Polymeric Microfiltration Membranes Research Articles

Designing poly(vinylidene fluoride) membranes with narrow pore size distribution for microplastics removal from water

AbstractMicroplastics have been recognized as a critical threat to the aquatic ecosystem. Membrane separation technology displays great potential to address this issue, while current commonly‐used polymeric microfiltration membranes fall short of high separation efficiency due to their wide pore distribution. A perfectly simple strategy for homoporous membranes fabrication using commercial poly(vinylidene fluoride) (PVDF) was reported in this work, enabling precise removal of microplastics. In this strategy, hydrophilicity of dope solution was enhanced by adding proper amphiphilic surfactants initially, followed by a novelly‐inserted air exposure progress to gently provide water vapor. Both of the two easy steps induced a surface microscopic phase separation to achieve the growth of homopores. Furthermore, the as‐prepared PVDF membrane displayed high surface porosity and bi‐continuous cross‐section structure. As expected, a high rejection (over 97%) towards 500 nm polystyrene microparticles could be achieved along with satisfying water flux of 662 L m−2 h−1 bar−1, which was superior to most current membranes. This work provides not only a new and facile strategy for preparing homoporous membranes employing commercial polymers rather than rarely‐obtained block polymers, but a promising alternative for the efficient separation of aquatic microplastics.

Development of carbon nanotube-metal organic framework (MOF) hybrid antiviral microfiltration membrane

We present the development of novel antiviral membranes by immobilizing metal organic framework (MOF) and carbon nanotubes (CNTs) on polymeric microfiltration membranes. The CNTs and the copper-based MOF (HKUST-1) were tested individually and in a hybrid form (MOF-CNT) against MS2 bacteriophage which was used as a surrogate virus. The membranes were synthesized at three different loading (5, 8 and 12% by weight) on a PVDF filtration membrane. The membranes were characterized using scanning electron microscopy, energy dispersive x-ray spectroscopy, thermogravimetric analysis, water contact angle, gas permeation tests and x-ray diffraction. Amongst the CNT immobilized (CNIM), MOF immobilized (MIM) and MOF-CNT (MCNIM) immobilized membranes, the permeate flux was highest for the CNIM (170% higher than MIM at 5% loading) followed by MCNIM (149% higher than MIM at 5% loading). This was because the small MOF particles blocked the membrane pores. No rejection of bacteriophages was observed with the plain PVDF membrane, but with the immobilization of MOF and CNTs, the antiviral activities increased with nano particles loading. The MCNIM with 12% loading exhibited a 99.6% phage deactivation. Kinetics of phage deactivation was studied for MOF, CNTs and MOF-CNT. The median lethal dose to kill 50% of the virus population (LD50) for MOF-CNT was as much as 70% lower than the CNTs and 30% lower than the pure MOF. Similarly, the time taken to deactivate 80% of the viral population (T80) for MOF-CNT was 50% less than the pure CNTs and 24% less than the pure MOF. Overall, the MOF-CNT immobilized membranes appear to be best option for antiviral activity.

Interfacial Wettability Regulation Enables One-Step Upcycling of the End-of-Life Polymeric Microfiltration Membrane

Polymeric membranes, which are typically synthesized from fossil-based polymers, will reach their end of life (EOL) and then be replaced, due to the inevitable accumulation of membrane fouling even though the periodic cleaning is applied. The conventional disposal methods of the EOL membranes are landfilling and incineration, which will lead to additional carbon emission and fossil resource depletion. Herein, we proposed a surfactant-regulated interfacial polymerization strategy, by adding sodium dodecylbenzene sulfonate (SDBS) in the piperazine (PIP) aqueous solution, for the one-step upcycling of the EOL polymeric microfiltration membrane to obtain a thin-film composite polyamide (PA) nanofiltration (NF) membrane. Revealed by the quartz crystal microbalance with dissipation analysis and molecular dynamics simulation, the presence of SDBS reduced interfacial tension (IFT) and regulated interfacial wettability, thereby facilitating adequate and uniform uptake of PIP monomers. The resulting upcycled NF membrane with 4 critical micelle concentration (CMC) of SDBS addition exhibited a favorable pure water permeance (20.1 ± 0.6 L m–2 h–1 bar–1) and a satisfactory Na2SO4 rejection of 98.6 ± 0.4% owing to the formation of a continuous PA layer with high cross-linking degree (89.3 ± 0.5%). The Na2SO4 permeability of the 4 CMC upcycled NF membrane was more than 1 magnitude lower than that of the upcycled NF membrane without SDBS addition. This study provides a facile, rapid, and cost-effective method for the one-step upcycling of EOL polymeric membranes, which thus improves the sustainability of membrane technology.

Application of a pulsed crossflow to improve chemical cleaning efficiency in hollow fibre membranes following skim milk microfiltration

As the efficient cleaning of membrane systems used for milk protein fractionation remains a challenge, more efficient concepts are required to reduce cleaning times and chemicals consumption. This study examined the so far not commonly applied concept of pulsed flow, characterised by a cyclic transition between high/low flow rates and high/low-pressure phases. To determine its effects on protein fouled polymeric microfiltration membranes, pulsed crossflow conditions were varied in frequency and amplitude during a cleaning step with NaOH as a chemical cleaning agent. The cleaning efficiency was characterised by protein removal and flux recovery. It could be shown that both increasing frequency and flow velocity amplitude can increase protein removal and flux recovery, provided extreme transmembrane pressures are avoided. With pulsed flow, the protein removal could be increased by up to 32% and the flux recovery by 11% compared to a conventionally used steady flow cleaning, thus confirming an increased mechanical cleaning effect when applying pulsed flow. Furthermore, the application of pulsed flow poses a more efficient way to enhance mechanical cleaning power than by increasing the flow velocity under steady flow. Hence, it allows a reduction of energy consumption and thus improves sustainability of the cleaning process. The results indicate a mode of action involving a combination of pulsation induced turbulence and fluctuating relaxation and compaction of the deposit, altogether weakening forces stabilising deposited layer material.

Impact of Ultraviolet Irradiation on the Performance Characteristics of Polymeric Microfiltration Membranes

Impact of Ultraviolet Irradiation on the Performance Characteristics of Polymeric Microfiltration Membranes

Polymeric Microfiltration Membranes Modification by Supercritical Solvent Impregnation-Potential Application in Open Surgical Wound Ventilation.

This study investigated supercritical solvent impregnation of polyamide microfiltration membranes with carvacrol and the potential application of the modified membranes in ventilation of open surgical wounds. The impregnation process was conducted in batch mode at a temperature of 40 °C under pressures of 10, 15, and 20 MPa for contact times from 1 to 6 h. FTIR was applied to confirm the presence of carvacrol on the membrane surface. In the next step, the impact of the modification on the membrane structure was studied using scanning electron and ion beam microscopy and cross-filtration tests. Further, the release of carvacrol in carbon dioxide was determined, and finally, an open thoracic cavity model was applied to evaluate the efficiency of carvacrol-loaded membranes in contamination prevention. Carvacrol loadings of up to 43 wt.% were obtained under the selected operating conditions. The swelling effect was detectable. However, its impact on membrane functionality was minor. An average of 18.3 µg of carvacrol was released from membranes per liter of carbon dioxide for the flow of interest. Membranes with 30–34 wt.% carvacrol were efficient in the open thoracic cavity model applied, reducing the contamination levels by 27% compared to insufflation with standard membranes.

Investigation of arsenic removal from aqueous solution through selective sorption and nanofiber-based filters.

This research paper focuses on removing of arsenic from contaminated water via a nanofibrous polymeric microfiltration membrane, applied in prospective combination with an inorganic sorbent based on iron oxide hydroxide FeO(OH). Nanofibrous materials were prepared by electrospinning from polyurethane selected by an adsorption test. The chemical composition (FTIR), morphology (SEM, porometry) and hydrophilicity (contact angle) of the prepared nanostructured material were characterized. The process of eliminating arsenic from the contaminated water was monitored by atomic absorption spectroscopy (AAS). The adsorption efficiency of the nanofibrous material and the combination with FeO(OH) was determined, the level of arsenic anchorage on the adsorption filter was assessed by a rinsing test and the selectivity of adsorption in arsenic contaminated mineral water was examined. It was confirmed that the hydrophilic aromatic polyurethane of ester type PU918 is capable of capturing arsenic by complexation on nitrogen in its polymer chains. The maximum As removal efficiency was around 62 %. Arsenic was tightly anchored to the polymeric adsorbent. The adsorption process was sufficiently selective. Furthermore, it was found that the addition of even a small amount of FeO(OH) (0.5g) to the nanofiber filter would increase the efficiency of As removal by 30 %. The presented results showed that an adsorption filter based on a polyurethane nanostructured membrane added with an inorganic adsorbent FeO(OH) is a suitable way for the elimination of arsenic from water. However, it is necessary to ensure perfect contact between the surface of the nanostructure and the filtered medium.

Efficiency of removal of whey protein from sweet whey using polymeric microfiltration membranes

Our objective was to measure whey protein removal percentage from separated sweet whey using spiral-wound (SW) polymeric microfiltration (MF) membranes using a 3-stage, 3× process at 50°C and to compare the performance of polymeric membranes with ceramic membranes. Pasteurized, separated Cheddar cheese whey (1,080 kg) was microfiltered using a polymeric 0.3-μm polyvinylidene (PVDF) fluoride SW membrane and a 3×, 3-stage MF process. Cheese making and whey processing were replicated 3 times. There was no detectable level of lactoferrin and no intact α- or β-casein detected in the MF permeate from the 0.3-μm SW PVDF membranes used in this study. We found BSA and IgG in both the retentate and permeate. The β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) partitioned between retentate and permeate, but β-LG passage through the membrane was retarded more than α-LA because the ratio of β-LG to α-LA was higher in the MF retentate than either in the sweet whey feed or the MF permeate. About 69% of the crude protein present in the pasteurized separated sweet whey was removed using a 3×, 3-stage, 0.3-μm SW PVDF MF process at 50°C compared with 0.1-μm ceramic graded permeability MF that removed about 85% of crude protein from sweet whey. The polymeric SW membranes used in this study achieve approximately 20%lower yield of whey protein isolate (WPI) and a 50% higher yield of whey protein phospholipid concentrate (WPPC) under the same MF processing conditions as ceramic MF membranes used in the comparison study. Total gross revenue from the sale of WPI plus WPPC produced with polymeric versus ceramic membranes is influenced by both the absolute market price for each product and the ratio of market price of these 2 products. The combination of the market price of WPPC versus WPI and the influence of difference in yield of WPPC and WPI produced with polymeric versus ceramic membranes yielded a price ratio of WPPC versus WPI of 0.556 as the cross over point that determined which membrane type achieves higher total gross revenue return from production of these 2 products from separated sweet whey. A complete economic engineering study comparison of the WPI and WPPC manufacturing costs for polymeric versus ceramic MF membranes is needed to determine the effect of membrane material selection on long-term processing costs, which will affect net revenue and profit when the same quantity of sweet whey is processed under various market price conditions.

Pairing electrochemical impedance spectroscopy with conducting membranes for the in situ characterization of membrane fouling

Protein fouling within a polymeric microfiltration membrane was characterized in situ and in real time with non-Faradaic electrochemical impedance spectroscopy (EIS). The polymeric membrane was prepared with a conductive gold coating, allowing the membrane surface to serve as a working electrode in a three-electrode EIS system. Utilizing the membrane surface as the working electrode allowed for differentiation between internal and external contributions to fouling. Protein fouling was able to be monitored qualitatively by observing changes in the resulting Bode and Nyquist plots and quantitatively by modeling the electrochemical system with equivalent circuit components comprised of resistive and capacitive elements. To our knowledge, this work represents the first attempt to deploy a conductive polymeric membrane as an active electrode in an EIS setup.

Preparation of electrospun magnetic polyvinyl butyral/Fe2O3 nanofibrous membranes for effective removal of iron ions from groundwater

AbstractRemoving iron ions from groundwater to purify, it is a challenge faced by countries across the globe, which is why developing polymeric microfiltration membranes has garnered much attention. The authors of this study set out to develop nanofibrous membranes by embedding magnetic Fe2O3 nanoparticles (MNPs) into polyvinylbutyral (PVB) nanofibers via the electrospinning process. Investigation was made into the effects of the concentration of the PVB and MNPs on the morphology of the nanofibers, their magnetic properties, and capacity for filtration to remove iron ions. The fabrication and presence of well‐incorporated MNPs in the PVB nanofibers were confirmed by scanning electron microscopy and transmission electron microscopy. Depending on the concentration of the MNPs, the membranes exhibited magnetization to the extent of 45.5 emu g−1; hence, they exceeded the performance of related nanofibrous membranes in the literature. The magnetic membranes possessed significantly higher efficiency for filtration compared to their nonmagnetic analogues, revealing their potential for groundwater treatment applications.

A Study of the Surface Morphology of Microfiltration Membranes of the MFFK and MPS Brands by Atomic-Force- and Scanning-Electron Microscopy

The methods of atomic-force- and scanning-electron microscopy are used to study the surface morphology of polymeric microfiltration membranes. Commercial membranes of the MFFK (on the basis of a hydrophobic fluoroplastic composite membrane, pore size of 0.45 μm) and MPS (polyethersulfone membrane, pore size of 0.45 μm) brands produced by OOO NPP Tekhnofil’tr (Vladimir, Russia) are used as the objects of study. A mature molasses brew produced by OAO Biokhim (Rasskazovo, Tambov Oblast) is used as the technological fluid for the working samples of MFFK and MPS membranes in the microfiltration process. An analysis of the surface morphology of the microfiltration membranes makes it possible to determine the regions of the location of pores, yeast, and polysaccharides, and the interpore connecting regions. By analyzing microscopic images, the flow lines of the solution to be separated are revealed in the profile hollows on the surface of the working microfiltration membranes. The initial MFFK and MPS membranes are found to have slit pores (0.4–0.6 μm in length and width), and the working membranes are contaminated (clogged) by yeast, polysaccharides, and their fragments, which is associated with residual dynamic membrane formation. The surface-roughness parameters of the working MFFK and MPS membranes are shown to be different: the Ra and Rz values differ by factors of 1.69 and 1.87, respectively; and the Rmax values in the case of oblique and frontal sections differ by factors of 1.67 and 1.05, respectively. This is explained by the specific features accompanying the process of the microfiltration separation of solutions containing yeast, polysaccharides, and their fragments (the presence of an adsorption layer on the membrane surface and cracks in the residual layer of the dynamic membrane, i.e., the clogged layer).

Water Purification using Recycled Polymeric Microfiltration Membranes

In our previous work, microfiltration membranes were successfully manufactured by non-solvent induced phase separation (NIPS) method using two concentrations (30 and 35 wt%) of recycled high impact polystyrene (HIPS-R). N, Ndimethyl formamide (DMF) was used as solvent and water as a coagulation bath. These membranes were characterized in terms of chemical composition, surface hydrophilicity, surface crosssection morphology, porosity, and pores size distribution. Accordingly, the membrane's surfaces showed a semihydrophilic behavior with contact angles of 81o and 91o for 30 wt% and 35 wt% membranes respectively. In the current study, The prepared membranes were examined for the removal of Humic acid (HA) and Rhodamine B (RhB) dye in a microfiltration process. Filtration experiment showed that pure water flux of 30 wt% membrane was higher than of 35 wt% membrane, also 30 wt% membrane has a higher humic acid and Dye removal efficiency than of 35 wt% membrane. Thus, the results suggest active membranes could be obtained using recycled high-impact polystyrene. And then, solve the polymer waste accumulation problem in parallel with help in drinking water crisis solution.

Diafiltration affects the gelation properties of concentrated casein micelle suspensions obtained by filtration.

Using membrane filtration it is possible to selectively concentrate proteins and, in the case of microfiltration, concentrate casein micelles. During filtration, water is often added and this practice, called diafiltration, causes further release of permeable components and maintains filtration efficiency. Filtration causes changes in composition of the protein as well as the soluble phase, including soluble calcium, which is a critical factor controlling the gelation properties of the casein micelles in milk. It was hypothesized that concentrates obtained using membrane filtration with or without diafiltration would have different gelation behavior. To test this hypothesis, two concentrates of similar casein micelle volume fraction were prepared, using spiral wound polymeric microfiltration membranes with a 800 kDa molecular weight cutoff, with or without diafiltration. The concentrates showed a gelation behavior comparable to that of skim milk, with a similar gelation time and with a higher firmness, due to the higher number of protein linkages in the network. In contrast, the hydrolysis of κ-casein by chymosin and casein aggregation were inhibited in diafiltered casein micelle suspensions. When the concentrates were recombined with the original skim milk to a final concentration of 5% protein, which re-established a similar soluble phase composition, differences in gelation behavior were no longer observed: both treatments showed similar gelation time and gel firmness. These results confirmed that membrane filtration can result in concentrates with different functionality, and that ionic environmental conditions are critical to the aggregation behavior of casein micelles. This is of particular significance in industrial settings where these fractions are used as a way to standardize proteins in cheese making.

High‐Pressure Jet Cleaning of Polymeric Microfiltration Membranes

AbstractThe cleaning effect of a high‐pressure jet of water on a polymeric microfiltration membrane was investigated at different pressures, durations, and angles. The angle of 70° at a pressure of 130 bar and a cleaning duration of 10 s were found to be promising parameters. Throughput measurements show that this cleaning method can restore about 80 % of the initial throughput of the membrane. Analyses by capillary flow porometer and UV‐vis spectrophotometer imply that an impact on the membrane was detectable after 1800 cleaning cycles at a pressure of 130 bar. Therefore, high‐pressure jet cleaning is a promising method for mechanical cleaning of track‐etched microfiltration membranes.

A comparison of fouling and cleaning properties between ceramic and polymeric micro-filtration membranes for algal rich water

A comparison of fouling and cleaning properties between ceramic and polymeric micro-filtration membranes for algal rich water

Comparative analysis of fouling mechanisms of ceramic and polymeric micro-filtration membrane for algae harvesting

Comparative analysis of fouling mechanisms of ceramic and polymeric micro-filtration membrane for algae harvesting

Assessing internal fouling during microfiltration using optical coherence tomography and evapoporometry

The internal fouling of membranes is typically presumed and inferred, but the direct characterization of representative samples is challenging. This study targeted to assess internal fouling using the Optical Coherence Tomography (OCT) and Evapoporometry (EP) techniques for real-time monitoring during filtration and off-line measurement of the pore size distributions (PSDs) of the fouled membranes, respectively. The results were validated by atomic force microscopy (AFM) measurements and also the three-mechanism fouling model. The foulant used was the well-studied bovine serum albumin (BSA), while the membranes were three commercially available polymeric microfiltration membranes with similar nominal pore sizes and porosities. Although the OCT affirmed the progressive worsening of internal fouling in real-time, the quantitative comparison of the extents of internal fouling among the three membranes was not possible. As for EP, it was able to quantitatively compare the pore size distributions and average pore diameters to ascertain the different extents of internal fouling. The phenomenological model available was effective in quantitatively comparing the extents of pore-constriction among the three membranes, while AFM tied the worst internal fouling to the most attractive BSA-membrane affinity. More in-depth understanding of internal fouling is warranted to not only recommend better membranes but also facilitate the advancement of models.

Sericin‐coated polymeric microfiltration membrane for removal of drug‐based micropollutants

AbstractBACKGROUNDDrug‐based micropollutants present in water sources are proven to be persistent, bioactive and toxic even at low concentration for human consumption. Therefore, the complete removal of the drugs from water is crucial to avoid long‐term medical complications. In the present study, a novel sericin‐coated adsorptive microfiltration (MF) membrane is used for the removal of drug‐based micropollutants.RESULTSThe sericin‐coated membrane was tested for removal of different classes of drugs from water. The membrane completely removed NSAIDs and antibiotics from water at 20 μg L−1 concentration. The adsorption mechanism was profoundly influenced by charge‐based interaction and hydrogen bonding, hence charged anionic drugs were more effectively removed than uncharged drugs. In multidrug mixtures, the removal efficiency was observed in the following sequence; ibuprofen > diclofenac > amoxicillin > ciprofloxacin > estrone > β‐estradiol. Desorption of the drugs from the membrane surface can be effectively controlled by altering the pH of the membrane‐cleaning solution. Presence of other inorganic salts in the aqueous drug solution did not interfere with the removal efficiency of the sericin‐coated membrane. The performance of sericin‐coated membrane was studied using continuous adsorptive membrane filtration approach. The dynamic adsorption behavior of a fixed‐bed membrane column was predicted using Bohart–Adams model. The model can predict the adsorption breakthrough curve with minimum experimental error.CONCLUSIONSThis study reveals the unique application of sericin‐coated MF membrane for effective removal of drug‐based micropollutants from water, and demonstrates its easy regeneration and effectiveness for multiple cycles of filtration. © 2019 Society of Chemical Industry

Substrate-independent polyzwitterionic coating for oil/water separation membranes

A zwitterionic polymer with a sticky catechol chain end was successfully synthesized by ARGET-ATRP (activators regenerated by electron transfer for atom transfer radical polymerization) and used to modify membranes for separation of oil/water mixtures and emulsions. The zwitterionic polymer was found to adhere to various substrates, including stainless steel meshes and polyethersulfone microfiltration membranes, via in-situ formation of polydopamine at the substrate surfaces by copolymerization of the catechol chain ends with a small amount of dopamine monomers added. The polyzwitterion coating was thin and uniform, which endowed the metal mesh and the polymeric microfiltration membrane with superhydrophilicity and underwater superoleophobicity without any marked change in morphology. The coated mesh and membrane, operating in the “water-removing” mode, exhibited very high fluxes and efficiency in separating oil/water mixtures and surfactant-stabilized emulsions, respectively. They also showed excellent anti-fouling ability against oil and protein as well as stability under various harsh environments, making them promising in commercial applications in various fields.

EVOH in situ fibrillation and its effect of strengthening, toughening and hydrophilic modification on PVDF hollow fiber microfiltration membrane via TIPS process

In order to enhance the strength and overcome the poor antifouling capacity of poly(vinylidene fluoride) (PVDF) membrane used in water treatment, herein, poly(ethylene-co-vinyl alcohol) (EVOH) was selected and the PVDF/EVOH blend hollow fiber microfiltration membrane was prepared via the thermally induced phase separation (TIPS) technique. The morphology for the pristine and blend membrane was compared, and the distribution of EVOH on outer surface and within matrix was explored. The fibrous-shaped EVOH enhanced the breaking strength of the membrane markedly (up to 13.63 MPa) due to the in situ fibrillation; especially, when the blend membrane was immersed into water, the internal plasticization of water molecular enhanced the toughness of the membrane and the elongation at break increased up to 86.39% compared with 27.63% for the corresponding dry membrane and 36.62% for the pristine membrane, respectively. The addition of EVOH introduced hydroxyl group into the bulk and thus endowed the membrane with a better hydrophilicity (the contact angle is as low as 43°) and higher pure water flux (up to 449.11 L m−2 h−1) compared with pristine PVDF membrane. Moreover, the blend membrane showed a better rejection of carbonic particle (nearly 100%) and higher flux recovery rate (up to 87.30%). The present investigation offers an effective and simple pattern to regulate microstructure and enhance mechanical strength, flux and hydrophilicity of the polymeric microfiltration membrane via the TIPS process for water treatment.