Μm Pore Size Membrane Research Articles

Author Index Vol. 74 (2001)

The first application of pasteurization to stabilize seawater samples for subsequent nitrate and nitrite determination in marine water is presented. Coastal seawater sampled from winter to late spring, with various chemical characteristics, was used. Samples were filtered through 0.7 and 1 μm pore size membranes before being treated. Promising results were obtained since concentration changes in the samples did not exceed about 1–2% for both nutrients (i.e., an absolute change of 0.005 μmol l−1 for nitrite) over periods from 16 to 22 months. The efficiency of the treatment is shown by comparing the behaviour of treated samples to untreated ones. Although this stabilization method requires an oven for processing samples, it is advantageous in that it does not alter the samples by chemical additions and enables samples to be stored at room temperature for many months, without special equipment, before analysis.

Inhibition of Dendritic Cell Differentiation by Fumaric Acid Esters

Fumaric acid esters have proved to be effective for the systemic treatment of severe psoriasis vulgaris. These compounds have been shown to induce a Th2-like cytokine secretion pattern in T cells and to reduce keratinocyte proliferation in vitro. Dendritic cells seem to be of major importance as regulatory cells driving the psoriatic tissue reaction. Monocytes or CD34-positive myeloid progenitor cells are precursors of dendritic cells that can be generated in vitro by culture with granulocyte-macrophage colony-stimulating factor and interleukin-4. Using this model the effect of fumaric acid esters on granulocyte-macrophage colony-stimulating factor/interleukin-4-induced differentiation of monocyte-derived dendritic cells was investigated. The results of this study show that dimethylfumarate as well as methylhydrogenfumarate-calcium-salt (0.01-100 microg per ml) concentration-dependently inhibit monocyte-derived dendritic cell differentiation. This was reflected by an inhibition of CD1a, CD40, CD80, CD86, and HLA-DR expression as well as by a reduced capacity of dimethylfumarate-treated monocyte-derived dendritic cells to stimulate lymphocytes in the allogeneic mixed lymphocyte reaction. Other fumaric acid esters showed no effect on monocyte-derived dendritic cell-differentiation. At higher concentrations (30-100 microg per ml) dimethylfumarate, but not methylhydrogenfumarate calcium-salt induced apoptosis in monocyte-derived dendritic cells as measured by expression of Apo 2.7 and DNA fragmentation (TUNEL assay). These data point to a high susceptibility of the monocyte/dendritic cell system to dimethylfumarate and its main metabolite methylhydrogenfumarate. Other fumaric acid esters investigated were without effect. As the effects of fumarates on monocyte-derived dendritic cells observed occur at concentrations 20-fold lower compared with lymphocytes, our data seem to be of relevance in explaining the possible mode of action of these compounds in psoriasis.

Enumeration of iron-oxidizing bacteria by the membrane filter technique

This work presents a simple methodology to enumerate ferrous-iron-oxidizing bacteria in solution, easily applicable in bioleaching industrial plants, because it does not require expertise or specific equipment. The enumeration is based on bacterial concentration by microfiltration through a membrane filter. The filter containing the bacteria is placed on an agarose plate containing ferrous sulphate for bacterial growth. No difference was observed for the enumeration of Acidithiobacillus ferrooxidans ATCC 19859 when either 0.1 or 0.22 μm pore size membrane filters were used. However, when the technique was applied to bacteria present in pregnant leaching solution, the smaller bacteria present in these solutions passed through the 0.22 μm pore size membrane. Therefore the number of bacteria could be underestimated if they are monitored and filtered using a filter with pore size greater than 0.1 μm. The limit of detection of this technique was one ferrous-iron-oxidizing bacterium in the filtered solutions.

Characterisation of trickling filter effluent by particle size distribution and high performance size exclusion chromatography

Wastewater treatment objectives are still typically defined in terms of nonspecific parameters such as biochemical oxygen demand and total suspended solids. However, wastewaters are a heterogeneous mixture of materials with a wide range of particle size and molecular weight, and most processes involved in treatment (sedimentation, mass transfer, adsorption, diffusion, biochemical reactions, filtration) are effected by particle dimension. This study deals with the evolution of the particular and dissolved content of synthetic sewage during treatment. The experimental system consisted of a pilot-scale low-rate trickling filter, with and without secondary settlement, followed by crossflow microfiltration (CFMF). In terms of particle size distribution (PSD), results show a shift towards larger particle sizes through biological filtration, most of which can then be removed by settlement. Some fine particles remain and these can be removed by CFMF with a 0.1 μm pore size membrane. High performance size exclusion chromatography (HPSEC) was used to study the evolution of the dissolved fraction of wastewater through treatment. Both PSD and HPSEC are shown to be valuable tools to assess the performance of wastewater treatment processes.

Food emulsions using membrane emulsification: conditions for producing small droplets

Ceramic membranes were used to produce oil-in-water (O/W) emulsions consisting of vegetable oil as the dispersed phase and skim milk as the dispersion medium. The purpose of the work was to find operating conditions suitable for producing small emulsion droplets, a small size being important for emulsion stability. The main parameters investigated were the effect of wall shear stress, emulsifier concentration and membrane pore size. Formation of small droplets was favoured at higher emulsifier concentrations and for a high wall shear stress using a membrane with a small nominal pore size. Submicron particles were produced at an 8% emulsifier concentration for a wall shear stress of 135 Pa using a 0.1 μm pore size membrane. Under these conditions the flux was >100 kg m −2 h −1. A high flux is important for industrial-scale production of food emulsions using membrane emulsification.

Pasteurization as an alternative method for preservation of nitrate and nitrite in seawater samples

The first application of pasteurization to stabilize seawater samples for subsequent nitrate and nitrite determination in marine water is presented. Coastal seawater sampled from winter to late spring, with various chemical characteristics, was used. Samples were filtered through 0.7 and 1 μm pore size membranes before being treated. Promising results were obtained since concentration changes in the samples did not exceed about 1–2% for both nutrients (i.e., an absolute change of 0.005 μmol l−1 for nitrite) over periods from 16 to 22 months. The efficiency of the treatment is shown by comparing the behaviour of treated samples to untreated ones. Although this stabilization method requires an oven for processing samples, it is advantageous in that it does not alter the samples by chemical additions and enables samples to be stored at room temperature for many months, without special equipment, before analysis.

The occurrence of Listeria spp. and Salmonella spp. in surface waters

Listeria ssp., mainly Listeria monocytogenes as well as Salmonella spp. are recognized as significant human pathogens. The purpose of this study was to examine the occurrence of Listeria spp. and Salmonella spp. in surface waters of Northern Greece and to investigate the correlation of these pathogens with the standard indicator bacteria. A total number of 128 water samples from four rivers and one lake were examined for the presence of Listeria, Salmonella, total coliforms, faecal coliforms and faecal streptococci. For isolating Listeria, 250 ml of water were filtered through 0.45 μm pore size membrane, that was transferred in 10 ml listeria enrichment broth and after incubation for 24 h at 30°C, a second enrichment in FDA and Fraser broths was followed. After 24 hour incubation, an amount of 0.1 ml was streaked out onto listeria selective medium. The typical colonies were further biochemically and serologically examined. Salmonella spp. were isolated after preenrichment in BPW, enrichment in Rappaport — Vassiliadis and selenite cysteine broths and identified from BGD and SS agar plates by biochemistry and serology. Listeria monocytogenes was isolated from five (3.9%) and Salmonella spp. from eigth (6.2%) samples. Mean log values of the standard indicator bacteria did not significantly differ between listeria and salmonella positive and negative samples.

Measurement of Titanium Dioxide in Cosmetic Products with X-Ray Fluorescence Spectrometry

Abstract This paper reports the development of a simple method for measuring titanium dioxide in cosmetic products using X-ray fluorescence. A sample is prepared by stirring in a dispersion medium and then filtering with a 0.1 μm pore size membrane filter. The titanium dioxide particles trapped on the dried membrane filter are then measured with a wave-length dispersive X-ray fluorescence spectrometer. This sample preparation procedure was investigated using scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDX) mapping, inductively coupled plasma atomic emission spectrometry (ICP-AES) and turbidimetry. Interferences can be separated from the titanium dioxide layer on the membrane filter with this preparation procedure. The relative standard deviation for the analysis is less than 0.4%, the recovery is more than 99.0%, and the calibration curve gives a correlation coefficient of R = 1.000. The detection limit for titanium dioxide using this procedure is 0.02% by weight in product. ...

A useful and rapid method to recover bacterial cells from milk samples for microscopic count

A description is given of a pre-treatment for milk samples which allows it to be filtered through 0.2 μm pore-size membrane filters without reducing the initial number of bacteria. The efficiency of the method was demonstrated in milk samples inoculated with Escherichia coli O25:H-42, a food-borne pathogen, by comparison with a control in tryptone soya broth (TSB). No significant differences were found between direct microscopic counts in milk samples and controls in TSB.

Synthesis and characterization of supramolecular biovector (SMBV) specifically designed for the entrapment of ionic molecules

Supramolecular biovectors (SMBV) are nanoparticular drug carriers composed of an internal crosslinked solid core externally grafted with fatty acids and surrounded with a phospholipid layer. We show in this paper that the internal core can be derivatized with anionic ligands such as phosphate in order to allow the efficient entrapment of cationic molecules through a process akin to ion exchange. Synthesis of SMBV involved first a cross linking and derivatization step of polysaccharides followed by a homogenization, a drying and a regioselective acylation step. Acylated polysaccharide cores are thus obtained which can be loaded with drugs and wrapped with a phospholipid layer. The SMBVs obtained are characterized through their size, 20 nm, and their ability to filter through 0.22 μm pore size membrane. Gel permeation chromatography experiments performed with various phospholipid/acylated cores ratios indicate that SMBVs form entities distinct from liposomes and that the optimum phospholipid/acylated cores ratio for this specific type of SMBVs is close to 100%. The supramolecular structure of SMBVs and in particular the spatial proximity between acylated cores and phospholipids is demonstrated through resonance energy transfer experiments. The drug loading capability of SMBVs is illustrated by the preparation of gentamicin and doxorubicin loaded SMBV. The therapeutic potential of SMBVs is then discussed notably in the light of a possible biomimetism with low density lipoproteins (LDL).

Tangential flow filtration: A method to concentrate freshwater algae

The suitability of the application of the tangential flow filtration system (TFF) for the concentration of living freshwater phytoplankton for water treatment studies was examined. We investigated the capability of a TFF system, equipped with a 0.45 μm pore-size membrane, to concentrate algae from large volumes of reservoir water characterized by low algal biomass. The samples examined were concentrated 5 to 40 times. The assessment criteria of systems's performance were algal recovery rates and cell viability. It was found that large volumes of water could be processed without problems. The algal recovery was high and correlated to the applied concentration factor and the prevailing algal species. An overall algal biomass recovery of 70–89 percent was found. The assessment of algal viability in the concentrated samples was based on the growth rates and degree of preservation of their complex structure and other properties that affect their behaviour in water treatment. Algal cells in the concentrated samples and in natural reservoir water were found to be identical, with all delicate cell structures undamaged. Motile species preserved their active locomotion. Algal reproduction capacity was not affected by the concentration process. The results obtained confirm that the TFF system is a powerful apparatus for the preparation of model waters to be used in experimental algal-related water treatment studies.

Diamond like carbon coated films for enzyme electrodes; characterization of biocompatibility and substrate diffusion limiting properties

The biocompatibility and substrate diffusion limiting properties for a range of diamond like carbon (DLC) coated microporous polycarbonate and DLC coated dialysis (haemodialysis) membranes have been studied. This characterisation builds upon previous findings where DLC coated membranes imparted enhanced enzyme electrode performance. In this study electrode linear ranges have been extended from 10 mM glucose for a 0.01 μm pore size membrane to 160 mM. These findings correlated with the duration of DLC deposition and associated reductions in permeability for glucose. Permeability coefficient ratios for both microporous and dialysis membranes were also found to be important with low glucose/O 2 permeability ratios imparting extensions in glucose linear response range. DLC coated membranes employed within enzyme electrodes have also been shown to exhibit enhanced haemocompatibility as determined by both sensitivity change and surface deposition of blood components examined by scanning electron microscopy. Correlations are made between the reduced losses in sensor response to biofouling/ working electrode passivation processes, and extended linear ranges that DLC coated membranes may impart to enzyme electrode performance. Particular reference is made to the determination of glucose levels within whole blood.

Transfer of symbiotically fixed nitrogen from berseem (Trifolium alexandrinum L.) to maize via vesicular-arbuscular mycorrhizal hyphae.

In order to examine whether hyphae of VA mycorrhizal fungi may aid the transfer of symbiotically fixed nitrogen from a legume to a non-legume, the roots of berseem plants inoculated with the VAM fungus Glomus intraradices and Rhizobium leguminosarum biovar. trifolii (strain RCR 5) were separated by a 2 cm root-free zone from the roots of maize plants. A 40 um pore size nylon net allowed VAM hyphae to pass through the root-free zone but prevented root penetration. Replacement of this net by a 0.45 μm pore size membrane prevented penetration of VAM hyphae to the root-free compartment. When the berseem plants were 63 d old, the plant chambers were sealed in plastic bags to allow the roots of the plants to be exposed to a l0 N2 -enriched atmosphere for 5 d. Berseem plants that were exposed to a 15 N2 -enriched atmosphere fixed more 15 N than did berseem plants maintained under air at natural 15 N abundance. The total 15 N excess content of berseem was similar whether or not the mycorrhiza had access to the maize roots. Plant mass (dry weight) of maize was not affected by the mycorrhizal fungus, but total nitrogen content tended to be higher in VAM-colonized maize than in non-colonized maize. Furthermore, both atom %15 N excess and 15 N excess content of mycorrhizal maize were significantly increased as compared with non-mycorrhizal maize or with maize controls without berseem. The amounts of 15 N transferred were small, accounting for less than 4% of the 15 N in the N2 -fixing plant. In spite of the 2 cm root-free separating zone, the presence of the mycorrhizal fungus in the non-legume increased the transfer of symbiotically fixed nitrogen from berseem to maize plants that were physiologically younger. The implications of these results for nitrogen transfer from a legume to an accompanying non-legume via VAM hyphae are discussed.

PROTEIN ADSORPTION AND FOULING OF CERAMIC MEMBRANES AS MEASURED BY SCANNING ELECTRON MICROSCOPY WITH DIGITAL X-RAY MAPPING

A technique for studying fouling in ceramic membranes using the energy dispersive x-ray spectroscopy capability of an electron microscope is described. The location and amount of foulant within the membrane are presented on a digital x-ray map showing elements constituent to or stained on the foulant. Fouling of alumina membranes during filtration of the protein hemoglobin has been studied as a function of filtration time, pH, and membrane pore size. After each filtration run, the protein within a piece of the membrane was stained with phosphotungstic acid and located on a digital map of either phosphorus or tungsten. For a 0.2 μm pore size membrane, time dependent fouling was observed consistent with an observed flux decline within the first few minutes of filtration. A pH dependence was also observed indicating much greater fouling at pH 6.9 near the protein isoelectric point than at pH 8.5. This observation is consistent with pH dependent adsorption, flux, and rejection studies. No internal fouling was observed for a 40 Å pore size membrane, which is consistent with the size of hemoglobin in solution being larger than the 40 Å pores and with the fact that the 40 Å membrane can be more easily cleaned after use than can the 0.2 μm membrane.

Effects of bottle size in determinations of primary productivity by phytoplankton

Determinations of primary productivity were made by the radiocarbon method at regular intervals over a year in samples, taken from the eutrophic waters of the Menai Strait, North Wales, and contained in bottles of capacities from 135 ml up to 2290 ml. Fixation per unit volume in particulate matter retained by 0 · 45 μm pore size membrane filters was independent of bottle size over most of the year. There was a consistent divergence, however, during the period of rapid phytoplankton growth in the spring, when small bottles gave up to three times higher values than large ones. Possible effects of bottle size on primary productivity determinations are discussed but the cause of this particular result is not apparent.

Effect of Filtration and Centrifugation on the Determination of Alminium in Water

Abstract The effect of filtration and centrifugation on the determination of aluminium in surface and leachate water has been studied. For surface and leachate water samples only small effects were observed by filtration through 0.45 μm or 0.22 μm pore size membrane filters compared to unfiltered samples. For over 80% of the samples, which contained 0.01-15mg AlL−1, the differences between unfiltered and filtered samples were less than 0.10 mg AlL−1, and only for about 5% of the samples were differences above 0.20 mg AlL−1 observed.

Filtration of Particulates and Emulsions with a Pleated, Thin Channel, Cross-Flow Module

Abstract The pleated thin channel crossflow module represents a novel flat sheet membrane configuration combining the modular advantages of hollow fiber design with the hydrodynamics of plate and frame units containing turbulence promoting elements. It consists of a circular array of parallel pleated thin channels, each of whose inner wall is a membrane supported by a porous backing resting on a central product drain tube. The outer flexible wall is separated from the membrane by a turbulence promoting spacer and serves to create the flow channel, without fulfilling a direct filtrative purpose. The design allows operation at elevated particulate levels and is highly suited to microfiltration of stray matter and bacteria from aqueous solutions to be injected into well heads for enhanced oil recovery. Data are presented for 0.45 and 0.2 μm pore size membrane modules containing 3.3 ft2 of membrane area and operating on dispersions of standard particulates of known size distribution (80 μm to 0.2 μm). Effects...

Trace metal analysis of sediments and particulate matter in sea water by energy-dispersive X-ray fluorescence

The capability of energy-dispersive X-ray fluorescence was investigated for fast and simple chemical analysis of trace elements in sediments and particulate matter in sea water. Nuclepore 0.4 μm pore-size membranes are recommended as optimal filters for a straightforward collection of suspended material. The collection of suspended trace metals by filtration seemed to give a sufficiently homogeneous filter load (s% <2.5). Data are presented on the concentrations of K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Pb, Rb and Sr with a fair precision (s% < 5.6) and accuracy.