Adsorptive Fouling Research Articles

Impact of membrane pore morphology on multi-cycle fouling and cleaning of hydrophobic and hydrophilic membranes during MBR operation

This study investigated the impact of membrane pore morphology on repeated fouling and physical cleaning behavior during > 1000 h operation of a membrane bioreactor process. Four microfiltration membranes with different backbone polymers (PVDF and PTFE) and varied hydrophobicity, operated in parallel, were compared. The PVDF membranes presented a porous particulate-packing morphology, while the PTFE/PVDF blend membranes (PTFE accounting for > 80% of monomer proportion) resembled a nonwoven network of thin fibrous material. These membranes had similar short-term apparent fouling rates in a single fouling-and-cleaning cycle, but different long-term fouling development due to their physical cleaning efficiencies differing in the order: hydrophobic PVDF << hydrophobic blend < hydrophilic (PVDF and blend) membranes, as revealed by statistical analyses. The physically irreversible fouling was likely attributed to hydrophobic adsorption onto the membranes, with the adsorbed polysaccharides and proteins detected using confocal laser scanning microscopy. The irreversibility of fouling on the blend membranes was much less sensitive to membrane hydrophobicity than that on the PVDF membranes, probably because the blend membranes had smaller adsorption propensity. For further evidence, the adsorption properties of the membranes were explored via batch tests of dynamic adsorption using model compounds, with the adsorption rate and equilibrium constants quantified using the Thomas model. The thin thread-like pore walls (which characterized the morphology of the blend membranes) may provide limited contact area for foulant adsorption, and/or weaken the interfacial membrane–foulant interaction via shape effect. Therefore, it is suggested that membranes with thin fibrous network-like pore morphology may perform more robustly and be less troubled by adsorptive irreversible fouling for long-term operation of MBR.

Impact of operation conditions, foulant adsorption, and chemical cleaning on the nanomechanical properties of ultrafiltration hollow fiber membranes

This study analyzed the change in nanomechanical properties of ultrafiltration hollow fiber membranes harvested from pilot-scale units after twelve months of operation. Quantitative Nanomechanical Mapping technique was used to distinguish between adhesion, dissipation, deformation, and modulus while simultaneously generating a topographic image of membranes. Nanomechanical maps of virgin membranes evidenced surfaces of heterogeneous properties and were described by probability density functions. Operating conditions and feed quality exerted an impact on membranes. Clean harvested membranes showed a higher mean modulus and dissipation, and a lower deformation than virgin membranes, indicating stiffer membranes of lower elastic deformation. A significant fraction of these measurements displayed peak values deviating from the distribution; which represents regions of the membrane with properties highly differing from the probability density function. The membrane polymeric material experienced severe physicochemical changes by foulant adsorption and reaction with cleaning agents. Foulant adsorption on membranes was heterogeneous in both morphology and mechanical properties and could not be statistically described. Foulants, i.e., mainly consisting of polysaccharides and proteinaceous structures, displayed low elastic deformation and high roughness and adhesion. The presence of foulants after chemical cleaning and their high adhesion would be a direct nanoscale evidence of irreversible fouling. By the end of the operation, the Trans-Membrane Pressure experienced a 40% increase. The cleaning process was not able to fully recover the initial TMP, indicating irreversible fouling, i.e., permanent change in membrane characteristics and decrease in performance. These results suggest a link between the macroscopic properties and nanomechanical characteristics of membranes. This study advances our nanoscale understanding of the impact of fouling and operating conditions on membranes characteristics.

Structural characteristics of extracellular polymeric substances (EPS) in membrane bioreactor and their adsorptive fouling.

The soluble (S), loosely bound (LB) and tightly bound (TB) extracellular polymeric substances (EPS) were extracted from sludge flocs of a membrane bioreactor to evaluate their characteristics and adsorptive fouling. The degrees of adsorptive fouling by the EPS fractions were in the order S-EPS < TB-EPS < LB-EPS. The images of atomic force microscopy showed the membrane fouled by LB-EPS was rougher than that fouled by the other fractions. The adsorbed EPS layer, which was sensed by quartz crystal microbalance with dissipation, was found to be more rigid and compact for LB-EPS, compared with the other EPS fractions. The excitation-emission matrix and Fourier transform infrared techniques were also used to characterize the individual EPS fractions. Compared with S-EPS and TB-EPS, the LB-EPS contained a larger amount of aromatic protein and less carbohydrates and lipids, exhibiting characteristics of greater aromaticity and hydrophobicity. These characteristics should be responsible for more severe fouling, and the stiffer and more compact structure of the adsorbed layer.

A novel interfacial polymerization approach towards synthesis of graphene oxide-incorporated thin film nanocomposite membrane with improved surface properties

The conventional interfacial polymerization (IP) technique that requires a rubber roller in removing amine aqueous solution is likely to cause uneven distribution of nanomaterials on microporous substrate during thin film nanocomposite (TFN) membrane fabrication. A novel IP technique was developed in this work to pre-coat the substrate with graphene oxide (GO) nanosheets followed by vacuum filtration of amine aqueous solution through the substrate before initiating polyamide cross-linking process. This novel technique was also employed to fabricate a composite membrane that contained no nanomaterials. The results showed that the GO-incorporated TFN membrane exhibited 71.7% and 129.4% higher pure water flux compared to the composite membranes without GO incorporation that were synthesized using conventional and filtration IP technique, respectively. The water enhancement of the TFN membrane could be attributed to the existence of hydrophilic GO that was distributed evenly throughout the substrate surface coupled with the formation of porous selective layer that reduced water transport resistance. Besides exhibiting promising rejection against divalent ions, the newly developed TFN membrane also showed significantly lower water flux deterioration in filtrating bovine serum albumin and Reactive Black 5 solution. The enhanced membrane antifouling resistance was mainly due to the improved membrane surface properties that minimize deposition and adsorption of foulants on the TFN membrane surface.

Static adsorption of protein-polysaccharide hybrids on hydrophilic modified membranes based on atomic layer deposition: Anti-fouling performance and mechanism insight

Initial membrane fouling affects fouling behavior and characteristic significantly. Static adsorption investigation contributes to intensively understand the initial fouling process. In order to determine the superior anti-fouling material prepared by atomic layer deposition, the TiO2, Al2O3 and ZnO modified membranes were successfully fabricated, characterized by XPS, XRD and SEM and then employed for static adsorption of BSA and SA foulants. More importantly, the anti-fouling mechanism was interpreted by adsorption isotherms and thermodynamics. Results showed that the adsorption amount of BSA and SA on PVDF membrane decreased by 43.2% and 73.0% with ZnO modification, reaching the highest among all the modified membranes. As a consequence, the minimum reduction of pure water flux and increase of membrane resistance were realized after fouling. The Sips model presented the most satisfactory fitting for BSA and SA adsorption on ZnO modified membrane. Thermodynamic investigation revealed that the ZnO modified membrane exhibited the lowest degree of spontaneity and the weakest interaction with foulants (London dispersion forces of physisorption). Moreover, the smallest ΔS value indicated the regular distribution of foulants on membrane surface, which greatly alleviated membrane fouling. The relatively smooth surface of ZnO modified membrane with lower roughness and water contact angle confirmed the excellent anti-fouling property. The reported results in this study could provide fundamental basis for the anti-fouling performance of ALD modified membranes, which would accelerate the actual application process.

Photoactive Gel for Assisted Cleaning during Olive Mill Wastewater Membrane Microfiltration.

A photoactive gel has been fabricated on the surface of polyethylene membranes for enhancing the fouling resistance during olive mill wastewater treatment. Light and pH responsive materials have been introduced in the membrane surface through the build up of a layer-by-layer pattern, which is formed by photocatalytic nanoparticles and ionic polyelectrolytes. The best working conditions to contrast foulants adsorption have been explored and identified. Repulsive interfacial forces and assisted transfer of foulants to catalytic sites have been envisaged as crucial factors for contrasting the decline of the flux during microfiltration. Tests in submerged configuration have been implemented for six continuous hours under irradiation at two different pH conditions. As a result, a worthy efficiency of the photoactive gel has been reached when suitable chemical microenvironments have been generated along the shell side of the membranes. No additional chemical reagents or expensive back-flushing procedures have been necessary to further clean the membranes; rather, fast and reversible pH switches have been enough to remove residues, thereby preserving the integrity of the layer-by-layer (LBL) complex onto the membrane surface.

Physicochemical characterization of tight nanofiltration membranes for dairy wastewater treatment

Interrelationship between physicochemical properties and separation performance of nine commercial nanofiltration (NF) membranes was systematically investigated. Seven NF membranes, NT103 and NT102 from Microdyn-Nadir, DF90 and DF30 from OriginWater, NF70, NF40-I and NF40-II from Hangzhou Development Center of Water Treatment Technology, were reported for the first time. FTIR spectra demonstrated that the skin layer of NF90, NT103 and DF90 was made from fully aromatic polyamide, while other membranes were the semi-aromatic ones. The fully aromatic membranes had rougher, thicker and less hydrophilic polyamide layer as well as lower permeability than the semi-aromatic ones. When applying these membranes to concentrate the pretreated dairy wastewater, NF270, DF30 and NF40-I with high lactose rejection, low salt rentention low transmembrane pressure (TMP) and negligible irreversible fouling (IF) are preferable. Furthermore, it was found that the pore size and skin thickness dominated the membrane permeability. Meanwhile, the pore size and TMP produced a negligible effect on the IF, while the higher roughness and contact angle resulted in the higher IF, implying that the main fouling mechanism in this case is the foulants adsorption at membrane surface rather than pore blocking (affected by pore size) or cake formation (its compressibility was influenced by TMP). Moreover, the retentions of both lactose and salts by the tight NF membranes appeared to be governed by steric hindrance. Thus, this work provides a new method to study membrane separation and fouling mechanisms by correlating the physiochemical properties and separation performance of different membranes.

Comparison of organic fouling resistance of thin-film composite membranes modified by hydrophilic silica nanoparticles and zwitterionic polymer brushes

We conducted a comparative study to investigate the efficacies of two different types of highly hydrophilic materials (i.e., silica nanoparticles (SiNPs) and zwitterionic polymers) for antifouling surface modification of polyamide thin-film composite (TFC) membranes. Dense layers of SiNPs and zwitterionic polymer brushes were grafted on the membrane surfaces via dip-coating with aminosilane-functionalized SiNPs (i.e., SiNP-TFC membrane) and surface-initiated atom-transfer radical-polymerization of sulfobetaine methacrylate (i.e., PSBMA-TFC membrane), respectively. With the same degree of enhancement of surface hydrophilicity and identical surface roughness, the PSBMA-TFC membrane exhibited significantly higher fouling resistance than the SiNP-TFC membrane in adsorption tests of proteins and bacteria as well as in forward osmosis (FO) dynamic fouling experiments using alginate as a model organic foulant. Chemical force microscopy measurements revealed that membrane-foulant electrostatic attraction aggravates organic fouling of the SiNP-TFC membrane to a certain degree, but the primary fouling mechanism is the complexation of organic foulants with carboxylic groups on the polyamide membrane surface. We attribute the lower fouling resistance of the SiNP-TFC membrane to the high density of surface carboxylic groups that may still be accessible to foulants as well as to membrane-foulant electrostatic interaction. On the contrary, the zwitterionic polymer brushes effectively shield the surface carboxylic groups and provide steric hindrance against foulant adsorption due to significant hydration of the zwitterionic brushes.

Evaluation of biochar-ultrafiltration membrane processes for humic acid removal under various hydrodynamic, pH, ionic strength, and pressure conditions

The performance of an ultrafiltration (UF)-biochar process was evaluated in comparison with a UF membrane process for the removal of humic acid (HA). Bench-scale UF experiments were conducted to study the rejection and flux trends under various hydrodynamic, pH, ionic strength, and pressure conditions. The resistance-in-series model was used to evaluate the processes and it showed that unlike stirred conditions, where low fouling resistance was observed (28.7 × 1012 m−1 to 32.5 × 1012 m−1), higher values and comparable trends were obtained for UF-biochar and UF alone for unstirred conditions (28.7 × 1012 m−1 to 32.5 × 1012 m−1). Thus, the processes were further evaluated under unstirred conditions. Additionally, total fouling resistance was decreased in the presence of biochar by 6%, indicating that HA adsorption by biochar could diminish adsorption fouling on the UF membrane and thus improve the efficiency of the UF-biochar process. The rejection trends of UF-biochar and UF alone were similar in most cases, whereas UF-biochar showed a noticeable increase in flux of around 18–25% under various experimental conditions due to reduced membrane fouling. Three-cycle filtration tests further demonstrated that UF-biochar showed better membrane recovery and antifouling capability by showing more HA rejection (3–5%) than UF membrane alone with each subsequent cycle of filtration. As a result of these findings, the UF-biochar process may potentially prove be a viable treatment option for the removal of HA from water.

Thermodynamic assessment of adsorptive fouling with the membranes modified via layer-by-layer self-assembly technique

In this study, polyvinylidene fluoride (PVDF) microfiltration membrane was coated by dipping the membrane alternatingly in solutions of the polyelectrolytes (poly-diallyldimethylammonium chloride (PDADMAC) and polystyrenesulfonate (PSS)) via layer-by-layer (LBL) self-assembly technique to improve the membrane antifouling ability. Filtration experiments showed that, sludge cake layer on the coated membrane could be more easily washed off, and moreover, the remained flux ratio (RFR) of the coated membrane was obviously improved as compared with the control membrane. Characterization of the membranes showed that a polyelectrolyte layer was successfully coated on the membrane surfaces, and the hydrophilicity, surface charge and surface morphology of the coated membrane were changed. Based on the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) approaches, quantification of interfacial interactions between foulants and membranes in three different scenarios was achieved. It was revealed that there existed a repulsive energy barrier when a particle foulant adhered to membrane surface, and the enhanced electrostatic double layer (EL) interaction and energy barrier should be responsible for the improved antifouling ability of the coated membrane. This study provided a combined solution to membrane modification and interaction energy evaluation related with membrane fouling simultaneously.

Modeling three-dimensional surface morphology of biocake layer in a membrane bioreactor based on fractal geometry

While the adsorptive fouling in membrane bioreactors (MBRs) is highly dependent of the surface morphology, little progress has been made on modeling biocake layer surface morphology. In this study, a novel method, which combined static light scattering method for fractal dimension (Df) measurement with fractal method represented by the modified two-variable Weierstrass-Mandelbrot function, was proposed to model biocake layer surface in a MBR. Characterization by atomic force microscopy showed that the biocake surface was stochastic, disorder, self-similarity, and with non-integer dimension, illustrating obvious fractal features. Fractal dimension (Df) of sludge suspension experienced a significant change with operation of the MBR. The constructed biocake layer surface by the proposed method was quite close to the real surface, showing the feasibility of the proposed method. It was found that Df was the critical factor affecting surface morphology, while other factors exerted moderate or minor effects on the roughness of biocake layer.

Effect of fluidized granular activated carbon (GAC) on critical flux in the microfiltration of particulate foulants

The fluidization of Granular Activated Carbon (GAC) particles has received much attention in recent years as a promising method for mitigating membrane fouling particularly in membrane bioreactors (MBRs). In particular, the fluidized GAC particles are acknowledged to be beneficial in terms of adsorption of organic foulants, and mechanical scouring and surface shear of the membrane surface. Both lab-scale and pilot-scale studies have affirmed the efficacy of GAC fluidization in maintaining a depressed extent of membrane fouling in anaerobic fluidized bed - membrane bioreactors (AnFMBRs). More in-depth studies have also correlated the hydrodynamics of fluidized GAC particles with the effectiveness of membrane fouling mitigation. This study aimed at understanding the improvement of fine (micron-sized) particle critical flux in the presence of fluidized GAC via the Direct Observation Through the Membrane (DOTM) technique. The model foulant was a suspension of polystyrene particles (5µm sized), and the parameters investigated included GAC particle diameter (dp), superficial liquid velocity (Ul) and thereby power requirement (Pr), and height along the vertically aligned membrane. Results indicate that: (i) fluidized GAC increased the critical flux by an order-of-magnitude relative to that with tangential liquid shear alone; (ii) the overall critical flux (Jcritical, overall) expectedly increased with power input (Pr), but the relationship between local critical flux (Jcritical) and power input (Pr) depended on the position along the membrane height; (iii) at the same Pr, although the larger GAC particles were more effective locally (i.e., higher Jcritical) due to greater particle inertia, the smaller GAC particles were more effective overall (i.e., higher Jcritical, overall) due to greater bed expansion enabling scouring of more membrane heights; and (iv) a higher power input (Pr) was required for sufficient bed expansion to enable more consistent critical flux (Jcritical) values over the whole membrane height.

Control of membrane fouling with the addition of a nanoporous zeolite membrane fouling reducer to the submerged hollow fiber membrane bioreactor

ABSTRACTThe membrane fouling control via the addition of nanoporous zeolite membrane fouling reducer (Z-MFR) to the submerged membrane bioreactor (MBR) was investigated. Using scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis techniques, the characteristics of fouling on a hollow fiber membrane surface were also analyzed. The addition of Z-MFR to the MBR led to the adsorption of foulants and the flocculation of mixed liquor suspended solids (MLSSs), which resulted in substantially enhancing the membrane filterability. The critical flux values obtained from the sewage mixed liquors of 3400 mg L−1 at the effective dosage rate of 0.03 mg Z-MFR mg−1 MLSS was 85 L m−2 h−1 (LMH), which was enhanced by 42%. The transmembrane pressure (TMP) variation under the operating conditions of 30 LMH with 3500 mg MLSS L−1 showed that the addition of Z-MFR extended the time required to reach the critical flux of 0.32 bar by 2.6-fold longer than the control. Thus, due to the hybrid functions of adsorbing foulants and precipitating colloidal substances with the addition of Z-MFR, a decrease in the foulant amount and an improvement of sludge flocculation have been attained simultaneously. As a result, the membrane fouling control was achieved effectively with the addition of the Z-MFR.

Anti-fouling potential evaluation of PVDF membranes modified with ZnO against polysaccharide

In this study, hydrophilic modification of polyvinylidene fluoride (PVDF) membranes with zinc oxide (ZnO) using atomic layer deposition (ALD) was conducted for fouling alleviation of polysaccharide. A uniform and conformal layer of ZnO was formed on both membrane surface and pore walls after modification, leading to slightly reduced pore size but greatly enhanced permeability at only 100 ALD cycles. Besides, the standard blocking model fit well with flux data of the original membrane as well as modified membranes (R2>0.99) during sodium alginate (SA, a typical polysaccharide) filtration, indicating that adsorption fouling was the main reason for flux decline. More importantly, both the slower diminishing rate of flux (SA filtration) and decreased adsorption capacity of SA showed better anti-fouling property of modified membranes with ZnO. Further exploration of the anti-fouling mechanism based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory found that the modified membranes exhibited higher energy barriers and lower second minimums compared to the original PVDF membrane. This suggested that larger repulsive energy was needed to be overcome and weaker attractive energy was experienced for the SA adsorption onto the surfaces of modified membranes. Moreover, the analysis of surface topography showed that the PVDF membranes modified with ZnO presented smaller protuberances and lower surface roughness after SA filtration, weakening the attachment of polysaccharide onto the modified membranes.

Harvesting of Scenedesmus obliquus using dynamic filtration with a perforated disk

Dynamic filtration adopting the rotation of a perforated disk was applied to harvest Scenedesmus obliquus. The highest rotation speed of the disk was found to give rise to 464 and 454 L/m2/h of plateau permeate flux for microfiltration (MF) membrane and ultrafiltration (UF) membrane, respectively, which were approximately 9 and 11 times higher than those with no rotation. This marked performance improvement for both filtration methods, with the UF exhibiting lower irreversible fouling, was attributed to the reduction of not only cake fouling (up to 97%) but also adsorption fouling (up to 71%) by way of high shear stress on the membrane surface. At the high rotation speed in which fouling was effectively suppressed, flux was linearly increased by trans-membrane pressure; at low speeds where fouling formation remained less disrupted, on the other hand, it reached a certain limit. Besides, fouling built and worsened particularly by high amounts of extracellular polymeric substance (EPS), which was as in the case of the seawater-supplemented culture, was effectively alleviated by fast rotation. The dynamic UF based on the rotation of the perforated disk was indeed a promising and suited means of harvesting S. obliquus, especially cells grown under economical yet EPS-inducing cultivation conditions.

Tuning anti-adhesion ability of membrane for a membrane bioreactor by thermodynamic analysis

Developing strategies that allow tuning anti-adhesion ability of membranes in membrane bioreactors (MBRs) is of primary interest in membrane fouling research. In this study, interaction energies between foulants and membrane in three different interaction scenarios were systematically assessed based on thermodynamic methods. It was found that, membrane surface electron donor tension (γ−) rather than surface hydrophilicity was a more reliable indicator to predict adsorptive fouling. The interaction energy would be continuously repulsive in the initial range of separation distance when membrane γ− is higher than a critical value, suggesting that designing membrane with γ− higher than a critical value would confer membrane with high anti-adhesion ability. It was also found that, zeta potential on the membrane surface exerted certain effects on adsorptive fouling. This study proposed a novel strategy regarding adjusting membrane γ− to tune anti-adhesion ability of membrane, and also offered a thermodynamic theoretical background to this strategy.

Improving the performance of an aerobic membrane bioreactor (MBR) treating pharmaceutical wastewater with powdered activated carbon (PAC) addition.

In this study, the effects of organic loading rate (OLR) and the addition of powdered activated carbon (PAC) on the performance and membrane fouling of MBR were conducted to treat real pharmaceutical process wastewater. Over 145 days of operation, the MBR system was operated at OLRs ranging from 1 to 2 kg COD m(-3) day(-1) without sludge wasting. The addition of PAC provided an improvement in the flux, despite an increase in the OLR:PAC ratio. The results demonstrated that the hybrid PAC-MBR system maintained a reduced amount of membrane fouling and steadily increased the removal performance of etodolac. PAC addition reduced the deposition of extracellular polymeric substance and organic matter on the membrane surface and resulted an increase in COD removal even at higher OLRs with low PAC addition. Membrane fouling mechanisms were investigated using combined adsorption fouling models. Modified fouling index values and normalized mass transfer coefficient values indicated that predominant fouling mechanism was cake adsorption.

A synergetic analysis method for antifouling behavior investigation on PES ultrafiltration membrane with self-assembled TiO2 nanoparticles

Fouling of ultrafiltration (UF) membranes is a major impediment for their use in drinking water production. Mixed matrix membranes (MMMs) may have great opportunities in dealing with this challenge due to their hierarchical structures and multiple functionalities. In this study, a synergetic analysis method based on intermolecular adhesion force measurement and fouling process simulation was applied to investigate the fouling mechanism of polyethersulfone (PES) UF membranes containing in situ self-assembled TiO2 nanoparticles (NPs). The fouling resistance behavior and antifouling mechanism of the newly developed composite membranes were investigated with sodium alginate (SA), bovine serum albumin (BSA) and humic acid (HA) as model organic foulants. An improved antifouling effect was conspicuously observed for the composite membranes, expressed by a lower flux decline and significantly better cleaning efficiency. A strong correlation between the self-assembled structure of TiO2 NPs and the antifouling behavior of the composite membrane was observed. A lower magnitude and a narrower distribution of adhesion forces for the composite membrane suggest the effective suppression of foulants adsorption on the clean or fouled membrane. The simulation analysis indicates that the main fouling mechanism was standard blocking and cake filtration, further confirming the superiority of the NPs self-assembled structure in mitigating membrane fouling. This dual analysis method may provide a promising technological support for the application of modified UF membranes with self-assembled NPs in drinking water production.

Leaching of PVP from PVDF/PVP blend membranes: impacts on membrane structure and fouling in membrane bioreactors

Polyvinylidene fluoride (PVDF) membranes are widely used in membrane industry, especially for membrane bioreactors (MBRs). Many PVDF membranes contain residual polyvinyl pyrrolidone (PVP) that acts as a pore-forming additive. The presence of residual PVP in some commercial PVDF membranes is often not specified and, therefore, its impact is mostly overlooked in the literature. In this study, we investigated the effect of PVP leaching on membrane structure and its implication on membrane fouling in a lab-scale MBR. PVP leaching can occur in two ways: (1) over the course of filtration from PVDF/PVP blend membranes or (2) prior filtration operation by treating the aforementioned membrane. We prepared PVDF, PVDF/PVP blend, and PVDF/PVP blend post-treated with sodium hypochlorite (NaClO), then assessed their performance. Leaching of PVP prior to the filtration operation significantly enlarged membrane pore size and thus reduced the membrane resistance. However, this advantage was dismissed during operation in MBR because PVP leaching also induced surface hydrophobicity that promoted membrane fouling, suggesting the detrimental effect of post-treatment. For PVDF/PVP blend sample, two counter-acting phenomena occurred: (1) slow leaching of PVP which gradually enlarged the membrane pores and rendered the membrane surface more hydrophobic and (2) adsorption of foulants that formed a secondary layer atop of membrane surface, restricted the pore mouth, and rendered the surface hydrophilic. The findings are significant since the change of membrane morphology over the course of filtration, as demonstrated in this study, is often overlooked when assessing membrane performance.

Headspace-solid phase microextraction: useful technique to characterize volatile and semi-volatile organic compounds in water reuse applications

Sample preparation is an essential step in analysis, greatly influencing the reliability and accuracy, the time and cost of analysis. Solid-phase microextraction (SPME) is a very simple and efficient, solventless sample preparation technique, which has been widely used in different fields of analytical chemistry. In this study, four different polarity SPME fibres coupled with gas chromatography-mass spectrometry have been used for the determination of volatile and semi-volatile organic substances from the reverse osmosis (RO) influent in water reuse applications and the results have been compared with those obtained with conventional liquid–liquid extraction. Adsorption of organic foulants on the membrane surface causes organic and biological fouling which also produces flow loss and consequently pressure must be high to maintain the flow. PA and PDMS/DVB/CAR were complementary fibres which together could characterize the organic compounds in the influent water. Organic compounds characterized belong to different families including: aromatic hydrocarbons, linear hydrocarbons, ketones, alcohols, fatty acids, phenols, nitro-containing compounds, phthalates, fragrance allergens, hormones, halogenated compounds, acetate derivates, sulphur-containing compounds, amines and sugars. In addition, RO-influent water values of total organic carbon, chemical oxygen demand, biological oxygen demand and colour were analysed during the study in order to complement water analysis.