Microfiltration System Research Articles

Coupling Low-Frequency Ultrasound to a Crossflow Microfiltration Pilot: Effect of Ultrasonic Pulse Application on Sono-Microfiltration of Jackfruit Juice.

To reduce membrane fouling during the processing of highly pulpy fruit juices into clarified beverages, a crossflow Sono-Microfiltration (SMF) system was employed, strategically equipped with an ultrasonic probe for the direct application of low-frequency ultrasound (LFUS) to the juice just before the entrance to the ceramic membrane. Operating conditions were standardized, and the application of LFUS pulses in both corrective and preventive modes was investigated. The effect of SMF on the physicochemical properties and the total soluble phenol (TSP) content of the clarified juice was also evaluated. The distance of ultrasonic energy irradiation guided the selection of the LFUS probe. Amplitude conditions and ultrasonic pulses were more effective in the preventive mode and did not cause membrane damage, reducing the operation time of jackfruit juice by up to 50% and increasing permeability by up to 81%. The SMF did not alter the physicochemical parameters of the clarified juice, and the measured LFUS energy ranges did not affect the TSP concentration during the process. This study is the first to apply LFUS directly to the feed stream in a pilot-scale crossflow microfiltration system to reduce the fouling of ceramic membranes and maintain bioactive compounds in jackfruit juice.

A new anti-biofouling microfiltration: Combining sharkskin-inspired topology with in-situ silver nanoparticles

Recently, significant research has been undertaken to address drinking and wastewater treatment, food and beverage manufacturing, and the pharmaceutical industry in a sustainable and advanced manner. Contemporary microfiltration systems demonstrate notable efficacy in achieving high-precision separation for the products of these processes; however, they are profoundly susceptible to biofouling, which involves the accumulation of proteins and microorganisms, ultimately leading to a deterioration in separation performance. Here, we introduce the fabrication of a multifunctional anti-biofouling microfiltration membrane comprising a high-fidelity sharkskin-inspired pattern, anti-adhesive, and biocidal surface. Additionally, passive (e.g., pattern and negatively charged surface) and active (e.g., Ag nanoparticle) anti-biofouling features are spontaneously introduced through non-solvent induced phase separation and consecutive mild alkali treatment. The resulting membrane demonstrates a 188 % reduction in the accumulation of bovine serum albumin and exhibits a long-lasting biocidal effect without compromising separation performance.

Innovative composite fluidized hydrogel GAC particles for effective membrane fouling mitigation and membrane integrity protection

Membrane filtration is recognized as an environmentally friendly and cost-efficient technology for water treatment, but membrane fouling is still a significant challenge that increases maintenance costs and reduces membrane lifespan. Particle scouring can effectively mitigate fouling with lower energy consumption. This study investigates the use of fluidized granular activated carbon (GAC) particles encapsulated with hydrogel layers to enhance fouling mitigation in microfiltration systems treating surface water. The proposed hydrogel-modified GAC particles aim to balance scouring efficiency with membrane integrity. The results demonstrate that optimizing hydrogel preparation conditions significantly enhanced the mechanical strength and surface hydrophilicity of GAC particles. The incorporation of hydrogel layers notably improved membrane fouling mitigation, reducing transmembrane pressure (TMP) by 19.3 %, 27.1 %, and 34.3 % for layer thicknesses of 0.5 mm, 1.0 mm, and 1.5 mm, respectively. The hydrodynamic behavior of fluidized GAC particles was significantly improved, enhancing the effectiveness of fouling mitigation in water treatment processes. Additionally, the hydrogel layer effectively protected membrane integrity and inhibited carbon release, ensuring minimal damage and stable permeability. This study underscores the pivotal role of hydrogel layers in improving the performance and longevity of membrane filtration systems, when fluidized GAC particles are used for membrane fouling control.

A novel integrated membrane bioreactor-stirred tank bioreactor system for simultaneous biodegradation of bisphenol A contaminated wastewater and biopolyol production: An approach towards circular bioeconomy

The present work examined the biodegradation of bisphenol A (BPA) under batch and continuous modes using hydrocarbonoclastic bacterium, Pseudomonas aeruginosa PR3. The strain showed great biodegradation potential under batch shake flask and stirred tank reactor. Bacterial growth was considerably inhibited at initial BPA concentrations > 50 mg/L. Further, membrane bioreactor (MBR) for BPA biodegradation was also evaluated under different inlet BPA concentration and hydraulic retention time (HRT) and the maximum BPA removal efficiency of 94.4 % was attained with an influent BPA concentration of 25 mg/L at 5 d of HRT. MBR also showed better performance under shock loading conditions. Identification of BPA biodegraded pathways was also performed using liquid chromatography-mass spectrometry, elucidating the different metabolites and end products formed. A subsequent enhancement in BPA removal efficieny was also observed owing to the microfiltration system of MBR that was applied to separate bacterial biomass from effluent. The maximum removal efficiency was further enhanced to 98.5 % under the same operational schedule. As the strain has the ability to produce extracellular diol synthase enzyme which transforms oleic acid into the biopolyol 7,10-dihydroxy-8(E)-octadecenoic acid, the effluent containing the enzymes was supplemented with 1 % (v/v) oleic acid under whole cell and cell-free approaches. Cell-free technique showed an enhanced bioconversion efficiency in comparison to the traditional whole cell approach. Further, the produced biopolyol was characterized using Fourier transform infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and 1H nuclear magnetic resonance analyses and also depicted the antibacterial activity.

Performance assessment and economic aspects for water reclamation from UASB reactor effluent: Influence of coagulant type and membrane pore size

ABSTRACT This paper investigates the influence of coagulant type in coagulation, flocculation and sedimentation processes and membrane pore size on the performance and economic aspects of water reclamation from UASB reactor effluent. The methodology involved laboratory-scale experiments using two different coagulant types (a modified tannin coagulant, TANm, and a polyaluminum chloride, PACl) and membrane filtration tests with microfiltration (MF) and ultrafiltration (UF). Compared to PACl, TANm had a smaller effect on the pH, consumed less alkalinity, and generated less sludge. However, PACl was more efficient in removing turbidity (89–97%), organic matter (70–72%), and phosphorus within the dosage range of 25 to 100 mg.L−1. Both membranes achieved high removal rates for turbidity and organic matter. Despite the higher flux decay, the MF system could have higher operating flux and lower fouling resistance. The operating costs were higher for the C/F systems, which was attributed to the cost of coagulants and sludge disposal. The system with MF membranes had a lower total cost, and the estimated payback period for the investment was between 0.73 to 0.24 years, based on the values charged for reuse water. This information can be used to optimize the design and operation of UASB-based water reclamation systems.

A Universal Piezoelectric Micropump With Capabilities of Self-Cleaning, Stable Filtration and Precise Pumping

The micro liquid supply system based on piezoelectric micropump has been deeply studied. However, it is difficult to realize stable and efficient filtration in quantitative liquid supply due to the blockage of filter membrane. In this work, we propose a self-cleaning filtration and pumping system based on piezoelectric micropump, which can realize stable and long-term directional quantitative filtration and pumping at the same time. The self-cleaning of the filter membrane is realized by using its reflux characteristics and the blockage problem of the current microfiltration system is solved. The key structure size of the system is optimized to realize continuous self-cleaning of filter membrane and high efficiency transportation of micro fluid. The control methods of pumping and filtration performance are proposed. Experiments results shows that the transmembrane pressure tends to be stable after about 4 pulse voltages which proves that the continuous self-cleaning is achieved. The reflux rate can be reduced to 25%, and the minimum pumping volume control accuracy is about 40 nL per cycle. This work can be used as a reference for microanalysis systems that need stable filtration and on-demand liquid supply.

Cross Flow Microfiltration System in Separating Fermented Nixtamal Corn for Preparation of Natural Folic Acid

A purification process of biomass of nixtamal yellow corn fermented by Rhizopus oligosporus strain C1 (FNC-A) and Rhizopus sp (FNC-B) was performed using a microfiltration (MF) membrane with pore size 0.15 µm installed in a crossflow microfiltration (CFMF) system to obtain retentate and permeate fractions as natural folic acid preparations. CFMF process was conducted at room temperature with a pump motor frequency (PMF) of 10 Hz (flow rate of 3.5 L/min) and a transmembrane pressure (TMP) of 4 bar for 0, 15, 30, 45, 60, 75, and 90 minutes. Based on optimum folic acid, the results showed that the best treatments of FNC-B and FNC-B were achieved at 90 min, resulting in a folic acid increase in retentate of FNC-A and FNC- B of 72.61 and 95.26%, reducing sugar of 20.41 and 170.93% (1.7-folds), total sugars of 155.51% (1.55-folds) and 426.76% (4.27-folds), and dissolved protein of 55.33 and 39.20%, and decrease in total solids of 88.91 and 91.64%, respectively, compared to initial biomass of FNC-A and FNC-B. The MFCF system effectively separated folic acid in retentates of FNC-A (33.77%) and FNC-B (95.27%) at the optimal condition. Folic acid monomers predominated the characteristics of FNC-A and FNC-B in optimum conditions with molecular weights of 442.10 and 442.18 Dalton, the average particle size of 38.31 μm and 37.97 μm, and distribution of particles at 10, 50, and 90% from the particle size 10.31, 26.32 and 81.55 μm, and 10.37, 28.04 and 76.09 μm, respectively.

Cross Flow Microfiltration System in Separating Fermented Nixtamal Corn for Preparation of Natural Folic Acid

A purification process of biomass of nixtamal yellow corn fermented by Rhizopus oligosporus strain C1 (FNC-A) and Rhizopus sp (FNC-B) was performed using a microfiltration (MF) membrane with pore size 0.15 µm installed in a crossflow microfiltration (CFMF) system to obtain retentate and permeate fractions as natural folic acid preparations. CFMF process was conducted at room temperature with a pump motor frequency (PMF) of 10 Hz (flow rate of 3.5 L/min) and a transmembrane pressure (TMP) of 4 bar for 0, 15, 30, 45, 60, 75, and 90 minutes. Based on optimum folic acid, the results showed that the best treatments of FNC-B and FNC-B were achieved at 90 min, resulting in a folic acid increase in retentate of FNC-A and FNC- B of 72.61 and 95.26%, reducing sugar of 20.41 and 170.93% (1.7-folds), total sugars of 155.51% (1.55-folds) and 426.76% (4.27-folds), and dissolved protein of 55.33 and 39.20%, and decrease in total solids of 88.91 and 91.64%, respectively, compared to initial biomass of FNC-A and FNC-B. The MFCF system effectively separated folic acid in retentates of FNC-A (33.77%) and FNC-B (95.27%) at the optimal condition. Folic acid monomers predominated the characteristics of FNC-A and FNC-B in optimum conditions with molecular weights of 442.10 and 442.18 Dalton, the average particle size of 38.31 μm and 37.97 μm, and distribution of particles at 10, 50, and 90% from the particle size 10.31, 26.32 and 81.55 μm, and 10.37, 28.04 and 76.09 μm, respectively.

Advancing produced water treatment: Scaling up EC-MF-MDC technology from lab to pilot scale

Membrane distillation integrated with crystallization (MDC) holds promise for sustainable produced water treatment. Addressing challenges like fouling and wetting, common due to high inorganic content and oil-grease presence, requires efficient pretreatment for stable performance. To establish a compact, manageable treatment solution, we examined a pilot-scale integrated electro-coagulation (EC) - microfiltration (MF) system as pretreatment. This step produced 3600 L daily, significantly improving water quality. A remarkable 40% reduction in total organic carbon, 22-fold decrease in total suspended solids, and 600-fold decrease in turbidity underscore its effectiveness. This enhances the suitability for subsequent membrane distillation. In addition, a significant decrease in fouling and scale formation was observed. Long-term batch and continuous MD tests investigated crystallization between MD cycles that prevents significant flux decline. Implementing continuous MDC increased total water recovery six-fold, with stable membrane performance over six cycles, recovering approximately 10% of feed per cycle. These observations highlight the scalable potential of the less-explored integrated treatment (EC-MF-MDC) for effective produced water treatment. This study suggests the viability of the integrated approach for sustainable, larger-scale produced water treatment.

One-step separation of fat globules based on size from bovine milk using a cross-flow microfiltration

Milk microfiltration has gained attention in the dairy industry due to its ability to selectively separate and concentrate bioactive components from milk and its further application in food fortification. One such compound is milk fat globules, a bioactive component with potential health benefits, which undergoes structural and functional damage, membrane phospholipids loss, experience longer processing time, and higher recovery cost due to its current multi-step separation process. We developed a single-step approach based on size for the separation of smaller-size milk fat globules from cow and buffalo milk using a porous polysulfone membrane through a cross-flow microfiltration system. An asymmetric polysulfone membrane with an average pore size of 0.8 ± 0.03 µm was synthesized via phase inversion and subsequently characterized for surface morphology, hydrophilicity, porosity, thermo-mechanical properties, and water contact angle. The membrane demonstrated good performance, with initial milk permeate flux ranging from 296 to 613 L/m2h at different transmembrane pressures (e.g., 0.2, 0.4, 0.6 bar) for both animal groups, with a gradual decline due to concentration polarization, and eventually reaching a steady state. Notably, at lower transmembrane pressure, the membrane exhibited excellent antifouling properties (flux recovery of 81.56–83 %) and reusability over three cycles. Microscopic examination of milk fat globules confirmed the successful size-based separation with intact globule membrane, high phospholipid yield, and mass balance. The results, to the best of our knowledge, demonstrate for the first time an in-depth analysis of membrane fouling and reusability for selective isolation of milk fat globules.

Qualitative analysis and simulations of the biological fouling problem on filtration membranes

The mitigation of fouling formation and development in filtration systems represents the most critical aspect for water treatment, as it naturally affects both the operational costs for management procedures, and the duration of filtration devices. As it constitutes an artificial physical barrier for solid particles retention, membrane systems are perfect environments for the adhesion and development of biological fouling layers, especially in wastewater treatment reactors. Based on recent results, the present work focuses on the qualitative analysis of a mono dimensional continuous model for biofouling dynamics in microfiltration systems. The free boundary problem accounting for the evolution of the biofouling layer during the filtration regimen has been discussed in terms of existence and uniqueness of the solution. The achieved results represent a consistent base for numerical studies related to the correct prediction of transmembrane pressure in membrane systems. Numerical examples related to the heterotrophic–autotrophic interaction occurring in wastewater treatment plants have been presented to highlight the effect of crucial biological aspects, such as extracellular polymeric substances (EPS) accumulation, usually neglected in the classical membrane filtration modeling. The description of biofouling dynamics and membrane performance during the filtration regimen highlight key aspects for microfiltration system management in all industrial applications.

Investigation of factors affecting sodium alginate fouling mechanisms in a microfiltration process under non-constant-flux and non-constant-pressure conditions.

Variations in transmembrane pressure and permeate flux are closely related to membrane fouling. In this study, a laboratory-scale submerged microfiltration system was used to investigate the influence of sodium alginate (SA) concentration and peristaltic pump rotation speed on the fouling under the conditions of (1) the same driving force and non-aerated-PAC, (2) different driving forces and non-aerated-PAC, and (3) different driving forces and aerated-PAC. The results showed that the normalized transmembrane pressure (TMP') increased linearly with decreasing normalized permeate flux (J') during the early microfiltration stage regardless of the operating conditions, indicating that the SA microfiltration process controlled by the peristaltic pump was non-constant-flux and non-constant-pressure. The latter filtration stage was considered constant-pressure filtration when 200-1,200 mg/L of SA was filtrated at the same rotation speed. During filtration of 800 mg/L of SA under the non-aerated-PAC condition, the later filtration stage was considered constant-pressure filtration when the peristaltic pump rotated at slower speeds of 15 and 30 rpm. This approached constant-flux filtration when the peristaltic pump rotated at faster speeds of 60 and 90 rpm, and PAC-aeration scouring was an effective measure for mitigating membrane fouling by SA.

Clarification of red araçá (Psidium cattleianum Sabine) juice by membrane process: Analysis of permeate flux and loss of bioactive compounds

Red araçá (Psidium cattleianum Sabine) juice was processed using porous membranes to obtain a clarified product with a high amount of phenolic compounds prior to its use as a juice or other beverage. The variations in the permeate flux and concentrations of phenolics were determined in a cross-flow system using a polyetherimide microfiltration membrane (0.44 µm) and polyethersulfone ultrafiltration membrane (50 kDa). Both membranes reduced the initial turbidity (445 ± 2) to almost zero, and resulted in a clear and transparent permeate with a yellow colour. The microfiltration membrane showed better performance with the lowest phenolic compound retention (23.6%) and the highest permeate flux (40.6 ± 2 kg/m2h) in batch mode operation. The permeate flux of the microfiltration system showed an initial sharp decrease followed by a gradual decrease, reaching almost 60% lower than the initial permeate flux. The permeate flux resistance was mainly due to the polarised layer (70.2%), and the predominant fouling mechanism was the partial pore blockage, thus indicating that the solids present in the raw juice had size of the same order as the membrane pores.

Contribution of proteins to ceramic membrane fouling at the early stage of membrane filtration

Membrane-based filtration is widely applied for water and wastewater treatment, while membrane fouling caused by contaminants such as proteins is an inevitable problem. Protein-containing mixtures or intact model proteins (e.g., bovine serum albumin, BSA) have been conventionally adopted and recognized as important membrane foulants. However, due to the complex composition of the protein-containing mixture or the inappropriate concentrations of model substances adopted, the real contribution of protein-like fractions toward ceramic membrane fouling remains unknown yet. In this work, the fouling behaviors of BSA and tryptones, representing the intact protein and the mixture of peptides, respectively, in a ceramic membrane microfiltration system were investigated. Both of them exhibited a negligible flux decrease and membrane fouling. For comparison, the fouling behaviors of the environmental protein-like substances (EP) extracted from different sludge sources were also examined. In addition, the experimental and simulation results demonstrate that all the EP samples were easier to aggregate and be adsorbed on the membrane surface than the two model proteins because the environmental protein-like substances had more unsaturated groups. However, those properties were insufficient to cause rapid membrane pore blockage or biocake formation compared with the previous studies. Both the model and actual protein fractions led to light membrane fouling, implying that proteins were not mainly responsible for membrane fouling at the early stage of ceramic membrane microfiltration.

Analysis of wastewater reuse options using a multicriteria decision tool for Phuket, Thailand

The act of balancing between water demand and water supply in Phuket Island is facing challenges, suggesting water reuse options in various activities on the island should be properly promoted considering the potential benefits in a variety of dimensions. This research presented options to reuse effluent water from wastewater treatment plants for Phuket Municipality in 3 main activity groups, namely, domestic reuse, agricultural reuse, and raw water for water treatment plants (WTP). Water demand, additional water treatment trains, and the length of the major water distribution pipeline for each water reuse option were designed, and its cost and expenses were calculated. Multi-criteria decision analysis (MCDA) was used by 1000Minds internet-based software to prioritize the suitability of each water reuse option based on a four-dimensional scorecard, including economic, social, health, and environmental aspects. The decision algorithm for the trade-off scenario based on the government's budget allocation was proposed to obtain weighing without subjective expert opinions. The results revealed that recycling effluent water as raw water for the existing WTP was the first priority, followed by agriculture reuse for planting coconut, Phuket's economic crops, and domestic reuse. There was a significant difference in the total scores of economic and health indicators between the first- and second-priority options because of the difference in the additional treatment system in which the first-priority option applied the microfiltration and reverse osmosis system, which could effectively eliminate viruses and chemical micropollutants. In addition, the first priority option required a much smaller piping system than other water reuse options because it relied on the existing plumbing system of WTP, lowering the investment cost, which was a very important indicator for decision-making.

Permeate microbiome reflects the biofilm microbial community in a gravity-driven woven-fiber microfiltration (WFMF) system for wastewater treatment

The gravity-driven WFMF system reduced microbial concentrations and activity. Its biofilm was more determinant than the influent on the permeate microbiome.

Modulation of gut microbiota and their metabolites by functional mulberry juice non-thermally pasteurized using microfiltration

Background: Mulberry fruit is a source of phenolic compounds and has biological properties. This study aimed to assess the effects of isomaltooligosaccharide (IMO) added to mulberry juice on prebiotic activity and gut fermentation properties.Objectives: The study aimed to produce mulberry juice supplemented with IMO, which might generate short chain fatty acids (SCFA), and to examine the effects of a prebiotic activity after fecal fermentation.Materials and methods: Functional mulberry juices were prepared with three different levels of isomaltooligosaccharide (IMO), namely 0% (MBI0), 2% (MBI2), and 8% (MBI8). The study tested mulberry juices supplemented with IMO, which generated short-chain fatty acids (SCFA), phenolic metabolites, and favored beneficial gut bacteria, and examined the prebiotic activity after fecal fermentation by the colonic microbiota. A crossflow hollow fiber microfiltration system with a 0.22 μm pore size was employed to deliver permeates considered non-thermally pasteurized juices.Results: The results show that short chain fatty acids (SCFA) included large propionic acid and butyric acid concentrations at 48h. The percent of bifidobacteria significantly increased to 5.03% and 17.53% in 24 hours fermentation of MBI2 and MBI8, respectively. After fecal batch culture fermentation, some anthocyanin metabolites such as 3-(2-hydroxyphenyl) propionic acid, 3,4-dihydroxybenzaldehyde, L-phenylalanine, and aminocaproic acid, were detected. Therefore, IMO can serve as a potential prebiotic ingredient added in mulberry juice for promoting the growth of beneficial gut microbiota.Conclusion: The results show that IMO favored beneficial microorganisms in the gut and contributed to biologically active compounds such as metabolites of polyphenols and anthocyanins in the gut.Keywords: Mulberry, isomaltooligosaccharide, prebiotic, gut microbiota, metabolites

Comparison of Artificial Intelligence Control Strategies for a Peristaltically Pumped Low-Pressure Driven Membrane Process.

Peristaltic pumping is used in membrane applications where high and sterile sealing is required. However, control is difficult due to the pulsating pump characteristics and the time-varying properties of the system. In this work, three artificial intelligence control strategies (artificial neural networks (ANN), fuzzy logic expert systems, and fuzzy-integrated local models) were used to regulate transmembrane pressure and crossflow velocity in a microfiltration system under high fouling conditions. A pilot plant was used to obtain the necessary data to identify the AI models and to test the controllers. Humic acid was employed as a foulant, and cleaning-in-place with NaOH was used to restore the membrane state. Several starting operating points were studied and setpoint changes were performed to study the plant dynamics under different control strategies. The results showed that the control approaches were able to control the membrane system, but significant differences in the dynamics were observed. The ANN control was able to achieve the specifications but showed poor dynamics. Expert control was fast but showed problems in different working areas. Local models required less data than ANN, achieving high accuracy and robustness. Therefore, the technique to be used will depend on the available information and the application dynamics requirements.

Potential Use of Cross-flow Microfiltration System in Separation of Functional Compound from Fermented Beetroot (Beta vulgaris L.) as Natural Oxidation Prevention

This study was conducted to determine the potential utilization of microfiltration (MF) membrane in separating functional compounds from beetroot (Beta vulgaris L.) biomass as a functional drink for natural oxidation prevention. Separation was performed through MF membrane (pore size of 0.15 µm) at room temperature, flow rate ~7.5 L/min, and TMP 2 and 6 bar for 0, 5, 15, 25, and 35 minutes. The results showed that process optimization based on gallic acid as total polyphenols and acetic acid were achieved at TMP 2 and 6 bar for 35 minutes, respectively. At TMP 2 and 6 bar produced retentate with acetic acids 1.24 and 0.95%, gallic acid 0.42 and 0.41%, total solids 3.49 and 3.47%, total sugars 36.64 and 44.66 mg/mL, pH 3.11 and 3.10, and inhibiting ability of 62.45 and 58.48%, respectively, meanwhile permeate had acetic acid 0.73 and 0.82%, gallic acid 0.31 and 0.33%, total solids 3.39 and 3.38%, total sugars 40.95 and 61.56 mg/mL, pH 3.12 and 3.13, inhibiting ability of 47.62 and 52.43%, respectively. In these conditions, CF-MF is technically able to retain acetic acid (2.63-folds) and gallic acid (1.21-folds) in the retentate and increase inhibition by 25.12 and 11.25% in comparison with the initial process (0 minutes). The LC-MS analysis of permeate at TMP 2 and 6 bar for 35 minutes were predominated by monomers of acetic acid and gallic acid with MW 61.2450 Da. (M+) and 193.0327 Da. (M+Na+) and relative intensities 100 %.

Ceramic membrane filtration of skim milk for the production of a casein-enriched permeate

The protein composition of skim milk was adjusted using a pilot-scale membrane microfiltration system to produce a casein-enriched permeate with a ratio of casein to serum protein close to 1:1. Microfiltration was performed at 50 °C to a volume concentration factor of 3 followed by 2 diafiltration steps. Three different membrane pore sizes (0.10, 0.14 and 0.20 μm) were used to compare the separation effect, then the effect of three different transmembrane pressures (100, 120 and 150 kPa) on protein composition in the permeate was studied. Membranes of 0.10 and 0.14 μm retained most of the casein. The 0.20 μm membrane allowed casein to pass through and made the ratio of casein to serum protein in the permeate close to 50:50 with a mean flux of 128.3 kg m−2 h−1 at 120 kPa, demonstrating the potential application of a 0.20 μm membrane to produce a new dairy ingredient.