Changes In Membrane Performance Research Articles

Performance of a SWRO membrane under variable flow conditions arising from wave powered desalination

A wave-powered desalination unit couples a wave energy converter and reverse osmosis (RO) membrane to produce fresh water from pressurized seawater. Although renewable energy technologies have been increasingly used for desalination, the concept of direct wave-powered desalination system is still at an early stage of development. One of the challenges with direct wave-powered desalination is that while reverse osmosis (RO) membranes are typically designed to operate at a constant feed flow and pressure, wave energy converter outputs in the form of hydraulic pressures and flows are typically highly variable. In this work, a RO membrane is investigated under variable feed flow conditions to determine the potential impact of such operation on membrane performance. The feed flow and pressure are varied using both a traditional sinusoidal profile and a rectified sinusoidal profile - a case more representative for wave-powered desalination. The permeate recovery and permeate salinity for both cases are compared with the equivalent time-averaged steady-state conditions. For purely sinusoidal flow, the performance of the RO membrane was similar to the equivalent steady-state flow conditions. For rectified sinusoidal flow, there is a marginal increase in permeate recovery, while a significant increase in permeate salinity is observed. In addition, a membrane integrity test was carried out after both sets of varying flow conditions. A significant change in membrane performance was detected after the test with the rectified sinusoidal flow.

TEMPO-mediated oxidation as surface modification for cellulosic ultrafiltration membranes: Enhancement of ion rejection and permeability

In membrane technology, rejection of dissolved salts often requires the use of nanofiltration or reverse osmosis membranes due to their sufficiently dense structure and favourable charge effects. In this work, the concept of charge-based salt rejection is extended to the more open ultrafiltration class. Surface charge of a commercial regenerated cellulose acetate ultrafiltration membrane is enhanced with TEMPO-mediated oxidation. With the modification, a membrane whose properties lie between the traditional nanofiltration and ultrafiltration classes is obtained. Moreover, a purely charge-based salt rejection mechanism is introduced to an ultrafiltration membrane.Increasing hypochlorite exposures are found to induce successively increasing surface carboxylate densities, negative zeta potentials, permeabilities and molecular weight cut-off values. In the low exposure region, the treatment mostly affects surface charge, whereas high exposures begin to open the membrane pores. Ultimately, the pH 7 zeta potential is increased from −30 up to −100 mV, and 500 ppm Na2SO4 rejections increase from an initial 4% to 36%. At the same time, pure water permeability is doubled, and cut-off value increased from 2.8 to 8.0 kDa. The reactions causing the change in membrane performance seem to take place almost exclusively on the membrane surface, while the bulk material appears unchanged.

Halloysite nanoclay doped ceramic membrane fabrication and evaluation of textile wastewater treatment performance

In this study, halloysite nanoclay-doped ultrafiltration and tight-ultrafiltration ceramic membranes were fabricated by sequential layer deposition using relatively low temperatures. The produced membranes were structurally characterized by contact angle tests and a scanning electron microscope. The pure water flux and bovine serum albumin removal were also examined, in order to determine the performance of the membranes. Finally, 3 different real wastewater treatability tests were carried out and the change in membrane performance was observed by using hot textile wastewater. In the coated membranes, the pure water flux decreased from 2000 L/(m2.h) to 100 L/(m2.h) for the ultrafiltration membrane and from about 370 L/(m2.h) to 23 L/(m2.h) for the tight-ultrafiltration membrane. In the bovine serum albumin removal efficiency test, approximately 30 % removal was obtained for the ultrafiltration membrane and 100 % for the tight-ultrafiltration membrane. In real wastewater filtration tests performed with the tight- ultrafiltration membrane, the average removal efficiency of approximately 40 % and above 44 % was obtained for chemical oxygen demand and total organic carbon and color removal, respectively. Finally, in the hot water test, it was observed that the permeate flux increased approximately 3 times, but there was no significant decrease in the treatment efficiency.

Seeking realistic membrane ageing at bench-scale

Fouling and cleaning of water treatment ultrafiltration membranes are well understood, but long-term changes (i.e. ageing) have not been fully explored. Changes in physical and chemical characteristics, and changes in membrane performance, have been attributed to ageing; however, the tools to probe these effects and their causality are limited. Most membrane ageing research focuses on bench-scale ageing of membranes, with scant attention to full-scale ageing or how bench-scale ageing can be useful in understanding full-scale ageing.The present research links membrane ageing changes observed at bench-scale with changes observed in previous full-scale studies. Two bench-scale ageing techniques were used to probe changes in performance and characteristics: soaking membranes in NaOCl as the cleaning agent, and cycling them with foulant and the cleaning agent. Changes in membrane chemistry were similar for both bench-scale and full-scale ageing, but performance differed. Membrane process complexity increases from bench-scale soaking, to bench-scale cycled operation, to full-scale operation. For some properties, the progression due to ageing differs depending on process complexity. By comparing the two bench-scale techniques with the full-scale ageing findings, it was established that irreversible foulants are critical components of full-scale ageing, and the impact of these foulants can be approximated to some extent by cycling membranes at bench-scale.

Controlled chlorination of polyamide reverse osmosis membranes at real scale for enhanced desalination performance

State-of-the-art desalination and water purification processes use reverse osmosis and nanofiltration membranes. Their thin polyamide (PA) top-layers ensure concurrent high water permeances and salt rejections, but are also intrinsically sensitive to chlorine, originating from disinfectant added upstream. The chlorine resistance of PA-based membranes has been thoroughly studied at lab-scale, as opposed to industrial-scale membrane modules, where fundamental studies are lacking. Therefore, to better understand chlorine-induced changes in membrane performance and physicochemical properties at industrial scale, chlorination of commercial 8” elements was conducted at different pH (4-7-10) in pressurized modules with low chlorine concentrations (0, 1, 20, 50 ppm NaOCl) during 2.5 h. After 50 ppm acidic chlorination, water permeability decreased (−40%) but salt rejection increased significantly (+0.4%, i.e., salt passage decreased with −78.8%). Boron (+27%) and isopropanol (+8%) rejection also increased. Chlorination with 20 ppm NaOCl at pH 7 and with 50 ppm NaOCl at pH 10 caused boron rejection to drop with −17% and −33%, respectively, but had negligible influence on isopropanol rejection. However, neutral and alkaline chlorination drastically improved water permeability with +40% and salt rejection with +0.6% (i.e., salt passage decreased with −66.9%), approaching and in some cases even slightly exceeding the salt/water permselectivity limit. It can thus be concluded that, under controlled conditions, chlorination can boost the performance of membrane modules. Significant changes in the membrane physicochemical properties were observed at pH 4. At pH 7 and pH 10, a low chlorine-uptake in the PA network was observed, although no significant PA deterioration was observed with XPS and ATR-FTIR. This study is the first to fundamentally investigate chlorination of PA-based real-scale membrane modules as a function of feed pH. Furthermore, it provides a promising strategy to boost membrane performance at real scale and highlights the importance of chlorination conditions.

Understanding the influence of solvents on the intrinsic properties and performance of polyamide thin film composite membranes

The polyamide thin film composite (TFC) has been the standard platform for reverse osmosis and nanofiltration membranes for aqueous separations for decades. It combines the properties of high permeance and unmatched selectivity for desalination applications. The highly cross-linked structure of polyamides may enable its use in organic solvent separations with several studies showing promising results. The field lacks, however, a complete understanding of how polyamides may be impacted by solvent exposure. To investigate the impacts of solvent on polyamide, we formed polyamide selective layers through interfacial polymerization onto ceramic UF supports. We quantified the permeability and selectivity changes after polyamides were exposed to an alcohol (methanol), and a ketone (acetone), and a polar aprotic solvent (DMF). We used aqueous testing before and after exposure to quantify permanent changes in membrane performance. Our results show that not only are the polyamide properties altered by the exposure to solvents, but they also show that different solvents have very different impacts on polyamide performance. The results indicate that polyamides may not be robust enough to perform nanofiltration separations in solvent environments with predictable permeability and selectivity.

Analysis of membrane unit performance in presence of wet CO2-containing mixtures

Membrane gas separation is more and more gaining room of application in biogas upgrading to biomethane to be directly fed to pipelines. The water vapour contained in the biogas stream affects the separation performance of membranes; therefore, it is important to consider this aspect for the design of the separation stage.In this work, we developed performance maps taking into account the water vapour effect on the performance of a membrane gas separation by considering different CO2/CH4 selectivities (from 25 to 100), pressure ratio and flow rate/membrane area ratio. The presence of water vapour induced significant changes in membrane performance, with consequent repercussions in CH4 recovery, which in some cases, reduced from 85.3% to 80.9% from dry to wet conditions.

Nafion-Based Low-Hydration Polyelectrolyte Multilayer Membranes for Enhanced Water Purification.

The increase of micropollutant concentration in both surface and groundwater is an emerging concern for the environment and human health. Most of such small organic molecules (medicines, hormones, and plasticizers) enter the environment via our wastewater, because they are not sufficiently removed by the current techniques applied in wastewater treatment plants. A possible solution to remove micropollutants is the usage of polyelectrolyte multilayer (PEM) based membranes. PEM membranes have received a growing interest in the past decade due to their high chemical and physical stability and their high permeability and selectivity. A popular polyelectrolyte pair to make dense PEM membranes with high salt retentions is the combination of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS). Unfortunately, smaller micropollutants (such as bisphenol A, sulfamethoxazole, naproxen, and bezafibrate) still show significant permeation through this membrane. In this study, for the first time, a single final layer of Nafion is applied on the PEM to increase the density of the PEM membrane. It is shown that when terminating with Nafion, the swelling of the multilayer decreases by 50%. These pronounced changes in layer structure are reflected by changes in membrane performance, such as a lower molecular weight cutoff (MWCO) and an increasing hydraulic membrane resistance. Furthermore, we show that the Nafion content of the multilayer can be increased by constructing a Nafion/PAH multilayer on top of the existing PSS/PAH multilayer, thereby lowering the MWCO. Although hydraulic resistance increases, these PSS/PAH/Nafion-based multilayers show excellent performance in rejecting difficult-to-remove micropollutants that have low molecular weight (200–650 Da) and different charges. Overall, a cocktail of eight small micropollutants can be removed up to 97% by these membranes, allowing strongly enhanced water purification.

Synthesis and Characterization of a High Flux Nanocellulose-Cellulose Acetate Nanocomposite Membrane.

Despite the advantages of membrane processes, their high energy requirement remains a major challenge. Fabrication of nanocomposite membranes by incorporating various nanomaterials in the polymer matrix has shown promise for enhancing membrane flux. In this study, we embed functionalized cellulose nanofibers (CNFs) with high aspect ratios in the polymer matrix to create hydrophilic nanochannels that reduce membrane resistance and facilitate the facile transport of water molecules through the membrane. The results showed that the incorporation of 0.1 wt % CNF into the polymer matrix did not change the membrane flux (~15 ) and Bovine Serum Albumin (BSA) Fraction V rejection, while increasing the CNF content to 0.3 wt % significantly enhanced the flux by seven times to ~100 , but the rejection was decreased to 60–70%. Such a change in membrane performance was due to the formation of hydrophilic nanochannels by the incorporation of CNF (corroborated by the SEM images), decreasing the membrane resistance, and thus enhancing the flux. When the concentration of the CNF in the membrane matrix was further increased to 0.6 wt %, no further increase in the membrane flux was observed, however, the BSA rejection was found to increase to 85%. Such an increase in the rejection was related to the electrostatic repulsion between the negatively-charged CNF-loaded nanochannels and the BSA, as demonstrated by zeta potential measurements. SEM images showed the bridging effect of the CNF in the nanochannels with high CNF contents.

Surface modification of polysulfone ultrafiltration membrane by in-situ ferric chloride based redox polymerization of aniline-surface characteristics and flux analyses

On the basis of the water-loving nature of Polyaniline (PANI), super hydrophilic polysulfone (PS) ultrafiltration membranes were prepared via in-situ polymerization of aniline on the surface of the membrane. Growing polyaniline in-situ leads to permeability enhancement of the ultrafiltration membrane. Surface-attenuated total reflection Fourier transform infrared spectroscopy, Atomic force microscopy, Scanning electron microscopy and energy dispersive X-spectroscopy and water contact angle demonstrated the successful attachment of PANI on PS membrane surface. Modified membranes containing increased amount of PANI were compared to the unmodified PS membrane to estimate the change in membrane performance, hydrophilicity and anti-fouling properties. PANI modified membranes showed higher water fluxes in comparison to unmodified membranes, while protein rejection was almost similar in both PANI modified and unmodified PS membranes. Atomic force microscopy and contact angle measurements confirmed increased membrane surface hydrophilicity with increasing PANI content. Fouling study and flux recovery experiments revealed that modified membranes exhibit higher flux recovery ratio (65%) and more stability to strong cleaning agents.

Using neutron methods SANS and PGAA to study evolution of structure and composition of alkali-doped polybenzimidazole membranes

Potassium hydroxide (KOH) doped polybenzimidazole (PBI) membranes are investigated as compelling candidates for water electrolysis applications, drastically reducing the ohmic losses in contrast to thick ZrO2 based diaphragms. Using small angle neutron scattering (SANS) we have found that the structure of the (KOH doped) PBI changes with doping time on a minute time scale, and that the development of the structure is highly dependent on the KOH concentration. This data is correlated with macroscopic measurements of membrane swelling resulting from the doping process which also occurs on a minute time scale. Then, using prompt gamma activation analysis (PGAA) to follow the changes in time of the chemical composition, we have found that the K concentration of these samples only increases slightly with doping times after a very rapid initial uptake, reaching a saturation value that is relatively independent of KOH concentration for long doping times of up to 24 h. However measurements of similarly doped samples show increases in ion-conductivity of nearly 3 fold, and resistivity reductions of over 2 fold on the same time scales. These measurements prove that PGAA is a sensitive method to follow changes in the chemical compositions during doping, while SANS can give information on the sub-micro structural changes of polymer electrolyte membranes. Since these methods can be correlated with ex-situ measurements of composition, resistance, ion-conductivity and macro-structure, the combined use of PGAA and SANS provides a promising means for in-operando study in order to elucidate changes in membrane performance due to electrochemical cycling, as well as to help characterize and optimize doping parameters though in-situ doping measurements, by enabling real-time study of such membrane systems.

Reversibility of membrane performance and structure changes caused by extreme cold water temperature and elevated conditioning water temperature

The effects of extreme cold water temperature, elevated cleaning water temperature, cleaning time on membrane performance, and pore size distribution were studied using flat-sheet polyvinylidene fluoride (PVDF) membranes. Extreme cold water temperature led to a decrease in membrane permeability, and membrane pore size shrinkage. The use of periodical warm water (35 °C) membrane conditioning could almost completely recover the membrane permeability and pore size structure loss caused by extreme cold water temperature, while the use of room temperature (23±1 °C) conditioning recovered majority of the membrane permeability and structure loss caused by extreme cold water temperature. Changes in membrane performance correlate well with changes in membrane structure. Membranes periodically conditioned in warmer water temperature showed a higher permeability than that periodically conditioned at room temperature from a long-term operation of three months. The results suggest the change in PVDF membrane performance and structure caused by extreme cold water temperature is almost completely reversible after periodical warm water conditioning, and thus the use of warm water conditioning and/or chemical cleaning will benefit the recovery of membrane performance and structure change caused by extreme cold water temperature in cold regions.

Self-Cleaning Nanocomposite Membranes with Phosphorene-Based Pore Fillers for Water Treatment.

Phosphorene is a two-dimensional material exfoliated from bulk phosphorus and it possesses a band gap. Specifically, relevant to the field of membrane science, the band gap of phosphorene provides it with potential photocatalytic properties, which could be explored in making reactive membranes that can self-clean. The goal of this study was to develop an innovative and robust membrane that is able to control and reverse fouling with minimal changes in membrane performance. To this end, for the first time, membranes have been embedded with phosphorene. Membrane modification was verified by the presence of phosphorus on membranes, along with changes in surface charge, average pore size, and hydrophobicity. After modification, phosphorene-modified membranes were used to filter methylene blue (MB) under intermittent ultraviolet light irradiation. Phosphorene-modified and unmodified membranes displayed similar rejection of MB; however, after reverse-flow filtration was performed to mimic pure water cleaning, the average recovered flux of phosphorene-modified membranes was four times higher than that of unmodified membranes. Furthermore, coverage of MB on phosphorene membranes after reverse-flow filtration was four times lower than that of unmodified membranes, which supports the hypothesis that phosphorene membranes operated under intermittent ultraviolet irradiation can become self-cleaning.

Synthesis of high-performance thin film composite (TFC) membranes by controlling the preparation conditions: Technical notes

Reverse osmosis (RO) is one of the most globally competitive technologies for desalination and water purification, in which thin film composite (TFC) membrane is the common form of membranes used. In this paper, we examined changes in membrane performance by studying the effects of 1) m-phenylenediamine (MPD) and trimesoyl chloride (TMC) exposure times; 2) different phase inversion methods to prepare polysulfone (PSU) support sheets; 3) the support sheet thickness, and 4) the fabricated membrane’s drying temperature. Operational conditions of 300 psi, 25 °C, 2000 ppm NaCl, and sample run time of at least 8 h were applied. Optimal performance results were achieved when the interfacial polymerization time was short, and a vertical immersion during PSU layer preparation was applied. Increasing PSU sheet thickness increased the salt rejection but decreased the water flux, while rising the curing temperature led to an enhancement in salt rejection and water flux at short reaction times. Based on this study, a TFC membrane of NaCl rejection 98.8 ± 0.5% and water flux 76.1 ± 2.7 L/m2 h was fabricated using 25 s MPD contacting time, 5 s TMC reaction time, and 110 °C drying temperature. This result is considered high among reported outcomes in the literature for simply prepared TFC membranes.

Development of a positively charged nanofiltration membrane for use in organic solvents

In this work, a positively charged nanofiltration membrane was developed by chemical modification of a P84 copolyimide ultrafiltration membrane using branched polyethylenimine. The effect of reaction temperature on membrane morphology, surface charge, and separation performance was investigated. A reaction temperature of 70°C was optimal as the membrane showed best performance in terms of salt rejections and water fluxes when Na2SO4, NaCl and CaCl2 aqueous solutions were used as feeds. Such membrane had a molecular weight cut off (MWCO) of 226Da indicating its effectiveness for separation of organics. Rejections to three dyes in methanol solutions were in the order of methyl orange (negative, MW: 327Da)<disperse red (neutral, MW: 314Da)<safranine O (positive, MW: 351Da). The results suggest that the positive charge on membrane surface induce higher rejection to positive organic molecules due to the charge repulsion effect. Additionally, the membrane had very high stability in organic solvents; no significant changes in membrane performance and membrane structure were observed after being immersed in dimethyl formamide (DMF) for 1 month.

Investigation of pervaporation performance of POMS membrane during separation of butanol from water and the effect of added acetone and ethanol

Abstract In this work the pervaporation performance of a POMS [polyoctylmethyl siloxane] membrane to separate acetone-butanol-ethanol from aqueous solutions was studied. Butanol – water solutions with the addition of acetone and ethanol were analyzed to investigate the effect of multicomponent feed systems on the pervaporation performance of the membrane. Additionally membrane performance in contact with real fermentation broth was investigated. For the binary mixture transmembrane butanol flux increases with increasing feed temperature and feed concentration. Over the whole investigation range the membrane is selective for butanol. It was observed that positive flux coupling for butanol as well as water flux occurs when acetone is present in the feed solution. This results in higher permeance for butanol and water in the investigated range, but similar selectivities. For the quaternary mixture total permeation flux increased, while butanol flux stayed the same. Pervaporation of the real fermentation broth showed, that component permeances increased drastically resulting in high selectivities of 9.8, 3.8 and 0.9, for butanol, acetone and ethanol respectively. This change in membrane performance makes pervaporation with POMS optimal for the product recovery during ABE-fermentation.

Effect of extended exposure to alkaline cleaning chemicals on performance of polyamide (PA) nanofiltration membranes

Abstract This study aimed to increase the knowledge on the influence of alkaline cleaning on performance of polyamide based nanofiltration membranes. In the experiments the Desal-5 DL, XN45 and NF270 membranes were exposed to alkaline conditions at temperatures of 40, 50, 60 and 70 °C and the influence of the extended alkaline exposure to the membrane permeability, glucose and MgSO 4 retention was measured. The characteristic features of the experimental kinetic data for permeability were a rapid increase in permeability after a short time exposure and a subsequent steady increase when the exposing time was continued while the characteristic features for the retention data were a rapid decrease in retentions of glucose and MgSO 4 after a short time exposure and a subsequent steady decrease when the exposing time was continued. The model developed in this study described well the both rapid and slow changes and it can be used to predict the performance of the tested membranes at the temperature range between 40 and 60 °C. The increase in exposure temperature accelerated the changes in membrane performance. The alkali induced changes caused at the 70 °C exposure could not be described with the simple rate law. However, only minor changes in chemical structure of the membranes were noticed in IR spectra after the exposure to alkaline conditions at 70 °C. This indicates that changes observed in permeability and retention could mainly be linked to conformational changes occurring in the polymeric matrix of the membrane skin layers. It was also shown that after a relatively long recovery time (144.5 h) the alkali induced changes in membrane performances were at least partly recovered.

Ageing of polyethersulfone ultrafiltration membranes under long-term exposures to alkaline and acidic cleaning solutions

Six commercial ultrafiltration membranes made of polyethersulfone from Microdyn Nadir, Koch Membrane Systems and GE Osmonics were exposed to 0.01, 0.1 and 1.0M nitric acid (HNO3) and sodium hydroxide (NaOH) solutions at 50°C for 150 days. Water permeability, molecular weight cut-off curves, ATR-FTIR, SEM-EDS, AFM and contact angle measurements were employed to evaluate membrane ageing.All membranes showed a high resistance to acidic solutions keeping their chemical and morphological properties almost invariant. The alkaline ageing did not induce any substantial change in the Nadir membranes but, the stability of Koch and GE Osmonics support layers was compromised at high NaOH concentrations, leading to even the complete degradation of these supports in some cases. This was confirmed by ATR-FTIR, SEM and GC–MS analysis. The Nadir membrane resistance to alkaline conditions was found to be in the support layer material composition (mixture of polyethylene and polypropylene). Koch and GE Osmonics membranes support material (polyethylene terephthalate) broke down into its monomers under strong alkaline conditions via hydrolysis reaction.Almost all membranes showed changes in membrane performance which were attributed to their conditioning or their degradation. Regardless of the cause, those changes took place mainly in the first 10 days of exposure.The influence of temperature on the ageing was also studied under the strongest alkaline condition. Its effect on chemically stable membranes were negligible whereas for the others, higher temperatures led to faster support layer degradation.

Preparation and properties of novel pH-stable TFC membrane based on organic–inorganic hybrid composite materials for nanofiltration

A series of thin-film composite nanofiltration membranes have been fabricated by coating the poly(vinyl alcohol) and 3-mercaptopropyltriethoxysilane aqueous solution prepared by a sol–gel process on porous polysulfone support, followed by thermal cross-linking treatment. In order to improve the hydrophilicity of the nanofiltration membranes, the –SH in the membranes are oxidized into –SO3H by immersing the membranes in H2O2 aqueous solution. Notably, no organic solvent is used during the membrane preparation, showing enough green chemistry technology for environmental protection. The properties of the composite nanofiltration membranes are characterized by ATR-FTIR, SEM, AFM and static contact angle. The optimal composite nanofiltration membrane (PVA-SMPTES-0.6) developed exhibits a rejection of 98.0% and a water flux of 43.3Lm−2h−1 for a feed containing 2000mgL−1 Na2SO4 at 2.0MPa. Furthermore, no irreversible changes in membrane performance have been observed after prolonged exposure (up to 30 days) of PVA-SMPTES-0.6 membrane to extreme acid or alkali aqueous solution.

N-chlorosuccinimide as a novel agent for biofouling control in the polyamide reverse osmosis membrane process

One of the biggest challenges in reverse osmosis membrane process is formation of biofilms on membrane surface (biofouling) which significantly lowers membrane performance and shortens life cycle of the membrane. In an effort to find a more effective biocide to control biofouling, we investigated the potential of N-chlorosuccinimide (NCS) as a biofouling control agent in polyamide membrane. The results of this study show that there are no significant changes in the surface characteristics of polyamide membrane (measured by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR)) when it is exposed to a high concentration of NCS (5000mg/L as Cl2). Also, there were no significant changes in membrane performance based on permeate flux and salt rejection after exposure to the same concentration of NCS. Most importantly, inactivation of Pseudomonas aeruginosa PAO1 GFP biofilm cells by 10mg/L of NCS was 2.2 log after 30min, which is far greater than that of chlorine. Overall, the results of this study suggest that NCS is a promising novel agent for biofouling control in polyamide membrane processes due to its effective inactivation of biofilm cells on membrane and minimum effect on membrane structure and performance.