Cross-flow Filtration Experiments Research Articles

Development of a crossflow nanofiltration process for polishing of wastewater by-product from biogas production processes

The growing adoption of biogas production from source-separated organics (SSOs) has resulted in a need for advanced treatment processes for the resulting liquid waste by-products. While previous studies have demonstrated the potential of using nanofiltration (NF) membranes to polish the outlet stream of a membrane bioreactor (MBR) in municipal wastewater applications, there is little known about the performance of such membranes to treat the more complex multi-component streams that result from the processing of SSOs. In this study, crossflow filtration experiments with three commercial flat-sheet NF membranes (NFS, NFX, NF90) were run on two batches of MBR permeate (identified as Batch A and Batch B) which were sourced four months apart from a biogas production facility. For each batch, there was a remarkable difference in performance of the three NF membranes, where a clear trade-off between permeate quality and recovery was observed. For example, the NF90 membrane gave the best permeate quality but the lowest recovery. Interestingly, the NFS permeate COD for Batch B was approximately 60 % lower than that for Batch A; it is believed that this was due to differences in the amount of ammonia between the two batches. This work bridges a technical gap in the water-energy nexus by demonstrating the viability of using NF technology to polish liquid waste streams from biogas production processes, while also highlighting their susceptibility to variable feed conditions caused by upstream process deviations.

Preparation and benchmarking of highly hydrophilic polyaniline poly(2-acrylamido-2-methyl-1-propanesulfonic acid) PANI PAMPSA membranes in the separation of sterols and proteins from fruit juice

A straightforward approach is presented to prepare highly hydrophilic ultrafiltration polyaniline poly(2-acrylamido-2-methyl-1-propanesulfonic acid (PANI PAMPSA) membranes. Their application in the fractionation of phytosterols and proteins from fruit juice is described. Poly(2-acrylamido-2-methyl-1-propanesulfonic (PAMPSA) is added to aniline during the polymer synthesis and the membrane is prepared via phase inversion forming a highly hydrophilic and mechanically stable ultrafiltration membrane of 200 µm thickness and pure water flux of 126 LMH at 1 bar. The membrane so produced is benchmarked against a hydrophilic commercial regenerated cellulose acetate membrane (RCA) for the separation of phytosterols and proteins from orange juice. Cross-flow filtration experiments show comparable protein separation efficiency of the membranes, but better rejection of phytosterols for the commercial RCA membrane. Both commercial and lab prepared membranes are subject to fouling, with the PANI PAMPSA membrane showing higher irreversible fouling. Nevertheless, the PANI PAMPSA membrane showed a good cleaning efficiency of 74% after three fouling-cleaning cycles. Overall, this work has demonstrated the possibility of use PANI PAMPSA for ultrafiltration application and provided a better understanding of its fouling ability when compared to a commercial membrane in a multicomponent system.

Azido-group functionalized graphene oxide/polysulfone mixed matrix ultrafiltration membrane with enhanced interfacial compatibility for efficient water and wastewater treatment

• Oxygen-containing azido functionalized GO were synthesized via facile EMR-FD method. • Novel MMMs were synthesized by incorporating azido functionalized GO nanosheets. • Oxygen-containing AGO enhanced interaction with polymer to achieve high compatibility. • AGO/PSF membranes displayed high permeability and good antibacterial performance. Bio-fouling of membranes caused by microorganisms seriously limited the development of membrane technology in practical applications. Design and synthesis of antifouling and antibacterial membranes with high quality are of paramount importance. In this study, we report a facile and safe method of extended Mitsunobu reaction (EMR)-freeze drying (FD) method to achieve oxygen-containing azido functionalized GO (AGO) nanosheets and synthesize novel azido-group functionalized graphene/polysulfone mixed matrix ultrafiltration membranes with enhanced permselective, antifouling and antibacterial property. Unlike reported thermochemical or chemical reactions to modify GO nanosheets, GO nanosheets were functionalized at low temperature which effectively prevented the decomposition of structural frame of pristine GO materials and the self-stacking phenomenon. Because of strong interactions between oxygen-containing AGO nanosheets and polymer matrices, high dispersity and interfacial compatibility were obtained in polysulfone membranes, resulting in sharp decrease of interfacial defects. Different kinds of techniques include SEM, ATR-FTIR, XPS, XRD, TEM and EDX were used to investigate the structure and morphology of AGO nanosheets and blended membranes, and cross-flow filtration experiments, anti-fouling and antibacterial test were applied to predict the behavior of hybrid membranes. High performance AGO/PSF mixed matrix membranes with excellent anti-fouling ability were successfully synthesized, which exhibited pure water flux as large as 245.1 L m −2 h −1 with satisfactory rejection of 95.8% for BSA. Moreover, the prepared membranes displayed good antibacterial activity against E. coli and S. aureus in long-term duration.

Water Recovery from Bioreactor Mixed Liquors Using Forward Osmosis with Polyelectrolyte Draw Solutions.

This paper reports on the use of forward osmosis (FO) with polyelectrolyte draw solutions to recover water from bioreactor mixed liquors. The work was motivated by the need for new regenerative water purification technologies to enable long-duration space missions. Osmotic membrane bioreactors may be an option for water and nutrient recovery in space if they can attain high water flux and reverse solute flux selectivity (RSFS), which quantifies the mass of permeated water per mass of draw solute that has diffused from the draw solution into a bioreactor. Water flux was measured in a direct flow system using wastewater from a municipal wastewater treatment plant and draw solutions prepared with two polyelectrolytes at different concentrations. The direct flow tests displayed a high initial flux (>10 L/m2/h) that decreased rapidly as solids accumulated on the feed side of the membrane. A test with deionized water as the feed revealed a small mass of polyelectrolyte crossover from the draw solution to the feed, yielding an RSFS of 80. Crossflow filtration experiments demonstrated that steady state flux above 2 L/m2·h could be maintained for 70 h following an initial flux decline due to the formation of a foulant cake layer. This study established that FO could be feasible for regenerative water purification from bioreactors. By utilizing a polyelectrolyte draw solute with high RSFS, we expect to overcome the need for draw solute replenishment. This would be a major step towards sustainable operation in long-duration space missions.

Understanding the Role of Pattern Geometry on Nanofiltration Threshold Flux.

Colloidal fouling can be mitigated by membrane surface patterning. This contribution identifies the effect of different pattern geometries on fouling behavior. Nanoscale line-and-groove patterns with different feature sizes were applied by thermal embossing on commercial nanofiltration membranes. Threshold flux values of as-received, pressed, and patterned membranes were determined using constant flux, cross-flow filtration experiments. A previously derived combined intermediate pore blocking and cake filtration model was applied to the experimental data to determine threshold flux values. The threshold fluxes of all patterned membranes were higher than the as-received and pressed membranes. The pattern fraction ratio (PFR), defined as the quotient of line width and groove width, was used to analyze the relationship between threshold flux and pattern geometry quantitatively. Experimental work combined with computational fluid dynamics simulations showed that increasing the PFR leads to higher threshold flux. As the PFR increases, the percentage of vortex-forming area within the pattern grooves increases, and vortex-induced shielding increases. This study suggests that the PFR should be higher than 1 to produce patterned membranes with maximal threshold flux values. Knowledge generated in this study can be applied to other feature types to design patterned membranes for improved control over colloidal fouling.

Treatment of Electroplating Wastewater Using NF pH-Stable Membranes: Characterization and Application.

Industrial adoption of nanofiltration (NF) for treatment of low-pH wastewater is hindered by the limited membrane lifetime at strongly acidic conditions. In this study, the electroplating wastewater (EPWW) filtration performance of a novel pH-stable NF membrane is compared against a commercial NF membrane and a reverse osmosis (RO) membrane. The presented membrane is relatively hydrophobic and has its isoelectric point (IEP) at pH 4.1, with a high and positive zeta potential of +10 mV at pH 3. A novel method was developed to determine the molecular weight cut-off (MWCO) at a pH of 2, with a finding that the membrane maintains the same MWCO (~500 Da) as under neutral pH operating conditions, whereas the commercial membrane significantly increases it. In crossflow filtration experiments with simulated EPWW, rejections above 75% are observed for all heavy metals (compared to only 30% of the commercial membrane), while keeping the same pH in the feed and permeate. Despite the relatively lower permeance of the prepared membrane (~1 L/(m2·h·bar) versus ~4 L/(m2·h·bar) of the commercial membrane), its high heavy metals rejection coupled with a very low acid rejection makes it suitable for acid recovery applications.

Anti-fouling piezoelectric PVDF membrane: Effect of morphology on dielectric and piezoelectric properties

Piezoelectric membrane serves as an alternative to vibratory shear-enhanced process, which potentially offers lower cost of operation as the source of agitation is the membrane itself. The effect of morphology on dielectric and piezoelectric properties of polyvinylidene fluoride (PVDF) membranes prepared via non-solvent induced phase separation method was investigated. The membranes were fabricated using different solvents: N,N-dimethylformamide (PVDF-DMF), 1-methyl-2-pyrrolidinone (PVDF-NMP) and triethyl phosphate (PVDF-TEP). Dielectric strength analysis and piezo-response force microscopy (PFM) revealed that PVDF-DMF, displaying finger-like morphology, presented highest dielectric strength and desired piezoelectric properties. The presence of macrovoids in PVDF-NMP resulted in weak dielectric strength. Electrical poling was performed, enhancing the piezoelectric properties of membranes. No noticeable change in microstructure was observed for PVDF-NMP after poling. However, cross-section morphology of PVDF-DMF visibly changed from finger-like to drop-like cavities. Infrared (IR) spectroscopy and PFM showed improvements in fraction of β phase and piezoelectric coefficient d33 after poling. Cross-flow filtration experiments using colloidal silica were performed to investigate effect of electrical signal (10 Vpp, 500 Hz) on the membranes. It showed negligible effect on performance of unpoled PVDF-DMF, while 46% increase in critical flux and 66% reduction in transmembrane pressure increase (dTMP/dt) was observed for poled PVDF-DMF under electrical signal.

Electrically conducting duplex-coated gold-PES-UF membrane for capacitive organic fouling mitigation and rejection enhancement

Recent studies showed that the application of an electrical potential onto an ultrafiltration membrane surface exhibit several advantages with respect to the fouling and rejection behaviour. Sputter deposition of ultra-thin metal layers onto commercial flat sheet membranes proved to be a simple way of producing conductive metal-polymer-composite membranes. Adopting the novel approach of duplex-coating the active and support layer of a flat sheet membrane eliminates the need for an additional counter electrode and significantly simplifies module design for conductive flat sheet systems. Cross-flow filtration experiments were conducted with organic model foulants such as sodium alginate, bovine serum albumin (BSA), humic acids as well as with natural organic matter (NOM) from Hohloh lake water. The duplex-coating induced an additional electric field through the membrane itself, resulting in enhanced performance not only for cathodic but also for anodic charging of the active membrane layer. Hohloh lake water fouling experiments showed decreased permeability of 47% for the uncharged membrane to 16% and 38% for the cathodic and anodic charging, respectively. Moreover, a significant increase in NOM-rejection was observed with 27% for the uncharged membrane and 72% and 49% for the cathodic and anodic potentials, respectively. Finally, the effectiveness of externally charged duplex-coated membranes was demonstrated by comparing rejection and fouling rates with conventional membrane-electrode vs. counter electrode configuration, showing an almost similar enhancement in performance.

Impact of incubation conditions and post-treatment on the properties of bacterial cellulose membranes for pressure-driven filtration

Bacterial cellulose (BC) has shown potential as a separation material. Herein, the performance of BC in pressure-driven separation is investigated as a function of incubation conditions and post-culture treatment. The pure water flux of never-dried BC (NDBC), was found to be 9 to 16 times higher than that for dried BC (DBC), in a pressure range of 0.25 to 2.5 bar. The difference in pressure response of NDBC and DBC was observed both in cross-flow filtration and capillary flow porometry experiments. DBC and NDBC were permeable to polymers with a hydrodynamic radius of ∼60 nm while protein retention was possible by introducing anionic surface charges on BC. The results of this work are expected to expand the development of BC-based filtration membranes, for instance towards the processing of biological fluids.

Fabrication of a superhydrophilic PVDF-g-PAA@FeOOH ultrafiltration membrane with visible light photo-fenton self-cleaning performance

A self-cleaning surface can effectively solve the accumulation problem of irreversible contamination of ultrafiltration membranes. In this work, a (polyvinylidene fluoride)-g-(polyacrylic acid) (PVDF-g-PAA) ultrafiltration membrane, hereafter denoted as FAS, was prepared by a one-pot method. A superhydrophilic self-cleaning ultrafiltration membrane, hereafter denoted as FASF, was then obtained based on the strong complexation of Fe3+ with the abundant carboxyl groups at the FAS surface, which then mineralized Fe3+ into β-FeOOH nanoparticles and deposited them onto the FAS surface. This deposition was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Bovine serum albumin (BSA) cross-flow filtration experiments confirmed the high ultrafiltration performance of FAS and FASF. FASF exhibited highly efficient degradation of methylene blue (MB) solution under visible light photo-Fenton conditions. The optimum amount of acrylic acid was 6 wt% in the one-pot reaction system, and the alkaline coagulation bath enhanced the wettability of FAS. The β-FeOOH nanoparticle content of the surface-mineralized FASF tended to be saturated after 24 h. β-FeOOH can significantly enhance the hydrophilicity and wettability of FASF and further enhance the antifouling performance of BSA. After four cycles of cleaning operation under visible light photo-Fenton conditions, the flux recovery rate of BSA-contaminated FASF reached 96.2%, and the rejection rate remained stable. FASF had superhydrophilicity, high antifouling, and fast photocatalytic self-cleaning performances, indicating good application prospects in organic wastewater treatment.

Novel bio-based polymer membranes fabricated from isosorbide-incorporated poly(arylene ether)s for water treatment

Development of bio-based polymers for high-performance applications using isosorbide as renewable feedstock has garnered considerable research attention. Isosorbide, a bio-derived compound, is known to enhance the mechanical, thermal, and optical properties of a host polymer due to its unique molecular structure. In this study, two types of novel membrane polymer, isosorbide-based poly(arylene ether sulfone) (I-PAES) and poly(arylene ether ketone) (I-PAEK) were used to develop ultrafiltration membranes by the phase inversion technique. The physicochemical properties and filtration performance of the isosorbide-based membranes were investigated. I-PAES and I-PAEK membranes exhibited contact angles of 62.2° and 63.5°, respectively, which are lower than that of the polyethersulfone (PES) membrane (68.4°). The I-PAES and I-PAEK membranes showed lower flux decline ratios than PES membrane at the pHs examined in this study. Furthermore, the flux recovery ratios of the two bio-based membranes in cross-flow filtration experiments of a protein solution at pH 4 were about 16% and 17% higher than that of PES, respectively. At pH 9.5, the I-PAEK membrane exhibited an 11% higher flux recovery than the PES membrane. Ultrafiltration experiments with BSA revealed that the I-PAES and I-PAEK membranes are advantageous in terms of membrane fouling due to their high hydrophilicities; hence, they are possible replacements for PES membranes derived from petrochemicals.

Fouling mechanisms of membrane filtration of mixed microalgal biomass grown in wastewater.

Membrane fouling mechanisms of the filtration of a mixed-culture microalgal biomass grown in real wastewater were investigated using crossflow filtration experiments. The results of flux measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses for three membranes, two microfiltration (PES01 and PES003) and one ultrafiltration (UC030), showed that the UC030 membrane may be more appropriate for microalgae harvesting due to its higher steady flux rate and lower flux reduction during filtration compared to the initial flux (44% for UC030, compared to 86% for PES01 and 79% for PES003). It was also observed that the membrane resistance due to concentration polarization was the dominant membrane resistance in this study for all three membranes, constituting about 67%, 61% and 51% for PES01, PES003, and UC030, respectively. The next largest membrane resistance was provided by pore blocking, while the resistance provided by cake formation was found to be very small for all membranes (3%, 15% and 18% for PES01, PES003 and UC030, respectively), which were also supported by SEM and AFM analyses.

Reverse osmosis performance on stripped phenolic sour water treatment – A study on the effect of oil and grease and osmotic pressure

Technologies for water recycling within oil refineries have been gaining interest at an extensive rate due to the large volume of wastewater generated, high dependency of water and the progressive scarcity of this valuable resource. Phenols are part of a specific class of organic pollutants that have been contributing to a low-quality effluent in oil refineries due to their hazardous nature and strict environmental legislation associated. The reuse of stripped sour water within refineries is often blocked due to its rich phenolic content.This study evaluates the retention of phenols in refinery wastewater through reverse osmosis (RO) at its major source of emission, for water reclamation. The RO membrane selected exhibited rejections of up to 98% of phenols and 99% of both chemical oxygen demand (COD) and total organic carbon (TOC). Permeate quality remained intact despite flux decline caused by phenolic and hydrocarbon adsorption when the oil content, in the feed, reached 771 ppm. The effluent's low conductivity due to lack of salts led to minor osmotic pressure differences (less than 2.5 bar at a volume concentration factor of 3), therefore, showing appealing performances of reverse osmosis filtration. Characterization of all permeates obtained from cross-flow filtration experiments showed COD levels in line with water reuse quality standards for make-up water in cooling processes.

Ultrafiltration Mixed Matrix Membranes Based on Mesoporous Silica (MCM-41, HMS)Embedded in Polysulfone

Three composite membranes (M1-M3), with mesoporous silica (MCM-41 or HMS-C12/C16-type) embedded in polysulfone (Psf) were obtained by phase-inversion method and their performances were tested for use in ultrafiltration membrane processes. The structures of M (Psf 12%, reference membrane), M1 (Psf 12% + MCM-41), M2 (Psf 12% + HMS-C12), M3 (Psf 12% + HMS-C16) have been assessed by FTIR, TG-DSC and SEM-EDAX and the morphology and their hydrodynamic performances have been evaluated by contact angle measurements, dead-end and cross-flow filtration experiments.

Technical Concepts for the Investigation of Spatial Effects in Spiral-Wound Microfiltration Membranes

Existing works on the influence of spatial effects on flux and permeation of proteins in microfiltration (MF) have focused on ceramic membranes. There is little information on spiral-wound membranes (SWMs). Since the inner core of a SWM is practically inaccessible by non-destructive techniques, three different prototypes were constructed in this study to optimize suitability for the investigation of spatial effects on filtration performance. To measure the pressure drop, shortened SWMs 0.25, 0.50, and 0.75 times the length of a standard industrial SWM (0.96 m) were designed. Second, a sectioned membrane (0.96 m) with separated compartments on the permeate side was constructed to analyze spatial effects on flux and protein permeation along the flow path of a SWM. Three different features characterized this sectioned module: sectioned permeate pockets, a sectioned permeate collection tube, and sectioned permeate drain and measurement systems. Crossflow filtration experiments showed that these modifications did not alter the filtration performance compared to an unmodified control SWM. Thus, it can be applied to assess spatially-resolved filtration performance in SWMs. The third prototype designed was a test cell with accessible flat sheet membranes and spacer material, as in SWMs. The flow path in this test cell was designed to match the characteristics of the channels between the membrane sheets in a standard SWM as closely as possible. The flow path length and the combination of membrane material and spacer architecture were the same as in the control SWM. This test cell was designed to assess the effects of length and processing conditions on the formation of a deposit layer. The combined results of these test modules can yield new insights into the spatial distribution of flux, permeation of target components, and deposit formation.

Streaming potential properties of ceramic nanofiltration membranes – Importance of surface charge on the ion rejection

The aim of the present research is the electrokinetic determination of the inner surface centercharges of ceramic nanofiltration membranes under varying electrochemical conditions and their influences on the filtration properties especially on salt/ion rejection. Ceramic microporous nanofiltration membranes of TiO2 with pore size of 0.9 nm were characterized. The membrane charge was determined under real filtration conditions at different salt solutions, concentrations and pH-values using flow-through streaming potential measurement. In the case of liquid saturated oxide ceramic membranes a surface charge results from protonated und deprotonated surface groups and specifically adsorbed ions. The charge properties of the amphoteric titania nanofiltration membrane significantly depending on the pH value of the feed. The specific adsorption of multivalent ions modifies additionally the membrane charge and shifts the isoelectric point. Depending on the valence and art of the ions and the pH value/range of the solution the membrane charge is shielded or increased. Using magnitude and sign of the measured streaming potential at different salt solution, concentration and pH-values the salt/ion rejection can be predicted. This could be checked by cross-flow filtration experiments. Single and multivalent ion separation in the nanofiltration range does not only result from a sieving effect/steric exclusion of the pore structure but is strongly influenced by the surface charge characteristics of the pore/channel walls. When the membrane is charged, the ions are retained, and when shielded, the ions pass through the membrane. The investigations show the possibility for adjusting the separation characteristic up to a nearly complete salt rejection by choosing the appropriate pH-value, concentration and the kind of the salt solution. The measurement of the streaming potential during real filtration processes supports in the simplest way the optimization and monitoring of desalination processes with charged nanofiltration membranes.

Application of Colloidal Precipitation Method Using Sodium Polymethacrylate as Dispersant for TiO2/PVDF Membrane Preparation and Its Antifouling Properties

Immobilized titanium dioxide (TiO2) nanoparticles on flat sheet polymeric membranes have been found effective for fouling reduction in recent researches. The main challenge in this field is to obtain ultrafine and stable nanodispersions. In this study, composite polyvinylidene fluoride/TiO2 (PVDF/TiO2) ultrafiltration membranes were prepared via phase inversion and colloidal precipitation method. Stable TiO2 suspensions were prepared using sodium polymethacrylate as dispersant and sonication without altering of the coagulation bath pH. The effect of different concentrations of TiO2 nanoparticles in the coagulation bath was also investigated. The membrane morphology (distribution of nanoparticles on the membrane surface) was observed by scanning electron and atomic force microscopy. Properties of the neat and the composite membranes were also characterized using energy dispersive X‐ray spectroscopy and contact angle and membrane porosity measurements. The neat and the composite membranes were further investigated in terms of bovine serum albumin rejection and flux decline in cross flow filtration experiments. The results showed that the PVDF/TiO2 composite membrane using dimethylacetamide/triethyl phosphate as solvent and 0.05 g/L of TiO2 in the coagulation bath exhibits improved antifouling properties. POLYM. ENG. SCI., 59:E422–E434, 2019. © 2018 Society of Plastics Engineers

Synergistic effect of carboxylated-MWCNTs on the performance of acrylic acid UV-grafted polyamide nanofiltration membranes

Surface modification of a commercial polyamide nanofiltration membrane was achieved by UV induced graft polymerization of acrylic acid and incorporation of carboxylated-MWCNTs (COOH-MWCNTs). The grafting process was done under different monomer concentrations and UV exposure times. The modified membranes were characterized through scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle and zeta-potential analysis, and cross-flow filtration experiments. Changes in the surface hydrophilicity, negative charge and roughness of the modified membranes improved their permeability and fouling resistance significantly. The membrane grafted with 50 g/L acrylic acid under 5 min UV exposure showed the best filtration performance including pure water flux of 38.8 L/m2 h, salt rejections of 97.43% (Na2SO4) and 93.4% (NaCl), and flux recovery ratio (FRR) of 80.2% during bovine serum albumin (BSA) filtration. After optimizing grafting condition, different amounts of COOH-MWCNTs were dispersed in the monomer solution for embedding in the grafting layer. By adding 0.2 wt% COOH-MWCNTs to the grafting layer, a water flux improvement of around 30% was observed. But, excess loading of the COOH-MWCNTs led to compaction of the grafting layer and made it inflexible and subsequently, reduced the hydrophilicity and permeability of the membrane. Fouling tests with BSA aqueous solution showed that antifouling ability of the modified membranes was remarkably improved at all concentrations of the COOH-MWCNTs. Furthermore, salt rejection results displayed that simultaneous surface modification through grafting and COOH-MWCNTs embedding could effectively improve the nanofiltration performance of the membranes in the term of permeability, desalination and fouling resistance.

Electro-Conductive Composite Gold-Polyethersulfone-Ultrafiltration-Membrane: Characterization of Membrane and Natural Organic Matter (NOM) Filtration Performance at Different In-Situ Applied Surface Potentials.

Next to the pore size distribution, surface charge is considered to be one main factor in the separation performance of ultrafiltration (UF) membranes. By applying an external surface potential onto an electro-conductive UF membrane, electrostatic induced rejection was investigated. This study introduces in a first part a relatively simple but yet not reported technology of membrane modification with direct current sputter deposition of ultrathin (15 nm) highly conductive gold layers. In a second part, characterization of the gold-coated UF flat sheet membrane with a molecular weight cut-off (MWCO) of 150 kDa is presented. Membrane parameters as contact angle (hydrophobicity), pure water permeability, MWCO, scanning electron microscopy imaging, zeta potential, surface conductivity and cyclic voltammetry of the virgin and the modified membrane are compared. Due to the coating, a high surface conductivity of 107 S m−1 was realized. Permeability of the modified membrane decreased by 40% but MWCO and contact angle remained almost unchanged. In a third part, cross-flow filtration experiments with negative charged Suwannee River Natural Organic Matter (SRNOM) are conducted at different cathodic and anodic applied potentials, different pH values (pH 4, 7, 10) and ionic strengths (0, 1, 10 mmol L−1). SRNOM rejection of not externally charged membrane was 28% in cross-flow and 5% in dead-end mode. Externally negative charged membrane (−1.5 V vs. Ag/AgCl) reached rejection of 64% which was close to the performance of commercial UF membrane with MWCO of 5 kDa. High ionic strengths or low pH of feed reduced the effect of electrostatic rejection.

Selective concentration of uranium from bioleach liquor of low-grade uranium ore by nanofiltration process

Three commercially available nanofiltration membranes (PES-2, NF-1 and NF-2) were employed for selective concentration of uranium from a bioleach liquor of low-grade uranium ore. Performance of the membranes under a variety of operational conditions was evaluated by dead-end and cross-flow filtration experiments. Results showed that the NF-2 membrane had high uranium rejection (˃85%), appropriate permeate flux, and acceptable fouling propensity. Also, NF-2 was more selective than the two other membranes. In general, the nanofiltration process is recommended to be applied in practice for extraction of uranium from the bioleach liquor of low-grade uranium ore.