Dead-end Cell Research Articles

Pattern size relative to oil droplet size effect on oil fouling in nanofiltration

Membrane fouling is a major issue in many membrane applications. There are numerous methods used in attempt to mitigate membrane fouling, with one method being membrane surface patterning. However, it is still unclear how the ratio of foulant size to pattern size affects membrane fouling. In this study, we investigated constant foulant size while varying the pattern size on the membrane surface to be smaller than (300-nm), equal to (10-μm), and larger than (50-μm) the foulant (10-μm) on polyamide nanofiltration membranes. These membranes were compared to a commercial nanofiltration membrane and a control flat synthesized membrane. The membranes were tested with water, 2000 ppm Na2SO4, and three cycles of a n-dodecane (as oil) brine solution in a dead-end cell to assess the fouling resistance and flux recovery ability of each polyamide membrane type. From the fouling experiments, it was determined that none of the pattern sizes significantly affect the flux recovery ratio, but smaller than and larger than patterns decreased the fouling rate on the polyamide membranes by a small margin.

Polydopamine-functionalized polyethersulfone membrane: A paradigm advancement in the field of α-amylase stability and immobilization

Biocatalytic membranes have great potential in various industrial sectors, with the immobilization of enzymes being a crucial stage. Immobilizing enzymes through covalent bonds is a complex and time-consuming process for large-scale applications. Polydopamine (PDA) offers a more sustainable and eco-friendly alternative for enzyme immobilization. Therefore, surface modification with polydopamine as mussel-inspired antifouling coatings has increased resistance to fouling. In this study, α-amylase enzyme was covalently bound to a bioactive PDA-coated polyethersulfone (PES) membrane surface using cyanuric chloride as a linker. The optimal activity of α-amylase enzyme immobilized on PES/PDA membrane was obtained at temperature and pH of 55°C and 6.5, respectively. The immobilized enzyme can be reused up to five reaction cycles with 55 % retention of initial activity. Besides, it maintained 60 % of its activity after being stored for five weeks at 4°C. Additionally, the immobilized enzyme demonstrated increased Michaelis constant and maximum velocity values during starch hydrolysis. The results of the biofouling experiment of various membranes in a dead-end cell demonstrated that the PES membrane’s water flux increased from 6722.7 Lmh to 7560.2 Lmh after PDA modification. Although α-amylase immobilization reduced the flux to 7458.5 Lmh due to enhanced hydrophilicity, compared to unmodified membrane. The findings of this study demonstrated that the membrane produced through co-deposition exhibited superior hydrophilicity, enhanced coating stability, and strong antifouling properties, positioning it as a promising candidate for industrial applications.

Enhancing ultrafiltration performance for dairy wastewater treatment using a 3D printed turbulence promoter

Dairy factories annually generate an increasing amount of wastewater, which can cause eutrophication due to high concentrations of amino acids and lipids. To address this issue, membrane technology has emerged as a promising solution, but membrane fouling remains a significant challenge, since it can cause decreased flux, decrease membrane rejection performance, and increased energy demand. This study aimed to reduce membrane fouling by integrated a three-dimensional printed (3DP) turbulence promoter into an ultrafiltration dead-end cell and varying stirring speeds. Two mathematical models, Hermia and resistance-in-series, were used to analyze the fouling process. According to both models, the cake layer formation model indicated the most prevalent fouling mechanism. Specific energy demand, permeate flux, membrane rejection, and membrane reversible and irreversible resistances were measured, calculated, and compared. The results suggest that the combination of an integrated 3DP turbulence promoter and high stirring speeds can effectively reduce membrane fouling in a dairy wastewater treatment module.

Improvement of salt rejection efficiency of cellulose acetate membrane through modification by poly(amidoamine) dendrimer-functionalized graphene oxide

In this work, the grafting method using graphene oxide (GO) - poly(amidoamine) dendrimer (PAMAM) nanocomposite as filler for the functionalization of cellulose acetate membrane is reported. Here, cellulose acetate membrane incorporated by nanocomposite in the polymer solution was prepared through the phase inversion technique. The effect of embedding GO-PAMAM on the characterization properties and rejection performance was studied. The results of zeta potential, thermogravimetric analysis (TGA), contact angle measurements, Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM) established successful modification. Based on the data found, adding the filler improves membrane properties. Loading of 1.00 wt% of GO/PAMAM was found to be the optimized amount of the filler in the membrane processing with the highest porosity (74%), antifouling behavior (88%), reversible fouling ratio (45.71%), and the least contact angle (∼40°). Hence, the rejection and permeability tests of the prepared membrane were examined by Na2SO4 (98.40%), NaCl (52%), and MgCl2 (57%) solutions through a lab dead-end cell. According to the results, the value of salt rejection established more permeability and rejection than neat cellulose acetate membrane.

Investigation of Photocatalytic PVDF Membranes Containing Inorganic Nanoparticles for Model Dairy Wastewater Treatment.

Membrane separation processes are promising methods for wastewater treatment. Membrane fouling limits their wider use; however, this may be mitigated using photocatalytic composite materials for membrane preparation. This study aimed to investigate photocatalytic polyvinylidene fluoride (PVDF)-based nanocomposite membranes for treating model dairy wastewater containing bovine serum albumin (BSA). Membranes were fabricated via physical coating (with TiO2, and/or carbon nanotubes, and/or BiVO4) and blending (with TiO2). Another objective of this study was to compare membranes of identical compositions fabricated using different techniques, and to examine how various TiO2 concentrations affect the antifouling and cleaning performances of the blended membranes. Filtration experiments were performed using a dead-end cell. Filtration resistances, BSA rejection, and photocatalytic cleanability (characterized by flux recovery ratio (FRR)) were measured. The surface characteristics (SEM, EDX), roughness (measured by atomic force microscopy, AFM), wettability (contact angle measurements), and zeta potential of the membranes were also examined. Coated PVDF membranes showed higher hydrophilicity than the pristine PVDF membrane, as evidenced by a decreased contact angle, but the higher hydrophilicity did not result in higher fluxes, unlike the case of blended membranes. The increased surface roughness resulted in increased reversible fouling, but decreased BSA retention. Furthermore, the TiO2-coated membranes had a better flux recovery ratio (FRR, 97%) than the TiO2-blended membranes (35%). However, the TiO2-coated membrane had larger total filtration resistances and a lower water flux than the commercial pristine PVDF membrane and TiO2-blended membrane, which may be due to pore blockage or an additional coating layer formed by the nanoparticles. The BSA rejection of the TiO2-coated membrane was lower than that of the commercial pristine PVDF membrane. In contrast, the TiO2-blended membranes showed lower resistance than the pristine PVDF membrane, and exhibited better antifouling performance, superior flux, and comparable BSA rejection. Increasing the TiO2 content of the TiO2-blended membranes (from 1 to 2.5%) resulted in increased antifouling and comparable BSA rejection (more than 95%). However, the effect of TiO2 concentration on flux recovery was negligible.

Antifouling polymeric nanocomposite membrane based on interfacial polymerization of polyamide enhanced with green TiO2nanoparticles for water desalination

In the present investigation, the preparation and characterization of polyamide/TiO2as thin film nanocomposites (TFN) for brackish water desalination was investigated. TiO2nanoparticles (NPs) were synthesized by a green method using thyme plant extract as a reducing and capping agent. The TiO2NPs was successfully prepared in pure crystalline anatase phase with 15 nm size, and −33.1 mV zeta potential. The antimicrobial tests confirmed the antimicrobial activity of TiO2against gram-positive and gram-negative bacteria. In addition, TiO2NPs showed a good photocatalytic activity in degradation of methylene blue dye. TFN based on interfacial polymerization was enhanced by embedding 5% of the greenly synthesized TiO2NPs within the polyamide thin film active layer. The incorporation of TiO2NPs was confirmed by SEM, atomic force microscope (AFM), surface wettability, and FTIR. Membranes performance was investigated based on flux, salt rejection and fouling resistance. The antifouling was examined using bovine serum albumin (BSA) as protein fouling by dead-end cell filtration system at 2 bar. The results showed the TFN increased in water flux by 40.9% and a slight decrease in NaCl rejection (6.3%) was observed, with enhancement in antifouling properties. The flux recovery rate of the modified TFN membranes after fouling with BSA solution was enhanced by 21.5% (from 61.7% for TFC to 83.2% for TFN). Also, they demonstrated remarkable anti-biofouling behavior against both bacterial strains.

Inhibition caused by adsorption of organic micropollutants (MPs) on PES@CoFe2O4 polymeric ultrafiltration membranes and the enhanced MPs degradation by a continuous pH regulation

In this work, catalytic membranes were fabricated by blending CoFe2O4 catalysts into polyethersulfone (PES) and then used to treat naproxen with the addition of peroxymonosulfate (PMS). It was found that the addition of PMS results in a decrease in pH, which increases the adsorption of naproxen. This often overlooked phenomenon is demonstrated here to have an important role since the adsorption of naproxen on the polymeric matrix and catalytic particles decreases the degradation efficiency of naproxen. To verify this hypothesis and rule out the decrease in pH after the addition of pH, two ways of controlling the pH of the naproxen solution were compared: adjusting pH before and after the addition of PMS, respectively. Our results indicate that in the batch experiment, adjusting the pH of naproxen solution after adding PMS led to a dramatic 23-fold increase in the kinetic constant of the naproxen oxidation (0.42/min, pH6) compared to when pH was adjusted before adding PMS (0.018/min, pH 6). This enhancement in the overall kinetics was attributed to the elimination of the inhibition caused by MPs adsorption at low pH. In a dead-end cell, the catalytic membranes with 2.0 % of CoFe2O4 achieved quantitative conversion of naproxen, bisphenol A, and atrazine, with values of 98 %, 97 %, and 74 %, respectively, demonstrating the efficacy of this approach to convert multitype of MPs in wastewater streams. In a reusability study, the naproxen removal of the catalytic membranes with 2.0 % of CoFe2O4 decreased by 81 % and 45 % after 5 rounds in the batch experiment and dead-end cell, respectively. However, with a chemical cleaning process between each round, the degradation efficiency can be effectively recovered, proving the negative effects of the adsorption of MPs or their intermediates during the SR-AOPs. Our work demonstrates that pH in SR-AOP-based catalytic membrane processes determined both the reaction rate and the adsorption of MPs or their intermediates on the membrane and its reactive sites. We envision that these results will be valuable in developing efficient catalytic membranes for the treatment of MPs in wastewater streams.

Promotional effect of ammonium chloride functionalization on the performance of polyethersulfone/chitosan composite-based ultrafiltration membrane

This study aims to determine the effect of ammonium chloride (NH4Cl) on the characteristics and performance of polyethersulfone (PES)/Chitosan (CS)-based ultrafiltration composite membranes. The PES membranes were synthesized using phase inversion technique in dimethylacetamide (DMAc) solvent. A mixture of chitosan solution (fixed concentration) and NH4Cl (concentration 100–400 ppm) with ratio 2:1 (v/v) were coated into the PES membrane. The synthesized membranes morphology and properties were characterized by FTIR, SEM, contact angle, mechanical properties, and porosity tests. The membrane performance parameters including water permeability, rejection, and antifouling properties were studied. Incorporation of NH4Cl modified the membrane morphology and improved membrane porosity (49.64–71.5 %). The decrease in the water contact angle (80.21° to 63.53°) has confirmed the improvement of membrane hydrophilicity. Moreover, improved mechanical properties (11–16 MPa) were observed due to NH4Cl addition. The incorporation of NH4Cl improved water flux and specific flux membranes in dead-end cell from 51.34 to 159.18 L/m2∙h and 22–26.53 L/m2∙h∙bar, respectively, and in the cross-flow cell from 82.38 to 182.53 L/m2∙h and from 16.47 to 36.51 L/m2∙h∙bar, respectively. The addition of NH4Cl into membrane remarkably improved the rejection of bovine serum albumine (75.90 %, to 96.79 %), methyl orange (47.18–89.29 %), and methylene blue (60.14–97.34 %) Composite membranes have good fouling resistance as indicated by an increase in the flux recovery ratio (53.58–70.67 %). It is inferred that the addition of NH4Cl improved the performance of PES/chitosan composite membranes in ultrafiltration.

Enhanced anti-fouling performance in Membrane Bioreactors using a novel cellulose nanofiber-coated membrane

• The fouling of TFNC-CNF membranes is reversible when filtering wastewater. • Enhanced flux was achieved in the submerged TFNC-CNF membrane bioreactor. • TFNC-CNF membranes showed higher rejection potential of bio-foulants. • Air scouring enhanced the flux of TFNC-CNF membranes when filtering wastewater. The filtration performance, fouling and flux recovery efficiency of a novel thin film nanofibrous composite-cellulose nanofiber (TFNC-CNF) coated membrane was studied and compared with polyvinylidene fluoride (PVDF) membranes treating domestic wastewater. The enhanced anti-fouling property of the TFNC-CNF membrane was associated with the super-hydrophilic nature and negative charge on the membrane surface. The dead-end cell filtration tests demonstrated the TFNC-CNF membrane recovered more than 90% of the initial flux after mechanical cleaning, compared with 26–43% recovery by PVDF membranes. Continuous wastewater ultrafiltration tests with mechanical air scouring confirmed the outstanding permeability (71.3–138.9 LMH/bar) and the superior anti-fouling characteristics (59.2–86.8% recovery of the initial flux) of the TFNC-CNF membrane. Furthermore, higher total organic carbon rejection rates were also observed in the TFNC-CNF membrane (>83.2%) than the PVDF membrane (<69.8%). Collectively, the superior flux recovery and high permeability makes the TFNC-CNF membrane a promising material for membrane bioreactors.

Effect of Surfactants’ Tail Number on the PVDF/GO/TiO2-Based Nanofiltration Membrane for Dye Rejection and Antifouling Performance Improvement

In this work, the novel utilisation of customised double- and triple-tail sodium bis(3,5,5-trimethyl-1-hexyl) sulphosuccinate (AOT4) and sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-silphonate (TC14) surfactants to assist the direct graphene oxide (GO) synthesis via electrochemical exfoliation utilising dimethylacetamide (DMAc) as a solvent were investigated. The synthesised DMAc-based GO and titanium dioxide (TiO2) nanoparticles were then used to fabricate polyvinylidene fluoride (PVDF)-based nanofiltration (NF) membranes by the non-solvent-induced phase separation method. The incorporation of GO and TiO2 as hydrophilic nanoparticles were to enhance membrane hydrophilicity. The utilisation of higher surfactants’ tail number obviously alters the fabricated membrane’s morphology which further affects its performance for dye rejection and antifouling ability. Higher surfactants’ tail number resulted in higher oxidation process which then provided more interaction between the GO and PVDF. Based on the dead-end cell measurement, PVDF/TC14-GO/TiO2 presented a slightly higher dye rejection efficiency of 92.61% as compared to PVDF/AOT4-GO/TiO2 membrane (92.39%). However, PVDF/TC14-GO/TiO2 possessed three times higher water permeability (48.968 L/m2 h MPa) than PVDF/AOT4-GO/TiO2 (16.533 L/m2 h MPa) and also higher hydrophilicity as presented by lower contact angle (65.4 ± 0.17°). This confirmed that higher surfactants’ tail number improved the fabricated membrane’s performance. Both fabricated membranes also exhibited high flux recovery ratio (FRR) ( $$>$$ 100%) which indicated better antifouling properties.

Robust siloxane/graphene oxide thin film membranes: Siloxane size adjustment for improved separation performance and flux recovery

Siloxane/graphene oxide (GO) nanocomposites were synthesized by hydrolysis and condensation of tetraethyl orthosilicate in the presence of GO nanosheets through a sol-gel process. The influence of synthesis parameters on the properties of the siloxane/GO samples was studied and their structural, morphological and physicochemical characteristics were compared using various techniques. Polyether sulfone-supported GO and siloxane/GO thin film membranes were prepared using a pressure-assisted self-assembly method using a dead-end cell, and their separation performance and antifouling ability were evaluated. Siloxane/GOs appeared to have higher interlayer spacing, higher zeta potential and thus higher dispersion stability in aqueous media compared to GO. This gave rise to slower and more uniform sedimentation of the siloxane/GOs during the filtration process and formation of thin film membranes possessing denser and smoother morphology. The porosity, mean pore radius, water contact angle and pure water flux of the prepared membranes were compared. The separation performance of the prepared membranes to remove methylene blue (MB) and penicillin G-procaine (PG-P) from water was evaluated as a function of used GO solution concentration. The antifouling ability of membranes was studied by determining reversible fouling (Rr), irreversible fouling (Rir) resistances and flux recovery ratio (FRR). The siloxane/GO thin film membranes containing larger siloxane network exhibited the highest rejection percentage for MB (∼99%) and PG-P (∼88%), which were about 40% and 90% higher than that achieved for GO thin film membranes, while the water flux remained as high as 78.1 l·m−2h−1. Furthermore, these membranes exhibited the highest chlorine resistance, stability under ultrasonication, FRR (89%) and Rr (57%) values, implying higher chemical and mechanical stability, flux recovery capacity and antifouling ability.

Development of ZSM-22/Polyethersulfone Membrane for Effective Salt Rejection.

ZSM-22/polyethersulfone membranes were prepared for salt rejection using modelled brackish water. The membranes were fabricated via direct ZSM-22 incorporation into a polymer matrix, thereby inducing the water permeability, hydrophilicity and fouling resistance of the pristine polyethersulfone (PES) membrane. A ZSM-22 zeolite material with a 60 Si/Al ratio, high crystallinity and needle-like morphologies was produced and effectively used as a nanoadditive in the development of ZSM-22/PES membranes with nominal loadings of 0–0.75 wt.%. The characterisation and membrane performance evaluation of the resulting materials with XRD, BET, FTIR, TEM, SEM and contact angle as well as dead-end cell, respectively, showed improved water permeability in comparison with the pristine PES membrane. These ZSM-22/PES membranes were found to be more effective and superior in the processing of modelled brackish water. The salt rejection of the prepared membranes for NaCl and MgCl2 was effective, while they exhibited quite improved water flux and flux recovery ratios in the membrane permeability and anti-fouling test. This indicates that different amounts of ZSM-22 nanoadditives produce widely divergent influences on the performance of the pristine PES membrane. As such, over 55% of salt rejection is observed, which means that the obtained membranes are effective in salt removal from water.

Self-cleaning properties of L-Histidine doped TiO2-CdS/PES nanocomposite membrane: Fabrication, characterization and performance

The polyethersulfone (PES) membrane incorporated with L-Histidine doped TiO2-CdS photocatalytic nanocomposite is fabricated to improve the membrane performance and its antifouling properties. The L-Histidine doped TiO2-CdS/PES nanofiltration membrane was characterized by scanning electron microscopy (SEM), contact angle and atomic force analysis (AFM) analyses. SEM images and contact angle results are demonstrated that membrane porosity and its hydrophilic properties increase with adding of L-Histidine doped TiO2-CdS photocatalytic nanocomposite. Moreover, AFM images of the modified membranes indicate favorable changes in surface roughness resulting in the improvement of antifouling properties. The pure water flux, flux recovery ratio (FRR) during filtration of milk powder and activated sludge suspension were also measured in a dead end cell. Increasing membrane permeability and FRR value approved its effective role of the added nanoparticles into the PES matrix. The M3 (0.5 wt% of NPs) membrane is selected as an optimal nanocomposite membrane which exhibits a much higher pure water flux (42.1 kg/m2 h) and FRR value (90 and 97% during filtration of milk powder and activated sludge suspension, respectively). The photocatalytic capability and antifouling properties of the M3 membrane as an optimum membrane were also investigated in a cross flow cell under continuous visible light irradiation. As a result, the high permeation flux (34.7 kg/m2 h), COD removal (100%) and FRR value (99%) was achieved during filtration of biologically treated palm oil mill effluent (POME) with COD concentration of 1000 mg/L at feed flow rate of 150 L/h and pressure of 5 bar. Effect of feed flow rate (50 and 150 L/h) and COD concentration (1000, 3000 and 5000 mg/L) on the membrane performance and its fouling resistance was also evaluated. Increasing feed concentration shows a negative effect on the membrane performance while feed flow rate increases separation performance and self-cleaning properties of the M3 membrane.

Bienzymatic modification of polymeric membranes to mitigate biofouling

Staphylococcus aureus and Staphylococcus epidermidis are considered as major human pathogens and their resistance to antibiotic treatment and host defense systems can be increased due to the formation of biofilms. The biofilm-associated biofouling of industrial surfaces, particularly membranes, remains a serious concern that challenges investigators to develop practical solutions for the reduction of their impact. The present study developed antibacterial membrane surfaces that can mitigate biofilm formation. α-Amylase and lysozyme, as antibacterial enzymes, were covalently immobilized on polydopamine/cyanuric chloride functionalized polyethersulfone (PES) membranes to form biocompatible antibacterial surfaces. Several methods including SEM, AFM, Bradford, water contact angle goniometry, and surface free energy measurement techniques have been used to demonstrate the attachment of enzymes onto PES membranes by changing the physicochemical properties of the surface. The two enzymatic systems alter the membrane surface chemistry by rendering lower free surface energy and higher hydrophilicity, which leads to the creation of a layer of hydration energy barrier preventing microorganisms from being anchored on the surface. Those microorganisms that managed to overcome the energy barrier and get attached to the surface are attached by the enzymes' bond cleavage functionality. This multilevel defense system protects the membrane against any biofilm formation. The results of microtiter test and flow cytometry assay indicated that α-amylase/lysozyme mixture treated membrane samples came with more than 87% removal of biofilms. The results of the biofouling experiment in a dead-end cell demonstrated that the modified membrane surface had only a slightly impaired water flow compared to an unmodified membrane, which was due to the removal of biofilms by the enzymes’ activity. The results also showed that the modification of membranes with antibacterial enzymes could create a new biotechnological horizon to prevent biofilm formation.

Fabrication of self-doped sulfonated polyaniline membranes with enhanced antifouling ability and improved solvent resistance

The fabrication of self-doped sulfonated polyaniline S-PANI membranes is reported here for the first time and addresses key challenges of PANI membranes including fouling, solvent stability issues and acid leaching. Sulfonation of the PANI-powder was confirmed by FTIR, UV-VIS and SEM-EDX characterisation. The membranes were prepared via phase inversion approach in water from a solution of 23% w/v S-PANI and were chemically cross-linked with three different organic cross-linkers: α,α′-Dichloro-p-xylene (DCX), glutaraldehyde (GA) and terephtaloyl chloride (TCL). PANI, S-PANI, S-PANI DCX, S-PANI TCL and S-PANI-GA were evaluated for their hydrophilicity, morphology, chemical properties and filtration performance showing that the chemically cross-linked S-PANI membranes have superior stability and reusability in DMF when tested in dead-end cell at 5 bar. Filtration experiments in water showed that S-PANI-GA has an increase in PEG rejection of 2.3 times and a MWCO of 1800 Da in contrast with PANI and SPANI, which showed a MWCO above 5000 Da. Fouling performance using BSA, showed a significant improvement of flux recovery for S-PANI and S-PANI GA, with the membranes regaining 87% and 83% of their original flux after one cleaning-fouling cycle. Conversely, PANI had a flux recovery of only 40%. The low irreversible fouling of the membranes, 13% for S-PANI and 17% for S-PANI GA, against 65% for PANI after 3 cycles is an encouraging result for the reduction of costly and high environmentally impact chemical cleaning in membrane processes. Overall, this study provides a simple method to produce low fouling and long-term solvent resistant membranes to enhance the widespread use of membrane technology in industrial processes.

Layer-by-layer assembly of graphene oxide nanoplatelets embedded desalination membranes with improved chlorine resistance

Membranes with polyamide thin film active layer are used in reverse osmosis-based water desalination applications. Incorporation of graphene oxide nanoplatelets (GONPs) in the polyamide layer can alter the surface characteristics, permeability, selectivity, and can enhance the chlorine resistance of these membranes. In this study, a layer-by-layer (LbL) synthesis technique has been developed for embedding GONPs in the polyamide layer. Polyamide layers with GONPs were synthesized in various sequences, such as alternating layers of GONPs and polyamide, and GONPs on top of the polyamide layer. Incorporation of GONPs resulted in an increase of surface hydrophilicity as captured by the change of the water contact angle. Water flux and salt rejection properties of synthesized membranes have been investigated by using a dead-end cell. The salt rejection ability of membranes increased slightly with the incorporation of GONPs, while the water flux found to be similar to that observed for the pristine membranes without GONPs. Upon exposure to chlorine, GONPs embedded membranes retained salt rejection performance better than the pristine membranes. Our approach provides an alternative framework to incorporate nanoparticles in thin film membranes in a precise manner and to investigate the effect of such nanoparticles on the membrane performances.

Predicting the performance of pressure filtration processes by coupling computational fluid dynamics and discrete element methods

To obtain a fundamental understanding of the various factors affecting pressure filtration performance, we developed a coupled computational fluid dynamics (CFD) and discrete element method (DEM) model for simulating the effect of solvent flow through the solid particle cake. The model was validated using data collected by filtering mixtures of spherical glass beads and deionized water through a dead-end cell over a range of applied pressures. Numerical experiments were performed to study the effects of particle properties, liquid properties and operating conditions on filtration performance. The model predicted that the filtrate flow rate could be strongly affected by the mean size of the particles, the presence of small particles (i.e. fines) in the particle distribution, the viscosity of the liquid, and particle deformation leading to cake compression. Our study demonstrated that CFD-DEM modeling is a powerful approach for understanding cake filtration processes and predicting filtration performance.

Incorporation of Electrochemically Exfoliated Graphene Oxide and TiO2 into Polyvinylidene Fluoride-Based Nanofiltration Membrane for Dye Rejection

In this work, the novel direct synthesis method of dimethylacetamide-based graphene oxide (GO) was performed through electrochemical exfoliation assisted by commercially available single-tail sodium dodecyl sulphate (SDS) surfactant. Then, the synthesised GO (SDS–GO) was incorporated into polyvinylidene fluoride (PVDF) solution to produce a nanofiltration (NF) membrane through the phase immersion method. The addition of GO into the preparation of membrane solution alters the membrane morphology and improves the hydrophilicity. TiO2 was also used as an additive for the NF membrane fabrication to further increase the membrane hydrophilicity. The fabricated PVDF/SDS–GO/TiO2 and PVDF/SDS–GO NF membranes were compared with pure PVDF membrane. Then, the fabricated NF membranes were tested for methylene blue (MB) rejection with 10 ppm MB concentration. On the basis of the dead-end cell measurement operated at the pressure of 2 bar, the PVDF/SDS–GO/TiO2 presents high MB rejection (92.76%) and the highest dye flux (7.770 L/m2 h). This dye flux value was sevenfold higher than that of pure PVDF membrane (1.146 L/m2 h) which was due to the utilisation of both GO and TiO2 that improved the membrane hydrophilicity as indicated by the lowest contact angle (64.0 ± 0.11°). High porosity (57.46%) also resulted in the highest water permeability (4.187 L/m2 h bar) of the PVDF/SDS–GO/TiO2 NF membrane.

Effect of the lactose hydrolysis on galacto-oligosaccharides mixtures subjected to nanofiltration: A detailed fractionation analysis

Galacto-oligosaccharides (GOS) are short oligosaccharides chains containing several galactoses and one terminal glucose. Raw GOS are mixtures containing oligosaccharides, unreacted lactose and monosaccharides; hence nanofiltration is an alternative for product purification. However, poor membrane selectivity towards separation of lactose from GOS is the main drawback. So, in order to improve the purification of enzymatically-produced GOS by nanofiltration, the incorporation of a previous lactose hydrolysis step, to convert the remaining lactose into monosaccharides, is proposed. The purification of raw and hydrolyzed raw GOS was evaluated using two nanofiltration polymeric membranes (Synder NFG and TriSep XN45) at different transmembrane pressures (8–30 bar) in a stirred dead-end cell. Results indicate that the incorporation of the lactose hydrolysis step allows increasing GOS retention and monosaccharides and lactose removal, improving GOS purification. Best operational conditions for hydrolyzed raw GOS nanofiltration were obtained with the TriSep XN45 membrane at 20 bar, 45 °C and 1500 rpm.

Enhanced Hydrophilicity and Water Flux of Poly(ether sulfone) Membranes in the Presence of Aluminum Fumarate Metal-Organic Framework Nanoparticles: Preparation and Characterization.

The aim of this study is to examine the effect of the addition of aluminum fumarate (AlFu) nanoparticles on the properties of poly(ether sulfone) (PES) membranes, where the AlFu nanoparticles were synthesized as the nanofillers with the metal-organic framework and their structure was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FESEM) analyses. Subsequently, PES/AlFu mixed-matrix membranes (MMMs) were fabricated in different weight percentages of nanofiller through the phase inversion method and the membrane characterization was accomplished by FTIR, XRD, FESEM, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, and elemental mapping analyses. The effect of the addition of nanoparticles on the membrane properties was investigated by measuring the membrane hydrophilicity, pure water flux, solute rejection, and fouling resistance using a dead-end cell under constant pressure and bovine serum albumin as a foulant. The molecular weight cutoff (MWCO) of MMMs was measured by the rejection of poly(ethylene glycol) in various molecular weights, and the membrane surface roughness, porosity, and mean pore radius were calculated. The results showed that AlFu nanoparticles increased the hydrophilicity and porosity of the neat PES membranes and consequently increased the water permeability such that MMM including 0.75 wt % of AlFu possessed the maximum porosity (62.2%), mean pore radius (10.2 nm), and MWCO (154 kDa). Furthermore, this membrane exhibits a superlative flux recovery and minimal total resistance in the antifouling properties examinations.