Low Reverse Salt Flux Research Articles

Forward osmosis membrane with lightweight functionalised multiwall carbon nanotube nanofillers

ABSTRACT Thin-film nanocomposite (TFN) membranes with a polyamide (PA) active layer modified with carbon nanotubes (CNTs) hold promise for water desalination and wastewater reuse via forward osmosis (FO). We hypothesise that modifying the PA active layer with hydroxyl-functionalised multi-wall carbon nanotubes (f-MWCNTs) will enhance the water flux of the FO membrane while maximising salt rejection. TFN membranes were modified using in situ interfacial polymerisation, with varying f-MWCNT mass content to minimise agglomeration. These modified FO membranes are designated as CTFN-x, where x represents the mass content of f-MWCNTs, ranging from 0.001%, CTFN-1 to 0.008%, CTFN-8 (w/v). The surface properties of CTFN-x were characterised using electron microscopy, atomic force microscopy, and molecular spectroscopy. IR spectroscopic data confirm the successful adherence of f-MWCNTs as a bridging agent between the 1,3-phenylenediamine (MPD) and trimesoyl chloride (TMC) polymers, preserving FO membrane integrity. The CTFN-4 FO membrane shows the highest water flux (29 LMH) and the lowest reverse salt flux (2.90 gHM), attributed to preferential water flow channels in the f-MWCNTs. The integration of f-MWCNTs into the active layer improved water flux, reduced reverse salt flux, and enhanced the antifouling properties of FO membranes.

ABPBI-based hollow fiber membranes for forward osmosis (FO) possessing low reverse salt flux

The poly(2,5-Benzimidazole), known for its excellent thermochemical stability, was evaluated as a membrane material for forward osmosis. The dope in methane sulfonic acid was used to make hollow fiber membranes. The availability of bound MSA in HFMs was compared with its neutral form. Aqueous solutions of two common salts reported for FO (NaCl and MgCl2) were used as a draw solution at varying concentrations. The performance was determined in terms of water flux and reverse salt flux. The long-term performance of the membrane was assessed. The heat pretreatment of membranes was beneficial in offering low reverse salt flux, a crucial parameter in FO. The heat treatment at 350 °C exhibited excellent performance of low-RSF, irrespective of the draw solute used. The presence of MSA in the membrane matrix was found to be beneficial. Present HFMs exhibited reverse salt flux as low as 0.003 mol m−2 h−1 using 2 mol L−1 MgCl2 as a draw solution. The water flux of present membranes was lower than that of reported FO-membranes, which is attributable to the larger thickness of the present membranes. The findings will be used to make ABPBI-based membranes in thin form to elevate the fluxes and their practical applicability.

High-performance thin film composite forward osmosis membrane for efficient rejection of antimony and phenol from wastewater: Characterization, performance, and MD-DFT simulation

The effective removal of heavy metals and phenolic pollutants from aqueous solutions has received widespread attention in the field of wastewater treatment. In this work, a novel PAN/CNTs/UiO-66-NH2 modified forward osmosis (FO) membrane was prepared for efficient removal of antimony (Sb) and phenol from wastewater. The membrane was synthesized using a facile and cost-effective method. The PAN/CNTs substrate membrane was prepared using electrospinning technology, and UiO-66-NH2 MOF particles were loaded onto the surface of the active layer during the interfacial polymerization (IP) process. The presence of CNTs in the spinning solution regulated the pore structure and properties of nanofibers. Characterization of the membrane confirmed its unique structure and enhanced properties. When the CNTs addition was 0.01 g, and UiO-66-NH2 addition was 0.05 wt%, the FO membrane exhibited the optimal operational performance. In the AL-FS mode, the water flux, reverse salt flux (RSF), and Js/Jw ratio were 14.68 LMH, 0.17 gMH, and 0.01 g/L, respectively. As a comparison, the water flux, RSF, and Js/Jw ratio were 21.19 LMH, 0.65 gMH, and 0.032 g/L in the AL-DS mode, respectively. Simultaneously, efficient removal of antimony and phenol was achieved in both modes, with antimony removal efficiencies of 99.26 % and 97.98 %, and phenol removal efficiencies of 96.61 % and 93.18 %, respectively. The modified membrane exhibited excellent performance in rejecting Sb and phenol. Molecular dynamics simulations and density functional theory calculations provide theoretical support for the excellent performance of membranes. The membrane demonstrated a high water flux, making it promising for practical applications. Additionally, it exhibited remarkably low reverse salt flux, highlighting its suitability for desalination processes. The exceptional removal efficiency of Sb and phenol, coupled with the membrane's impressive hydraulic performance, makes it a promising candidate for the treatment of industrial effluents containing these challenging contaminants. The results presented in this study underscore the potential of PAN/CNTs/UiO-66-NH2 FO membranes as an advanced solution for addressing water pollution challenges.

High-performance support-free molecular layer-by-layer assembled forward osmosis membrane incorporated with graphene oxide

Forward osmosis (FO) membranes generally have a thin-film composite (TFC) structure comprising an ultrafiltration (UF)-grade support layer and a polyamide (PA) active layer. However, the lack of high-performance membranes limits FO. To improve the FO performance, internal concentration polarization (ICP) should be controlled to reduce the water flux within the support layer. In this study, a novel support-free molecular layer-by-layer (SF-mLbL) technique using a microfiltration (MF)-grade support layer for minimum ICP was applied to produce a robust and uniform active layer, even on large pores of the support layer. Based on the location of graphene oxide (GO) nanoparticles, thin-film nanocomposite (TFN) and thin-film nanocomposite-interlayer (TFNi) membranes were fabricated. Among these, the TFNi membrane with the highest performance contained 0.7 wt% GO nanoparticles and was stacked in 15 cycles. The 0.7 wt%-15 cycles TFNi membrane showed high water flux (87.18 ± 0.15 LMH) and low reverse salt flux (5.06 ± 0.11 gMH) when deionized (DI) water and 0.5 M NaCl solution were used as feed and draw solutions, respectively, in FO mode. This study demonstrates that the SF-mLbL technique is suitable for manufacturing high-performance FO membranes.

High performance forward osmosis membrane with ultrathin hydrophobic nanofibrous interlayer

The novel thin film composite (TFC) forward osmosis (FO) membrane with electrospinning nanofibers as support layer can alleviate internal concentration polarization (ICP). While the macropores of the nanofiber support layer cause defects in the polyamide (PA) layer. Therefore, hydrophobic polyvinylidene fluoride (PVDF) fine nanofibers were used as an interlayer to modulate the process of interfacial polymerization (IP) in this study. The results showed that the introduction of the interlayer improved the hydrophobicity of the support layer for achieving uniform, thin and defect-free selective polyamide (PA) layer. The water flux of TFC-PVDF was 58.26 LMH in the FO mode of 2 M NaCl, which was two times higher than that of the unmodified FO membrane. Lower reverse salt flux (4.91 gMH) and structural parameter (179.43 μm) alleviated the ICP. In addition, TFC-PVDF membrane showed good anti-fouling performance for SA (flux recovery ratio of 93.97%) due to high hydrophilicity, low zeta potential and low roughness. This study provides an easy and promising method to prepare defect-free PA selective layer on the macropores nanofiber support layer. The novel FO membrane shows high desalination performance and anti-fouling properties.

Fabrication of high-performance forward osmosis membrane based on asymmetric integrated nanofiber porous support induced by a new controlled photothermal induction method

The high surface roughness and large pore size of electrospun nanofibers (ESNF) make it impossible to form good polyamide (PA) layers through interfacial polymerization. Therefore, ESNF cannot be directly used as the supporting layer of nanofiber-supported thin film composite forward osmosis (NTFC-FO) membrane. However, its advantages of high porosity and large pore size are required for forward osmosis (FO) process. In this work, for the first time, an asymmetric integrated ESNF is constructed by introducing photothermal materials PANI into the supporting layer and using in situ photothermal annealing to controllably reduce the surface roughness and pore size of the support membrane, which not only meets the requirements of interface polymerization to form a good PA layer, but also maintains the high porosity, large pore size and structural stability of the ESNF. With this strategy, the FO membrane with highly selective PA layer and low membrane structural parameter (S) were obtained. The results shows that NTFC-FO membrane shows high water flux of 40.2 L·m−2·h−1 and low reverse salt flux of 4.9 g·m−2·h−1, and specific salt flux of Js/Jw is only 0.12 with deionized water and 1.0 M NaCl solution as the feed solution and draw solution, respectively, and the FO membrane also exhibit excellent rejection to dye wastewater. It can be considered that the asymmetric integrated ESNF supporting layer constructed by the photothermal annealing strategy provides a simple and feasible method for the preparation of high-performance NTFC-FO membranes.

Bioinspired nanobubble water channel membranes for ultrafast osmosis desalination

Biological water channels (BWCs) and artificial water channels (AWCs) exhibit standout water-to-ion selectivity. However, difficult membrane integration threatened their desalination application. Inspired by biological cell membranes, an ultrafast osmosis desalination membrane is fabricated with air nanobubbles adhered on fluorinated carbon nanotubes (ANBs-FCNTs) interlayer sandwiched between polyacrylonitrile (PAN) nanofiber layers. Water transport through nanobubble water channel is accelerated by nanobubble gating for selective transport and nanobubble-lubricated water channels for low friction, which was confirmed by varying combination modes of forward osmosis (FO) and membrane distillation (MD). Superior salt rejection is achieved by efficient nanobubble gating, resulting from the combined action by size screening, fast surface slip, electrostatic shielding and sufficient adsorption of ANBs-FCNTs interlayer. In nanofluidic diode membrane concatenation model, multistep capillary force provides enhanced water flux, whereas multi-staged concatenation layers offer more barrier gating for the ion's diffusion, thus resulting in higher permselectivity. The bioinspired nanobubble membranes can achieve high water flux (479.8 L m−2 h−1), high rejection (>95%) to solutes and low reverse salt flux (0.686 g m−2 h−1) under robust and continuous cross flow operation, which outperformed the state-of-the-art forward osmosis membranes. The electrospinning and deposition technique allows for scalable membrane preparation for desalination, resources and energy production.

Development of high-performance CuBTC MOF-based forward osmosis (FO) membranes and their cleaning strategies

Though the forward osmosis (FO) process has been primarily accepted for desalination and wastewater treatment, it still faces significant challenges of (i) low water flux and high reverse solute flux and (ii) membrane fouling. In the present study, a new thin film composite (TFC) FO membrane was prepared by interfacial polymerization of chitosan biopolymer and trimesoyl chloride (TMC) as a separation layer and porous CuBTC MOF embedded polyethersulfone (PES) as the support layer to increase transport and antifouling properties. When compared to the bare membrane (Jw: 26 LMH, Js: 0.12 GMH) and similar literature reported membranes, the optimized FO membrane with 0.5 wt % CuBTC (Cu@FO-0.5) exhibits higher water flux (Jw: 58 LMH) with low reverse salt flux (Js: 0.57 GMH). This improvement is due to the additional pathways for water transportation due to CuBTC MOF. The modified membrane also had a reduced structural parameter (S), a lower reverse salt flux, and increased water wettability. Various physical and chemical membrane cleaning agents were studied to eliminate organic (algae) and inorganic (clay) foulants added to synthetic feed wastewater. The selected cleaning agents were later studied in series and in combinations for both foulants. Chemical cleaning showed higher water flux recovery than physical cleaning and obtained similar results for water collected from natural sources (river, reservoir, and pond). The findings suggest that Cu@FO-0.5 FO membranes integrated with reverse osmosis could be an effective technology in treating drinking water and wastewater sources.

Incorporation of porous materials in forward osmosis membrane for increased water recovery from waste streams

Forward osmosis (FO) is a membrane separation process that involves an osmotic pressure-driven, semi-permeable membrane to selectively separate water from waste streams. Increased water flux and salt removal characterize an ideal FO membrane. In contrast to the first-developed symmetric cellulose triacetate (CTA) membrane, the thin film composite (TFC) membrane had a higher water flow and a lower reverse salt flux. The incorporation of porous and non-porous nano-sized particles in the membrane structure has improved TFC performance even further. The TFC-FO membrane was created in this study by incorporating porous ZIF-8 MOF into the polyethersulphone (PES) support layer. Interfacial polymerization of chitosan (CS) biopolymer and trimesoyl chloride (TMC) produced the thin separation layer. The porous MOFs provided additional water pathways. The water wettability of the separation layer was also improved by CS-TMC polymerization. In comparison to the bare membrane, the water fluxes of the ZIF-8@FO membrane improved by 2.8 times. The newly developed FO membrane was found effective for use in sewage and wastewater treatment.

Synthesis and characterization of PES/PSF/PEG by immersion precipitation for Mediterranean seawater desalination by FO membrane

AbstractIn the present study, a simple, inexpensive, nontoxic, and environmentally friendly polyethylene glycol (PEG) polymer was used to enhance the hydrophilicity of the forward osmosis (FO) membrane using various PEG concentrations as a pore forming agent in the casting solution of polyethersulfone/polysulfone (PES/PSF) blend membranes. A nonwoven PES/PSF FO blend membrane was fabricated via the immersion precipitation phase inversion technique. The membrane dope solution was cast on polyethylene terephthalate (PET) nonwoven fabric. The results revealed that PEG is a pore forming agent and that adding PEG promotes membrane hydrophilicity. The membrane with 1 wt% PEG (PEG1) had about 27% lower contact angle than the pristine blend membrane. The PEG1 membrane has less tortuosity (which reduces from 3.4–2.73), resulting in a smaller structure parameter (S value) of 277 μm, due to the presence of open pores on the bottom surface structure, which results in diminished ICP. Using 1 M NaCl as the draw solution and distilled water as the feed solution, the PEG1 membrane exhibited higher water flux (136 L m−2 h−1) and lower reverse salt flux (1.94 g m−2 h−1). Also, the selectivity of the membrane, specific reverse salt flux, (Js/Jw) showed lower values (0.014 g/L). Actually, the PEG1 membrane has a 34.6% higher water flux than the commercial nonwoven‐cellulose triacetate (NW‐CTA) membrane. By means of varied concentrations of NaCl salt solution (0.6, 1, 1.5, and 2 M), the membrane with 1 wt% PEG showed improved FO separation performance with permeate water fluxes of 108, 136, 142, and 163 L m−2 h−1. In this work, we extend a promising gate for designing fast water flux PES/PSF/PEG FO blend membranes for water desalination.

Forward osmosis, reverse osmosis, and distillation membranes evaluation for ethanol extraction in osmotic and thermic equilibrium

One of the significant challenges of the industry is the economic extraction of ethanol from aqueous solutions of interest to the food industry. Specifically, in the alcoholic beverages industry, the non-alcoholic beverage market has gained importance, demanding more non-alcoholic drinks with higher organoleptic quality. In this context, the technology related to the use of membranes has shown great potential. Our research aims to determine the performance of forward osmosis using FO, RO, and MD membranes as an option in the extraction of alcohol in an osmotic (Δπ = 0) and thermal (ΔT° = 0) equilibrium process. The results showed that all the membranes have the potential to dealcoholize a 12% v.v. synthetic ethanol solution. The results showed that Membrane Distillation is a viable strategy as a complement in a hybrid FO-MD approach, achieving ethanol flux values close to those offered by FO membranes and much higher than those shown by RO membranes. We also proposed other technical criteria for membrane performance evaluation, such as maintaining a low reverse salt flux and a low or no water flux to keep the organoleptic properties of a hypothetical alcoholic beverage subjected to the FO-MD hybrid process. For a high Ethanol/Salt flux ratio, the RO-82V and FO-CTA membranes presented the best performance. Furthermore, in an Ethanol/Water flux ratio, RO membranes perform best when working in an osmotic equilibrium process with a water flux equal to zero. Regarding the FO membranes, in an Ethanol/Water flux ratio, the FO-TFC membrane presented the best performance.

Recovering and reuse of textile dyes from dyebath effluent using surfactant driven forward osmosis to achieve zero hazardous chemical discharge

This experimental study explores the feasibility of the reuse of dyes recovered from denim and polyester dyebath effluents using forward osmosis (FO) system to achieve zero hazardous material discharge. In batch experiments, the sodium dodecyl sulfate (SDS) at 0.5 M concentration generated an average flux of 3.5 L/m2/h (LMH) and reverse salt flux (RSF) of only 0.012 g/m2/h (GMH), while maintaining 100% dye rejection. This flux stability comes from the property of surfactants to form micelles and exert a stable osmotic pressure (π) above their critical micelle concentration (CMC). The low RSF is due to the greater micelle size. A colored fouling layer was formed on the membrane active layer (AL), which was easily removed using sodium hydroxide (NaOH) and citric acid. According to Fourier transform infrared spectra and atomic forces microscopy images of the AL, the interaction between foulants and membrane active groups did not significantly affect the physiochemical properties of the membrane. In the semi-continuous experiment, a very stable average flux of 7.3 LMH and RSF of 0.03 GMH was obtained using 0.75 M SDS as draw solution. The stacked 1D proton nuclear magnetic resonance analysis (1HNMR) spectra of both original and recovered disperse dyes showed 100% similarity, which validates the concept that the recovered dyes maintained their integrity during reconcentration and can be reused in the next batch dyeing process. Importantly, the diluted SDS concentration can be directly reused within the same textile industry in scouring and finishing processes. The processes of dye recovery and reuse developed in this study do not produce any waste or hazardous by-products and are suitable for scale-up and onsite industrial applications.

Highly permeable thin film nanocomposite membrane utilizing a MoS2@NH2-UiO-66 interlayer for forward osmosis removal of Co2+, Sr2+ and Cs+ nuclide ions

Novel MoS2@NH2-UiO-66 thin-film nanocomposites with interlayer (TFNi) membranes were developed to improve forward osmosis (FO) membrane performance. The prepared TFNi membrane shows a high water permeability of 38.13 ± 0.8 L m−2h−1 and low reverse salt flux (JS/JV) of 0.038 when using 2.0 mol/L sodium chloride as the draw solution (DS) and deionized water as the feed solution (FS) under AL-FS mode. This is attributed to MoS2@NH2-UiO-66 modifications of substrate properties, which fix m-phenylenediamine (MPD) on the nanomaterial surface, increase the polyamide (PA) layer crosslinking degree on the material surface, and allow trimesoyl chloride (TMC) to stay on the substrate surface during interfacial polymerization (IP) and prevent accumulation in the pores of the substrate. Therefore, the trade-off between permeability and selectivity of TFN membranes is overcome. The MoS2@NH2-UiO-66 TFNi membrane effectively removes Co2+, Sr2+ and Cs+ from aqueous solution via FO retention. When Co2+, Sr2+ and Cs+, nuclide ions with small hydration radii, are present in the FS at 20 mg/L, the retention rates are maintained at 99.6%, 99.7% and 97%, respectively, which are higher than those of existing commercial membranes. These results indicate the potential of MoS2@NH2-UiO-66-TFNi membranes for treatment of nuclide ions in wastewater.

A freestanding graphene oxide framework membrane for forward osmosis: Separation performance and transport mechanistic insights

Graphene oxide (GO)-based membranes have been explored for application in forward osmosis (FO). However, the mass transfer inside GO framework membranes is far from sufficiently understood, and designing freestanding GO framework membranes with further enhanced performance remains a challenge. In this study, freestanding GO framework membranes were synthesized and investigated in a FO system. The membrane water flux, reverse salt flux, and forward salt flux were systematically investigated using different feed and draw solutions. The membrane synthesized using GO nanosheets and polyelectrolyte spacers (poly(sodium 4-styrenesulfonate) (PSS) (GO-PSS membrane) possesses high water flux, low reverse and forward salt flux, and low specific reverse salt flux (i.e., high water/salt selectivity). We found that both the size and surface charge density of the membrane pores influenced the salt transport inside the membrane in FO. By combining results from experiments and numerical modeling, the influence of the electrical double layer (EDL) extension inside the membrane pores on salt transport was quantitatively analyzed. Additionally, it was found that the EDL extension can influence the forward and reverse solute transport simultaneously (i.e., bidirectional transport). Furthermore, viable strategies toward designing GO framework membranes with enhanced performance for application in FO as well as their potential application niche were discussed.

Fabrication of dialyzer membrane-based forward osmosis modules via vacuum-assisted interfacial polymerization for the preparation of dialysate

Direct preparation of dialysate from tap water based on osmotic dilution is beneficial for home hemodialysis which requires a defect-free forward osmosis (FO) membrane module. This report introduced a new vacuum-assisted interfacial polymerization (VAIP) process for optimal distribution of the aqueous phase and a well-controlled IP using dialyzer membranes. We demonstrated statistically that the vacuum-assisted process is beneficial for the preparation of integral FO modules with multiple fine fibers due to the good distribution of the aqueous phase. The as-prepared FO module displayed a low structural parameter (262 μm), an acceptable water flux (17.6 L m−2 h−1), and a low specific reverse salt flux (0.16 g/L) using deionized (DI) water as the feed and 1 M NaCl as the draw in AL-FS mode. Direct dialysate preparation from tap water using the FO module was presented and modeled with a good fit. The work showcases a new FO module based on dialyzer and its potential applications in the medical field.

Coupling solar-driven interfacial evaporation with forward osmosis for continuous water treatment.

Forward osmosis (FO) driven by osmotic pressure difference has great potential in water treatment. However, it remains a challenge to maintain a steady water flux at continuous operation. Herein, a FO and photothermal evaporation (PE) coupling system (FO-PE) based on high-performance polyamide FO membrane and photothermal polypyrrole nano-sponge (PPy/sponge) is developed for continuous FO separation with a steady water flux. The PE unit with a photothermal PPy/sponge floating on the surface of draw solution (DS) can continuously in situ concentrate DS by solar-driven interfacial water evaporation, which effectively offsets the dilution effect due to the injected water from FO unit. A good balance between the permeated water in FO and the evaporated water in PE can be established by coordinately regulating the initial concentration of DS and light intensity. As a consequence, the polyamide FO membrane exhibits a steady water flux of 11.7 L m-2 h-1 over time under FO coupling PE condition, effectively alleviating the decline in water flux under FO alone. Additionally, it shows a low reverse salt flux of 3g m-2 h-1. The FO-PE coupling system utilizing clean and renewable solar energy to achieve a continuous FO separation is significantly meaningful for practical applications.

Preparation and characterization of novel thin film composite forward osmosis membrane with halloysite nanotube interlayer

In this study, the electrospun polyacrylonitrile (ePAN) fiber mats were used as support layer and natural mineral-halloysite nanotubes (HNTs) was used to construct the interlayer. Polydopamine modification was utilized to enhance the hydrophilicity of ePAN substrates and dispersibility of HNTs. The mHNTs interlayer effectively minified the surface pore size of substrates providing a better interface for interfacial polymerization forming an integrated and thin PA selective layers. Compared to the unmodified membranes, the water flux of the optimized membrane with mHNTs interlayer about 61.60% and 79.70% higher and the reverse salt flux of which was 38.95% and 45.08% lower in AL-FS mode and AL-DS mode respectively. These results suggested that introducing halloysite nanotube interlayer is an effective, and low-cost way to fabricate high-performance FO membrane. ● Highly accessible and low-cost halloysite nanotubes (HNTs) were utilized to construct interlayers on electrospun nanofiber substrates. ● A high-performance thin film composite forward osmosis membrane was successfully prepared. ● HNTs interlayer showed benefits in generation of polyamide selective layers in interfacial polymerization. ● High water flux and low reverse salt flux were observed synchronously.

Apple Juice, Manure and Whey Concentration with Forward Osmosis Using Electrospun Supported Thin-Film Composite Membranes.

Forward osmosis (FO), using the osmotic pressure difference over a membrane to remove water, can treat highly foul streams and can reach high concentration factors. In this work, electrospun TFC membranes with a very porous open support (porosity: 82.3%; mean flow pore size: 2.9 µm), a dense PA-separating layer (thickness: 0.63 µm) covalently attached to the support and, at 0.29 g/L, having a very low specific reverse salt flux (4 to 12 times lower than commercial membranes) are developed, and their FO performance for the concentration of apple juice, manure and whey is evaluated. Apple juice is a low-fouling feed. Manure concentration fouls the membrane, but this results in only a small decrease in overall water flux. Whey concentration results in instantaneous, very severe fouling and flux decline (especially at high DS concentrations) due to protein salting-out effects in the boundary layer of the membrane, causing a high drag force resulting in lower water flux. For all streams, concentration factors of approximately two can be obtained, which is realistic for industrial applications.

Double-barrier forward osmosis membrane for rejection and destruction of bacteria and removal of dyes

In this paper, a novel FO membrane with antibacterial and antifouling properties was prepared for the first time by forming a multifunctional negatively-charged active layer via the surface amidation reaction with two antibacterial agents, namely, sulfamethoxazole (SMX) and trimethoprim (TMP). The membranes modified by SMX and TMP showed superior water flux, the highest reaching 31.86 (±1.2) LMH for M-T-2, and a lower reverse salt flux (7.74 gMH), which significantly improved the FO performance. In addition, the SMX and TMP immobilized on the FO membrane formed an electrostatic repulsive force towards the negatively-charged bacteria, and showed the inherent destruction capabilities for bacteria when in contact, constructing a double barrier for the fouling of bacteria. As an example, M-T-2 membrane showed good anti-bacteria performance (OD value of 0.058) in the actual municipal sludge wastewater, meanwhile maintaining good water permeability (88% of the initial flux). Furthermore, the prepared membrane owned suitable antifouling and antibacterial ability in the negatively-charged dye wastewater, achieving the efficient removal of more than 95.5% of the dyes. These results show that the modification of the active layer with antibacterial agents can significantly improve the application prospect of FO membranes.

Functionalized polyamide membranes yield suppression of biofilm and planktonic bacteria while retaining flux and selectivity

• Ag-MOFs incorporated into the surface of FO polyamide membranes at 0.03–0.06% mass. • Wettability and surface charge characteristics were favorable for antifouling. • Forward osmosis operation demonstrated suitable water flux and low reverse salt flux. • Nearly complete suppression of P. aeruginosa biofilm and planktonic E. coli achieved. • Flux and selectivity retained during organic fouling and biofouling experiments. Biofouling is a major challenge for desalination, water treatment, and water reuse applications using polymer-based membranes. Two classes of novel silver-based metal azolate frameworks (MAF) are proposed to decorate polyamide (PA) forward osmosis membranes and to improve numerous aspects of fouling and transport. Membranes functionalized with two concentrations of each MAF are compared with a pristine control material, with results that clearly highlight their tunability and bio-inhibitory effects. We report for the first time PA membranes yielding near complete suppression of a robust biofilm-forming bacterium ( Pseudomonas aeruginosa ) and inactivation of planktonic bacteria, while maintaining high selectivity. These features improve the long-term water flux performance of the membranes, tested during 24 h of accelerated biofouling and organic fouling conditions, and showing lower than 10% and 20% decline in water flux. These enhancements were achieved with only 0.03–0.06% mass of additives and little generation of hazardous waste products, indicating that low-cost and environmentally benign functionalization can prevent biofouling growth while maintaining selectivity and transport for high-performance desalination, water treatment and reuse.