Cross-flow Membrane Filtration Research Articles

Gravity-driven crossflow membrane filtration and mechanical centrifugation yield plasma with equivalent total and COVID-19-specific immunoglobulin content

While the administration of convalescent plasma is a promising therapy for coronavirus disease 2019 (COVID-19), upfront costs and technological barriers of conventional plasmapheresis have limited the collection and processing of COVID-19 convalescent plasma (CCP) in Low- and Middle-Income Countries (LMICs). We previously reported that bedside plasma separation using gravity-driven microfiltration has made CCP therapy accessible as a treatment option in Suriname. However, the question remains whether the gravity-driven microfiltration method yields similar amounts of immunoglobulins as compared to conventional plasmapheresis. Here, we compared the gravity-driven microfiltration method with conventional plasma centrifugation for the total and COVID-19-specific immunoglobulin content of the obtained CCP. Blood donations from 10 donors recovered from PCR-confirmed COVID-19 were processed using both methods. Samples were collected pre- and post-processing for analysis to allow direct comparison of both methods. There were no differences in COVID-19-specific IgG levels between convalescent plasma obtained by microfiltration and centrifugation for 4 of the 5 assays used. Anti-RBD-Omicron IgG levels were slightly higher in the plasma obtained after filtration (median 274, range 69 to 1258) than after centrifugation (median 249, range 67 to 1175), Wilcoxon P = 0.0488. No significant differences were detected between the two methods for levels of total albumin, total cholesterol, total IgA, IgM and IgG levels. These results indicate that gravity-driven microfiltration and conventional centrifugation yield CCP with equivalent amounts of total and COVID-19-specific antibodies. This makes the gravity-driven microfiltration method a viable option for the collection and treatment with CCP in the LMICs setting.

Effect of Flowrate and Pressure on the Crossflow Filtration in Textile Wastewater Treatment by Commercial UF Membrane

Textile industries are one of the greatest wastewater producers as they require a significant amount of water to be used in the dyeing and finishing processes of textile manufacturing. The number of unit operations in the technological process, the product range, the bath ratio, the mass of fiber in relation to the bath volume, and the finishing machine are some variables that will affect water consumption in the textile industry. As a result, generally, a typical textile plant may consume a volume of water between 100,000 and 300,000 m3 annually. As textiles address a substantial portion of human requirements, it is predicted that by 2050, there will be 160 million metric tonnes, three times as much clothing as there is today. Membrane technology in wastewater treatment is a recent interest arising technique and garnering the industrial application’s interest, owing to its ease of setup and low energy requirement. Crossflow membrane filtration is commonly used in the industry, attributed to its tangential flow across the membrane mechanism, leading to low fouling. This study investigated the textile wastewater’s effluents using crossflow ultrafiltration (UF) membrane filtration. The effect of the operating parameter in terms of pressure and flowrate of the crossflow system were performed to evaluate it permeate flux performance. The study’s outcome reveals pressure increases from 2 bar to 4 bar, the water flux enhances dramatically from 156.26 L/m2hr to 591.98 L/m2hr, and the water flux further increases constantly from 4 bar to 10 bar. On the other hand, the flowrate positively affects the permeate flux, where the flux was enhanced from 651.01 L/m2hr to 726.08 L/m2hr when adjusting the flow rate from 2 LPM to 6 LPM. The results from this study suggested that crossflow membrane filtration system could be commercially feasible due to its permeate flux performance.

Comparing operating strategies for unsteady crossflow membrane filtration with pore blocking

Crossflow filtration with pore blocking is an unsteady system affected by operating conditions. We model pore blocking and solve the governing partial differential equations using the method of lines. The loss in permeability is neither spatially nor temporally uniform. Operating at constant flux results in a greater permeate of clean water but at a higher operating cost than operating at constant pressure.

Evolution of particle deposits at communicating membrane pores during crossflow filtration

Understanding the influence of operating conditions on fouling is a great challenge in crossflow membrane filtration since it is determined by a complex interplay between the shear force of the crossflow and the drag toward the membrane arising from the applied trans-membrane pressure. This study uses a coupled CFD-DEM approach to simulate the motion and deposition behavior of monodisperse spherical particles within a membrane-mimicking geometry. Trans-membrane pressure and crossflow velocity are varied to reveal their respective influence on different aspects of fouling at a pore scale. A visual analysis of the simulation results demonstrates distinct behavior regarding the initial deposition of particles and the resulting filter cake morphology, which can be attributed to defined phenomena. Additionally, quantitative data reveals that the dynamic fouling behavior is dominated by the applied crossflow velocity, while the resistance to the removal of particles by crossflow and the level of flux decline is mainly influenced by the trans-membrane pressure. This study links visual pore-scale phenomena to macroscopic filtration quantities, not only underlining the importance of pore-scale investigations but also narrowing the gap between pore-scale events and the filtration process.

Evaluation of spacer-induced hydrodynamic mixing using particle image velocimetry: Impact on membrane distillation performance

Net-type spacers are used to promote hydrodynamic mixing in the feed channel of crossflow membrane filtration. The induced fluid flow mitigates concentration and temperature polarization effects on the membrane surface, leading to the enhancement of heat/mass transfer across the membrane. The objective of this research is to study the effect of spacer geometry on fluid flow and heat/mass transfer in the feed channel. The particle image velocimetry (PIV) technique was used to measure flow velocity in the feed channel with net-type spacers. Flow characteristics at a wide range of Reynolds numbers were described in terms of time-averaged mean velocity and turbulence kinetic energy (TKE). The PIV result revealed distinct profiles of mean velocity and TKE at different channel heights with bi-planar spacers. The spacer with the largest hydrodynamic angle of 120° (Net120) was found to be the most efficient in promoting flow unsteadiness because it led to the largest channel-averaged TKE among the selected spacers. The unsteady flow regime on Net120 was accompanied by the greatest pressure drop over the feed channel. Moreover, the effect of spacer-induced mixing on heat/mass transfer across the membrane was further evaluated via the flux measurement with vacuum membrane distillation experiments. In comparison with other spacers, Net120 resulted in a relatively higher flux because of the improved hydrodynamic mixing. These findings reveal the validity of the experimental approach in identifying the impact of key spacer design parameters on hydrodynamic mixing. Nusselt number was calculated to relate the hydrodynamic flow and thermal flow in the feed channel of membrane distillation, and a modified Nusselt number correlation was proposed to better predict convective heat transfer in the spacer-filled channel in VMD.

Transport of emerging organic ultraviolet (UV) filters in ceramic membranes: Role of polyethylene (PE) microplastics

Microplastics can be considered potential carriers of emerging organic ultraviolet (UV) filters due to their considerable adsorption capacity in wastewater treatment. The adsorption behavior of organic UV filters, which are commonly contained in personal care products to preserve the skin against UV radiation, onto polyethylene (PE) microplastics were systematically studied to investigate their combined effects. Kinetics and isotherm analyses revealed that the adsorption of four organic UV filters onto PE microplastic surfaces followed a multi-rate and a heterogeneous multi-layer pattern. Several factors including salinity, microplastic size, and dosage also influenced the adsorption efficiency due to hydrophobic interactions. A bench-scale cross-flow ceramic membrane filtration experiment was investigated to evaluate the role of PE microplastics on the retention performance of organic UV filters. The retentions for organic UV filters were 34.2%–37.8% in the non-existence of PE microplastics. Conversely, organic UV filter retentions were significantly increased up to 82.2%–97.9% when they were adsorbed onto the PE microplastics, which were almost completely retained by the ceramic membrane. Therefore, organic UV filters can likely migrate and eventually be carried by PE microplastics, thus increasing the retention of both emerging organic UV filters and microplastics prior to discharge from wastewater treatment facilities.

Oil–Water Emulsion Separation and Cleaning Performance Study by Cross-Flow Membrane Filtration

Oil–Water Emulsion Separation and Cleaning Performance Study by Cross-Flow Membrane Filtration

Coupled electrochemical transformation and filtration of water pollutants by cathodic-carbon nanotube membranes

This study aimed at evaluating the concomitant electrochemical reduction and separation of organic and inorganic model contaminants from water. A highly conductive (40,000 S/m) support free carbon nanotube (CNT) membrane was used as a cathode in a three-electrode electrochemical crossflow membrane filtration system. Diatrizoate (DTZ), a recalcitrant iodinated contrast media; resazurin (RZ), a redox indicator; and hexavalent chromium ion (Cr(VI)), a ‘gold’ standard for characterization of reducing systems, were tested as model contaminants. Voltages of −0.6 to −1.0 V were enough to remove between 90% and 95% of the three model contaminants tested. Removal of Cr(VI) proceeded by reduction to Cr(III) followed by adsorption onto the cathode, which could be efficiently regenerated (up to 95%) applying reversal (anodic) potential. Preliminary findings applying AC current (0.6–1.5 V, 10 Hz-1 kHz) suggest that it could be a feasible approach for detoxification with minimization of membrane clogging. Resazurin was immediately transformed into resorufin to near completion which was in turn further reduced to dihydroresorufin. The reductive transformation of DTZ resulted in almost complete deiodination, leading to the accumulation of 3,5-diacetamidobenzoic acid as the main end-product. Although other five secondary transformation products were detected, four of them were fully deiodinated. Concluding, the proposed electrochemical filtration cell equipped with a highly conductive CNT-cathodic membrane can be regarded as a potential technique for water decontamination and effective dehalogenation of organic compounds.

End-users are encouraged to investigate a wide range of filtration options

As the increasing use of crossflow membrane filtration becomes ever more beneficial to manufacturing companies, UK-based Axium Process Ltd is actively encouraging end-users to investigate further the wide range of filtration options available for their applications.

Study of Turbulence Promoters in Prolonging Membrane Life.

Nanofiltration membrane technology is an effective method for secondary treated sewage purification. However, membrane fouling, which is inevitable in the membrane-separation process, can reduce membrane performance and shorten membrane life. Installing a turbulence promoter is a promising means of improving the hydraulic conditions inside the membrane chamber. In this study, the effect of turbulence promoter on prolonging membrane life was studied for the first time. Flat-sheet polyethersulfone nanofiltration membrane was used to filter humic acid solution, used for simulating secondary treated sewage. By comparing photographs and SEM images of the membrane before and after the simulated secondary treated sewage filtration, it was found that humic acid tended to be deposited on the low-velocity region, which was reflected by COMSOL simulation. After incorporating a turbulence promoter, the reduction of the humic acid deposition area and membrane fouling resistance indicated that the turbulence promoter could reduce membrane fouling due to the improved hydraulic conditions. Additionally, the turbulence promoter also increased the flux and reduced the flux decay rate. The turbulence promoter was then place in the crossflow flat-sheet membrane filtration module, and the variation of flux with time was tested in simulated secondary treated sewage with different concentrations. The results showed that the membrane life for the filtration of simulated secondary treated sewage comprising 50, 250, and 500 ppm humic acid increased by 23.1%, 80.4%, and 85.7%, respectively. The results of this article can serve as a reference for the prediction of membrane life and the performance enhancement mechanism of membranes containing a turbulence promoter.

Estimation of energy consumption during cross-flow membrane filtration of oil/water emulsion

s: Pressure driven membrane filtration has been widely adopted for oil and water recovery from oil/water emulsion. The technology offers numerous economic and environmental advantages. However, specific energy consumption remains a critical factor for its economic assessment. The specific energy consumption depends on several factors, among which is the fouling filtration period/time. Therefore, the fouling filtration time indirectly affects the overall economic viability of the system. Herein, the effect of fouling filtration time on the specific energy consumption during cross-flow filtration of 1000 ppm oil/water emulsion was evaluated. During the first 20 min of oil/water emulsion filtration, the energy consumption was found to be 0.0225 KWh/m3. While the filtration was continued to 90 min, the system requires 0.0301 KWh/m3 energy input. The tradeoff between fouling filtration time and energy consumption was found to be just before 30 mins. Suggesting that at 30 mins fouling filtration time, clean water flushing/backwashing would restore significant hydraulic performance and thus, less increase in energy input would be required. At the tradeoff point 0.0254 KWh/m3 energy was required to drive the filtration. This represents up to ∼19 % energy saving compared to the straight nonstop 90 min fouling filtration time. The overall results demonstrated that fouling filtration time affects the overall economics of cross-flow membrane filtration.

On the reversibility of membrane fouling by deposits produced during crossflow ultrafiltration of casein micelle suspensions

The formation of a deposit layer on membrane surfaces is an important problem, particularly in milk filtration. Properties of the deposit and efficiency of deposit removal can be studied using various indirect methods based mainly on average membrane resistance in deposit formation–deposit removal cycles, but their conclusions on deposit reversibility depend on conditions surrounding deposit analysis.Here we present a method for direct characterization of the reversibility of deposit compression via analysis of local solid concentration distribution during deposit formation at constant pressure and cross-flow velocity and deposit removal after pressure relaxation. Two models are proposed for deposit characterization: a model of crossflow filtration with deposit formation to characterize deposit compressibility-permeability from the data on concentration distribution at steady-state of deposit formation, and a model for evaluating deposit swelling kinetics from the data on steady-state compressibility-permeability.The method was applied here for analysis of the deposit formed on the surface of a polymeric ultrafiltration membrane during crossflow filtration of casein micelle suspensions at 25°C. Local solid concentration distribution in the deposit and concentration polarization layer was probed in situ using small-angle X-ray scattering (SAXS). Experiments were performed in a special-purpose SAXS–filtration cell. It was demonstrated that casein micelle deposits obtained at 1.1 bar transmembrane pressure swell after pressure relaxation. However, swelling rate was significantly lower than that obtained by modeling using deposit compressibility–permeability obtained from the analysis of steady-state concentration distribution. We thus find evidence that casein micelle deposits produced during crossflow membrane filtration undergo compression that is partially irreversible.

Removal of reactive black 5 dye by using polyoxometalate-membrane

A POM-membrane was fabricated by immobilizing a keggin type polyoxometalate (POM) H5PV2Mo10O40 onto the surface of microporous flat-sheet polymeric polyvinylidene fluoride (PVFD) membrane using a chemical deposition method. The POM-membrane was characterized by FT-IR, SEM and EDX to confirm existing of the POM onto the membrane surface. The POM-membrane was used to remove an anionic textile dye (Reactive Black 5 named as an RB5) from aqueous phases with a cross-flow membrane filtration and a batch adsorption system. The dye removal efficiency of the POM-membrane using the cross-flow membrane filtration system and the batch adsorption system was about 88% and 98%, respectively. The influence factors such as contact time, adsorbent dosage, pH, and initial dye concentration were investigated to understand the adsorption mechanism of the RB5 dye onto the POM-membrane. To find the best fitting isotherm model, Langmuir, Freundlich, BET and Harkins-Jura isotherm models were used to analyze the experimental data. The isotherm analysis showed that the Langmuir isotherm model was found to the best fit for the adsorption data (R 2=0.9982, qmax=24.87 mg/g). Also, adsorption kinetic models showed the pseudo second order kinetic model was found the best model to fit the experimental data (R2=0.9989, q=8.29 mg/g, C0=15 ppm). Moreover, after four times regeneration with HNO3 acid, the POM-membrane showed high regenerability without losing dye adsorption capacity.

Direct membrane filtration of municipal wastewater: Linking periodical physical cleaning with fouling mechanisms

Direct membrane filtration (DMF) is a promising alternative secondary wastewater treatment process in Iceland, where biological treatment is not effective due to low strength wastewater nature and low temperature. This study aims to investigate membrane fouling mechanisms and mitigation approaches during DMF of municipal wastewater using a crossflow membrane filtration system integrated with an optical coherence tomography (OCT) imaging system. During DMF of wastewater, it was observed that intermediate pore blocking was dominant during the early stage of fouling, followed by cake filtration. Multi-filtration cycles were performed under different conditions, and the results revealed that (1) elevating flushing water temperature from 25 to 50 °C greatly reduced the intermediate pore blocking constant accompanied with a decreased physically-irreversible fouling; (2) increasing both filtration and flushing crossflow velocities did not influence the pore blocking constant, but caused a lower cake filtration constant with reducing both physically-reversible and irreversible fouling; (3) extending filtration-flushing duration interval appeared to slightly lower the pore blocking constant; (4) with extending filtration cycles, a shift of reversible fouling to irreversible fouling was noticed and associated with the compression of the tightly attached cake layer that was not readily removed by periodical flushing. A combination of periodical physical flushing with short term chemical-enhanced cleaning was employed and sustainable long-term operation of DMF was achieved. Furthermore, the foulants autopsy indicated that biofouling combined with organic/inorganic fouling influenced the cake fouling development.

PDMS/ceramic composite membrane synthesis and evaluation of ciprofloxacin removal efficiency

The present study employs an unexplored, one-step route for remediation of ciprofloxacin, an emerging contaminant, using hydrophobically modified ceramic membranes. Hydrophobic interaction between the membrane and the target contaminant, i.e., ciprofloxacin, is the governing factor responsible for its removal. The hydrophilic surface of hollow, single channel, macroporous clay-alumina membranes was made hydrophobic using cross-linked polydimethylsiloxane. The influencing parameters—concentration of polymer, cross-linking agent, catalyst and coating time—were optimized by Taguchi analysis to yield a membrane with enhanced ciprofloxacin rejection and high permeate flux. The synthesized membrane was characterized for its contact angle, clean water permeability, degree of swelling, degree of cross-linking, X-Ray diffraction, atomic fluorescence microscopy, field emission scanning electron microscopy. Effect of various operating parameters—cross flow velocity, transmembrane pressure, filtration time, solution pH—was investigated upon removal of ciprofloxacin in cross flow membrane filtration. Maximum rejection of 99.3% was obtained by the hydrophobic membrane having contact angle of 138.5° for 5 mg/L feed solution. The stability of the membrane was judged in terms of change in ciprofloxacin rejection upon filtration for five consecutive cycles, each cycle being 180 min. The developed PDMS/ceramic composite membranes could have great prospect for long-term application in removal of emerging contaminants from water.

Partially coated TiO2 on Al2O3 membrane for high water flux and photodegradation by novel filtration strategy in photocatalytic membrane reactors

Partially coated TiO2 (pc-TiO2) layer on the porous Al2O3 membrane substrate was developed by using low-cost poly (vinyl chloride) (PVC) to generate interstitial voids to be applied in a photocatalytic membrane reactor for the treatment of organic dye contaminant. The combination of dead-end filtration with cross-flow filtration under intermittent UV irradiation onto a developed composite ceramic membrane was suggested to reduce the membrane fouling effectively. Our study showed that the water flux and anti-fouling properties of the pc-TiO2/Al2O3 composite membrane was much higher than those of uniformly coated TiO2 (uc-TiO2)/Al2O3. Cross-flow membrane filtration provided a much greater synergistic impact on photocatalytic activity for both uc- and pc-TiO2/Al2O3 composite membranes than Al2O3 bare membrane substrate. Less fouling caused by hydrodynamic shear along the membrane surface is thought to be associated with better accessibility of UV irradiation by the reactive surface of the TiO2/Al2O3 composite membrane, promoting the photodegradation of the organic dye contaminant in water filtration.

Acetic acid and methanol recovery from dimethyl terephthalate process wastewater using pressure membrane and membrane distillation processes

In this study, acetic acid and methanol were recovered from dimethyl terephthalate process wastewater using cross flow membrane and membrane distillation processes. Different types of ultrafiltration (UP150 and UP005) and nanofiltration (NF270 and NF90) were tested in cross flow membrane filtration to recover acetic acid from wastewater. NF90 membrane supplied maximum acetic acid rejection efficiency and it increased from 39.6% to 46.9% when applied pressure increased from 10 to 20 bar. The effect of solution pH was also tested and the rejection efficiency of acetic acid increased from 46.9% to 100% when the pH was increased from 2.5 to 7.0. However, methanol rejection efficiency did not affect with pressure and pH change. Methanol rich solution obtained from NF90 membrane permeate was recovered by vacuum membrane distillation. 95 % methanol recovery was obtained by hydrophobic polypropylene (PP) membrane at 250 mL/min flow rates. SEM images and contact angles of clean and used membranes were also provided and the results showed that hydrophilic organic acids deposited on the membrane surface increased the hydrophilicity.

Microbial Fermentation of Industrial Rice-Starch Byproduct as Valuable Source of Peptide Fractions with Health-Related Activity.

The rice-starch processing industry produces large amounts of a protein-rich byproducts during the conversion of broken rice to powder and crystal starch. Given the poor protein solubility, this material is currently discarded or used as animal feed. To fully exploit rice’s nutritional properties and reduce this waste, a biotechnological approach was adopted, inducing fermentation with selected microorganisms capable of converting the substrate into peptide fractions with health-related bioactivity. Lactic acid bacteria were preferred to other microorganisms for their safety, efficient proteolytic system, and adaptability to different environments. Peptide fractions with different molecular weight ranges were recovered from the fermented substrate by means of cross-flow membrane filtration. The fractions displayed in vitro antioxidant, antihypertensive, and anti-tyrosinase activities as well as cell-based anti-inflammatory and anti-aging effects. In the future, the peptide fractions isolated from this rice byproduct could be directly exploited as health-promoting functional foods, dietary supplements, and pharmaceutical preparations. The suggested biotechnological process harnessing microbial bioconversion may represent a potential solution for many different protein-containing substrates currently treated as byproducts (or worse, waste) by the food industry.

Experimental study on filtering papermaking black liquor by dynamic blade crossflow membrane

Abstract The fundamental reason for the environmental pollution caused by the papermaking industry is the inadequate treatment of the black liquor. How to dispose of the lignin macromolecules, which is the main pollutants in the black liquor, is the key to addressing the environmental pollution. At present, cross-flow membrane filtration is one of the effective ways to retain and recycle lignin macromolecules in black liquor. The paper proposes the adoption of a dynamic blade cross-flow membrane filtration equipment provided by German BOKELA company to treat papermaking black liquor. The experiment shows that when the black liquor is treated with dynamic blade rotation cross-flow, the membrane with a molecular weight cut-off of nanofiltration (NP010) delivers the best retaining effect, with 28 % more lignin in black liquor than that in untreated black liquor. Meanwhile, when the blade rotational speed reaches 300 rpm and the transmembrane pressure is 0.5 or 2 bar, the flux of black liquor through nanofiltration NP010 is relatively desirable.

Enlargement of oil droplets by using asymmetric structure of polyvinylidene fluoride membranes

This work demonstrates a study for enlarging the oil droplets by using the asymmetric polyvinylidene fluoride (PVDF) membranes in a cross-flow membrane filtration system. The membranes were fabricated from PVDF/DMA/LiCl: 10/88/2% wt. and coagulated in the ethanol solutions at concentrations of 0, 10, 20, and 30% v/v. The alkaline-surfactant-polymer (ASP) produced water was simulated and tested as the feed solutions. Results indicate that the variation of the ethanol concentrations did not affect the membrane porosity and thickness remarkably while control the membrane surface pore size significantly. The water permeation flux increased with the average membrane surface pore size when increasing the ethanol concentrations in the coagulation baths from 10 to 30% v/v. However, the membrane surface pore sizes have no notable effect on the enlargement of the oil droplets because at least 50% of the membrane pores were larger than the oil droplets in the feed solutions. Coalescence of the oil droplets did occur due to the tortuous pore structures of the asymmetric membranes especially when the filtration process was pressurized. At least 65% of the coalesced oil droplets in permeate having the diameters exceeding 1.0 μm. The resistance to the permeation increased with the transmembrane pressure due to more oil droplets accumulated on the membrane pores.