Protein Fouling of Track-Etched Polycarbonate Microfiltration Membranes

doi:10.1006/jcis.1994.1338

Journal of Colloid and Interface Science

Volume 167, Issue 1, 1 October 1994, Pages 104-116

https://doi.org/10.1006/jcis.1994.1338 Get rights and content

Abstract

Bovine serum albumin (BSA) solutions of 0.1 g/liter and 1.0 g/liter were filtered through 0.05 μm and 0.2 μm polycarbonate microfiltration membranes using a stir cell. Total resistance versus time and permeate concentration versus time curves and scanning electron micrographs were generated. From these, together with comparing the results to internal and external fouling models, several different founding mechanisms are hypothesized. For 0.1 g/liter concentration and 0.2 μm pore diameter, the fouling occurs at the mouths of the pores, slowly closing off pore entrance areas while allowing complete transmission of the protein for a period of time. Eventually, the pores become so constricted that protein transmission decreases and a layer of rejected protein forms on the external membrane surface. For 0.1 g/liter concentration and 0.05 μm pore diameter, fouling immediately closes off pores, and permeate concentration decreases quickly. For 1.0 g/liter concentration and 0.2 pm pore diameter, the fouling allows for nearly complete transmission of proteins for the entire length of the experiment, unlike the more dilute case of 0.1 g/liter. Since the diameters of BSA molecules are more than an order of magnitude smaller than the pore radii, it is believed that the proteins form aggregates which accumulate on or just below the top surface of the membrane, depending on their size relative to the pore openings.

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Cited by (231)

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Membrane processing is a subject of growing scientific and industrial interest as a valuable technology to replace conventional energy-intensive operations, but is hindered by the progressive decrease of permeate flux caused by membrane fouling. Although physico-chemical factors affecting membrane fouling have been widely investigated, less is known concerning the effects of processing conditions. Here, we focus on microfiltration of aqueous bovine serum albumin (BSA) solutions by using a novel miniaturized modular unit allowing to study both dead-end (DE) and crossflow (CF) filtration. Pure water flux measurements and Computational Fluid Dynamics (CFD) simulations were firstly performed to characterize the flow field inside the module. In presence of BSA, at the same transmembrane pressure (TMP) of 20 mbar and average pore size of 0.45 μm, a remarkable decrease in the fouling progression with time was found for CF with a peristaltic pump as compared to pressure-driven DE filtration. Furthermore, BSA concentration in the permeate was the same as in the feed for peristaltic CF, while negligible for DE. By either increasing transmembrane pressure or lowering membrane pore size, a stronger decay of permeate flux with time was observed. Scanning electron microscopy images of the membrane showed the presence of a thick surface cake layer under peristaltic CF, which became thinner by increasing TMP or reducing membrane pore size. Overall, the better performance of peristaltic CF can be interpreted in terms of reduced BSA residence time in the membrane, membrane deformability and formation of a permeable cake layer at lower TMP and larger membrane pore size. The innovative design of our filtration module and the combination of permeate flux and concentration measurements with CFD results and microscopy observations constitute the most significant aspects of this research work, which provides a multiscale picture of membrane fouling. The insight emerging from results aims to provide qualitative guidelines towards an optimal setting of processing conditions in membrane operations, which is highly needed to improve the membrane innovation pipeline.
Rejection and fouling of track-etched microfiltration membranes by Acholeplasma laidlawii: Clues to mycoplasma behavior during “sterile” dead-end filtration
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Mycoplasma contamination is commonplace during processing of biopharmaceuticals necessitating its sterile filtration. Consequently, we measured the passage of Acholeplasma laidlawii (a small bacterium lacking cell wall like mycoplasma) across track-etched membranes rated at 100 nm and 220 nm that are designated as “sterile filters” and analyzed the entire progression of fouling beginning with pore occlusion before transitioning to a cake. Initial biofouling was quantified to be intermediate blocking before bacteria formed highly compressible cakes. Under identical experimental conditions, phase inversion membranes of the same nominal pore rating rejected A. laidlawii to a significantly greater extent suggesting depth filtration and capture within the polymer matrix in contrast to surface capture by their track-etched counterparts. A facile fluorescence microscopy method to rapidly detect slow-growing A. laidlawii cells was demonstrated under conditions of low retention. Evidence of cake relaxation by depressurizing the filter and subsequent mobilization of individual cells upon re-pressurization is given. Multiple lines of evidence demonstrated the pressure-induced deformation of individual cells resulting in their incomplete rejection by membranes with pore ratings smaller than the bacterium's unstressed diameter: (i) complete retention of rigid silica colloids of similar size, shape, and zeta potential regardless of pressure in contrast to incomplete A. laidlawii removals, (ii) reduced bacterial removal by both membranes with increasing filtration pressure, (iii) 150–600 fold less permeable bacterial cakes at any given pressure compared with silica cakes, and (iv) presence of flattened and irregularly shaped A. laidlawii cells in electron micrographs whereas they were near perfect cocci at atmospheric pressure.
Genomic DNA causes membrane fouling during sterile filtration of cell lysates
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During biopharmaceutical production, efficient removal of impurities via filtration is essential. It is desirable to achieve high filter capacities along with a high degree of clearance. However, the complexity of bacterial cell lysates makes it difficult to properly estimate the filtration behavior. Here we investigated how host cell-derived impurities impacted the performance of commercially available sterile filters, with a focus on characterizing the dsDNA-induced decrease of filter capacity. Pressure flow curves at a constant flow, combined with particle analytics (e.g., nanoparticle-tracking analysis), indirectly revealed that dsDNA had a major influence on rapid membrane fouling. The observed phenomenon was more pronounced when using filters with small pore sizes (<0.2 µm). Filter capacity could be substantially increased by reducing the size of the present dsDNA fragments, or by decreasing the potential for dsDNA-driven electrostatic interactions with positively charged molecules. In general, our present findings highlight the importance of monitoring dsDNA even during the primary recovery of proteins in cell lysates.
A review of membrane fouling by proteins in ultrafiltration and microfiltration
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Citation Excerpt :
It has been reported that cake filtration is the dominant method of fouling irrespective of the membrane pore size for a concentrated BSA solution, indicating that BSA aggregates were responsible for resistance build-up [81]. However, protein rejection was almost 100 % for a smaller pore size (0.05 μm), while transmission was almost 100 % for a larger pore size (2 μm), indicating that BSA monomers that pass through the aggregate filter cake expectedly clog up the smaller-pore membrane faster than the larger-pore one [81]. Huisman et al. reported that protein-membrane interactions during initial filtration and protein-protein interactions in the later stages of filtration dictated membrane resistance for membranes with smaller pores (~5 nm), while these interactions had little effect on the fouling behavior for membranes with larger pores (~30 nm) and pH, instead, played a more dominant role, as shown in Fig. 18 [43].
Fouling of ultrafiltration (UF) and microfiltration (MF) membranes by proteins is a major challenge in the bioprocessing and dairy industries, as well as in surface and wastewater treatment applications. This review attempts at presenting a comprehensive state-of-the-art understanding on protein fouling of membranes. Effects of operating conditions, along with properties of proteins and membranes, are discussed. Various tools and techniques used to characterize and monitor fouling are described. Different mitigation techniques and cleaning methods used are also presented. Two main factors have been identified as playing important roles in governing protein fouling, namely, ratio of protein size to membrane pore size and interfacial interactions (i.e., protein-protein and protein-membrane). Some directions for future research are suggested: (1) explore a wider range of proteins and their mixtures with respect to their fouling tendencies; and (2) create a comprehensive dataset that can be used to develop machine-learning models to enhance both predictive capabilities and mechanistic understanding.
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Hollow fiber microfiltration (MF) and ultrafiltration (UF) membrane processes have been extensively used in water purification and biotechnology. However, complicated filtration hydrodynamics wield a negative influence on fouling mitigation and stability of hollow fiber MF/UF membrane processes. Thus, establishing a mathematical model to understand the membrane processes is essential to guide the optimization of module configurations and to alleviate membrane fouling. Here, we present a comprehensive overview of the hollow fiber MF/UF membrane filtration models developed from different theories. The existing models primarily focus on membrane fouling but rarely on the interactions between the membrane fouling and local filtration hydrodynamics. Therefore, more simplified conceptual models and integrated reduced models need to be built to represent the real filtration behaviors of hollow fiber membranes. Future analyses considering practical requirements including complicated local hydrodynamics and nonuniform membrane properties are suggested to meet the accurate prediction of membrane filtration performance in practical application. This review will inspire the development of high-efficiency hollow fiber membrane modules.
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Fouling of filtration membranes is a key process that degrades performance and reduces membrane lifetime. Nevertheless, obtaining direct information about fouling mechanisms is still a significant challenge, especially fouling that occurs within the internal pore spaces. Here, we combined highly multiplexed single-particle tracking methods with alternating laser excitation, which allowed the direct visualization of the transport of nanoparticles within microfiltration membranes, where the advective motion and retention of 200 nm and 40 nm diameter particles was simultaneously imaged within filtration membranes with 650 nm nominal pore size, as membranes became increasingly fouled as a function of total particle throughput. We found that internal membrane fouling consisted of three stages, fouling site formation, fouling site growth, and fouling site coalescence. Larger particles had a greater chance to be retained initially, nucleating the fouling sites. These sites tended to capture other particles passing through the membrane, causing the fouling sites to grow in size. Eventually, isolated fouling sites grew large enough to coalescence with neighboring sites, blocking a large region of membrane pores, leading to significant fouling. Importantly, the presence of small numbers of large particles significantly increased the retention of small particles and also accelerated the rate of particle retention. This mechanistic information about internal membrane fouling will assist in the design and optimization of filtration processes to reduce membrane fouling and expand the fundamental understanding of complex mass transport of polydisperse particle distributions.

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Regular ArticleProtein Fouling of Track-Etched Polycarbonate Microfiltration Membranes

Abstract

Regular Article
Protein Fouling of Track-Etched Polycarbonate Microfiltration Membranes