Filtration Of Suspensions Research Articles

Sensitive enumeration of Listeria monocytogenes and other Listeria species in various naturally contaminated matrices using a membrane filtration method

For the enumeration of Listeria monocytogenes (L. monocytogenes) in food, a sensitive enumeration method has been recently developed. This method is based on a membrane filtration of the food suspension followed by transfer of the filter on a selective medium to enumerate L. monocytogenes.An evaluation of this method was performed with several categories of foods naturally contaminated with L. monocytogenes. The results obtained with this technique were compared with those obtained from the modified reference EN ISO 11290-2 method for the enumeration of L. monocytogenes in food, and are found to provide more precise results. In most cases, the filtration method enabled to examine a greater quantity of food thus greatly improving the sensitivity of the enumeration. However, it was hardly applicable to some food categories because of filtration problems and background microbiota interference.

Deep bed and cake filtration of two-size particle suspension in porous media

Abstract Formation of low permeable external filter cake during drilling and water injection has been widely reported in the literature. It may cause significant decrease in well index. The process is very sensitive to size distribution of injected particles. We propose a new mathematical model for cake formation with deep bed filtration for two-particle-size injection. The basic equations account for three stages: formation of cake from large particles with simultaneous deep bed filtration of small particles; small particle capture in the cake with formation of the internal cake inside the external cake; build-up of the uniform cake from the mixture of two-size particles. The analytical model is derived for three stages. Two regimes of the cake formation are identified, which correspond to the high and low concentrations of injected small particles. The laboratory coreflood with two-particle-size suspension injection with monitoring the rate and pressure drop along the core is performed. The matched mathematical model shows good agreement with the laboratory data.

Preparation of patterned microfiltration membranes and their performance in crossflow yeast filtration

Patterned microfiltration membranes were fabricated via Phase Separation MicroFabrication (PSMF) using vapor-induced phase separation to avoid skin formation on the nonpatterned surface. A starting solution of 10% PES, 60% PEG400, 5% water and 25% NMP yielded symmetric membranes with similar pore size all throughout the cross section when 10 or 15min of vapor exposure was used before further coagulation in water. On the other hand, 5min of vapor exposure resulted in what may be called inverse asymmetric membranes, which had smaller pores on the patterned (mold) side and macrovoids throughout the cross-section. The fidelity in replicating the pattern was higher when the vapor exposure was shorter and surface area enhancements of 103% and 52% were obtained when vapor exposure times were 5 and 10min, respectively. The phase inversion rates of the polymer solutions in liquid water, humid air and humid air followed by liquid water were examined by measuring the light transmission through the solutions in time. It was observed that water in the starting solution increased the overall phase inversion rate and decreased the delay time before phase separation, in consistence with the membrane morphologies obtained with the solutions with and without water under different coagulation conditions. The patterned and nonpatterned membranes were tested in constant flux crossflow filtration of yeast suspensions at different fluxes and it was seen that the fouling rate of nonpatterned membranes was higher than patterned membranes. However, the major contribution to the improved fouling behavior appears to be the increased surface area since when the fluxes were normalized by the patterned (actual) surface area for foulant deposition, the difference between the fouling rate of patterned and nonpatterned membranes was not significant.

Silver nanoparticle-doped zirconia capillaries for enhanced bacterial filtration.

Membrane clogging and biofilm formation are the most serious problems during water filtration. Silver nanoparticle (Agnano) coatings on filtration membranes can prevent bacterial adhesion and the initiation of biofilm formation. In this study, Agnano are immobilized via direct reduction on porous zirconia capillary membranes to generate a nanocomposite material combining the advantages of ceramics being chemically, thermally and mechanically stable with nanosilver, an efficient broadband bactericide for water decontamination. The filtration of bacterial suspensions of the fecal contaminant Escherichia coli reveals highly efficient bacterial retention capacities of the capillaries of 8 log reduction values, fulfilling the requirements on safe drinking water according to the U.S. Environmental Protection Agency. Maximum bacterial loading capacities of the capillary membranes are determined to be 3 × 109 bacterial cells/750 mm2 capillary surface until back flushing is recommendable. The immobilized Agnano remain accessible and exhibit strong bactericidal properties by killing retained bacteria up to maximum bacterial loads of 6 × 108 bacterial cells/750 mm2 capillary surface and the regenerated membranes regain filtration efficiencies of 95–100%. Silver release is moderate as only 0.8% of the initial silver loading is leached during a three-day filtration experiment leading to average silver contaminant levels of 100 μg/L.

Hollow microgel based ultrathin thermoresponsive membranes for separation, synthesis, and catalytic applications.

Thermoresponsive core-shell microgels with degradable core are synthesized via surfactant based free radical polymerization using N,N'-(1,2-dihydroxy-ethylene)bis(acrylamide) (DHEA) as a cross-linker for core preparation. The 1,2-glycol bond present in DHEA is susceptible to NaIO4 solution, and thus, the structure can be cleaved off resulting in hollow microgel. Ultrathin membranes are prepared by suction filtration of a dilute suspension of core-shell microgels over a sacrificial layer of Cd(OH)2 nanostrand coated on track etched membrane. After removal of the degraded cores from microgels, the membranes are cross-linked with glutaraldehyde and the nanostrands are removed by passing a 10 mM HCl solution. The prepared membranes are thoroughly characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and dynamic contact angle for morphology, thermoresponsive, and hydrophilic properties, respectively. The prepared membranes showed thermoresponsive permeation behavior and remarkable separation performance for low molecular weight dyes and lysozyme protein. These membranes are also used to synthesize gold nanoparticles and immobilize lactate dehydrogenase enzyme for catalytic and biocatalytic application. The results for water permeation, solute rejection, and ability to immobilize gold nanoparticles and enzymes showed its wide range of applicability. Furthermore, the synthesis of hollow microgel is simple and environmentally friendly, and the membrane preparation is easy, scalable, and other microgel systems can also be used. These responsive membranes constitute a significant contribution to advanced separation technology.

Biogenic silver nanocomposite polyethersulfone UF membranes with antifouling properties

Biofouling remains one of the most challenging issues of membrane application in water industry. One of the practical strategies to control fouling is anti-biofouling membrane. High concentration and high stable biogenic nanoparticle silver with the averaged diameter of only 6nm (Bio-Ag0-6) was firstly extracted from the supernatant of Lactobacillus fermentum. The biogenic nanocomposite polyethersulfone (Bio-Ag0-6/PES) membranes were prepared by adding different amounts of biogenic nanoparticle silver into the dope solution. The nanocomposite membranes were systematically tested for physical properties with pure water permeability, MWCO (molecular weight cut-off), contact angle, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results demonstrated that the Bio-Ag0-6 nanoparticles well dispersed into PES matrix without aggregation. Bio-Ag0-6 slightly increased the hydrophilicity of the PES membranes, improved the water permeability and did not sacrifice the selectivity of BSA. The protein adsorption on the membrane surface decreased significantly due to the increased hydrophilicity and the improved smoothness of membrane surfaces. The evaluation of silver release from the composite membranes indicated the good stability of immobilized Bio-Ag0-6 in the membranes. The results of disk diffusion test revealed the excellent antibacterial activity of the nanocomposite membranes. In addition, the sludge immersion and the bacterial suspension filtration experiments showed that the Bio-Ag0-6/PES composite membranes not only prevent the bacteria attachment on the membrane surface but also inhibit the reproduction and development of biofims. The Bio-Ag0-6/PES composite membranes were considered to be an effective strategy to decrease the biofouling in the membrane process.

Critical flux of surface-patterned ultrafiltration membranes during cross-flow filtration of colloidal particles

Previous work has suggested that membrane patterning is a promising approach to fouling mitigation. In this systematic study, we describe performance metrics for the cross-flow filtration of colloidal suspensions through ultrafiltration membranes with lithographically patterned surfaces. The effects of particle size, cross-flow velocity, pattern size, and flow configuration on membrane performance are specifically considered. Using an unpatterned membrane as a reference, results show that the presence of surface patterns increases the critical flux associated with filtration of colloidal feed solutions. For the patterned membranes, the critical flux increases with particle size, cross-flow velocity, the angle between the feed flow and the pattern lines, and the pattern height. These experimental findings can be correlated with a back-transport mechanism such as shear-induced diffusion, which ultimately increases the threshold permeation flux associated with the onset of particle deposition.

Fouling of enhanced biological phosphorus removal–membrane bioreactors by humic-like substances

Fouling by free extracellular polymeric substances was studied in an enhanced biological phosphorus removal–membrane bioreactor. It was demonstrated that the free extracellular polymeric substances, primarily consisting of humic-like substances, were adsorbed to the membrane used in the enhanced biological phosphorus removal–membrane bioreactor plant. Infrared analyses indicated the presence of the humic-like substances on the membrane’s active surface after filtration of the free extracellular polymeric substances suspension. Scanning electron microscopy showed the presence of a gel layer on the membrane surface after filtration of the free extracellular polymeric substances suspension. The gel layer caused a significant decline in water flux. This layer was not entirely removed by a backwashing, and the membrane’s water flux could not be re-established. The membrane used in the enhanced biological phosphorus removal–membrane bioreactor plant showed infrared spectra similar to that fouled by the free extracellular polymeric substances suspension in the laboratory. Thus, the results of this study show the importance of humic-like substances in irreversible fouling of enhanced biological phosphorus removal–membrane bioreactor systems.

Properties of Selick's filtration of the double suspension E2

To help study the double suspension [Formula: see text] when localised at a prime p, Selick filtered Ω2S2n+1 by H-spaces which geometrically realise a natural Hopf algebra filtration of H*(Ω2S2n+1;ℤ/p). Later, Gray showed that the fiber Wn of E2 has an integral classifying space BWn and there is a homotopy fibration [Formula: see text]. In this paper we correspondingly filter BWn in a manner compatible with Selick's filtration and the homotopy fibration [Formula: see text], study the multiplicative properties and homotopy exponents of the spaces in the filtrations, and use the filtrations to filter exponent information for the homotopy groups of S2n+1. Our results link three seemingly different in nature classical homotopy fibrations given by Toda, Selick and Gray and make them special cases of a systematic whole. In addition we construct a spectral sequence which converges to the homotopy groups of BWn.

A microtubular all CNT gas diffusion electrode

We report a microtubular gas diffusion electrodes made of multi-walled carbon nanotubes (MWCNT). The electrodes were prepared by inside-out cake filtration of an aqueous MWCNT suspension onto a microfiltration hollow fiber (HF) membrane, followed by washing out the surfactant, drying and removal of the all CNT microtube from the HF membrane. Length, outer diameter, and wall thickness of the tubular electrodes are: up to 44cm, ~1.7mm and 275μm, respectively. The BET surface area is 200m2/g with a porosity of 48–67% and an electrical conductivity of~20S/cm. Application of this microtubular Gas Diffusion Electrodes (GDE) was studied for the oxygen reduction reaction (ORR) in divided and undivided electrochemical cells. Oxygen supply into the lumen of the tubular electrodes resulted in much higher current densities for ORR than in experiments where the electrolyte was saturated by bubbling with pure oxygen. Within the 0.25–1.0bar pressure (gauge) region, higher ORR rates were achieved at lower pressure. We also show that H2O2 production is possible using the new GDE. We propose to use such novel electrodes for the fabrication of tubular electrochemical reactors, e.g. fuel cells, H2O2 generators, CO2 reduction and other processes that involve GDE application.

Nanostructured membranes based on native chitin nanofibers prepared by mild process

Procedures for chitin nanofiber or nanocrystal extraction from Crustaceans modify the chitin structure significantly, through surface deacetylation, surface oxidation and/or molar mass degradation. Here, very mild conditions were used to disintegrate chitin fibril bundles and isolate low protein content individualized chitin nanofibers, and prepare nanostructured high-strength chitin membranes. Most of the strongly ‘bound’ protein was removed. The degree of acetylation, crystal structure as well as length and width of the native chitin microfibrils in the organism were successfully preserved. Atomic force microscopy and scanning transmission electron microscopy, showed chitin nanofibers with width between 3 and 4nm. Chitin membranes were prepared by filtration of hydrocolloidal nanofiber suspensions. Mechanical and optical properties were measured. The highest data so far reported for nanostructured chitin membranes was obtained for ultimate tensile strength, strain to failure and work to fracture. Strong correlation was observed between low residual protein content and high tensile properties and the reasons for this are discussed.

Impact of organic crop management on suppression of bacterial seedling diseases in rice

Organic farming systems can effectively control the pathogens that cause plant diseases. When rice seedlings inoculated with Burkholderia glumae at germination were cultivated on each of three independent organic soils supplied by organic growers, or on conventional soil as a control, development of seedling rot symptoms was significantly suppressed on all organic soils, but not on conventional soil. This disease-suppressive activity of the organic soils was also observed for rice seedling damping-off disease caused by Burkholderia plantarii. Interestingly, such disease suppression was completely compromised on organic soils sterilized at 121 °C, indicating biological activity included in organic soils seems to be associated with the suppression of rice seedling diseases. To explore the putative biological factor(s) conferring the disease-suppressive activity of organic soils, we isolated bacteria from the filtrates of organic soil suspensions. Among these filtrates, two bacterial isolates could suppress development of bacterial seedling rot symptoms, whereas Escherichia coli as a control could not. The 16S rDNA and rpoD nucleotide fragment sequences of two bacterial isolates conferring the observed disease-suppressive activity were highly homologous to those of Pseudomonas sp. Furthermore, phylogenetic analysis of these nucleotide sequences suggested that two isolates placed in the P. fluorescens group. These results reveal that certain Pseudomonas sp. that inhabit organic soils likely play a role in the suppression of rice seedling diseases in organic farming systems.

Highly Thermally Conductive Papers with Percolative Layered Boron Nitride Nanosheets

In this work, we report a dielectric nanocomposite paper with layered boron nitride (BN) nanosheets wired by one-dimensional (1D) nanofibrillated cellulose (NFC) that has superior thermal and mechanical properties. These nanocomposite papers are fabricated from a filtration of BN and NFC suspensions, in which NFC is used as a stabilizer to stabilize BN nanosheets. In these nanocomposite papers, two-dimensional (2D) nanosheets form a thermally conductive network, while 1D NFC provides mechanical strength. A high thermal conductivity has been achieved along the BN paper surface (up to 145.7 W/m K for 50 wt % of BN), which is an order of magnitude higher than that in randomly distributed BN nanosheet composites and is even comparable to the thermal conductivity of aluminum alloys. Such a high thermal conductivity is mainly attributed to the structural alignment within the BN nanosheet papers; the effects of the interfacial thermal contact resistance are minimized by the fact that the heat transfer is in the direction parallel to the interface between BN nanosheets and that a large contact area occurs between BN nanosheets.

Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes

Graphene-based materials can have well-defined nanometer pores and can exhibit low frictional water flow inside them, making their properties of interest for filtration and separation. We investigate permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions. The laminates are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves, blocking all solutes with hydrated radii larger than 4.5 angstroms. Smaller ions permeate through the membranes at rates thousands of times faster than what is expected for simple diffusion. We believe that this behavior is caused by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The anomalously fast permeation is attributed to a capillary-like high pressure acting on ions inside graphene capillaries.

Enhanced antibiofouling of RO membranes via polydopamine coating and polyzwitterion immobilization

It has been reported that polyzwitterions (PZs) can significantly improve the antibiofouling properties of membrane surfaces. In addition, it is known that polydopamine (PDA) can deposit non-selectively from solution onto virtually any solid surface and creates a versatile surface for further modification through its reactive groups. In this paper, we attempted to use a PDA coating as a precursor layer to enhance the durability and antibiofouling potential of a PZ-immobilized membrane. The deposition of PDA and PZ was confirmed by X-ray photoelectron spectroscopy. The hydrophilicity was not markedly increased by surface modification. Moreover, the membrane surface charge density was changed from negative to neutral by PZ immobilization. Nevertheless, an improvement in antibiofouling properties was confirmed by cross-flow filtration of a bacterial (Pseudomonas putida) suspension. The high antiadhesion properties of membranes modified with a PDA coating and/or PZ immobilization was confirmed by scanning electron microscope surface images after 1200min filtration of the bacterial suspension. Moreover, the PDA precursor layer was confirmed to increase the stability of a PZ layer immobilized on the membrane surface by bacterial suspension filtration experiments after one month of immersion in 2M NaCl aqueous solution.

Biofouling resistance of reverse osmosis membrane modified with polydopamine

It has been reported that surface modification with polydopamine (PDA) increases the hydrophilicity and the negative charge density of membrane surfaces, which improves their antifouling potential against organic foulants. Thus, in this paper, we attempted to modify a reverse osmosis (RO) membrane with PDA to improve antibiofouling potential. The deposition of PDA was confirmed by several methods, including X-ray photoelectron and Fourier-transform infrared spectroscopy. However, increases in hydrophilicity and negative charge density were not clearly observed. Nevertheless, the improvement of antibiofouling properties was confirmed by cross-flow filtration of a bacterial (Pseudomonas putida) suspension. The high antiadhesion property of the PDA-modified membrane was confirmed by scanning electron microscope surface images after 1200minute continuous filtration of the bacterial suspension. In addition, it was confirmed by using a shake flask test with Escherichia coli that the PDA-modified membrane had a bactericidal property. Using shake flask tests in the different pH solutions, it was concluded that the antibiofouling property of PDA-modified membranes could be attributed to the bactericidal property of protonated amine groups of PDA deposited on the membrane surface.

Investigation of the dynamical slowing down process in soft glassy colloidal suspensions: comparisons with supercooled liquids

The primary and secondary relaxation timescales of aging colloidal suspensions of Laponite are estimated from intensity autocorrelation functions obtained in dynamic light scattering (DLS) experiments. The dynamical slowing down of these relaxation processes are compared with observations in fragile supercooled liquids by establishing a one-to-one mapping between the waiting time since filtration of a Laponite suspension and the inverse of the temperature of a supercooled liquid that is rapidly quenched towards its glass transition temperature. New timescales associated with primary and secondary relaxation processes, such as the characteristic timescale associated with the slowdown of the secondary relaxation process and the glass transition time, are extracted to describe the phenomenon of dynamical arrest in Laponite suspensions. In results that are strongly reminiscent of those extracted from supercooled liquids approaching their glass transitions, it is demonstrated that a strong coupling exists between the primary and secondary relaxation processes of aging Laponite suspensions in the cage-forming regime. Furthermore, the experimental data presented here clearly demonstrate the self-similar nature of the aging dynamics of Laponite suspensions within a range of sample concentrations.

Multistage centrifugation method for determination of filtration and consolidation properties of mineral and biological suspensions using the analytical photocentrifuge

The article describes a new method of multistage centrifugation (MC) for determination of filterability (local filtration and consolidation properties) of mineral and biological suspensions. The method comprises centrifugal compression–permeability and sedimentation–consolidation experiments, performed with the help of analytical photocentrifuge at different centrifugal rotation speeds. The experimental procedure implies determination of the analytical centrifugation curves: dependencies of (i) sediment height on centrifugal acceleration in sedimentation–consolidation experiments and (ii) permeate volume and filter cake dryness on centrifugation time and centrifugal acceleration in filtration–consolidation experiments. The combined analysis of these curves yields the pressure dependencies of local cake dryness, specific cake resistance, and consolidation coefficient in the wide range of solid pressure (5×103–5×105Pa). Application of MC requires a relatively small quantity of suspension (about 2ml).The method was tested for suspensions with different filterabilities and compressibilities: calcium carbonate, kaolin and yeast suspensions. The pressure dependencies of cake dryness, specific cake resistance, and consolidation coefficient, determined by MC, were in correspondence with those determined in the series of conventional constant pressure dead-end filtration–consolidation experiments.

Strongly‐Coupled Freestanding Hybrid Films of Graphene and Layered Titanate Nanosheets: An Effective Way to Tailor the Physicochemical and Antibacterial Properties of Graphene Film

An effective way to tailor the physicochemical properties of graphene film is developed by combining colloidal suspensions of reduced graphene oxide (rG‐O) nanosheets and exfoliated layered titanate nanosheets for the fabrication of freestanding hybrid films comprised of stacked and overlapped nanosheets. A flow‐directed filtration of such mixed colloidal suspensions yields freestanding hybrid films comprised of strongly‐coupled rG‐O and titanate nanosheets with tunable chemical composition. This is the first example of highly flexible hybrid films composed of graphene and metal oxide nanosheets. The intimate incorporation of layered titanate nanosheets into the graphene film gives rise not only to an increase of mechanical strength but also to increased surface roughness, chemical stability, and hydrophilicity; thus, the physicochemical properties of the graphene film can be tuned by hybridization with inorganic nanosheets. These freestanding hybrid films of rG‐O‐layered titanate show unprecedentedly high antibacterial property, resulting in the complete sterilization of Escherichia coli O157:H7 (≈100%) in the very short time of 15 min. The antibacterial activity of the hybrid film is far superior to that of the pure graphene film, underscoring the beneficial effect of the layered metal oxide nanosheets in improving the functionality of the graphene film.

Porphyrin-silica microparticle conjugates as an efficient tool for the photosensitised disinfection of water contaminated by bacterial pathogens

A tetracationic meso-substituted amphiphilic porphyrin (abbreviated as C14) was encapsulated within silica microparticles to yield a conjugate with a mean particle diameter of ca. 0.9 μm. The conjugate displayed a complete stability for at least 3 months when suspended in a neutral aqueous medium. The encapsulated C14 underwent a limited photobleaching when the conjugate was exposed to full spectrum visible light. Illumination of the silica microparticle-bound C14 by visible light resulted in the generation of singlet oxygen and induced a decrease in the survival of 4 log for a 20 min irradiation of the Gram-positive bacterium meticillin-resistant Staphylococcus aureus (MRSA) and a 30 min irradiation of the Gram-negative bacterium Escherichia coli (E. coli). Under identical experimental conditions photoexcited free C14 caused a decrease in viability of 5 log for MRSA and 6 log for E. coli. When the conjugate loaded with 12 μM C14 was added to a water sample contaminated with MRSA (10(8) cells per ml) a tight association of the bacterial cells with the silica microparticle-porphyrin system was achieved. Subsequent illumination of the conjugate with visible light (30 min, 100 mW cm(-2)) caused a 3 log reduction in the population of MRSA cells in the water sample. Importantly, the conjugate was readily recovered by filtration of the aqueous suspension and shown to maintain a high antibacterial photoactivity when introduced into a new MRSA-contaminated medium and irradiated.