Factors affecting the attachment of micro-organisms isolated from ultrafiltration and reverse osmosis membranes in dairy processing plants

Aims:  To identify the types of micro-organisms involved in the formation of biofilms on dairy ultrafiltration and reverse osmosis membranes and investigate factors affecting the attachment of those isolates.
Methods and Results:  Micro-organisms isolated from industrial membranes following standard cleaning were identified using the API culture identification system. Thirteen different isolates representing eight genera were isolated and their ability to attach to surfaces was compared using a microtitre plate assay. Three Klebsiella strains attached best, while mixed strains of Pseudomonas and Klebsiella attached better than individual strains. Whey enhanced the attachment of the isolates. The micro-organisms were characterized according to cell surface hydrophobicity using the microbial adhesion to hydrocarbon (MATH) test, and cell surface charge by measuring the zeta potential. These cell surface characteristics did not show a clear relationship with the attachment of our strains.
Conclusions:  A variety of different micro-organisms is associated with dairy ultrafiltration and reverse osmosis membranes after cleaning, suggesting several possible sources of contamination. The cleaning of these membranes may be inadequate. The attachment of the different isolates is highly variable and enhanced in the presence of whey.
Significance and Impact of the Study:  Knowledge of persistent microflora colonizing dairy membrane systems will help develop strategies to mitigate biofilm development in this environment, improving hygiene in membrane processing plants.     

Developing an antibacterial super-hydrophilic barrier between bacteria and membranes to mitigate the severe impacts of biofouling

Biofouling produces concentrated microbial populations with highly resistive biofilms and is considered to be a serious obstacle for a wide range of membrane technology applications. An antibacterial super-hydrophilic barrier could help to reduce biofouling by preventing direct contact between membranes and bacteria. In this study, an antibacterial super-hydrophilic barrier consisting of a layer of TiO₂ nanoparticles (NPs) was developed on polyvinylidene fluoride (PVDF)-based membrane via a facile technique. The results demonstrated that the presence of TiO₂ NPs eliminated the first step of biofouling, ie bacterial adhesion to the membrane. In addition, after bacterial deposition onto the membrane during ultrafiltration (UF), the TiO₂ NPs significantly retarded bacterial growth and reproduction (the second step of biofouling). During UF, the membrane flux decreased due to bacterial deposition, but 85% of the flux was recovered through physical cleaning using water. This study sheds light on the potential advantages of antibacterial super-hydrophilic membranes for biofouling mitigation.     

Effect of magnetic field on the ultrafiltration of bovine serum albumin

This work evaluates the effects of a static magnetic field on the permeation of bovine serum albumin (BSA) in a tangential ultrafiltration membrane module. Experimental tests were carried out at different pHs using a poly(sulfone) membrane with molecular weight cut off of 60 kDa under the influence of a 0.4 T neodymium-iron-boron magnetic field. Results showed an increase in the permeate flux of water after the cleaning procedures of the new and reused membranes in the presence of the magnetic field. The elusive mechanism of magnetic memory is also shown to take place for the water fluxes fully recovered after the cleaning procedures when the magnetic field was applied to the system before the permeation. When the magnetic field was applied during permeation, the water fluxes presented lower percent of recuperation after the cleaning procedures, thus suggesting that the BSA solution may have somewhat been influenced by magnetic memory.     

Acetonobutylic fermentation: improvement of performances by coupling continuous fermentation and ultrafiltration

The technology of coupling ultrafiltration and fermentation has been tested with the acetonobutylic fermentation in continuous mode. The device developed was sterilizable by steam and permitted drastic cleaning of the ultrafiltration (UF) membrane without interrupting the continuous fermentation. It has been shown to be an easily operated and reliable experimental tool for studying high-cell-density cultures and inhibition phenomena. With total recycle of biomass, a dry weight concentration of 125 g/L was attained, which greatly enhanced the volumetric solvent productivity of acetonobutylic fermentation in averaging 4. 5 g/L h for significant periods of time (>70 h) and maintaining solvent concentration and yield at acceptable levels.     

Highly selective membranes in protein ultrafiltration

A new ultrafiltration technique based on a multimembrane stack has been developed to fractionate solutes closer in size than conventionally possible. The technique is illustrated here by obtaining a pure protein product from a binary protein mixture. By employing membranes in series without any gaskets or spacers in-between, ultrafiltration is carried out to separate two proteins relatively close in molecular weight or size. Flat YM30 regenerated cellulose membranes, all of the same molecular weight cut-off (MWCO) 30,000, are stacked together in the desired number, and ultrafiltration takes place. The membrane rejection of a protein is amplified with each additional membrane, ultimately resulting in a completely rejected species. Complete purification of the more permeable protein may be achieved regardless of the physicochemical condition that may be optimal or suboptimal for selective separation by a single membrane. Two systems, myoglobin and beta-lactoglobulin, as well as myoglobin and alpha-lactalbumin were studied, under various operating conditions. The solvent flux reduction encountered when each membrane is added may also be avoided, by operating at increased pressure, while still achieving the desired purification. Cleaning in situ is achievable with reproducible experimental results before and after on-line cleaning. The results clearly demonstrate that multimembrane stacks can be used for fractionation of proteins that are quite close in molecular weight/size.     

Optimal operating policy of the ultrafiltration membrane bioreactor for enzymatic hydrolysis of cellulose

The dilution rate of an ultrafiltration membrane bioreactor in the enzymatic hydrolysis of cellulose was optimized using the kinetic model developed by Fan and Lee.(4) The sequence of optimal dilution rates was found to generally consist of an initial period of a minimal value (batch period), a subsequent period of maximum dilution rate, a period of a second batch, and a final period of a singular dilution rate. The effects of operating conditions, such as beta-glucosidase activity, operating time, maximum dilution rate, substrate feeding rate, and enzyme-to-substrate ratio on both the conversion yield and the sequence of optimal dilution rates were investigated. To evaluate the validity of kinetic model employed in this work, enzymatic hydrolysis was carried out using alpha-cellulose as a substrate in the ultrafiltration membrane bioreactor. The experimental data were well consistent with the simulation results. (c) 1993 John Wiley & Sons, Inc.     

Effect of membrane charge on flow and protein transport during ultrafiltration

Although several recent studies have demonstrated the importance of electrostatic interactions in ultrafiltration, there have been few quantitative studies of the effects of membrane charge density on protein transport and membrane hydraulic permeability. Data were obtained using a series of charge-modified cellulose membranes, with the surface charge density controlled by varying the extent of addition of a quaternary amine functionality. The membrane charge was evaluated from streaming potential measurements. Protein transmission decreased by a factor of 100 as the membrane zeta potential increased from 0.3 to 6.6 mV. The protein sieving data were in good agreement with a partitioning model accounting for electrostatic effects, while the hydraulic permeability data were consistent with a flow model accounting for the effects of counter-electroosmosis. The results provide the first quantitative analysis of the effects of membrane charge density on the performance of ultrafiltration membranes.     

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.     

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.     

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.     

Role of some whey components on mass transfer in ultrafiltration

Ultrafiltration through Carbosep M(4) mineral membrane of protein solutions of decreasing complexity (whey before and after centrifugation or clarification, beta-lactoglobulin) was studied. Mathematical models were used to explain variations in flux with time. Taking into account variations in protein retention and hydraulic resistance of the membrane during ultrafiltration, proteins and lipoproteins were found to be involved not only in the polarization layer (reversible fouling leading to a difference in the osmotic pressure), but also in irreversible fouling by adsorption. Morever, the presence of particles (e.g., inorganic precipitates) in whey explains the build-up of a deposit over and within the membrane which contributes to the decline in flux after 1 h ultrafiltration. The relative importance of these phenomena was quantified.     

Effect of solution pH on protein transport through ultrafiltration membranes

Although a number of previous studies have demonstrated that solution pH can have a dramatic effect on protein transport through ultrafiltration membranes, the exact origin of this behavior has been unclear. Experimental data were obtained for the transport of a broad range of proteins with different surface charge and molecular weight. The effective hydrodynamic size of the proteins was evaluated using size‐exclusion chromatography. The membrane charge, both before and after exposure to a given protein, was evaluated using streaming potential measurements. In most cases, the electrostatic interactions were dominated by the distortion of the electrical double layer surrounding the protein, leading to a distinct maximum in protein transmission at the protein isoelectric point. Attractive electrostatic interactions did occur when the protein and membrane had a large opposite charge, causing a second maximum in transmission at a pH between the isoelectric points of the protein and membrane. The sieving data were in good agreement with theoretical calculations based on available models for the partitioning of charged solutes in cylindrical pores. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 27–37, 1999.     

Hydraulic conductivity of chondroitin sulfate proteoglycan solutions

The hydraulic conductivity of solutions of Swarm rat chondrosarcoma proteoglycan subunit and of chondroitin 4- and 6-sulfate up to concentrations of 80 mg ml-1 have been measured under physiological conditions using sedimentation velocity and membrane ultrafiltration techniques. This study establishes the very high flow resistance of the proteoglycan and that this resistance is due to its constituent chondroitin sulfate chains. We have also demonstrated little difference in the hydraulic conductivity of chondroitin 4-sulfate as compared to chondroitin 6-sulfate. Studies of hydraulic conductivity of chondroitin sulfate and proteoglycan subunit over a range of salt concentrations demonstrate that the chondroitin sulfates exhibit only a small degree of electrolyte dissipation indicating that their constituent charge groups do not significantly contribute to flow resistance at high mechanical pressures. It appears that the shape and conformation of the polysaccharide backbone and its glycosidic linkages are the factors that primarily govern flow resistance. This is also consistent with the fact that hydraulic conductivity of the proteoglycans and chondroitin sulfates is considerably lower than that of its more charged counterpart heparin but has similar values to hyaluronate. Qualitative agreement between sedimentation analysis and ultrafiltration measurements is also established although the latter technique suffers from not knowing over what distance, adjacent to the membrane, ultrafiltration takes place. It is predicted that the proteoglycans will significantly contribute to flow resistance of cartilagenous tissues which confirms the Maroudas correlation that high proteoglycan concentration in cartilage yields high flow resistance. Further, we establish through a comparison of hydraulic conductivity measurements on hyaluronate, desulfated chondroitin sulfate, chondroitin sulfate, and proteoglycan subunit and osmotic pressure measurements of hyaluronate and proteoglycan that the sulfate groups of the chondroitin sulfate chain play only a small role in the net movement of water relative to the proteoglycan.     

Effects of chemical sanitization using NaOH on the properties of polysulfone and polyethersulfone ultrafiltration membranes

Membranes used in bioprocessing applications are typically sanitized before use to insure aseptic operation. However, there is almost no information in the literature on the effects of this preuse sanitization step on the properties of the membrane. Experiments were performed with commercially available hollow fiber polysulfone (PSf) and polyethersulfone (PES) membranes with different nominal molecular weight cutoffs. Data were obtained for the membrane hydraulic permeability, dextran retention coefficients, zeta potential (surface charge), and extent of protein adsorption both before and after sanitization with 0.5 N NaOH at 45°C for 30 min. Changes in chemical composition were examined using ATR‐FT‐IR and XPS. Sanitization caused a large increase in the net negative charge for all membranes. There was a small reduction in hydraulic permeability and a significant increase in dextran retention for the polyethersulfone membranes, consistent with a reduction in the effective pore size. Spectroscopic analyses suggest that this change is likely due to the base‐catalyzed hydrolysis of the lactam ring in polyvinylpyrrolidone (PVP) that is typically is used as a wetting/pore‐forming agent in PSf and PES membranes. Preuse sanitization also appeared to have a small effect on protein adsorption, although the extent of adsorption was quite low for both the virgin and sanitized membranes. The observed changes in membrane properties could have a significant impact on the ultrafiltration performance, demonstrating the importance of standardizing the sanitization procedures even in process development and scale‐down validation studies. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 31:90–96, 2015     

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.     

Concentration Polarization in an Ultrafiltering Capillary

Concentration polarization, the accumulation of retained solute next to an ultrafiltering membrane, elevates osmotic pressure above that which would exist in the absence of polarization. For ultrafiltration in a cylindrical tube, use of the radially averaged solute concentration results in an underestimate of osmotic pressure, yielding an effective hydraulic permeability (k) less than the actual membrane hydraulic permeability (k_m). The extent to which k and k_m might differ in an ultrafiltering capillary has been examined theoretically by solution of the momentum and species transport equations for idealized capillaries with and without erythrocytes. For diameters, flow velocities, protein concentrations and diffusivities, and ultrafiltration pressures representative of the rat glomerular capillary network, results indicate that the effects of polarization are substantial without erythrocytes (k/k_m = 0.7) and persist, but to a lesser extent, with erythrocytes (k/k_m = 0.9), the reduction in polarization in the latter case being due to enhanced plasma mixing. In accord with recent experimental findings in rats, k is found to be relatively insensitive to changes in glomerular plasma flow rate.     

超滤膜纯化绞股蓝皂苷的工艺

探讨采用超滤膜分离纯化绞股蓝总皂苷的工艺。以固形物得率和绞股蓝总皂苷含量为评价指标进行正交试验,对操作压力、溶液温度和膜的规格等因素进行优选。发现最佳工艺条件为选择截留相对分子质量为3×104的超滤膜,在溶液温度40℃、操作压力2.0×106Pa条件下纯化效果较好;所选择的超滤膜纯化绞股蓝皂苷的工艺操作简单可靠,所得产品纯度高。     

Effects of biofilm formation on membrane performance in submerged membrane bioreactors

The effects of biofilm formation on membrane performance were evaluated for a submerged membrane bioreactor (sMBR) system with six different types of micro- and ultrafiltration membranes (working volume = 19 l). After operation for 24 h the permeability of the membranes with a larger pore size (microfiltration) decreased to that of the membranes with a much smaller pore size (ultrafiltration). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) confirmed that biofilms could reduce the influence of the membrane surface properties. The chemical oxygen demand (COD) removal efficiency was 95% for the oily wastewater treatment in the sMBR where the filtration process made an important contribution (47% based on feed COD). Significant enhancement in COD removal occurred at the initial filtration stage because of biofilm formation and the dynamic member role of the biofilm layer. Membranes with various pore sizes had approximately the same permeate quality that was attributed to the biofilm on the membrane surfaces. Nevertheless, the ultrafiltration membranes had 43% more COD removal efficiency than the other applied membranes at the beginning of filtration (before biofilm formation) because of the smaller pore sizes and better sieving.     

膜-生物硝化反应器处理含氨废水效能的研究

研究了膜 生物硝化反应器对含氨废水的处理效能以及分离膜的截留和渗透效能。膜_生物反应器启动迅速 ,在水力停留时间为 1d的情况下 ,反应器最高进水浓度达 80mmol(NH₄⁺-N)·L^-1 ,最高容积负荷达 1 12kg(NH₄⁺ -N)·m^-3·d^-1 ,氨氮去除率保持在 95%以上。试验证明 ,分离膜对微生物有良好的截留作用 ,50天内反应器的污泥浓度从 5g·L^-1 增长到 10g·L^-1 ,分离膜表面附着的生物层则对废水氨氮和亚硝氮有进一步的转化作用。在液位差低于 80cm时 ,提高液位差可增大膜渗透通量 ;液位差超过 80cm后 ,增大液位差的膜渗透通量效应很小 ;其中 ,当液位差为 2 0cm左右时 ,膜通量达 2 . 5 1L·m^-2 ·h^-1 ,阻力最小 [(2 . 6 3× 10^-5)m^-1]。该膜_生物硝化反应器可依靠液位差压力驱动出水 ,无需外加动力。     

Effect of antifoam agents and efficiency of cleaning procedures on the cross-flow filtration of microbial suspensions

Summary The influence of several biocompatible antifoam agents on the performance of ultrafiltration membranes for yeast cell concentration is described. Flux rates of water solutions and cell suspensions decreased in the presence of the antifoam agents. The anti-foam fouling effect was cumulative. Water was ineffective as a cleaning substance, while 0.1 NaOH and ethanol were used successfully for membrane washing.