Cleaning of inorganic membranes after whey and milk ultrafiltration

Cleaning of an inorganic ultrafiltration membrane has been quantified through hydraulic, physicochemical, and spectroscopic (infrared and x-photoelectron spectroscopy) analyses. An efficient cleaning sequence of nitric acid followed by sodium hypochlorite has been proposed for cleaning of defatted whey protein concentrate and milk ultrafiltration membranes. The influence of reversed sequence and time reduction are discussed together with the action of both cleaning chemicals. In spite of residual fouling left after every cleaning sequence studied, hydraulic cleanliness of the membrane was achieved, particularly after the standard procedure.     

Surfactant pretreatment of a polysulfone ultrafilter for reduction of antifoam fouling

Effectiveness of surfactant precoat treatment of the polysulfone ultrafilter was first investigated for reduction of membrane fouling in ultrafiltration of antifoam. Fifteen different surfactants, including alcohols and synthetic nonionic surfactants, were tested. In general, pretreatment with nonionic surfactant gave a larger flux than that with alcohol did. The flux increase by pretreatment with nonionic surfactant depended on a hydrophile lipophile balance (HLB) value and type of hydrophobic tail. The most effective surfactant for reducing antifoam fouling among the 15 surfactants was Brij-58 which has an HLB value of 16 and a straight alkyl hydrophobic chain. The ultrafiltration flux of the membrane treated with Brij-58 was almost three times larger than that of untreated membrane. The precoat treatment with Brij-58 was the most effective for reducing antifoam fouling in terms of rejection properties.Furthermore, flux was also improved by the surfactant pretreatment in ultrafiltration of model process streams, such as fermentation media, broth, and yeast suspension with or without antifoam. The surfactant Brij-58 was found to be more effective for reducing membrane fouling in ultrafiltration of model stream YG compared with ethanol or Brij-35. The mean flux increase by the pretreatment with Brij-58 was about 80% in ultrafiltration of the model stream without antifoam. When antifoam was added to the model stream, flux was almost doubled by the pretreatment with Brij-58. The effectiveness of surfactant precoat treatment for reducing membrane fouling was also confirmed in terms of rejection properties. (c) 1994 John Wiley & Sons, Inc.     

Analysis of protein fouling during ultrafiltration using a two-layer membrane model

Protein fouling can significantly alter both the flux and retention characteristics of ultrafiltration membranes. There has, however, been considerable controversy over the nature of this fouling layer. In this study, hydraulic permeability and dextran sieving data were obtained both before and after albumin adsorption and/or filtration using polyethersulfone ultrafiltration membranes. The dextran molecular weight distributions were analyzed by gel permeation chromatography to evaluate the sieving characteristics over a broad range of solute size. Protein fouling caused a significant reduction in the dextran sieving coefficients, with very different effects seen for the diffusive and convective contributions to dextran transport. The changes in dextran sieving coefficients and diffusive permeabilities were analyzed using a two-layer membrane model in which a distinct protein layer is assumed to form on the upstream surface of the membrane. The data suggest that the protein layer formed during filtration was more tightly packed than that formed by simple static adsorption. Hydrodynamic calculations indicated that the pore size of the protein layer remained relatively constant throughout the adsorption or filtration, but the thickness of this layer increased with increasing exposure time. These results provide important insights into the nature of protein fouling during ultrafiltration and its effects on membrane transport.     

Quantitative analysis of membrane fouling by protein mixtures using MALDI-MS

Binary aqueous solutions of bovine serum albumin (BSA) and beta-lactoglobulin (bLG) were subject to flux-stepping and constant flux ultrafiltration to identify the apparent critical flux and to study the mechanisms and factors affecting fouling when the membrane is permeable to one protein component. Membranes from these filtration experiments were analyzed using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) to locate and quantify levels of fouling below and above the apparent critical flux. Hydrophilic (PLTK) regenerated cellulose and hydrophobic (PBTK) polysulfone asymmetric membranes were used, both of 30 kDa nominal molecular weight cut-off. For the hydrophilic PLTK membrane, protein deposition was shown to depend on electrostatic forces, exhibiting little or no fouling when the proteins had the same charge sign as that of the membrane. This was found to apply for both dilute equal mass-per-unit-volume and equimolar binary mixtures. For the PBTK membrane, hydrophobic protein-membrane attractive forces were sufficiently strong to cause deposition of bLG even in the presence of repulsive electrostatic forces. For the PBTK membrane deposition exceeded monolayer coverage below and above apparent critical flux conditions but for the PLTK membrane this generally occurred when the apparent critical flux was exceeded. MALDI-MS was shown to be a facile direct analytical technique for individually quantifying adsorbed proteins on membrane surfaces at levels as low as 50 fmol/mm(2). The high levels of compound specificity inherent to mass spectrometry make this approach especially suited to the quantification of individual components in mixed deposits. In this study, MALDI-MS was found to be successful in identifying and quantifying the protein species responsible for fouling.     

大豆乳清中蛋白质和异黄酮的超滤分离技术

研究了用超滤技术分离大豆乳清中的蛋白质和异黄酮的工艺条件. 结果表明,大豆乳清在超滤之前要进行预处理以减轻膜污染;通过2因素3水平正交试验,确定了最佳的预处理工艺：按大豆乳清中固形物含量的5%,向其中加入CaCl₂,并在85 ℃下加热15 min,在此条件下,蛋白质的沉淀率为49.8%,异黄酮的保留率为90.4%;通过单因素试验,确定了比较合适的超滤条件：选择切割分子量（MWCO）为10000的聚醚砜膜,超滤压力选择51～68 kPa,超滤温度选择30 ℃～40 ℃.在此条件下,大豆乳清中蛋白质的截留率为83.9%,而异黄酮的截留率为7.6%.     

Membrane separation of protein precipitates: Studies with cross flow in hollow fibers

Hollow fiber ultrafiltration and microfiltration membranes are examined for the processing of isoelectric soya protein precipitate suspensions. A model based on the various resistances to permeate flux is used to describe membrane performance. The main resistance to permeate flux is due to the interaction between the active membrane and the soluble and precipitated protein; that is, as compared with resistances due to the active membrane itself or the membrane support structure, or arising from concentrated soluble or precipitated protein layers over the membrane surface. Soluble protein rejection and precipitate mean particle diameter are correlated with observed values of this main resistance.In contract to the ultrafiltration of soluble proteins, the flux rates observed when processing protein precipitate suspensions under a similar range of operating conditions do not approach a limiting value with increased transmembrane pressure. At high protein concentrations, greater flux rates may be achieved for precipitated as compared with soluble proteins. The use of a microfiltration membrane does not give further improvement in flux rate; this may be attributed to problems of pore fouling with precipitate particles.     

Recovery of protein from poultry processing wastewater using membrane ultrafiltration

The feasibility of using ultrafiltration (UF) to recover protein from poultry processing wastewater (PPW) after primary treatment was investigated. By using polysulfone membrane with 30,000 molecular-weight-cut-off, almost all crude proteins in PPW were retained, subsequently reducing the chemical oxygen demand (COD) in the effluent to less than 200 mg L(-1). Similar to the processing of proteinaceous materials, the average fluxes reached only 100 Lm(-2) h(-1). By identifying the optimal values of key operation parameters, including pH, volumetric flow rate, and transmembrane pressure (6.74, 683 mL min(-1) and 14 psi, respectively) using response surface methodology (RSM), the flux was improved to higher than 200 Lm(-2) h(-1). Although severe membrane fouling was still inevitable after processing, flushing the membrane with a cleaning reagent was found capable of effectively restoring membrane performance.     

Membrane biofouling by chlorine resistant Bacillus spp.: effect of feedwater chlorination on bacteria and membrane biofouling

In this study, bacteria isolated from a lake were characterised for their chlorine resistivity and the effects of chlorination on growth, mortality, protein expression and attachment propensity towards membranes. Biofouling and membrane performance were analysed. All isolated chlorine resistant strains, characterised by 16s rRNA gene sequencing, belonged to the genus Bacillus. Chlorination caused limited effects on bacterial growth and mortality. B. safensis and B. lechinoformis suffered the maximum effects due to chlorination. Live-to-dead ratios immediately after chlorination were above 1.3, with some exceptions. The membrane pure water flux recovery was highly strain dependent. Irreversible membrane fouling was observed with B. aquimaris. Membrane flux decreased substantially during ultrafiltration of water containing chlorine resistant bacteria.     

Rhamnolipid as new bio‐agent for cleaning of ultrafiltration membrane fouled by whey

In this work, rhamnolipid biosurfactant as an eco‐friendly and biodegradable cleaning agent was produced by Pseudomonas aeruginosa bacteria and was used to evaluate the chemical cleaning efficiency of whey fouled ultrafiltration membranes. Thin layer chromatography (TLC) and Fourier transform infrared spectroscopy (FTIR) confirmed the successful synthesis of rhamnolipid. The produced rhamnolipid was compared to chemical cleaners including sodium hydroxide (NaOH), sodium dodecyl sulfate (SDS) and Tween 20. Ultrafiltration membranes used for fouling and cleaning analysis were prepared using phase inversion via immersion precipitation technique. For studying the fouling mechanisms, Hermia's model adapted to cross‐flow was used. From the fouling mechanism experiments, it was found that the complete blocking and cake formation were the dominant fouling mechanisms. The highest values of cleaning efficiency were achieved using rhamnolipid and NaOH as cleaning agents with the flux recovery of 100%, but with considering the low concentration of the rhamnolipid used in the cleaning solution compared to NaOH (0.3 versus 4 g/L for NaOH), its application is preferred.     

Arthrospira platensis harvesting with membranes: fouling phenomenon with limiting and critical flux

The present work deals with the harvesting of Arthrospira platensis (Spirulina) from a diluted culture medium. This cyanobacterium was retained by the European Space Agency as food supply for long term manned spatial missions, and integrated in the MELiSSA project: an artificial microecosystem which supports life in space. Membranes techniques seem to be adapted to efficiency, reliability and safety constraints, even if a well-known limitation is the progressive fouling and permeation flux decrease. Among usual solid/liquid separation processes, Arthrospira harvesting is performed by tangential ultrafiltration (tubular inorganic membrane 50 kD Céram-Inside from Tami, Nyons, France). To ensure a reliable separation step with the best biomass quality, a good comprehension of the ultrafiltration progress and fouling phenomenon is needed, in particular, the link between operating parameters, permeation flux and cleanability. Comparative experiments were made between limiting and critical flux with different suspensions: fresh biomass, stressed biomass and a suspension of Arthrospira platensis enriched with exopolysaccharides.     

Simultaneous separation of acid and basic bioactive peptides by electrodialysis with ultrafiltration membrane

beta-Lactoglobulin (beta-lg), one of the major whey components, can release by enzymatic hydrolysis different bioactive peptidic sequences according to the enzyme used. However, these protein hydrolysates have to be fractionated to obtain peptides in a more purified form. The aim of the present work was to evaluate the feasibility of separating peptides from a beta-lg hydrolysate using an ultrafiltration (UF) membrane stacked in an electrodialysis (ED) cell and to study the effect of pH on the migration of basic/cationic and acid/anionic peptides in the ED configuration. Electrodialysis with ultrafiltration membrane (EDUF) appeared to be a selective method of separation since amongst a total of 40 peptides in the raw hydrolysate, only 13 were recovered in the separated adjacent solutions (KCl 1 and KCl 2). Amongst these 13 migrating peptides, 3 acid/anionic peptides migrated only in one compartment (KCl 1), while 3 basic/cationic peptides migrated only in the second compartment (KCl 2) and that whatever the pH conditions of the hydrolysate solution. Furthermore, the highest migration was obtained for the ACE-inhibitory peptide beta-lg 142-148, with a value of 10.75%. The integrity of the UF membrane was kept and EDUF would minimize the fouling of UF membrane.     

The possibility for improvement of ceramic membrane ultrafiltration of an enzyme solution

Ultrafiltration represents an attractive downstream processing technique for enzymes concentration and their primary purification. However, the process efficiency is often limited by protein fouling and shear-induced enzyme deactivation, resulting in permeate flux decline and loss of enzyme activity. The objective of this work was to investigate the possibility for improvement of ceramic membrane ultrafiltration of endo-pectinase solution. Experimental investigations were performed on a 5 nm ceramic membrane with the Kenics static mixer placed inside the membrane in order to improve the process performance. The use of the static mixer resulted in the flux improvement of about 45% at a volume concentration factor (VCF) of 3 leading to the reduction of operation time of 25% and the energy saving of about 40%. Although the rejection of endo-pectinase was higher than 96%, the extensive loss of the enzyme activity during operation indicated that the modification of the feed solution is essential for improved ultrafiltration performance. Addition of pectin to the original endo-pectinase solution led to a significant reduction of the enzyme deactivation: the enzyme activity yield was 90% at a VCF of 1.6 during operation with the static mixer.     

Performance characteristics of nanoporous carbon membranes for protein ultrafiltration

Nanoporous carbon membranes could be very attractive for applications of ultrafiltration in the biotechnology industry because of their greater mechanical strength and longer membrane life. The objective of this study was to obtain quantitative data on the performance characteristics of nanoporous carbon membranes formed within a stainless steel support that was first modified by deposition of silica particles within the macroporous support. The nanoporous carbon membrane effectively removed small solutes from a protein solution using diafiltration, with performance comparable to that of commercial polymeric membranes. Protein fouling was evident, although the nanoporous carbon membranes were easily regenerated; cleaning with 0.5 N NaOH at 50 degrees C completely restored the water permeability for multiple cycles. The nanoporous carbon membranes were also compatible with steam sterilization. Significant increases in process flux could be obtained using periodic back-pulsing, with no evidence of any structural alterations in the membrane. These results clearly demonstrate the potential benefits and opportunities for using nanoporous carbon membranes for protein ultrafiltration.     

Influence of a swirl motion on the interaction between microalgal cells and environmental medium during ultrafiltration of a culture of Tetraselmis suecica

The role of the environmental medium of a marine microalga culture (Tetraselmis suecica) in membrane fouling phenomenon is quantified for two ultrafiltration units: one generating a classical tangential plane flow and another involving a swirling decaying flow induced by a tangential inlet. Compared to the plane unit, the swirling configuration increases the performances of the ultrafiltration process (augmentation of 20% in terms of limiting flux). Interactions between the culture medium and cells depend on the module design. Furthermore, experiments emphasize the significant role of the particles whatever the module design: more than 70% of the total hydraulic resistance could be due to the microalgal cells, while about 30% of membrane fouling is relevant to soluble materials.     

Mechanism of bovine serum albumin aggregation during ultrafiltration

Protein fouling is a critical problem for ultrafiltration. In this study, we adopted bovine serum albumin (BSA) as a model protein and polysulfone membrane as a typical ultrafiltration membrane. We then investigated the factors of the protein denaturation and aggregation, such as stirring shear stress and intermolecular exchange of disulfide during ultrafiltration, and discussed the BSA fouling mechanism. Fourier transform-infrared analysis revealed that magnetic stirring did not cause any difference in the secondary structural change of BSA gel-like deposits on the ultrafiltration membrane. BSA aggregates were collected from BSA gel-like deposits on the ultrafiltration membrane by centrifugation. Polyacrylamide gel electrophoresis in SDS analysis of BSA aggregates proved that the major binding of the BSA aggregates involved intermolecular disulfhydryl binding and that capping the free thiol group in BSA molecules with cysteine induced a remarkable decrease in the amount of the BSA aggregates during ultrafiltration. We concluded that one of the main factors in the BSA aggregation during ultrafiltration is the intermolecular exchange of disulfide through cysteinyl residue. We also found that the BSA aggregation caused a decrease in alpha-helix from 66% to 50% and an increase in beta-sheet from 20% to 36%, which was presumably because the cysteine residues associated with the intermolecular disulfide bonds had been located in alpha-helices. Copyright John Wiley & Sons, Inc.     

Effects of intermolecular thiol-disulfide interchange reactions on bsa fouling during microfiltration

Several studies have shown that one of the critical factors governing protein fouling of microfiltration membranes is the presence of denaturedand/or aggregated protein in the bulk solutions. Experiments were performed to evaluate the role of intermolecular disulfide interchange reactionson protein aggregation and membrane fouling during stirred cell microfiltration of bovine serum albumin (BSA). The flux decline during BSA filtration was quite dramatic due to the formation of a protein deposit thatfully covered the membrane pores. This flux decline could be completely eliminated by capping the free sulfhydryl group present on the BSA with eithera carboxymethyl or cysteinyl group, demonstrating the critical importance of this free thiol in the intermolecular aggregation reactions and, in turn, protein fouling. BSA aggregation during storage could be reduced by the addition of metal chelators (EDTA and citrate) or dithiothreitol, orby storage at lower pH (7.0) these solutions all had a significantly lower rate of fouling upon subsequent filtration. This behavior is completely consistent with the known chemistry of the thiol-disulfide interchange reaction, demonstrating that an understanding of these intermolecular (aggregation) reactions can provide a rational framework for the analysis and control of protein fouling in these membrane systems. (c) 1994 John Wiley & Sons, Inc.     

A nonchromatographic process for purification of secretory immunoglobulins from caprine whey

Secretory immunoglobulins are an important antibody class being primarily responsible for immunoprotection of mucosal surfaces. A simple, non‐chromatographic purification process for secretory immunoglobulins from caprine whey was developed. In the first process step whey was concentrated 30–40‐fold on a 500 kDa membrane, thereby increasing the purity from 3% to 15%. The second step consisted of a fractionated PEG precipitation, in which high molecular weight impurities were removed first and in the second stage the secretory immunoglobulins were precipitated, leaving a majority of the low molecular weight proteins in solution. The re‐dissolved secretory immunoglobulin fraction had a purity of 43% which could then be increased to 72% by diafiltration at a volume exchange factor of 10. Further increase of purity was only possible at the expense of very high buffer consumption. If diafiltration was performed directly after ultrafiltration, followed by precipitation, the yield was higher but purity was only 54%. Overall, filtration performance was characterized by high concentration polarization, therefore process conditions were set to low trans‐membrane pressure and moderate protein concentration. As such purity and to a lesser extent throughput were the major objectives rather than yield, since whey, as a by‐product of the dairy industry, is a cheap raw material of almost unlimited supply. Ultra‐/diafiltration performance was described well by correlations using dimensionless numbers. Compared with a theoretical model (Graetz/Leveque solution) the flux was slightly overestimated. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:642–653, 2017     

A new integrated membrane filtration and chromatographic device

To improve protein separation, a novel integrated device combining membrane filtration and chromatography has been developed. The device basically consists of a hollow fiber filtration module whose shell side is filled with chromatographic resin beads. However, there is an essentially impermeable coated zone near the hollow fiber module outlet. The integrated device enjoys the advantages of both membrane filtration and chromatography; it also allows one to load the chromatographic media directly from the fermentation broth or lysate and separate the adsorbed proteins through the subsequent elution step in a cyclic process. Interfacial polymerization was carried out to coat the bottom section of the hollow fiber membrane; the rest of the hollow fiber membrane remained unaffected. Myoglobin (Mb) and alpha-lactalbumin (alpha-LA) were primarily used as model proteins in a binary mixture; binary mixtures of Mb and bovine serum albumin (BSA) were also investigated. Separation behaviors of binary protein mixtures were studied in devices having either an ultrafiltration (UF) or a microfiltration (MF) membrane. Experimental results show that the breakthrough time and the protein loading capacities were dramatically improved after introducing the impermeable coating in both UF and MF modules. For a synthetic yeast fermentation broth feed, four loading-washing-elution-reequilibration-based cyclic runs for separation of Mb and alpha-LA were performed in the device using a MF membrane with a coated zone without cleaning in between. The Mb and alpha-LA elution profiles for the four consecutive runs were almost superimposable. Due to lower transmembrane flux in this device plus the periodical washing-elution during the chromatographic separation, fouling was not a problem, unlike in conventional microfiltration.     

Three-Dimensionally Printed Microfluidic Cross-flow System for Ultrafiltration/Nanofiltration Membrane Performance Testing

Minimization and management of membrane fouling is a formidable challenge in diverse industrial processes and other practices that utilize membrane technology. Understanding the fouling process could lead to optimization and higher efficiency of membrane based filtration. Here we show the design and fabrication of an automated three-dimensionally (3-D) printed microfluidic cross-flow filtration system that can test up to 4 membranes in parallel. The microfluidic cells were printed using multi-material photopolymer 3-D printing technology, which used a transparent hard polymer for the microfluidic cell body and incorporated a thin rubber-like polymer layer, which prevents leakages during operation. The performance of ultrafiltration (UF), and nanofiltration (NF) membranes were tested and membrane fouling could be observed with a model foulant bovine serum albumin (BSA). Feed solutions containing BSA showed flux decline of the membrane. This protocol may be extended to measure fouling or biofouling with many other organic, inorganic or microbial containing solutions. The microfluidic design is especially advantageous for testing materials that are costly or only available in small quantities, for example polysaccharides, proteins, or lipids due to the small surface area of the membrane being tested. This modular system may also be easily expanded for high throughput testing of membranes.      

Protein fouling during constant-flux virus filtration: Mechanisms and modeling

As biomanufacturers consider the transition from batch to continuous processing, it will be necessary to re-examine the design and operating conditions for many downstream processes. For example, the integration of virus removal filtration in continuous biomanufacturing will likely require operation at low and constant filtrate flux instead of the high (constant) transmembrane pressures (TMPs) currently employed in traditional batch processing. The objective of this study was to examine the effect of low operating filtrate flux (5–100 L/m²/h) on protein fouling during normal flow filtration of human serum Immunoglobulin G (hIgG) through the Viresolve® Pro membrane, including a direct comparison of the fouling behavior during constant-flux and constant-pressure operation. The filter capacity, defined as the volumetric throughput of hIgG solution at which the TMP increased to 30 psi, showed a distinct minimum at intermediate filtrate flux (around 20–30 L/m²/h). The fouling data were well-described using a previously-developed mechanistic model based on sequential pore blockage and cake filtration, suitably modified for operation at constant flux. Simple analytical expressions for the pressure profiles were developed in the limits of very low and high filtrate flux, enabling rapid estimation of the filter performance and capacity. The model calculations highlight the importance of both the pressure-dependent rate of pore blockage and the compressibility of the protein cake to the fouling behavior. These results provide important insights into the overall impact of constant-flux operation on the protein fouling behavior and filter capacity during virus removal filtration using the Viresolve® Pro membrane.