Hollow Fiber Nanofiltration Membranes Research Articles

Operation and performance analysis of direct hollow fiber nanofiltration: A pilot study at IJsselmeer

This study investigated the performance of direct hollow fiber nanofiltration (dNF40) membranes from NX Filtration BV on a pilot scale for the treatment of pre-treated IJsselmeer water from Waterwinstation Prinses Juliana (WPJ) in Andijk, as well as the direct treatment of raw IJsselmeer water. The objective was to evaluate the long-term fouling potential and the retention of ions and natural organic matter (NOM) using both WPJ pre-treated IJsselmeer water and raw IJsselmeer water. Additionally, the rejection of organic micropollutants (OMPs) under artificially elevated conditions, referred to as ‘spiked solution’, using WPJ pre-treated IJsselmeer water was investigated.Limited to no fouling was observed on the dNF40 membrane during stable operation when treating both WPJ pre-treated IJsselmeer water and raw IJsselmeer water, even under changing process conditions. NOM removal consistently exceeded 90% regardless of process conditions or water type. The retention of per- and polyfluoroalkyl substances (PFAS) was above 80%, with even higher retention observed for higher molecular weight values. Low molecular weight pharmaceuticals, all below the molecular weight cut-off (MWCO) of the dNF40 membrane (400 Da), exhibited approximately 30% retention. The dNF40 membrane showed better retention of negatively charged pharmaceuticals in the spiked solution compared to positively charged and neutral pharmaceuticals.A total cost of ownership (TCO) analysis unveiled that operational expenditures (OPEX) were three times higher than capital expenditures (CAPEX) for a 5-stage full-scale dNF40 system. Among the components, membrane replacement costs constituted the majority of OPEX (68%), followed by energy costs (31%) and chemical costs (<1%). Overall, the study showcased the suitability of the dNF40 membranes for treating IJsselmeer water, achieving effective removal of NOM and PFAS.

Mixed-charged polyamide-4-sulfocalix [4] arene hollow fiber nanofiltration membranes for heavy metal removal under various pH

The presence of heavy metal ions in water sources poses significant risks to both human health and environments; hence, it is critical to develop effective and trustworthy removal techniques. This research aims to fabricate a novel hollow fiber membrane consisting of mixed-charged characteristics via the formation of a positively charged thin film composite (TFC), followed by the infiltration of 4-sulfocalix [4] arene (SCA4). The formation, architecture and separation performance of the mixed-charged nanofiltration (NF) membrane have been confirmed by various characterizations. The SCA4-0.03 NF hollow fiber membrane shows excellent rejection performance up to 99.2% for a variety of ion removals such as common arsenate, nickel (II), and lead (II) ions over a broad pH range. Additionally, the mixed-charged membrane exhibits higher performance stability over 48 h and fouling resistance in both basic and acidic conditions. Consequently, the mixed-charged membrane described in this work is promising to treat both cationic and anionic liquids, and eliminate a variety of ecologically harmful ion species in industries.

Controllable preparation of novel homogenous reinforcement poly(p-phenylene terephthamide) hollow fiber nanofiltration membrane with nanoscale ordered structures for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a green, energy-saving, and highly efficient emerging membrane separation technology, and there is an urgent need for robust, easy-to-process OSN membranes with high permeance and small solute selectivity for industrial applications. Herein, we propose a new strategy for accurately designing novel OSN membranes. Specifically, a polyamide (PA) interlayer was synthesized in-situ on the surface of homogeneous reinforced poly(p-phenylene terephthamide) (PPTA) hollow fiber membrane by interfacial polymerization (IP) using both ultra-low concentrations piperazine (PIP, 0.05 wt%) and trimesoyl chloride (TMC, 0.005 wt%), and then a defect-free and dense PPy layer was deposited on top of the hydrophilic PA interlayer by chemical vapor deposition (CVD) process to prepare PA/PPy composite membranes with spherical cluster or strip cluster “Turing-like” structure. The resulting PA/PPy composite membranes presented an excellent high selective permeability, the dimethylacetamide (DMAc) permeability was 21.1 L·m−2·h−1·MPa−1, and the molecular weight cut-off (MWCO) was as low as 185 Da. A 30-hour OSN test at elevated temperatures (80 °C) and in organic solvent (DMAc), as well as a one-month immersion test in ethanol and DMAc at room temperature, demonstrated superior separation performance and structural stability of the membranes, indicating their application potential in harsh solvent systems. Our novel method for developing nanoscale ordered structured PA/PPy composite membranes offers great potential for the development of multilevel structural designs in the preparation of high-performance OSN membranes with potential industrial applications.

Retention of nine micropollutants covering a wide range of physical-chemical properties using polyelectrolyte multilayer hollow fiber NF membranes

Our work investigates the efficiency of two polyelectrolyte multilayer hollow fiber nanofiltration (NF) membranes for the removal of nine micropollutants (MPs) from pre-treated wastewater. The Square Latin method was used to select the contaminants to study according to their molecular weight, hydrophilicity (log Kow), and charge at environmental pH. NF experiments were carried out in batch mode at 20 °C with a crossflow velocity of 1 m.s−1, and a transmembrane pressure of 3 bar. Retentions of MPs and salts were evaluated at various volume reduction ratios (1, 3 or 6), membrane molecular weight cut-off (400 or 800 Da) and fouling potential of the matrix (ultrapure water, synthetic water, or real pre-treated wastewater). Our study identified the 400 Da membrane as the best option as balance between MPs and salts retention was the most acceptable. With this membrane, two thirds of the investigated MPs showed a retention above 90 %, two MPs had a retention around 60 % and only one MP was retained less than 20 % while monovalent salts had a retention lower than 30 %. Our work identified size exclusion and electrostatic interactions as the main mechanisms involved in MPs retention by the negatively charged membrane. This membrane showed its efficiency to maintain high permeation flux during 24 h-filtration of stream with organic matter content comparable to secondary-treated wastewater to a volume reduction ratio up to 6. At this content, organic matter did not modify retention of micropollutants or salts. The selected membrane is an encouraging tool to produce MPs-free water from pre-treated wastewater without producing a highly saline retentate. In the future, permeate would possibly be employed for REUSE purposes.

Novel Direct Hollow Fiber Nanofiltration Membrane and Its Applications

Novel Direct Hollow Fiber Nanofiltration Membrane and Its Applications

A Selective Separation Mechanism for Mono/divalent Cations and Properties of a Hollow-Fiber Composite Nanofiltration Membrane Having a Positively Charged Surface.

Positively charged nanofiltration (NF) technology is considered a green and low-cost method for mono/divalent cation separation. Nevertheless, the separation rejection mechanisms of these NF membranes have yet to be extensively investigated. In this work, we fabricated a thin-film composite (TFC) hollow-fiber (HF) NF membrane with a positively charged surface via modification of the nascent interfacial polymerization layer using a branched polyethyleneimine (BPEI)/ethanol solution. Then, we extensively investigated its selective separation mechanism for mono/divalent cations. We proposed and proved that there exists a double-charged layer near the membrane surface, which helps to repel the divalent cations selectively via Donnan exclusion while promoting the fast penetration of monovalent cations. Meanwhile, the membrane skin layer is loose and hydrophilic due to the loose BPEI structure and the abundance of amine groups, as well as the changed fabrication conditions. In this way, we achieved very good mono/divalent cation selectivity and relatively high water permeance for the as-prepared HF NF membrane. We also obtained good anti-fouling, anti-scaling, and acid resistance, and long-term stability as well, which are urgently needed during practical application. Furthermore, we successfully amplified this HF NF membrane and proved that it has broad application prospects in mono/divalent cation separation.

Effect of substrate morphology on characteristics of layer-by-layer self-assembly nanofiltration membrane for micropollutants removal

Layer-by-layer (LBL) hollow fiber nanofiltration (NF) membranes have emerged as a promising technology for the removal of micropollutants (MPs). Previous research has been largely focused on polyelectrolyte pairs and coating parameters. This paper studied the substrate morphology, a critical factor often being overlooked. Poly (allylamine hydrochloride) /poly (styrene sulfonic acid) sodium salt (PAH/PSS) coating was utilized to evaluate the impact of the substrate morphology. Two polyethersulfone substrates were selected: Substrate 1# with dense skins at both lumen/shell and Substrate 2# with skin at the lumen and an open shell surface. All LBL NF membranes showed molecular weight cut-off ranging from 180 to 223 Da and MgCl2 rejection around 94 %. For LBL membrane 1#, with coatings on both shell/lumen sides, the outer coating was defective due to scratches. For LBL membrane 2# with a coating at the lumen, significant PAH overcompensation was observed, because of the open inner and outer surfaces comparing to LBL membrane 1#. Higher rejection to positively charged MPs was resulted from Donnan effect, outperforming steric exclusion. The backwash stability of both membranes was excellent and independent of the substrate structure. This work provides a basis for substrate selection for fabricating LBL NF membranes.

Evaluation of Membrane Integrity Monitoring Methods for Hollow Fiber Nanofiltration Membranes: Applicability in Gray Water Reclamation Systems

Evaluation of Membrane Integrity Monitoring Methods for Hollow Fiber Nanofiltration Membranes: Applicability in Gray Water Reclamation Systems

Removal of heavy metal ions from acidic wastewater by constructing positively charged hollow fiber nanofiltration separating-layer based on Fe (III)/co deposition-quaternization

A surface positively charged nanofiltration (NF) membrane was successfully constructed to effectively remove heavy metal ions by co-deposition and quaternization strategy. The combination between Fe3+ and H2O2 accelerated the co-deposition of tannic acid (TA) and polyvinyl amine (PVAM) on the membrane surface. The mechanism by which metal ions accelerated co-deposition process to regulate membrane surface structure was elucidated. The convenient quaternary ammonium modification was carried out by reacting glycidyl trimethyl ammonium chloride (GTMAC), which significantly increased the potential and density of the membrane surface. The membrane had a high retention rate for heavy metal ions (1000 ppm (mg· L−1), Cr3+ (94.6 %), Fe3+ (93.7 %), Cu2+ (92.1 %), Ni2+ (90.2 %)), while maintaining an excellent water permeance (27.8 L m−2 h−1 bar−1). The membrane also presented outstanding separation performance for rare earth metal ion. In particular, the retention rate for 500 ppm (mg·L−1) Ce3+ was 95.3 %. The relationship between membrane surface potential, pore size and rejection of heavy metal revealed the removal mechanism. Furthermore, the membrane exhibited excellent acid-base resistance and long-term operation stability. This study supplies an effective surface modification method for preparing hollow fiber NF membranes used for removing heavy metal and recovering rare earth metal from wastewater.

Fabrication of Hollow Fiber Nanofiltration Membrane with Poly(vinyl Chloride) Substrate for the Removal of Chemicals of Concern

Fabrication of Hollow Fiber Nanofiltration Membrane with Poly(vinyl Chloride) Substrate for the Removal of Chemicals of Concern

Understanding and predicting the adsorption and rejection of pesticides and metabolites by hollow fiber nanofiltration membranes

Layer-by-layer Hollow fiber Nanofiltration (LbL HF-NF) membranes have shown great potential in the removal of micropollutants from water. Nonetheless, further research is required as the number of tested compounds remains limited. In this study, the adsorption and rejection of 164 micropollutants by two commercial HF-NF membranes with MWCO of 400 and 800 Da, were investigated. The investigation was conducted by evaluating the influence of 11 physicochemical micropollutants’ properties on the separation performances. Results showed that highly adsorbed compounds had average log D values above 3, while no or low adsorption was observed for compounds with negative log D values. Furthermore, adsorption was more frequently observed for neutral compounds compared to negatively charged ones. Micropollutants rejection results showed that steric exclusion plays the most important role in the rejection of micropollutants, and that the charge of micropollutants can also heavily influence their rejection. Likewise, negatively charged compounds were better rejected than neutral ones. Finally, the study demonstrated that adsorption and rejection of micropollutants can be predicted with good accuracy using the random forest algorithm. The prediction accuracy for adsorption was 80% and 73% for the 800 and 400 Da MWCO membranes, respectively. The RMSE for rejection predictions was 10.6% and 6% for the two membranes respectively.

Positively charged thin-film composite hollow fiber nanofiltration membrane via interfacial polymerization and branch polyethyleneimine modification for Mg2+/Li+ separation

It is a vital technical challenge to extract lithium from salt-lake brine which has very high Mg2+ / Li+ mass ratio via green and low-cost methods, as these two cations have quite similar ionic hydration radius. Positively charged nanofiltration membranes can separate Li+ and Mg2+ through Donnan exclusion. In this work, a kind of hollow fiber nanofiltration membrane with positively charged skin layer was successfully fabricated via interfacial polymerization followed by a surface modification with branched polyethyleneimine (BPEI). The resultant membrane has a large number of amine groups, and thus shows positively charged surface with high rejection for divalent cation ions via Donnan exclusion. This gives it very high selectivity for the separation of Li+ ions from salt-lake brine. Under optimized conditions, it achieves a water permeance of up to 126.2 L m-2 h-1 MPa−1 at a transmembrane pressure difference of 4 bar, and a MgCl2 rejection of 94.6% with 2000 mg L-1 aqueous MgCl2 solution as feed. Meanwhile, it achieves a Mg2+ / Li+ selectivity of nearly 24 for MgCl2 and LiCl salt mixture solution with an overall concentration of 2000 mg L-1 and a Mg2+ / Li+ mass ratio of 150 : 1 as feed, which is high as compared with most of the literature, demonstrating its potential in the practical application of Mg2+ and Li+ separation.

Scale Design of Dual-Layer Polyphenylsulfone/Sulfonated Polyphenylsulfone Hollow Fiber Membranes for Nanofiltration.

This study focuses on the synthesis and characterization of dual-layer sulfonated polyphenylenesulfone (SPPSu) nanocomposite hollow fiber nanofiltration membranes incorporating titanium dioxide (TiO2) nanoparticles through the phase inversion technique. Advanced tools and methods were employed to systematically evaluate the properties and performance of the newly developed membranes. The investigation primarily centered on the impact of TiO2 addition in the SPPSu inner layer on pure water permeability and salt rejection. The nanocomposite membranes exhibited a remarkable three-fold increase in pure water permeability, achieving a flux of 5.4 L/m2h.bar compared to pristine membranes. The addition of TiO2 also enhanced the mechanical properties, with an expected tensile strength increase from 2.4 to 3.9 MPa. An evaluation of salt rejection performance using a laboratory-scale filtration setup revealed a maximal rejection of 95% for Mg2SO4, indicating the effective separation capabilities of the modified dual-layer hollow fiber nanocomposite membranes for divalent ions. The successful synthesis and characterization of these membranes highlight their potential for nanofiltration processes, specifically in selectively separating divalent ions from aqueous solutions, owing to their improved pure water flux, mechanical strength, and salt rejection performance.

Fabrication of high-performance MeI and HPEI assembled PES/CPES hollow fiber nanofiltration membranes with high positive charges for efficient removal of salt/heavy metal ions

Environmental protection and resource recovery require efficient separation of salts and heavy metal ions from wastewater. A new hollow fiber nanofiltration membrane (HFNM) with a highly positive charge was developed via Hyperbranched polyethyleneimine (HPEI) self-assembly and methyl iodide (MeI) quaternization on a polyethersulfone (PES) with carboxylic-PES (CPES) substrate. Effects of different layers on surface charge and roughness, wettability, and mechanical stability were evaluated. MgCl2 and ZnCl2 as representative of salts and heavy-metal ions, respectively, were used to investigate separating properties of the membranes in terms of feed temperature and concentrations, operating pressures, antifouling properties, and long-term stability. The relationship between salt/ions rejection and water flux, pore size, and surface positive charge degree was explained by comparing the structures and properties of the membranes. The 1wt.% HPEI and 0.5 wt.% GA solutions for 30 min crosslinking at pH of 11 and then 5 wt.% MeI solution could lead to the formation of the optimum membrane. Based on high hydrophilicity, low surface roughness, Donnan exclusion, and steric hindrance, the membrane could effectively exhibit superb rejection rates of Zn2+ (99.8 %), and Mg2+ (98.6 %), while showing high flux values (24.47 and 33.54 Lm−2h−1). The high flux rate (around 25.41 Lm−2h−1) during 4 cycles of regeneration, and high ions rejection (>98 %) were retained even after an 8-hour consistent operation. The prepared membrane, with high durability and structural stability, can introduce an effective solution for water purification from divalent ions.

Fabrication of polyamide hollow fiber nanofiltration membrane with intensified positive surface charge density via a secondary interfacial polymerization

In this work, a positively charged hollow fiber nanofiltration (NF) membrane based on twice interfacial polymerization (IP) reactions was developed for water soften and heavy metal ions removal. The first IP reaction was conducted on the polyethersulfone (PES) hollow fiber substrate using a mixture of branched polyethyleneimine (PEI) and piperazine (PIP) as the aqueous phase monomers in the aqueous phase reacting with trimesoyl chloride (TMC) in the cyclohexane solution. Then, a secondary IP reaction was performed between tris(2-aminoethyl) amine (TAEA) solution and the residual acyl chloride groups on the membrane to increase the positive charge density on the membrane surface. Consequently, a NF membrane with intensified positive surface charge density was successfully fabricated. The optimized membranes achieved a high rejection of MgCl2 of 97.6% while maintaining a pure water permeability (PWP) of 16.0 L m−2 h−1 bar−1. Meanwhile, the membranes exhibit high rejection values of 99.8% to Cu2+ and 99.7% to Zn2+, respectively. In conclusion, this work provides a facile way to prepare a positively charged membrane for efficient water softening and metal ions removal.

Retention of micropollutants by polyelectrolyte multilayer based hollow fiber nanofiltration membranes under fouled conditions

To meet the increasing global water demand, local solutions, such as the reuse of greywater, are becoming of greater importance. While greywater reclamation has been implemented, full-scale adaptation has been limited by the occurrence of micropollutants in treated greywater effluent. To reduce the risks posed by micropollutants, advanced post-treatment is required. One promising technology is the implementation of hollow fiber nanofiltration, which has proven to effectively remove micropollutants. However, the effect of fouling on the overall membrane performance has received limited attention. In this research, the effect of fouling on the performance of polyelectrolyte multilayer nanofiltration membranes was evaluated. Filtration experiments were performed using hollow fiber nanofiltration membranes using model solutions and greywater effluent. Synthetic greywater effluent with different model foulants was implemented to simulate bio- and colloidal fouling. Afterwards, the fouling propensity of greywater effluent from a source-separated treatment plant was evaluated. The performed experiments demonstrated that the studied hollow fiber nanofiltration membranes are mainly sensitive to biofouling. Permeability loss was observed in all foulant experiments, and overall, sodium alginate most severely reduced the flux. Regardless of the loss in permeability, micropollutant retention remained relatively constant, demonstrating the potential suitability of hollow fiber nanofiltration membranes in greywater reclamation schemes.

Influence of dominant salts on the removal of trace micropollutants by hollow fiber nanofiltration membranes

Nanofiltration (NF) is seen as a promising advanced treatment technology to deal with the increasing concentration of micropollutants (MPs) in water sources globally. To further improve the successful implementation of NF, an increased understanding of membrane transport mechanisms is important. One key aspect among these mechanisms concerns the influence of solution composition on the overall filtration performance. Although several studies report the influence of feed solution composition on the removal of micropollutants by NF membranes, the underlying mechanisms are often not fully understood. In this study, the impact of dominant salts (NaCl, Na2SO4, MgCl2) on the removal of trace MPs by commercial hollow fiber NF membranes (dNF40, dNF80) was investigated. Common conditions where salt concentrations greatly exceed MP concentrations were applied to assess their potential influence at environmentally relevant concentrations. Experimental observations reveal that a dominant salt alters MP transport behaviour substantially. The impact of a dominant salt on MP transport via electrostatic coupling increases for MPs of higher mobility inside the membrane. Overall, higher mobility, i.e. lower removal, of MPs through the dNF80 membranes was observed. Correspondingly, the strongest impact was observed for the dNF80 membrane, where the removal of positively charged atenolol increased from about 60% to >90% in the presence of Na2SO4. A theoretical transport model (DSPM&DE) was used to assist the interpretation of experimental observations further. Model predictions reveal the relevance of two effects: the influence of a dominant salt on the charge-based membrane properties and the electrostatic coupling in the form of the arising membrane potential.

Removal of arsenic from water using a CuBTC incorporated thin film nanocomposite hollow fiber membrane by interfacial polymerization on lumen side

A thin film nanocomposite (TFN) low-pressure driven hollow fiber (HF) nanofiltration (NF) membrane of CuBTC incorporated in polyamide layer was developed via interfacial polymerization (IP) of m-phenylenediamine (MPD) and CuBTC/trimesoyl chloride (TMC). The inner surface of the polysulfone (PSF) hollow fiber substrate was covered with a thin polyamide coating. During the IP process, a small quantity of CuBTC (0.2 wt%) was mixed into the TMC solution, which significantly enhanced the pure water permeate flux of the developed TFN hollow fiber membrane. The characteristics of developed HF membranes were studied using the scanning electron microscope (SEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM), molecular weight cut-off (MWCO), pure water permeability, X-ray photoelectron spectroscopy (XPS), contact angle, Fourier transform infrared spectroscopy (FTIR) and surface zeta potential. As CuBTC was included in the polyamide layer, the pure water permeability of the TFN membrane increased from 4.4 l/m2h.bar (TFC) to 16.6 l/m2h.bar, as supported by an increment in average pore radius from 6.9 Å to 10.6 Å and MWCO from 693 Da to 1723 Da. The TFN hollow fiber membrane exhibits 85.8 % rejection of arsenate with enhanced permeated flux compared to the nascent thin film composite membrane. Thus, the developed low-pressure driven TFN HF membrane was capable of arsenate rejection. Performance of the developed TFN HF membrane was tested for artificially arsenic-contaminated groundwater with a rejection of 79.7–84.5 % arsenate, 41.6 % TDS, 41.2 iron and 42.8 % hardness at 1 bar transmembrane pressure (TMP) with 12.5 l/m2h permeate flux.

Advanced drinking water production by 1 kDa hollow fiber nanofiltration – Biological activated carbon filtration (HFNF – BACF) enhances biological stability and reduces micropollutant levels compared with conventional surface water treatment

This study comprehensively investigates the quality of drinking water produced by novel advanced treatment encompassing 1 kDa hollow fiber nanofiltration (HFNF) – Biological Activated Carbon Filtration (BACF) from (reservoir) surface water, and compares this with drinking water after conventional ‘CSF’ pretreatment (coagulation – flocculation – sedimentation – media filtration – UV-disinfection) – BACF. The objective of HFNF – BACF treatment is to enhance the drinking water's quality in increased biological stability, reduced concentrations of organic micropollutants (OMP), and improvement in other chemical-physical parameters, whilst maintaining sufficient hardness to avoid subsequent remineralization. For this study a large suite of quality parameters was extensively monitored in pilot plants during nearly two years, enabling the incorporation of seasonal effects. HFNF – BACF treatment accomplished a similarly high level of biological stability as regrowth-free drinking waters (total organic carbon (DOC) 0.6 mg/L, assimilable organic carbon (AOC) 4 μg/L Ac–C and <1 μg/L biopolymer-C, total microbial growth potential (MGP) as BPC14 50 ng d/L and as BGP 170 × 103 cells/mL), unlike the conventional treatment (1.9 mg/L, 10 μg/L, 9 μg/L, 130 ng d/L and 170 × 103 cells/mL, respectively) where regrowth occurred in its distribution network. Average OMP removal, including perfluoro-alkyl substances (PFAS), by HFNF – BACF (54%) was higher than conventional treatment (37%). This improvement was mainly attributable to rejection in the HFNF membrane step, indicating that the DOC concentration after HFNF pretreatment was not yet sufficiently low to eliminate competitive adsorption and/or preloading in the BACF (confirmed by laboratory experiments). The advanced treatment also performed better in turbidity, particulates and most trace metals. Importantly, hardness retention by HFNF was only moderate, rendering remineralization unnecessary. Overall, this study demonstrates the superior performance in water quality of advanced HFNF – BACF treatment compared to conventional treatment.

Single‐step polyelectrolyte complex coating on hollow fibers yields nanofiltration or biocatalytic properties

The modification of membranes with polyelectrolytes via the Layer-by-Layer (LBL) method has become state of the art in recent years. It is used to fabricate nanofiltration hollow fiber membranes or to immobilize biomolecules on a membrane surface. However, it still remains a time consuming process. In contrast, this work explores a single-step membrane modification with coating solutions containing both polyanions and polycations. High salt concentration in the coating solution suppresses the complexation of the polyelectrolytes prior to the coating. Then, the controlled reduction of the salt concentration during the coating triggers the formation of a polyelectrolyte complex layer on the membrane. Three coating methods are proposed: (1) In interfacial complexation (IC), the polyelectrolyte solution coats the membrane and is subsequently precipitated by flushing with water. (2) Diffusive desalination (DDS) uses the concentration difference between the coating solution in the lumen and a water stream in the shell side to remove salt ions continuously. (3) In polyelectrolyte concentration (PC), the polyelectrolyte solution is coated at a constant flux. Here, the membrane retains the polyelectrolyte while ions permeate through. First, we evaluate the coating methods regarding their ability to produce nanofiltration membranes, which varies depending on the coating method used. With PC, membranes with up to 79% MgCl2 rejection and a permeability of 30 LMH/bar are obtained. Moreover, in-situ functionalization of the membranes is investigated by the addition of enzymes. Here, with DDS enzymes are immobilized, mostly achieved through adsorption via electrostatic interactions.