Combined Fouling Research Articles

Investigation of combined fouling behavior in nano-filtration process under various feed conditions

ABSTRACTDespite the great advance in nano-filtration (NF) process development in various applications, its performance in water treatment is still impeded by the undesired fouling phenomenon, which is not yet fully understood nowadays. In this study, a comprehensive investigation on the fouling behavior, more specifically the combined fouling behavior with the presence of more than one type of foulant was carried out under various solution chemistries and feed hydraulic pressures. The interaction between the model organic foulant (alginate) and inorganic foulant (silica colloid) was systematically studied with nano-filtration membranes, with a more severe fouling observed in the combined fouling than individual foulants. However, the results also revealed that the commonly observed synergistic effect of combined fouling in the forward osmosis process was not present in the nano-filtration process. In addition, the solution chemistries (pH and calcium ions) and feed hydraulic pressure were also found to have certain influence on the combined fouling, especially the feed hydraulic pressure which exhibited a more pronounced impact on the flux decline than the other factors, thus in turn, affecting more on the reversibility of the membrane fouling.

Role of various physical and chemical techniques for hollow fibre forward osmosis membrane cleaning

Fouling is an inevitable phenomenon with most of the water treatment systems. Similar to RO, NF and other membrane-based systems, fouling also seriously affects the performance of low-cost forward-osmosis (FO) systems and disturbs the overall efficiency of these systems, and various cleaning practices have been evaluated to restore their designed performances. This study evaluates the performance of various physical and chemical cleaning techniques for hollow fibre forward-osmosis (HFFO) membrane. HFFO membrane was subjected to various fouling conditions using different brackish groundwater qualities and model organic foulants such as alginate, humic acid and bovine serum albumin. Results indicated that physical cleaning affects differently the flux restoration according to the type of foulants (i.e. inorganic or organic) and the crossflow rates play an important role in membrane cleaning in both membrane orientation. The higher cross flow Re values at any particular area seem important for the cleaning. With hydraulic flushing, the flux performances of HFFO were recovered fully when operated in AL-FS orientation, as high shear force helps to detach all scaling layers from the surface; however, the lower shear force did not fully restore the flux for the FS membrane in AL-DS orientation. Chemical cleaning was planned for the fouled HFFO membrane, and HCl and NaOH were used in various combination sequences. It was found that HCl did not clean the membrane used for AL-DS orientation for combined fouling. HCl cleaning (at pH 2) was found to be more effective for removing inorganic scale, whereas NaOH cleaning (at pH 11) for a similar period successfully restored the flux for all the membranes used for FS with inorganic and/or organic foulants. ethylenediamine tetra acetic acid (EDTA) was also evaluated for its cleaning performances and it was found that compared to NaOH, EDTA cleaning (1mM concentration at pH 11) showed superior results in terms of membrane cleaning, as it helped to successfully restore the membrane flux in a very short time.

Combined colloidal and organic fouling of FO membranes: The influence of foulant–foulant interactions and ionic strength

In this work we determined the exact foulant–foulant interactions during combined membrane fouling in forward osmosis (FO). FO fouling tests were performed using sodium alginate and colloidal silica (ST-ZL, 139nm) as model foulants. The fouling potential of each foulant and their mixture was investigated using feed solutions containing fixed concentrations of Na+ and Ca2+ (total ionic strength of 0.5M). Changes on the foulant surface charges upon mixing with cationic species were monitored using zeta potential analysis. The inter-foulant interactions were determined by conducting sequential fouling experiments (the membrane was fouled by each foulants in alternating sequences) as well as Quartz Crystal Microbalance with Dissipating monitoring (QCM-D). Fouling tests with the mixture of alginate and silica colloids resulted in a flux decline trend very similar to that of alginate alone, an observation attributed to the primary effect of alginate during the gel layer formation. QCM-D analysis revealed that alginate macromolecules adsorb onto the surface of silica colloids and thus influencing the subsequent colloid–colloid interactions resulting in a cake layer with similar hydraulic resistance to that formed by alginate alone. There was no evidence of synergistic effects when alginate and silica colloids co-existed mixed in same feed matrix. It was also found that inter-foulant interactions were governed by non-electrostatic forces because at seawater level ionic strength there was excessive reduction of the Debyle length and electric double layer (EDL) such that normal electrostatic forces were greatly suppressed and short range non-electrostatic forces became dominant. The Extended-Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach was used to understand foulant membrane interactions during fouling and it could not compliment the flux decline trends observed from fouling with combined foulant feed stream. The newly proposed approach of determining combined fouling, whereby the membrane was fouled with the two different single foulants in alternating sequences revealed that gel layer hydraulic resistance, hindered colloid back diffusion and cake enhanced osmotic pressure (CEOP) were responsible for flux loss during combined alginate–colloid fouling.

Factors governing combined fouling by organic and colloidal foulants in cross-flow nanofiltration

There is some controversy in the literature on the effects of combined fouling of organics and colloids on water flux. There are reports of more flux decline for combined fouling than that of fouling by individual foulants, which has been attributed to synergistic effects. However, some authors observed lower flux decline in combined fouling. In addition, some authors have reported on increased flux declines by calcium addition, whereas others have shown improved fluxes after calcium addition. The discrepancies observed in the literature are systematically investigated in more detail in this manuscript. The organic–colloid concentration ratio was varied in order to explain discrepancies in previously observed effects in combined fouling. Further, the probable contributing factor of colloid type and calcium concentration in combined fouling was also examined. Organic, colloidal and combined fouling was found to be aggravated in the presence of Ca2+ due to organic–Ca2+ complexation and the reduction in foulant–membrane repulsive interactions, but this only occurred up to certain Ca2+-concentrations. Above these concentrations, the opposite effect was observed. In addition, membrane–foulant as well as foulant–foulant affinity interactions were determined and related to initial and later fouling rates. A novel type of “sequential” fouling experiments were carried out for the first time, and yielded information on how colloids and organics interact when both are present in fouling solutions. It was concluded from these experiments that hindered back diffusion of organics by a layer of colloids was the main factor responsible for flux decline in combined fouling.

A method for developing a prediction model of water-side fouling on enhanced tubes

Enhanced tubes have been used widely in the condenser of air conditioning systems with a cooling tower due to their superior heat transfer performance. Both the predicted and real-world performance of these heat exchangers is affected by the build-up of fouling on the heat transfer surfaces. An accurate model to predict the negative impact of fouling on heat transfer of enhanced tubes is important to the HVAC&R industry. In this paper, a method to develop a prediction model of fouling on enhanced tubes is presented. Based on this method, a generalized calculation approach can be developed to determine an appropriate fouling resistance for the application of enhanced tubes in a cooling-tower water heat exchanger application. The combined fouling (precipitation and particle fouling) is considered in this method to make a more accurate prediction. A correlation of the total dry matter concentration with respect to Langelier’s Saturation Index (LSI) is proposed to refer to the water quality in the fouling model. The application of this model will allow equipment manufacturers and designers in the HVAC&R industry at large to estimate typical fouling allowances.

Enhanced fouling by inorganic and organic foulants on pressure retarded osmosis (PRO) hollow fiber membranes under high pressures

We have studied, for the first time, the fouling behavior of pressure retarded osmosis (PRO) hollow fiber membranes under low, moderate and high hydraulic pressures. The thin film composite (TFC) polyethersulfone (PES) membrane has a high water permeability and good mechanical strength. Membrane fouling by gypsum (CaSO4·2H2O) scalants, sodium alginate, and the combined foulants was examined under various pressures up to an ultrahigh hydraulic pressure of 18bar. In the combined fouling experiments, the membranes were conditioned by one of foulants followed by the other. Flux decline results suggested that such conditioning could increase the rate of combined fouling because of the change in membrane surface chemistry. Specially, the co-existence of gypsum crystals and alginate under 0bar led to the synergistic combined fouling and resulted in a greater flux decline than the sum of individual fouling. Interestingly, such gypsum–alginate synergistic fouling was not observed under high pressure PRO tests because the increased reverse salt flux inhibited the formation of gypsum crystals. Therefore, alginate fouling could be the dominant fouling mechanism for both (1) alginate conditioning and then scalants fouling, and (2) scalants conditioning and then alginate fouling PRO processes under 8bar and 18bar. Since the reverse salt flux increases from 5.6±1.1g/m2h at 0bar to 74.3±9.7g/m2h at 8bar, and finally to 150.5±2.5g/m2h under 18bar, the reverse salt ions lead to substantial declines of normalized flux under 8bar and 18bar because the reverse sodium ions not only reduce the effective driving force across the PRO membrane but also induce a significant cake-enhanced sodium concentration polarization layer and facilitate alginate gelation near the membrane surface. Therefore, the removal of alginate type foulants from the feed water stream may become essential for the success of PRO processes under high pressures.

Combined biofouling and scaling in membrane feed channels: a new modeling approach

A mathematical model was developed for combined fouling due to biofilms and mineral precipitates in membrane feed channels with spacers. Finite element simulation of flow and solute transport in two-dimensional geometries was coupled with a particle-based approach for the development of a composite (cells and crystals) foulant layer. Three fouling scenarios were compared: biofouling only, scaling only and combined fouling. Combined fouling causes a quicker flux decline than the summed flux deterioration when scaling and biofouling act independently. The model results indicate that the presence of biofilms leads to more mineral formation due to: (1) an enhanced degree of saturation for salts next to the membrane and within the biofilm; and (2) more available surface for nucleation to occur. The impact of biofilm in accelerating gypsum precipitation depends on the composition of the feed water (eg the presence of NaCl) and the kinetics of crystal nucleation and growth. Interactions between flow, solute transport and biofilm-induced mineralization are discussed.

Influence of organic, colloidal and combined fouling on NF rejection of NaCl and carbamazepine: Role of solute–foulant–membrane interactions and cake-enhanced concentration polarisation

The effects of single and combined fouling by sodium alginate, latex and Al2O3 on membrane performance in terms of permeate flux, salt rejection and rejection of the pharmaceutical carbamazepine were evaluated in a laboratory-scale cross-flow filtration unit. Fouling resulted in different extents in permeate flux, salt rejection and carbamazepine rejection over time. Combined fouling resulted in larger flux declines, and the influence of Ca2+ addition on flux was pronounced. In contrast, the influence of combined fouling and Ca2+ addition on salt and carbamazepine rejection was limited. Several hypotheses were tested to assess the influence of fouling on carbamazepine rejection. Relating observed rejection results to the solution-diffusion model revealed insight in whether the effect of fouling on rejection was mainly flux-driven or not. For most foulants, rejection declined less than what was predicted as a function of flux by the solution-diffusion model, indicating that CECP is not the main mechanism responsible for the decline in rejection upon fouling, especially not for latex fouling layers (regardless of the presence of Ca2+). This was corroborated by CECP modelling data. Solute–membrane interaction energies revealed that carbamazepine had higher affinity for the foulants than for the clean membrane surface. As such, it could be hypothesised that for most fouling layers, the relatively small decrease in carbamazepine rejection was mainly due to the decline in flux and the formation of a dense fouling layer on the membrane surface, which had some rejection properties.

Combined organic and colloidal fouling in forward osmosis: Fouling reversibility and the role of applied pressure

In this study, we systematically investigated the propensity and reversibility of combined organic–colloidal fouling in forward osmosis (FO) under various solution chemistries (pH and calcium ion concentrations) and applied hydraulic pressure on the feed side. Alginate, silica colloids, and their mixture (i.e., combined organic–colloidal) were used as model foulants. Our findings demonstrate that combined organic–colloidal foulants caused more rapid flux decline than the individual foulants due to the synergistic effect of alginate and silica colloids. As a result, much lower flux recovery was achieved by physical cleaning induced by increasing the cross-flow rate, in contrast to single foulants of which the fouling layer was easily removed under all solution conditions. Interestingly, less flux decline was observed at neutral pH for combined fouling, while acidic conditions were favorable for alginate fouling and basic solutions caused more silica fouling, thereby providing clear evidence for the combined fouling effect. It was also found that calcium ions enhanced water flux decline and induced the formation of less reversible combined organic–colloidal fouling layers. Lastly, the role of applied hydraulic pressure on the feed side in FO was examined to elucidate the mechanism of fouling layer formation, fouling reversibility, and water flux recovery. Higher fouling propensity and lower fouling reversibility of combined organic–colloidal fouling were observed in the presence of applied hydraulic pressure on the feed side. This observation suggests that the lower fouling propensity and greater fouling reversibility in FO compared to reverse osmosis (RO), are attributable to unpressurized operating conditions in FO.

Effects of aluminum hydrolysis products and natural organic matter on nanofiltration fouling with PACl coagulation pretreatment

Coagulation is one of the most frequently applied pretreatment processes for nanofiltration. Polyaluminumchloride (PACl) has been commonly used as a coagulant for drinking water treatment. When used upstream of nanofiltration, PACl hydrolysis products formed during coagulation can act as foulants due to their retention on the membrane surface. Three distinctive PACl hydrolysis products were formed at different pH conditions: Al137+ and other polymeric Al at low pH; Al-hydroxide, i.e., Al(OH)3 at neutral pH; and aluminate ion, i.e., Al(OH)4- at high pH. In addition, humic acid was added to investigate effects of natural organic matter on the fouling by PACl hydrolysis products. The degree of fouling was characterized through analysis of flux decline behavior and fouling mechanisms were examined with mathematical models. The hydrolysis products at a low pH resulted in the most rapid flux decline regardless of the presence of humic acid. At a high pH condition, the aluminum (Al) species alone resulted in substantial flux decline with a fouling mechanism of pore constriction; while the combined foulants (Al species+humic acid) resulted in a relatively reduced flux decline that was well described by a cake formation mechanism. It should be noted that proper control of coagulation conditions is necessary to avoid residual polymeric Al or aluminate ion when used in the coagulation pretreatment before nanofiltration membrane process.

Powdered Activated Carbon-Microfiltration for Waste-Water Reuse

A range of activated carbon adsorbents have been assessed as pretreatment for microfiltration-based indirect potable reuse (IPR) pilot plant to evaluate the impact on combined membrane fouling and organics removal. Isotherm adsorption analysis showed wide variation between the different adsorbent materials with regards to organics removal and kinetics, and the removal for most of the reagents tested was found to be significantly influenced by temperature. The two commercial adsorbents with the highest removal rates and fastest kinetics were then each evaluated as pretreatment at pilot scale over a six hour period at two doses (5 and 25 mg/l) and operational fluxes (40 and 50 L m−2 h−1), based on a hollow fibre membrane module. One of the adsorbents provided a reduction in the irreversible fouling rate, and both were found to significantly improve the removal of organics.

Combined fouling of forward osmosis membranes: Synergistic foulant interaction and direct observation of fouling layer formation

This study investigated the combined fouling by organic and inorganic foulants in forward osmosis (FO) membrane processes. Alginate and gypsum were used as model foulants for organic and inorganic fouling, respectively. A synergistic effect between alginate fouling and gypsum scaling was observed in the combined fouling experiment: the coexistence of foulants caused faster flux decline than the algebraic sum of flux declines due to individual foulants. It was found that the synergistic effect was mainly a result of the aggravated gypsum scaling in the presence of alginate molecules: alginate molecules act as nuclei in gypsum crystal growth, thus significantly increasing the size of gypsum crystal and accelerating crystallization kinetics. Besides, in the presence of alginate, the dominating scaling mechanism switched from bulk crystallization to surface/heterogeneous crystallization. In order to better understand the effect of alginate on the kinetics of gypsum crystal growth, a membrane window cell coupled with a microscope was used to directly observe crystal formation on the FO membrane surface during the fouling experiments. The direct observation results showed that alginate shortens the nucleation time, increases the gypsum growth rate, and changes the morphology of gypsum crystals. Finally, cleaning experiments were performed by rinsing the fouled FO membranes with pure water and continuously introduced air bubbles. It was found that the cleaning efficiency for membranes fouled by combined foulants was lower than that for membranes fouled by individual foulants.

Monitoring of CaSO4 deposition behaviors on biofilm during nanofiltration via ultrasonic time-domain reflectometry (UTDR)

The ultrasonic time-domain reflectometry (UTDR) as a non-destructive real-time method was employed to monitor the CaSO(4) deposition behaviors on biofilm during nanofiltration (NF). Two parallel experiments were performed to compare the different behaviors of CaSO(4) deposition with and without biofilm on the membrane. Results showed that the flux decline during combined fouling was slower than that in case of CaSO(4) fouling alone. The Ca(2 + ) rejection obtained with biofilm was higher than that without. A larger acoustic differential signal obtained by UTDR in the combined fouling revealed a denser and thicker layer formed on the membrane surface. Furthermore, the amount of CaSO(4) deposition on the biofouled membrane was more than that on non-biofouled membrane as a result of microorganisms as crystal nucleus to induce CaSO(4) crystallization and deposition. SEM images indicate that the CaSO(4) crystals deposited in order on the non-biofouled membrane, whereas on the biofouled membrane they were embedded in the biofilm. The denser and thicker fouling layer formed with biofilm was impermeable, resulting in a high Ca(2 + ) rejection. The complexation of Ca with polysaccharide in biofilm would eliminate the cake-enhanced osmotic pressure effect leading to a slow flux decline. To sum up, the independent measurements corroborate the ultrasonic measurements.

The Combined Colloid-Organic Fouling on Nanofiltration Membrane for Wastewater Treatment and Reuse

Nanofiltration (NF) has been increasingly used for wastewater reuse purposes. However, membrane fouling is still the major barrier for this technology. Colloidal particles and soluble organic substances are the two main types of foulants present in wastewater effluent. However, little investigation has been conducted on the combined effect of colloids and organic on membrane fouling. The present study addresses the combined fouling effect by colloidal particles and organic substances on the NF membrane. The results show that the combined colloid-organic fouling occurred at a considerably faster rate than the sum of individual colloidal fouling and organic fouling rates.

Fouling effects of humic and alginic acids in nanofiltration and influence of solution composition

The objectives of this research were to investigate the combined and individual influence of hydrophobic and hydrophilic fractions of NOM on the fouling of thin-film composite nanofiltration (NF) membranes, and also the roles of solution chemistry on the permeate flux and fouling. Combined fouling is compared to the individual fouling behaviors (i.e., alginate or humic acid alone). Experiments were conducted using a “cross-flow” pilot-scale membrane unit with a full circulation mode. Fouling experiments were performed with individual and combined humic acid and alginate. The results demonstrated that increasing organic concentration increased greatly the rate and extent of flux reduction. Individual alginate fouling was more detrimental than individual humic acid fouling, and alginate exhibited greater flux decline than humic acid fouling alone at the same conditions. A higher flux decline was observed with increasing proportions of aliginate in combined fouling. In other word, there are antagonistic effects during combined fouling because the charge functional groups of two above foulants are negative and increase electrostatic repulsion between two foulants and also foulant-membrane. The flux reduction increased with increasing ionic strength, foulant concentrations, and with lower pH. This observation implies the importance of interaction between various foulants for deeper understanding of fouling phenomena. The membrane fouling was largely dependent on organic properties and fractions.

Separation of sericin from fatty acids towards its recovery from silk degumming wastewaters

Sericin is a valuable protein, which is currently discarded as a waste in silk industry. Silk degumming wastewaters (SDW) are abundant sources of sericin, however, they contain impurities such as salts of fatty acids (soap) in conventional degumming processes. In this study, a process consisting of centrifugation (CFG), low temperature crystallization (LTC) and ultrafiltration (UF) was developed to separate sericin from fatty acids towards its recovery from conventional SDW. Complete removal of fatty acids was achieved by CFG + LTC, where CFG possibly accelerated crystal formation and separation processes. In CFG + UF (20 kDa), sericin rejection increased as pH was reduced from alkaline to acidic levels, possibly due to decreased solubility of sericin and increased amounts of undissociated fatty acids. Fatty acids were partly retained, leading to inadequate separation. Despite very high flux declines, cakes formed by the combined foulants were removable at both pH conditions. In CFG + LTC + UF (5 kDa), sericin was rejected by 92%. Although solution pH did not affect rejection performance, flux decline decreased from 85% to 61% at alkaline pH. Different fouling mechanisms were observed for different foulant types. Only cake formation occured with combined foulant (sericin + fatty acids). The cake surfaces were irregular, with denser and more heterogeneous structure at acidic pH. However, smooth cake formation plus pore narrowing occured with sericin alone at alkaline pH. Additional pore clogging occured at acidic pH, possibly due to decreased solubility of sericin. Chemical cleaning was less effective at acidic pH due to adsorption and pore clogging. Sericin recovery from conventional SDW was achieved in a three-stage process; CFG + LTC for complete separation of sericin from fatty acids and UF for recovering sericin.

Fundamental Mechanisms of Three-Component Combined Fouling with Experimental Verification

The present article describes a novel fundamental theory for investigating combined fouling by colloids (STXL), macromolecules, and solute ions (NaCl). Three macromolecules were used for the combined fouling study, bovine serum albumin (BSA), alginate, and dextran. The presented theory unifies singlet, doublet, and triplet fouling phenomena, including cake-enhanced osmotic pressure and binary colloidal fouling models, giving rise to the combined flux equation for three-component fouling assuming a completely mixed fouling layer. The predicted combined flux was compared to two equivalent fluxes calculated from individual foulant contributions. The strong form of the equivalent flux, known as the additive flux, was based on a linear superposition of flux decline due to individual foulants. The weak form of equivalent flux assumed stratification of individual foulant layers and hence a linear superposition of the individual fouling resistance. A comparison of experimental data and theoretical calculations revealed that the weak form of equivalent flux and the combined flux that was predicted by the novel theory provided the upper and lower limits, respectively, of the observed permeate flux. Furthermore, the model simulation results suggested a structural compression of the BSA gel layer, whereas such a compression did not occur in cases of alginate and dextran. The gel concentrations of alginate and dextran in the combined fouling layer seemed to be less than those in the macromolecular gel layer.

Combined fouling of nanofiltration membranes: Mechanisms and effect of organic matter

The accurate prediction of nanofiltration membrane performance in industrial applications is dependent upon understanding the fouling behavior of representative feed solutions. However, most membrane studies focus on fouling of a single type of foulant, which is not a good predictor for realistic feed solutions that contain multiple foulant types. In this study, combined fouling by organic and inorganic colloidal foulants is studied. Through the use of model foulants, three hypothesized mechanisms responsible for the enhanced membrane flux decline in the presence of multiple foulant types are examined: increased hydraulic resistance of the mixed cake layer structure, hindered foulant diffusion due to interactions between solute concentration polarization layers, and changes in colloid surface properties due to organic adsorption. All three mechanisms were found to play a role in combined fouling to various degrees. Organic adsorption was shown to cause the greatest synergistic effect. The synergistic effect caused by increased resistance of a heterogeneous fouling layer indicates that current fouling layer models need to be reexamined to include the suggested mechanisms.

Mutual Influences between Natural Organic Matter and Inorganic Particles and Their Combined Effect on Ultrafiltration Membrane Fouling

Fouling is one of the most critical aspects of membrane technology and is strongly influenced by natural water characteristics.This studyfocuses on a mechanistic understanding of the impact of interactions between natural organic matter (NOM) and particles on fouling. The model substances used were humic acid, alginate (polysaccharide), and kaolinite. NOM-kaolinite adsorption experiments, particle characterization, and dead-end ultrafiltration (UF) batch experiments were performed. The adsorption experiments indicated particle stabilization at low NOM equilibrium concentrations, whereas calcium induced significant aggregation, especially with alginate. UF experiments implicated a synergistic fouling effect of particle-NOM combinations, which was greatly reduced by calcium. Moreover, irreversible NOM fouling was only prevented by particles in the presence of calcium. On the basis of our results, we present a mechanistic model suggesting that synergistic fouling effects occur due to particle stabilization by NOM adsorption, especially shown for HA, and antagonistic effects due to particle destabilization by calcium. However, synergistic fouling can also be based on sterical interferences between larger NOM in the form of polysaccharides and particles during simultaneous pore blocking and cake formation. A heterogeneous NOM-particle fouling layer is ultimately formed with membrane associations dominated by NOM. The combined fouling is conclusively determined bythe type of NOM, its specific fouling mechanisms, and its particle interactions prior to and during the filtration process.

Highly fouling resistant ultrafiltration membranes for water and wastewater treatments

Control of fouling is a critical issue to increase the competitiveness of ultrafiltration (UF) membranes for drinking water and wastewater treatments. Highly fouling resistant UF membranes synthesized by photo-graft copolymerization of a water soluble monomer, poly(ethylene glycol) methacrylate (PEGMA), onto a polyethersulfone UF membrane have been evaluated with respect to the adsorptive as well as the ultrafiltration fouling. Protein, humic substance and polysaccharide solutions were used as the model for foulants occurring in the water sources for drinking water as well as in wastewater effluents. The results show that the modified membranes exhibited a much higher fouling resistance for all foulants than the unmodified membranes. Their combined high fouling resistance and high rejection suggests that the obtained modified membranes are very promising as a new generation of thin-layer composite low fouling UF membranes for drinking water and wastewater treatment applications.