluating their potential as a technology for the recovery or separation of lanthanide cations (neodymium and lanthanum chloride as model salts) from aqueous sources. Particularly, the NF membranes with added PAH performed high and stable lanthanides retentions, with values around 99.3% in mixtures with high ionic strength (100 mM, equivalent to ~6,000 ppm), 99.3% rejection at 85% water recovery (and high Na+/La3+ selectivity, with 0% Na+ rejection starting at 65% recovery), and both constant lanthanum rejection and permeate flux at even pH 2.7. Donnan steric pore model with dielectric exclusion elucidated the transport mechanism of lanthanides and sodium, proving the potential of high selective separation at low permeate fluxes using positively charged NF membranes.

Polymer-based spherical activated carbon - ultrafiltration (UF-PBSAC) for the adsorption of steroid hormones from water: Material characteristics and process configuration

The European Union has proposed the value of 1 ng L^-1 as a drinking water quality standard for estradiol. With conventional technologies only partially removing estradiol, the investigation of novel alternatives is more than ever required. Tagliavini and Schäfer proposed that the use of a thin activated carbon layer combined with a membrane is worth considering. In this work, the process was further advanced through a systematic investigation of the role of activated carbon size, activation and surface chemistry on the removal of estradiol. The use of smaller carbon particles allows reaching the ambitious target value of 1 ng L^-1 in a millimetric layer. Further, adsorption kinetic enhancement by increasing the oxygen content on the carbon improves the removal from 96 to 99 % (for a layer of 2 mm) for OH-containing pollutants such as estradiol. High removal, together with low pressure and no by-product formation, are characteristics that make the UF-PBSAC a promising and competitive approach.

Surface Properties, Free Volume, and Performance for Thin-Film Composite Pervaporation Membranes Fabricated through Interfacial Polymerization Involving Different Organic Solvents

The type of organic solvents used in interfacial polymerization affects the surface property, free volume, and separation performance of the thin-film composite (TFC) polyamide membrane. In this study, TFC polyamide membrane was fabricated through interfacial polymerization between diethylenetriamine (DETA) and trimesoyl chloride (TMC). Four types of organic solvent were explored in the preparation of pervaporation membrane. These are tetralin, toluene, hexane, and isopentane. The solubility parameter distance between organic solvents and DETA follows in increasing order: tetralin (17.07 MPa1/2) < toluene (17.31 MPa1/2) < hexane (19.86 MPa1/2) < isopentane (20.43 MPa1/2). Same trend was also observed between the organic solvents and DETA. The larger the solubility parameter distance, the denser and thicker the polyamide. Consequently, field emission scanning electron microscope (FESEM) and positron annihilation spectroscopy (PAS) analysis revealed that TFCisopentane had the thickest polyamide layer. It also delivered the highest pervaporation efficiency (permeation flux = 860 ± 71 g m-2 h-1; water concentration in permeate = 99.2 ± 0.8 wt%; pervaporation separation index = 959,760) at dehydration of 90 wt% aqueous ethanol solution. Furthermore, TFCisopentane also exhibited a high separation efficiency in isopropanol and tert-butanol. Therefore, a suitable organic solvent in preparation of TFC membrane through interfacial polymerization enables high pervaporation efficiency.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.