Ultrafiltration Flux Research Articles

Effect of soluble and insoluble gas bubbling methods on ultrafiltration fouling control

Fouling phenomenon is well known as a main obstacle in membrane separation technology. In this study, the effects of bubbling with various hydrodynamic factors and gas–liquid solubility were evaluated on fouling control and permeation flux in ultrafiltration of skimmed milk solution. Direct gas injection and carbonated feed, as a new bubbling method, were used for bubbling. In the direct gas injection technique, various two-phase flow patterns (slug and bubble), gas flow rates, and bubbling modes (continuous and intermittent) were investigated during a cross-flow ultrafiltration. The results showed that the both of gas bubbling methods improved the permeation flux during 30-min filtration. The permeation flux was enhanced up to 72 and 40% by direct injecting of N2 and CO2, respectively, while it was only enhanced up to 58% with carbonated feed. The evaluation of hydrodynamic resistance of membranes indicated that the gas bubbling by carbonated feed was more effective on the fouling resistance, while the cake resistance was affected by the gas injection during infiltration. In addition, the slug flow pattern was more effective than the bubble flow pattern on decline of membrane fouling. In the slug flow pattern, the permeate flux increased when medium flow rate was applied. Furthermore, ultrafiltration performance was improved using the intermittent gas bubbling mode. This study indicated that slug flow pattern with insoluble gas has a higher performance than the other ones in preventing fouling and flux enhancement during ultrafiltration processing.

CLABSI Reduction using Novel Technology and Nursing Best Practice

Ultrafiltration (UF) is used for the concentration of whey proteins from whey. Membrane fouling during processing results in a decrease in flux, while the predominant molecular fouling reaction and fouling species are still largely unknown. Heat-induced whey protein aggregates are inevitably generated in industrial cheese-making processes, and were found to accelerate membrane fouling during whey concentration. By means of upstream microfiltration prior to UF, these aggregates can be selectively removed. By this means, UF flux could be increased up to twofold for the UF of sweet whey and threefold for acid whey. For filtration of sweet whey, significant calcium retention was observed. Therefore, membrane fouling for both whey types seem follow different molecular mechanisms. Besides the removal of whey protein aggregates, the retention of microorganisms and a log-reduction of up to log 3.5 was achieved by pre-filtration. Shelf-life of whey could be increased to two weeks without pasteurisation.

Removal of mercury (II) from wastewater by polyvinylamine-enhanced ultrafiltration

This study deals with the concentration and removal of mercury (II) from wastewater by polymer-enhanced ultrafiltration (PEUF) using polyvinylamine as the mercury-binding polymer. A mercury removal as high as 99% was obtained, which was otherwise impossible to achieve with conventional ultrafiltration. Over the feed mercury concentration range tested (0–50 ppm), the PVAm dosage used did not affect the mercury rejection considerably, while water flux was reduced significantly at a higher dosage of PVAm. A flux vs pressure relationship typical of ultrafiltration of macromolecular solutes was observed because of the amine polymer used to bind mercury, and the limiting flux appeared to follow the gel layer formation model. The fouled membrane surface was cleaned periodically with dilute hydrochloric acid to recover the membrane permeability. Mercury removal with the PEUF was also tested with a simulated chlor-alkali wastewater that contained mercury and other chemicals (i.e., sodium chloride and sulfate), and the accompanying compounds in the feed solution were shown to influence the performance of PEUF for mercury removal.

Separation of protein mixtures by an integrated electro-ultrafiltration–electrodialysis process

An integrated process for improving selectivity and permeate flux in ultrafiltration based protein fractionation was developed by combining electrodialysis (ED) with electro-ultrafiltration (EUF). The performance of such a process was first investigated using individual proteins (bovine serum albumin and lysozyme) and then with a mixture of the two. The experimental results showed that as with EUF on its own, the build-up of lysozyme concentration polarization near the cation exchange membrane in the permeate compartment significantly affected ion migration and led to change in pH and conductivity of the feed solution during an EUF–ED process with lysozyme, or bovine serum albumin and lysozyme mixture. As compared with EUF, EUF–ED of protein mixture resulted in a 20% increase in permeate flux with the lysozyme transmission remaining the same. The demineralization that occurred during EUF–ED made this process suitable for protein separation from the feed solutions with high conductivity.

Preparation and preliminary dialysis performance research of polyvinylidene fluoride hollow fiber membranes.

In this study, the separation properties of Polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were improved by optimizing membrane morphology and structure. The results showed that the PVDF membrane had better mechanical and separation properties than Fresenius Polysulfone High-Flux (F60S) membrane. The PVDF membrane tensile stress at break, tensile elongation and bursting pressure were 11.3 MPa, 395% and 0.625 MPa, respectively. Ultrafiltration (UF) flux of pure water reached 108.2 L∙h−1∙m−2 and rejection of Albumin from bovine serum was 82.3%. The PVDF dialyzers were prepared by centrifugal casting. The influences of membrane area and simulate fluid flow rate on dialysis performance were investigated. The results showed that the clearance rate of urea and Lysozyme (LZM) were improved with increasing membrane area and fluid flow rate while the rejection of albumin from bovine serum (BSA) had little influence. The high-flux PVDF dialyzer UF coefficient reached 62.6 mL/h/mmHg. The PVDF dialyzer with membrane area 0.69 m2 has the highest clearance rate to LZM and urea. The clearance rate of LZM was 66.8% and urea was 87.7%.

Enhancement of ultrafiltration-performance and improvement of hygienic quality during the production of whey concentrates

Ultrafiltration (UF) is used for the concentration of whey proteins from whey. Membrane fouling during processing results in a decrease in flux, while the predominant molecular fouling reaction and fouling species are still largely unknown. Heat-induced whey protein aggregates are inevitably generated in industrial cheese-making processes, and were found to accelerate membrane fouling during whey concentration. By means of upstream microfiltration prior to UF, these aggregates can be selectively removed. By this means, UF flux could be increased up to twofold for the UF of sweet whey and threefold for acid whey. For filtration of sweet whey, significant calcium retention was observed. Therefore, membrane fouling for both whey types seem follow different molecular mechanisms. Besides the removal of whey protein aggregates, the retention of microorganisms and a log-reduction of up to log 3.5 was achieved by pre-filtration. Shelf-life of whey could be increased to two weeks without pasteurisation.

Performance of integrated membrane filtration and electrodialysis processes for copper recovery from wafer polishing wastewater

This study assesses the efficiency of a combining ultrafiltration (UF) and electrodialysis (ED) processes to treat and reclaim wastewater, a discharge of the copper chemical mechanical planarization (Cu-CMP) process typical among semiconductor manufacturing procedures. The Cu-CMP wastewater generally contains nano-scale slurry particles and metal residues from polishing a wafer. The permeate water turbidity and UF flux for the removal of slurry particles using dilute solutions containing two commercial silica slurries were investigated. For both dilute silica slurries, permeate flux declined markedly as the particle concentration increased (500–2000mg/l). Particle rejection rate exceeded 99.7%, and was independent of particle concentration. The ED process for removal of Cu2+ exceeded 99.3% with applied field strength of 1.5V/cm and reaction time of 3h. The Cu2+ was removed primarily from the solutions through adsorption onto cationic exchange membranes (CEMs) in the ED reactor. The continuous-flow ED study for low Cu2+ concentrations typical of Cu-CMP waste streams also had an excellent removal >98%. Additionally, the Cu2+ adsorbed on the CEMs was effectively recovered by 3% (w/w) HCl extraction but not by a reverse electrical field. Applications of the UF/ED system for treating actual Cu-CMP wastewater demonstrates sequential particle removal by UF and Cu2+ removal by ED, confirming the feasibility of the combined process to reclaim Cu-CMP wastewater. Cost estimate based on the laboratory data also suggests that the integrated process is economically competitive as compared to the convention coagulation process for treating Cu-CMP wastewater.

Factors influencing critical flux of UF membrane in drinking water treatment

Very few fouling or even no fouling would happen when ultrafiltration (UF) was operated below the critical flux. Factors influencing the critical flux of UF for drinking water treatment were systematically investigated in both short-term and long-term tests. Results showed that critical flux could be increased by 5 L/m2 h by continuous aeration with the air flow rate of 10 m3/m2 h, and the same effect could be obtained by intermittent aeration with the air flow rate of 40 m3/m2 h which could not be further improved by increasing air flow rate. Intermittent filtration had no positive effect on improving critical flux, while intermittent filtration combined with aeration could effectively improve critical flux by 5 L/m2 h and reduce fouling a lot in long-term filtration. Critical flux could be increased by 10 L/m2 h when coagulation and sedimentation pretreatment was applied, and could be increased by 15 L/m2 h for combined process of coagulation combined with continuous aeration or coagulation combined with intermittent filtration and intermittent aeration. Coagulation coupled with intermittent filtration and aeration would produce a synergy effect on critical flux improvement. Critical flux determined by flux-step tests could help to instruct the UF operation in application.

Modeling of fouling and foulant attachments on heterogeneous membranes in ultrafiltration of latex solution

The aim of the present study was to obtain the predictive models that would allow for the accurate estimation of the depositional and coagulation attachments, at different operational conditions and using heterogeneous membranes with non-uniform pore size. The fouling attachments predicted by the model can in turn be applied in estimation of the added mass due to fouling and the increase in transmembrane pressure using the developed fouling model applicable in the case of non-uniform pore size membranes. The fouling model and the correlations found in the present study form a comprehensive set of predictive models, generalized for the applications of hydrophilic membranes to a variety of materials with different molecular weight cut off (MWCO) values. The effects of the operating conditions on the fouling attachments, mass of fouling, cake layer, and permeate flux in ultrafiltration of latex solution using heterogeneous membranes was also investigated. Polysulfone flat membrane with MWCO of 60,000 was used under a constant flow rate and cross-flow mode in ultrafiltration of the latex paint solution. Response Surface Methodology (RSM) was implemented in the experimental design. Furthermore, hydrophilic Ultrafilic membranes and hydrophobic Polyvinylidene Difluoride membranes, with a MWCO of 100,000, and hydrophilic cellulose acetate membranes, with a MWCO of 20,000, were used to test the accuracy of the correlations for applications with non-uniform pore size membranes. The model well predicted the deposition attachment of diverse hydrophilic membranes with different MWCO values.

Surface modification of PVDF ultrafiltration membranes by remote argon/methane gas mixture plasma for fouling reduction

Ultrafiltration (UF) is considered as a potential alternative to gravity settling in liquid surfactant membrane process for fast separation of water-in-oil (W/O) emulsions from the external aqueous phase. Flux behavior was studied in this work during batch UF of W/O/W solutions by poly(vinylidene fluoride) (PVDF) membrane with a molecular weight cut-off of 30kDa after the membrane was modified by remote cyclonic atmospheric-pressure plasma with argon gas and methane/argon gas mixture. Physicochemical properties of the membrane surfaces including hydrophilicity, functional group concentrations, and pore size distribution before and after plasma modifications were determined by static contact angle measurements, X-ray photoelectron spectroscopy, and capillary flow porometry, respectively. Higher surface concentrations of oxygen functional groups for plasma-functionalized membranes were observed compared to the unmodified membranes. It was shown that UF flux was significantly enhanced with the plasma-modified membranes under the conditions studied (feed, 5vol% W/O emulsions; stirring, 300rpm; pressure, 35–138kPa). Resistance-in-series analysis of the flux data indicated that the proposed remote plasma treatment, particularly with methane/argon gas mixture, could considerably reduce both resistances due to solute adsorption and cake layer formation on the membrane surface, although the above two resistances always contributed more than 71% of the total filtration resistance.

Effective clarification of pomegranate juice: A comparative study of pretreatment methods and their influence on ultrafiltration flux

The aim of this study was to introduce an effective pre-clarification step in order to improve performance of subsequent ultrafiltration (UF) and to obtain a high quality pomegranate juice (PJ) with improved clarity. The effects of various pre-clarification treatments utilizing gelatin, bentonite and polyvinyl polypyrrolidone (PVPP) on UF performance were evaluated comparatively through analysis of flux behavior and membrane fouling. Quality attributes of the PJs (pH, total acidity, total phenolic content, total monomeric anthocyanins, individual phenolic acids, organic acids, total antioxidant activity and color characteristics) following various pre-clarification treatments were also investigated. On the whole, pre-clarification treatments that included PVPP exhibited a higher overall adsorption capacity, especially of low molecular weight phenolics. The best results with regard to both the fouling behavior of the UF membrane and the juice clarity were achieved by sequential application of PVPP and bentonite. Since lesser amounts of fining agents were used in the pre-clarification treatments, quality attributes of PJ were well preserved comparing conventional clarification applications.

Preparation of Polyvinylidene Fluoride (PVDF) Hollow Fiber Hemodialysis Membranes

In this study, the polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS). The influences of PVDF membrane thickness and polyethylene glycol (PEG) content on membrane morphologies, pore size, mechanical and permeable performance were investigated. It was found that membrane thickness and PEG content affected both the structure and performance of hollow fiber membranes. The tensile strength and rejection of bovine serum albumin (BSA) increased with increasing membrane thickness, while the Ultrafiltration flux (UF) flux of pure water was the opposite. The tensile strength, porosity and rejection of BSA increased with increasing PEG content within a certain range. Compared with commercial F60S membrane, the PVDF hollow fiber membrane showed higher mechanical and permeable performance. It was proven that PVDF material had better hydrophilicity and lower BSA adsorption, which was more suitable for hemodialysis. All the results indicate that PVDF hollow fiber membrane is promising as a hemodialysis membrane.

Dialysis with ultrafiltration through countercurrently parallel-flow membrane modules

The application of ultrafiltration operation to the dialysis in countercurrently parallel-flow rectangular membrane modules was investigated. The assumption of uniform ultrafiltration flux was made for operation with slight concentration polarization and declination of transmembrane pressure. Considerable improvement in mass transfer is achievable if the operation of ultrafiltration is applied, especially for the system with low mass transfer coefficient. The enhancement in separation efficiency is significantly increased with increasing ultrafiltration flux, as well as with increasing the volumetric flow rates. Furthermore, increasing the volumetric flow rate in retentate phase is more beneficial to mass transfer than increasing in dialysate phase.

Study of Membrane Transport for Hemodiafilter and Reverse Osmosis Module

As a typical membrane technology by which the solute substances are separated from a solution, hemodiafilter and reverse osmosis module are studied, in particular regarding the solute transport through the membrane. The solute transport equation, as a key point of this paper, could be derived from the modified Kedem-Katchalsky equation combined with Film theory model. As the next key point for the numerical analysis, the solute transport equation was inserted into the previous module model, and the differential equations composing this module model were converted to the difference equations calculated with a nonlinear secant method. Then the solute concentration profiles of the membrane and the boundary layers in the hemodiafilter and the reverse osmosis module were obtained to visually illustrate in Figures 3 to 6. Finally, it was clear that the occurrence of concentration polarization in the boundary layer is dependent on values of the membrane parameters, including solute permeability (Pm) and reflection coefficient (σ), the ultrafiltration flux (Jv) and the mass transfer coefficient (k).

Analysis of dialysis coupled with ultrafiltration through cocurrently parallel-flow rectangular membrane modules

The mass transfer for the systems of dialysis with ultrafiltration in cocurrently parallel-flow rectangular membrane modules was investigated, based on mass balances with the assumption of uniform ultrafiltration flux. Considerable improvement in separation efficiency is achievable if the effect of ultrafiltration is applied, especially for the system with low mass transfer coefficient. The enhancement in separation efficiency is significantly increased with increasing ultrafiltration flux, as well as with increasing the volumetric flow rates. Furthermore, increasing the volumetric flow rate in retentate phase is more beneficial to mass transfer than increasing in dialysate phase.

Recovery and concentration of phenolic compounds in blood orange juice by membrane operations

Cross-flow ultrafiltration (UF) and osmotic distillation (OD) were implemented on laboratory scale to obtain formulations of interest for food and/or pharmaceutical industry starting from the blood orange juice produced in the Calabria region. The freshly squeezed juice, after a depectinization step, was submitted to an UF process in order to recover natural antioxidants, such as hydroxycinnamic acids, hydroxybenzoic acids, flavanones, flavan-3-ols, and anthocyanins. The UF permeate, with an initial total soluble solids (TSS) content of 10.5°Brix, was concentrated by OD up to a final concentration of 61.4°Brix.The performance of both processes was analyzed in terms of productivity (permeate fluxes in UF and evaporation fluxes in OD) and quality of clarified and concentrated samples through the identification and quantization of phenolic compounds.The UF membrane showed a rejection towards the identified phenolic compounds in the range 0.4–6.9% and a little decrease of the TAA (8.2%) was observed in the UF permeate in comparison with the fresh juice. Phenolic compounds were also well preserved in the retentate of the OD process as demonstrated by the constant value of the ratio between the concentration of phenolic compounds in the OD retentate and the concentration of these compounds in the UF permeate stream (in the range 5.54–6.39).

Effect of annatto addition and bleaching treatments on ultrafiltration flux during production of 80% whey protein concentrate and 80% serum protein concentrate

The goals of this study were to determine if adding annatto color to milk or applying a bleaching process to whey or microfiltration (MF) permeate influenced ultrafiltration (UF) flux, diafiltration (DF) flux, or membrane fouling during production of 80% whey protein concentrate (WPC80) or 80% serum protein concentrate (SPC80). Separated Cheddar cheese whey (18 vats using 900kg of whole milk each) and MF permeate of skim milk (18 processing runs using 800kg of skim milk each) were produced to make WPC80 and SPC80, respectively. The 6 treatments, replicated 3 times each, that constituted the 18 processing runs within either whey or MF permeate UF were as follows: (1) no annatto; (2) no annatto+benzoyl peroxide (BPO); (3) no annatto+hydrogen peroxide (H2O2); (4) annatto; (5) annatto+BPO; and (6) annatto+H2O2. Approximately 700kg of whey or 530kg of MF permeate from each treatment were heated to 50°C and processed in 2 stages (UF and DF) with the UF system in batch recirculation mode using a polyethersulfone spiral-wound UF membrane with a molecular weight cutoff of 10,000Da. Addition of annatto color had no effect on UF or DF flux. The processes of bleaching whey or MF permeate with or without added color improved flux during processing. Bleaching with H2O2 usually produced higher flux than bleaching with BPO. Bleaching with BPO increased WPC80 flux to a greater extent than it did SPC80 flux. Though no differences in mean flux were observed for a common bleaching treatment between the WPC80 and SPC80 production processes during the UF stage, mean flux during WPC80 DF was higher than mean flux during SPC80 DF for each bleaching treatment. Water flux values before and after processing were used to calculate a fouling coefficient that demonstrated differences in fouling which were consistent with flux differences among treatments. In both processes, bleaching with H2O2 led to the largest reduction in fouling. No effect of annatto on fouling was observed. The reasons for flux enhancement associated with bleaching treatments are unclear.

Fouling control and optimization of a drinking water membrane filtration process with real-time model parameter adaptation using fluorescence and permeate flux measurements

The implementation of fouling control strategies is crucial for the effective maintenance and long-term application of ultrafiltration (UF) membranes in drinking water treatment. Membrane cleaning methods such as membrane back-washing protocols are typically employed to remove the build-up of natural water species (foulants) on the surface and/or in the pores of the membranes, which causes membrane fouling, contributes to increased trans-membrane pressure and shortens membrane lifetime. In a previous work by the authors, a fluorescence-based principal component (PC) modelling approach, which was able to forecast membrane fouling behaviour of a bench-scale UF membrane set-up over a future time horizon, was introduced. This approach also proved suitable for estimating the optimum future membrane back-washing times required for controlling fouling and minimizing the energy demand for drinking water production. In this study, the forecasting ability of this model was improved by updating the model parameters with current process measurements. The Extended Kalman filter (EKF) approach was used to achieve this objective. The EKF approach accomplished real-time adaptive estimation of key model parameters based on either real-time UF flux measurements or PC scores related to fluorescence measurements of membrane permeate. The model predictions and the corresponding experimental UF flux data for different membrane fouling situations revealed that on-line permeate flux-based parameter adaptation showed improved model predictions as compared to PC score-based adaptation, especially for longer filtration times. The improvements in the accuracy of the fluorescence-based model forecasts also aided the estimation of optimum back-washing times with better accuracy resulting in considerable energy savings compared to back-washing estimates obtained without real-time parameter adaptation.

Application of Membrane Technology to Slaughterhouse Blood to Produce Edible Powdered Protein Mixture

Animal blood generated from slaughtered animals is often released into the environment resulting in significant pollution and also in the loss of a valuable protein source. This study aimed at developing a procedure that will allow for utilizing animal blood for protein powders production on an industrial scale. To meet this goal, hygienically collected animal blood was first treated with membrane technology: microfiltration (MF) or ultrafiltration (UF). A ceramic MF membrane and a PCI UF membrane were used. Average MF flux was 6.62 kg h-1 m-2 at transmembrane pressure of 2.5 bar. Average UF flux was 3.55 kg h-1 m-2 at transmembrane pressure of 4 bar. MF succeeded in separating the blood plasma proteins (permeate) from the red cell fraction (retentate). UF concentrated both the red cell and blood plasma proteins in a single sample (retentate). The volume ratio of retentate to permeate was 10:14 and 14:10, for the MF and UF, respectively. A membrane cleaning regime was developed. The treated blood fractions were then freeze dried and red and white protein powders were produced successfully. The potential of a SME (small-medium enterprise) to apply this procedure into practice is presented.

Study of permeate flux in micellar-enhanced ultrafiltration on a semi-pilot scale: Simultaneous removal of heavy metals from phosphorous rich real wastewaters

The study reports on the successful application of micellar-enhanced ultrafiltration (MEUF) for the purification of phosphorous rich real wastewaters of a fertilizer company. Flux decline was investigated in a cross-flow, semi-pilot scale equipment using a 10kDa spiral-wound polyethersulfone membrane. Full factorial design complemented to a central composite design was applied to evaluate the effect of factors (cross-flow velocity, transmembrane pressure and feed concentration of SDS) on permeate flux. Transmembrane pressure and cross-flow velocity showed a positive statistically significant effect on the permeate flux. When increasing the cross-flow velocity above 0.24m/s a plateau in permeate flux was observed. A significant interaction effect between the cross-flow velocity and pressure was observed. The effect of the pressure was affected by the level of the cross-flow velocity, and vice versa. The concentration polarisation phenomenon was significant leading to a relative flux of 0.5. However, after 2h of experiments, irreversible fouling was negligible. Concentration of SDS did not have statistically significant effect on the permeate flux but it affected positively the rejections coefficients of cadmium and copper. Rejection coefficient up to 85% and 81% were obtained for cadmium and copper, respectively, whereas phosphorous was not retained by the membrane.