Modeling flux in tangential flow filtration using a reverse asymmetric membrane for Chinese hamster ovary cell clarification

Tangential flow filtration is advantageous for bioreactor clarification as the permeate stream could be introduced directly to the subsequent product capture step. However, membrane fouling coupled with high product rejection has limited its use. Here, the performance of a reverse asymmetric hollow fiber membrane where the more open pore structure faces the feed stream and the barrier layer faces the permeate stream has been investigated. The open surface contains pores up to 40 μm in diameter while the tighter barrier layer has an average pore size of 0.4 μm. Filtration of Chinese hamster ovary cell feed streams has been investigated under conditions that could be expected in fed batch operations. The performance of the reverse asymmetric membrane is compared to that of symmetric hollow fiber membranes with nominal pore sizes of 0.2 and 0.65 μm. Laser scanning confocal microscopy was used to observe the locations of particle entrapment. The throughput of the reverse asymmetric membrane is significantly greater than the symmetric membranes. The membrane stabilizes an internal high permeability cake that acts like a depth filter. This stabilized cake can remove particulate matter that would foul the barrier layer if it faced the feed stream. An empirical model has been developed to describe the variation of flux and transmembrane pressure drop during filtration using reverse asymmetric membranes. Our results suggest that using a reverse asymmetric membrane could avoid severe flux decline associated with fouling of the barrier layer during bioreactor clarification.     

Biofouling development and rejection enhancement in long SRT MF membrane bioreactor

This study was conducted to investigate the development and extracellular polymeric substances (EPS) distribution in biofouling layer and biofouling effect on permeate quality. The experimental results suggested that formation of biofouling layer was started by the attachment of polysaccharides and formed a biogel like layer on top of membrane surface (adhesive attachment). It further induced the attachment of protein, polysaccharides and bioparticles, and formed cake layer (cohesive attachment). As evidenced in SEM photos and permeates quality, the formed biofouling layer had changed the properties of membrane surface such as the pore and porosity, and hence produce the better permeates quality. A great enhancement of rejection performance occurred at the early filtration period, and followed by a slight enhancement in rejection throughout the entire filtration. This enhancement of rejection performance by biofouling layer can be mathematically expressed by the logarithm function with the degree of membrane fouling.     

Separation of proteases from yellowfin tuna spleen by ultrafiltration

Separation of protease, trypsin and chymotrypsin from yellowfin tuna spleen extract by ultrafiltration (UF) using regenerated cellulose membranes with molecular weight cut off (MWCO) 30 and 100 kDa was studied. The 100 kDa membrane had a higher transmission of enzymes than that of the 30 kDa membrane. The enzyme transmission varied from 0.01 to 0.18 and from 0.6 to 0.8 for the 30 kDa membrane and 100 kDa membrane, respectively. The protein transmission was about 0.8 for both membranes. Increasing cross-flow rate and transmembrane pressure (TMP) increased permeate flux. The limiting fluxes at cross-flow rate 120, 240 and 360 L/h for the 30 kDa membrane were 17.3, 43.9 and 54.7 L/m2h, respectively and the limiting fluxes at the same flow rate for 100 kDa membrane were 34.1, 51.1 and 68.4 L/m2h, respectively. The separation of these proteases was achieved using the 30 kDa membrane. The purities of proteases were increased more than ten times at TMP 1.5 bar and cross-flow rate 360 L/h by diafiltration using 30 kDa membrane.     

Influence of fermentation conditions and microfiltration processes on membrane fouling during recovery of glucuronane polysaccharides from fermentation broths.

We have investigated the recovery of exopolysaccharides produced by Sinorhizobium meliloti M5N1 CS bacteria from fermentation broths using different membrane filtration processes: cross-flow filtration with a 7 mm i.d. tubular ceramic membrane of 0.5-microm pores under fixed transmembrane pressure or fixed permeate flux and dynamic filtration with a 0.2 microm nylon membrane using a 16-cm rotating disc filter. With the tubular membrane, the polysaccharide mass flux was mainly limited by polymer transmission that decayed to 10% after 90 min. The mass flux of polymer produced under standard fermentation conditions (70 h at 30 degrees C) stabilized after 70 min to 15 g/h/m(2). This mass flux rises to 36 g/h/m(2) when the mean stirring speed during fermentation is increased and to 123 g/h/m(2) when fermentation is extended to 120 h. In both cases, the mean molecular weight of polysaccharides drops from 4.0 10(5) g/mol under standard conditions to 2.7 10(5) g/mol. A similar reduction in molecular weight was observed when the fermentation temperature was raised to 36 degrees C without benefit to the mass flux. These changes in fermentation conditions have little effect on stabilized permeate flux, but raise significantly the sieving coefficient, due probably to molecular weight reduction and the filamentous aspect of the polymer as observed from SEM photographs. The polymer-mass flux was also increased by reducing transmembrane pressure (TMP) and raising the shear rate by inserting a rod in the membrane lumen. Operation under fixed permeate flux instead of constant TMP inhibited fouling during the first 4 h, resulting in higher sieving coefficients and polymer mass fluxes. The most interesting results were obtained with dynamic filtration because it allows operation at high-shear rates and low TMP. Sieving coefficients remained between 90 and 100%. With a smooth disc, the polysaccharide mass flux remained close to 180 g/h/m(2) at 1500 rpm and cell concentrations from 1 to 3 g/L. When radial rods were glued to the disc to increase wall shear stress and turbulence, the mass flux rose to 275 g/h/m(2) at the same speed and cell concentration.     

Non-destructive approaches for assessing biofouling of household reverse osmosis membranes

Abstract

This study determined economic non-destructive methods to assess biofouling in point of use reverse osmosis (RO) membrane treatment systems. Three parallel household RO membrane units were operated under controlled feed water conditions to promote biofouling, inorganic fouling and a combination of both. Operational and biological parameters were monitored throughout the systems’ lifespan. Membrane autopsies assessed the degree and type of fouling. Statistical models determined statistically relevant parameters for fouling types that were validated with membrane autopsies. Permeate flow rates decreased differently with biofouling vs inorganic fouling. Large increases in permeate conductivity were noted in membranes suffering from biofouling and not in inorganically fouled membranes. The concentration of cell clumps from detached biofilm in the retentate increased in membranes experiencing biofouling and no increase was seen for inorganically fouled membranes. A combination of these methods could be used to conveniently assess the types of fouling experienced by RO systems.     

Cross-flow membrane microfiltration of a bacteriol fermentation broth

Although cross-flow membrane filtration is a very attractive option for harvesting cells and recovering enzymes from cell homogenates, the process is not without its problems. Foremost of these is the deposit of dissolved and suspended solutes onto the membrane surface during operation. The formation of these dense and sometimes compressive sublayers (often called cakes) offers additional resistance to axial and permeate flows and often affects the retention characteristics of the process. In view of the complex nature of the sublayer formation process and its sensitivity to cross-flow velocity, this investigation was undertaken to determine the main factors responsible for the decline in performance during the harvesting of B. polymyxa broth by membrane microfiltration. System parameters varied include axial flow rate, concentration of cells, proteins and other components in the feed, membrane materials (ceramic, polypropylene, and stainless steel), and cleaning methods. To help explain the observed results, a new mass transport model-the solids flux model-based on the assumptions that back migration of particles from the sublayer or membrane surface is negligible and that particles that reach the solid-solution interface attach (stick) completely, is tested. Using a variety of diagnostic methods, magnesium ammonium phosphate precipitate is formed during steam sterilization of the medium and is implicated as the major foulant in this study.     

Comparing membrane and spacer biofouling by Gram-negative Pseudomonas aeruginosa and Gram-positive Anoxybacillus sp. in forward osmosis

Bacteria of different Gram-types have inherently different outer cell structures, influencing cell surface properties and bacterial attachment. Dynamic biofouling experiments were conducted over four days in a bench-scale forward osmosis (FO) system with Gram-negative Pseudomonas aeruginosa or Gram-positive Anoxybacillus sp. Biofouling resulted in ～10% decline in FO permeate water flux and was found to be significant for Anoxybacillus sp. but not for P. aeruginosa. Additionally, a stronger permeate water flux decline for P. aeruginosa in experiments with a superhydrophilic feed spacer demonstrated that mitigation methods require testing with different bacterial Gram-types. It was found that although permeate water flux decline can be affected by bacterial Gram-type the stable performance under enhanced biofouling conditions highlights the potential of FO for wastewater reclamation.     

Production and separation of alpha-agarase from Altermonas agarlyticus strain GJ1B

This paper presents results on the production of alpha-agarase by a fermentation process and its separation using membrane microfiltration (MF). Optimization of fermentation conditions for alpha-agarase production using Altermonas agarlyticus grown on medium containing agar as a carbon source was done in batch, fed-batch and continuous fermentations. Continuous culture at a dilution rate of 0.03 h(-1) appeared to be best suited for production of alpha-agarase by this organism. At 0.03 h(-1) dilution rate, enzyme activity was 0.9 U/ml. Clarification of broth was done using a hollow-fibre microfiltration membrane. The influence of hydrodynamic parameters on permeate flux and enzyme activity was studied. The best performance was obtained with prefiltered fermentation broth. A stable permeate flux of about 250-270 ml/min.m2 and an enzyme retention rate between 0% and 25% was obtained at temperatures between 6 degrees C and 22 degrees C, transmembrane pressure of 100 mm Hg and fluid cross-flow velocity of 4 x 10(-2) m/s. From the experiments on concentration of fermentation broth, the best compromise between enzyme activity transmission and permeate flux was obtained at a concentration factor of 2.     

Viability of an ectomycorrhizal fungus during cross-flow filtration

Factors affecting the viability and infectivity of an ectomycorrhizal fungus during moderate concentration by cross-flow filtration were determined. Mycelial suspensions were concentrated with three commercial membrane filters (Prostak Millipore Co., M14 Tech-Sep Co. and Ceraflo Norton Co.) under aseptic conditions. Medium components may reduce the filtration rate due to their low solubility. An antifoam agent did not reduce the average flux rates as much as did the malt extract. Clear unobstructed channels (I.D. 6mm) of the tubular modules (Tech-Sep) gave the best results both in terms of performance (filtration rate) and cell viability. Shear stresses caused by pumping and flow through narrow retentate channels were probably responsible for lowering viability and infectivity. There was no linear relationship between permeate fluxes and cell concentration. There is an optimum pore size both in terms of performance (filtration rate) and cell viability. Physical blockage of large pores by hyphae could explain lower permeate flux rates than those obtained with lower pore sizes membranes.     

Feasibility of supercritical CO₂ treatment for controlling biofouling in the reverse osmosis process

Physical cleaning and/or chemical cleaning have been generally used to control biofouling in the reverse osmosis (RO) process. However, conventional membrane cleaning methods to control biofouling are limited due to the generation of by-products and the potential for damage to the RO membranes. In this study, supercritical carbon dioxide (SC CO(2)) treatment, an environmentally friendly technique, was introduced to control biofouling in the RO process. SC CO(2) (100 bar at 35°C) treatment was performed after biofouling was induced on a commercial RO membrane using Pseudomonas aeruginosa PA01 GFP as a model bacterial strain. P. aeruginosa PA01 GFP biofilm cells were reduced on the RO membrane by >8 log within 30 min, and the permeate flux was sufficiently recovered in a laboratory-scale RO membrane system without any significant damage to the RO membrane. These results suggest that SC CO(2) treatment is a promising alternative membrane cleaning technique for biofouling in the RO process.     

Pressure effects in cross-flow microfiltration of suspensions of whole bacterial cells

The effect of Trans-Membrane Pressure (TMP) on permeate flux during cross-flow microfiltration of bacterial cell suspensions in tubular ceramic membranes is studied experimentally. Continuous filtration experiments with suspensions of whole bacterial cells (Mycobacterium M156) show a dramatic permeate flux decline with increasing TMP. During the very early stages of the filtration process, a linear relationship between permeate flux and TMP is observed, suggesting an initial surface sorption of cells on the membrane surface. At longer times, the permeate flux vs. TMP data exhibit a critical pressure beyond which the permeate flux declines with increasing trans-membrane pressure. This is interpreted in terms of the formation of a compressible cake, whose permeability can be described through the Carman-Kozeny equation.     

Separation of BSA through FAU-type zeolite ceramic composite membrane formed on tubular ceramic support: Optimization of process parameters by hybrid response surface methodology and biobjective genetic algorithm

In this study, Faujasite (FAU) zeolite was coated on low-cost tubular ceramic support as a separating layer through hydrothermal route. The mixture of silicate and aluminate solutions was used to create a zeolitic separation layer on the support. The prepared zeolite ceramic composite membrane was characterized using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), particle size distribution (PSD), field emission scanning electron microscopy (FESEM), and zeta potential measurements. The porosity of ceramic support (53%) was reduced by the deposition of FAU (43%) zeolite layer. The pore size and water permeability of the membrane were evaluated as 0.179?µm and 1.62?×?10^?7?m³/m²?s?kPa, respectively, which are lower than that of the support (pore size of 0.309?µm and water permeability of 5.93?×?10^?7?m³/m²?s?kPa). The permeate flux and rejection potential of the prepared membrane were evaluated by microfiltration of bovine serum albumin (BSA). To study the influences of three independent variables such as operating pressure (68.94–275.79?kPa), concentration of BSA (100–500?ppm), and solution pH (2–4) on permeate flux and percentage of rejection, the response surface methodology (RSM) was used. The predicted models for permeate flux and rejection were further subjected to biobjective genetic algorithm (GA). The hybrid RSM-GA approach resulted in a maximum permeate flux of 2.66?×?10^?5?m³/m²?s and BSA rejection of 88.02%, at which the optimum conditions were attained as 100?ppm BSA concentration, 2 pH solution, and 275.79?kPa applied pressure. In addition, the separation efficiency was compared with other membranes applied for BSA separation to know the potential of the fabricated FAU zeolite ceramic composite membrane.     

Influence of pH and salt concentration on the cross-flow microfiltration of BSA through a ceramic membrane

In this paper, the influence of pH in the 4–8 interval and NaCl concentration up to 25 mM on the cross-flow microfiltration of BSA was investigated. A tubular ceramic membrane with a pore size of 0.14 μm was employed and its point of zero charge was calculated. The evolution of permeate flow and BSA transmission with time was determined at 45 °C, a cross-flow velocity of 3.5 m/s and a transmembrane pressure of 100 kPa. The curves of permeate flow were explained according to the resistances in series model. Maximum protein transmission was obtained at the isoelectric point of BSA (4.9), with significant transmission also at the point of zero charge of the membrane and null transmission at pH 4 and 8. The highest permeate flow was observed at pH 7 and the lowest at 4.9. Finally, the addition of salt resulted to some extent in an improvement of both protein transmission and permeate flow.     

Biomass characteristics and membrane aeration: toward a better understanding of membrane fouling in submerged membrane bioreactors (MBRs)

Fouling in submerged membrane bioreactors (MBRs) was studied under different operating conditions and with varying biomass characteristics. Fouling rates were determined using a flux-step method for seven biomass conditions with mixed liquor solids concentrations ranging from 4.3 to 13.5 g x l(-1), six permeate fluxes (5.5, 11.0, 16.5, 22.0, 27.5, and 33.0 l x m(-2) x h(-1)), and three membrane airflow velocities (0.07, 0.10, and 0.13 m x s(-1)). Statistical analysis was used to specify the degree of influence of each of the biomass characteristics (solids concentration, dewaterability, viscosity, particle size distribution, concentrations of protein and carbohydrate in the soluble microbial products, SMP, and extracellular polymer substances, EPS), the permeate flux and the membrane aeration velocity on the membrane fouling rate. Among all these variables, only the permeate flux, the solids concentration (correlated to the viscosity and the dewaterability), the carbohydrate concentration in the EPS, and the membrane aeration velocity were found to affect the fouling rate. The permeate flux had the greatest effect. A transitional permeate flux was observed between 16.5 and 33 l x m(-2) x h(-1), below which no significant fouling was observed regardless of the biomass characteristics, the permeate flux, and the membrane aeration velocity.     

Protein overproduction in Escherichia coli: RNA stabilization, cell disruption and recovery with a cross-flow microfiltration membrane.

After optimizing overproduction of a heterologous gene product (chloramphenicol acetyltransferase, CAT) using an RNA stabilization vector * in Escherichia coli (Chan et al., 1988), a single step cell disruption and recovery method * for obtaining a product stream essentially free of cell debris was developed. The behavior of an RNA stabilization plasmid (pKTN-CAT) containing stabilizing intron RNA was investigated in two different media both in batch and chemostat modes. CAT production of pKTN-CAT was consistently higher (3- to 7-fold) than that of the control lacking the stabilization sequences (pK-CAT). Highest CAT production was observed for cells grown in minimal medium in batch mode and induced for CAT expression early in growth. CAT production of cells grown in the chemostat mode exhibited an optimal dilution rate of about 0.1 h-1. Enhancement of protein production by pKTN-CAT as compared to pK-CAT tended to be higher when grown in rich medium rather than in minimal medium. Presence of the RNA stabilization plasmid did not significantly alter the growth rate of the cell. Using a combination of chemical treatment (1 mM EDTA) and shear stress resulting from cross-flow in a stainless steel microfiltration membrane *, CAT was released into the medium through disruption of the E. coli cells. The permeate flux increased from 2000 to 9000 kg m-2 h-1 with increasing axial Reynolds number from 10,000 to 60,000 or increasing mean shear stress from 12 to 47 Pa. The turbidity of the permeate was approximately 4% that of the retentate over this range of axial flow rates, indicating excellent removal of cell debris. Also, the concentration of CAT in the permeate was equal to that in the retentate over this range of axial flow rates, indicating complete passage of protein through the membrane. Thus, using a combination of chemical treatment and fluid-induced shear stress in a cross-flow membrane module, we were able to disrupt and recover the heterologous protein in a stream low in debris.     

Feasibility of supercritical CO2 treatment for controlling biofouling in the reverse osmosis process

Physical cleaning and/or chemical cleaning have been generally used to control biofouling in the reverse osmosis (RO) process. However, conventional membrane cleaning methods to control biofouling are limited due to the generation of by-products and the potential for damage to the RO membranes. In this study, supercritical carbon dioxide (SC CO₂) treatment, an environmentally friendly technique, was introduced to control biofouling in the RO process. SC CO₂ (100 bar at 35°C) treatment was performed after biofouling was induced on a commercial RO membrane using Pseudomonas aeruginosa PA01 GFP as a model bacterial strain. P. aeruginosa PA01 GFP biofilm cells were reduced on the RO membrane by >8 log within 30 min, and the permeate flux was sufficiently recovered in a laboratory-scale RO membrane system without any significant damage to the RO membrane. These results suggest that SC CO₂ treatment is a promising alternative membrane cleaning technique for biofouling in the RO process.     

Dynamics of silver elution from functionalised antimicrobial nanofiltration membranes

In an effort to mitigate biofouling on thin film composite membranes such as nanofiltration and reverse osmosis, a myriad of different surface modification strategies has been published. The use of silver nanoparticles (Ag-NPs) has emerged as being particularly promising. Nevertheless, the stability of these surface modifications is still poorly understood, particularly under permeate flux conditions. Leaching or elution of Ag-NPs from the membrane surface can not only affect the antimicrobial characteristics of the membrane, but could also potentially present an environmental liability when applied in industrial-scale systems. This study sought to investigate the dynamics of silver elution and the bactericidal effect of an Ag-NP functionalised NF270 membrane. Inductively coupled plasma-atomic emission spectroscopy was used to show that the bulk of leached silver occurred at the start of experimental runs, and was found to be independent of salt or permeate conditions used. Cumulative amounts of leached silver did, however, stabilise following the initial release, and were shown to have maintained the biocidal characteristics of the modified membrane, as observed by a higher fraction of structurally damaged Pseudomonas fluorescens cells. These results highlight the need to comprehensively assess the time-dependent nature of bactericidal membranes.     

Forced-flow bioreactor for sucrose inversion using ceramic membrane activated by silanization

A forced-flow enzyme membrane reactor system for sucrose inversion was investigated using three ceramic membranes having different pore sizes. Invertase was immobilized chemically to the inner surface of a ceramic membrane activated by a silane-glutaraldehyde technique. With the cross-flow filtration of sucrose solution, the reaction rate was a function of the permeate flux, easily controlled by pressure. Using 0.5 mum support pore size of membrane, the volumetric productivity obtained was 10 times higher than that in a reported immobilized enzyme column reactor, with a short residence time of 5 s and 100% conversion of the sucrose inversion.     

Microfiltration of recombinant yeast cells using a rotating disk dynamic filtration system

To develop a highly efficient cell harvest step under time constraint, a novel rotating disk dynamic filtration system was studied on the laboratory scale (0.147-ft.(2) nylon membrane) for concentrating recombinant yeast cells containing an intracellular product. The existing cross-flow microfiltration method yielded pseudo-steady state flux values below 25 LMH (L/m(2). h) even at low membrane loadings (10 L/ft.(2)). By creating high shear rates (up to 120,000(-1)) on the membrane surface using a rotating solid disk, this dynamic filter has demonstrated dramatically improved performance, presumably due to minimal cake buildup and reduced membrane fouling. Among the many factors investigated, disk rotating speed, which determines shear rates and flow patterns, was found to be the most important adjustable parameter. Our experimental results have shown that the flux increases with disk rotating speed, increases with transmembrane pressure at higher cell concentrations, and can be sustained at high levels under constant flux mode. At a certain membrane loading level, there was a critical speed below which it behaved similarly to a flat sheet system with equivalent shear. Average flux greater than 200 LMH has been demonstrated at 37-L/ft.(2) loading at maximum speed to complete sixfold concentration and 15-volume diafiltration for less than 100 min. An order of magnitude improvement over the crossflow microfiltration control was projected for large scale production. This superior performance, however, would be achieved at the expense of additional power input and heat dissipation, especially when cell concentration reaches above 80 g dry cell weight (DCW)/L. Although a positive linear relationship between power input and dynamic flux at a certain concentration factor has been established, high cell density associated with high viscosity impacted adversely on effective average shear rates and, eventually, severe membrane fouling, rather than cake formation, would limit the performance of this novel system. (c) 1995 John Wiley & Sons, Inc.     

Use of rhamnolipid biosurfactant for membrane biofouling prevention and cleaning

Rhamnolipids were evaluated as biofouling reducing agents in this study. The permeability of the bacterial outer membrane was increased by rhamnolipids while the growth rate of Pseudomonas aeruginosa was not affected. The surface hydrophobicity was increased through the release of lipopolysaccharides and extracellular polymeric substances from the outer cell membrane. Rhamnolipids were evaluated as agents for the prevention and cleaning of biofilms. A high degree of biofilm detachment was observed when the rhamnolipids were used as a cleaning agent. In addition, effective biofilm reduction occurred when rhamnolipids were applied to various species of Gram-negative bacteria isolated from seawater samples. Biofilm reduction using rhamnolipids was comparable to commercially available surfactants. In addition, 20% of the water flux was increased after rhamnolipid treatment (300 μg ml^?1, 6 h exposure time) in a dead-end filtration system. Rhamnolipids appear to have promise as biological agents for reducing membrane biofouling.