Influence of particle concentration on initial collection efficiency and surface coverage in porous media filtration

Four sizes (0.095, 0.53, 1.0 and 2.01 μm) of polystyrene latex particles were used to prepare monodispersed suspensions at three different ionic strengths (10³,10^-2.5 and 10^-2 M KCl). Filtration experiments were conducted using those suspensions in a filter column with glass beads as porous medium. The filter bed depth and the filtration velocity were kept at 5 cm and 1 m/h, respectively. When suspensions with equal mass concentrations (0.2 mg/L) or equal surface area concentrations (0.12 cm²/mL) were filtered through the system, the largest particles exhibited higher initial single collector efficiency, ⪯. The difference between the ? of largest particles and the smaller particles was prominent for suspensions with equal surface area concentrations at higher ionic strengths. The collision efficiency,α of those particles exhibits higher values at higher ionic strengths. Both at equal mass concentration and equal surface area concentration,α is only slightly dependent on particle sizes when compared to its dependence on ionic strength. Further, it was found that the specific surface coverage was similar for 0.095 μm, 0.53 μm and 1.0 μm particles during the transient stage of filtration at any ionic strength when the surface area concentrations of those suspension were equal.     

Einsatz von Magnetfiltern in der Bioverfahrenstechnik. Teil 3 – Neues Messverfahren zur Quantifizierung von Magnetbeads in strömenden Suspensionen

High‐gradient magnetic separation (HGMS) allows solid/solid/liquid separation in one step and can therefore be used as first capture step in downstream processing of biotechnology products. Magnetic beads are retained in the filter compartment while biomass, solvent and dissolved substances should pass the magnetic filter unhindered. During magnetic filtration agglomeration areas of magnetic beads continuously build up and it is possible that the biomass drags with it some magnetic beads and hence a part of the sorbed product as well. For proper in‐process operation of a HGMS filter, it is necessary to measure the concentration of the magnetic beads in the suspension at the outlet of the filter. A novel measurement technique using a flow‐through magnetic sensor was developed which allows quantifying the magnetic beads in flowing suspensions.     

Tangential Flow Ultrafiltration Allows Purification and Concentration of Lauric Acid-/Albumin-Coated Particles for Improved Magnetic Treatment

Superparamagnetic iron oxide nanoparticles (SPIONs) are frequently used for drug targeting, hyperthermia and other biomedical purposes. Recently, we have reported the synthesis of lauric acid-/albumin-coated iron oxide nanoparticles SEON^LA-BSA, which were synthesized using excess albumin. For optimization of magnetic treatment applications, SPION suspensions need to be purified of excess surfactant and concentrated. Conventional methods for the purification and concentration of such ferrofluids often involve high shear stress and low purification rates for macromolecules, like albumin. In this work, removal of albumin by low shear stress tangential ultrafiltration and its influence on SEON^LA-BSA particles was studied. Hydrodynamic size, surface properties and, consequently, colloidal stability of the nanoparticles remained unchanged by filtration or concentration up to four-fold (v/v). Thereby, the saturation magnetization of the suspension can be increased from 446.5 A/m up to 1667.9 A/m. In vitro analysis revealed that cellular uptake of SEON^LA-BSA changed only marginally. The specific absorption rate (SAR) was not greatly affected by concentration. In contrast, the maximum temperature T_max in magnetic hyperthermia is greatly enhanced from 44.4 °C up to 64.9 °C by the concentration of the particles up to 16.9 mg/mL total iron. Taken together, tangential ultrafiltration is feasible for purifying and concentrating complex hybrid coated SPION suspensions without negatively influencing specific particle characteristics. This enhances their potential for magnetic treatment.     

Wastewater filtration performance of multilayer glassy microporous filters

The glassy composition (quartz, clinoptilolite and frit glass mixture) provides a filter having glassy pore wall microstructure and thus enables easily cleaning through the filter recovery by back flushing. The filter was obtained as multilayer compaction by one step slip cast-processing where a cylindrical filter, consisting of filtration layer on granular assemblies with specific interlayer was shaped by a fine particle migration phenomenon. The multilayer compaction has low resistance to liquid flow and thus the filter great potential to use for wastewater filtration. It is known that high capacity filtration also requires correct pore size/interval with respect to filtered particles. In this study, a wastewater overflow from marble factory (0.035 wt.% of solid with a size distribution of 0.58-1.46 μm) was filtered by different pore sizes of the glassy filters (pore size intervals: 0.4-10 μm, 0.2-4 μm, 0.1-1.5 μm and 0.04-2 μm) and significantly different filtering capacities was obtained; the irreversible fouling capacities were determined between 2.9 and 8.5 m³ of filtrate per m² of the filter area through the filtration produced 5 min intervals. The filtration pressure was 5 bar and backflushing was achieved at 1 bar. The high filterability (8.1 m³/m² in 5 min) with high filtrate clarity (∼0.5 nephelometric turbidity units) could be obtained using finer pore sized filters. The large size filter was seriously clogged during the filtration.     

Separation of sago starch from model suspensions by tangential flow filtration

Sago starch producing mills in Malaysia generate approximately 20 tons of effluent per ton of starch produced. The effluent contains mainly starch and very low concentrations of nitrogenous compounds. The starch could be recoverable by Tangential Flow Filtration (TFF). The aim of this study was to apply TFF to separate the starch from 1% (w/v) model suspensions in simulated sago effluent. Polysulfone membrane filter cassettes of 0.45 µm pore size and 0.1 m² were used for these experiments. Fifty-liter of a starch suspension was concentrated to less than 10-L. The main finding in this study was that increasing membrane filtration area improved the filtration efficiency from 81% to 85.4%, when lower transmembrane pressure (TMP) was employed. Turbidity, total suspended solids, and chemical oxygen demand before and after the treatment were significantly different (p?<?0.05). In conclusion, TFF functioned efficiently to separate sago starch from suspensions. It was found that membrane area and low TMP enhanced the flux rate and minimized the reversible clogging. Moreover, membrane permeability was recovered and cleaned almost to its original permeability.     

Preliminary study on suspension plasma sprayed ZrO2 + 8 wt.% Y2O3 coatings

ZrO₂ + 8 wt.% Y₂O₃ powder of a mean diameter d_VS = 38 μm was milled to obtain fine particles having mean size of d_VS = 1 μm. The fine powder was used to formulate a suspension with water, ethanol and their mixtures. The zeta potential of obtained suspensions was measured and found out to be in the range from −22 to −2 mV depending on suspension formulation. The suspension was injected through a nozzle into plasma jet and sprayed onto stainless steel substrates. The plasma spray experimental parameters included two variables: (i) spray distance varying from 40 to 60 mm and (ii) torch linear speed varying from 300 to 500 mm/s. The microstructure of obtained coatings was characterized with scanning electron microscope (SEM) and X-ray diffraction (XRD). The coatings had porosity in the range from 10% to 17% and the main crystal phase was tetragonal zirconium oxide. The scratch test enabled to find the critical load in the range of 9-11 N. Finally, thermal diffusivity of the samples at room temperature, determined by thermographic method, was in the range from 2.95 × 10⁻⁷ to 3.79 × 10⁻⁷ m²/s what corresponds to thermal conductivities of 0.69 W/(mK) and 0.97 W/(mK) respectively.     

Cross-flow separation of yeast cell suspensions using a sintered stainless steel filter tube

A new design of cross-flow filtration unit, the Transep filter, has been investigated for the separation of slurries of Saccharomyces cerevisiae. Porous cylindrical sintered stainless steel tubes of 2 μm and 3 μm nominal pore size ratings were used as filter media. Filtration rates were measured for cell suspensions ranging from 3 to 25 kg m^?3. The 3 μm filter produced particle-free filtrates at average rates from 1.25 m³ m^?2 h^?1 which declined to half this value over the range of cell concentrations studied.     

Development of a high-performance cake-less continuous filtration system

A new cake-less continuous filtration system with a rotating disk filter and slurry prepared in a well-dispersed state is discussed in this paper. It is expected that the new system can concentrate a feed suspension much more than traditional filtration systems and that the concentrate can be discharged by the filtration pressure without a scraping device. We tried to filter some difficult to filter materials such as sericite, hydrolyzed cellulose, pulp wastewater and algal suspension. Concentrated slurries of sericite and hydrolyzed cellulose were discharged at the 35 vol% and 12 mass%, respectively. The algal suspension and the pulp wastewater were concentrated up to 8 times more than the concentration of feed suspensions. The concentrates of every sample retained fluidity and flowed out of the new system by way of the filtration pressure.In this system, it was shown that the filtration flux increased with the rotation speed. At lower rotation speeds, the filtration flux was independent of pressure. Conversely at higher rotation speeds, the filtration flux increased along with the pressure. This dependency was clearer in the case of the large disk than when the small disk was used. We also proposed a model for a sweeping mechanism in this system which is explained in the above results.     

Magnetic field effects in electrochemical reactions

The influence of an external magnetic field B on the electrochemical behaviour of the systems Cu²⁺/Cu, Ni²⁺/Ni, and [IrCl₆]²⁻/[IrCl₆]³⁻ has been studied. In the case of Cu depositions in an electrochemical cell with a large ratio of the electrode area and the cell volume the increase of the limiting current density with B can be explained with the interplay of natural convection and the Lorentz force acting on the resulting flow profile (magneto hydrodynamic or MHD effect). Ni depositions also show an MHD effect as well as a tendency to form more fine grained material in the presence of a magnetic field. The results on the homogeneous redox system [IrCl₆]²⁻/[IrCl₆]³⁻ at 50 μm diameter micro electrodes are in qualitative agreement with recently proposed relationships to describe the influence of a B field on the limiting current density.     

Magneto-optical investigation and hyperfine interactions of copper substituted Fe3O4 nanoparticles

Copper substituted Fe₃O₄ nanoparticles (NPs) (Cu_xFe_1−xFe₂O₄ (0.0≤x≤1.0)) were synthesized by polyol method and the effect of Cu²⁺ substitution on structural, magnetic and optical properties of Fe₃O₄ was investigated. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), UV–Visible spectroscopy and Vibrating sample magnetometer (VSM) were used to study the physical properties of the products. The room temperature (RT) magnetization (σ–H) curves revealed the superparamagnetic nature of the products. The extrapolated specific saturation magnetization (σ_s) decreases from 42.69 emu/g to 14.14 emu/g with increasing Cu content (x). The particle size dependent Langevin fit studies were applied to determine the magnetic particle dimensions (D_mag). The average magnetic particle diameter is about 9.89 nm. The observed magnetic moments of NPs are in range of (0.61–1.77) µ_B and rather less than 4 µ_B of bulk Fe₃O₄ and 1 µ_B of bulk CuFe₂O₄. Magnetic anisotropy was assigned as uniaxial and calculated effective anisotropy constants (K_eff) are between 10.89×10⁴ Erg/g and 26.95×10⁴ Erg/g. The average value of magnetically inactive layer for Cu_xFe_1−xFe₂O₄ NPs was calculated as 1.23 nm. The percent diffuse reflectance spectroscopy (DR%) and Kubelka–Munk theory were applied to determine the energy band gap (E_g) of NPs. The extrapolated optical E_g values from Tauc plots are between minimum 1.98 eV to 2.31 eV. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer splitting, quadrupole splitting and hyperfine magnetic field values on Cu⁺² ion substitution have been determined. Although, the Mössbauer spectra for the sample x=0.2 and 0.8 are composed of paramagnetic doublets, ferromagnetic sextets were also formed for other products.     

Effect of suspension medium on the electrophoretic deposition of hydroxyapatite nanoparticles and properties of obtained coatings

The suspensions of hydroxyapatite (HA) nanoparticles were prepared in different alcohols. The zeta potential of HA nanoparticles was the highest in butanolic suspension (65.65 mV) due to the higher adsorption of RCH₂OH₂⁺ species via hydrogen bonding with surface P3OH group of HA. Electrophoretic deposition was performed at 20 and 60 V/cm for different times. Deposition rate was faster in low molecular weight alcohols due to the higher electrophoretic mobility of HA nanoparticles in them. The coating deposited from butanolic suspension had the highest adhesion strength and corrosion resistance in SBF solution at 37.5 °C. The surface of this coating was covered by apatite after immersion in SBF solution for 1 week.     

Effects of pore size, suspension concentration, and pre-sedimentation on the measurement of filter medium resistance in cake filtration

Theoretical and experimental study was conducted on the factors influencing the measurement of filter medium resistance by Ruth’s equation. It was determined that a filter medium having small pore size does not always give high filter medium resistance. The appropriate pore size of filter medium for filtration was analysed. The resistances of filter media measured with thick suspensions by Ruth’s equation have negative values. This phenomenon can be analyzed as the effect of sedimentation during the long filtration time due to thick suspension. When sedimentation occurs before the start of filtration, the filter medium resistance measured by Ruth’s equation gives a large value. It was determined that the result of the filtration of sediment was included in the filter medium resistance. A new method for measuring filter medium resistance by the filtration of the sediment is proposed. This method excludes the effects of suspension concentration and pre-sedimentation.     

Unsteady-State Permeate Flux of Crossflow Microfiltration: Effect of Particle Size Distribution

Abstract

A mathematical model based on a hydrodynamic theory and mass balance was developed for the prediction of the unsteady-state permeate flux in crossflow microfiltration under the influence of particle size distribution. Experiments were also conducted in a membrane filtration cell to verify this model. Spherical polystyrene latex particles of 0.303, 0.606, and 1.020 μm were used to make suspensions of various particle size distributions. The flow of the suspension in the channel of the filtration cell was controlled under the laminar flow region. It was found that the unsteady-state permeate flux increased as the mean particle size of the suspension was increased. Moreover, the model predicted satisfactorily the unsteady-state permeate flux under the effect of particle size distribution.     

Novel pre-treatment method for seawater reverse osmosis: Fibre media filtration

A high rate fibre filter was used as a pre-treatment to seawater reverse osmosis (SWRO) to reduce membrane fouling. Seawater was drawn from Chowder Bay where the Sydney Institute of Marine Science, Australia is located. A lab-scale fibre filter with a height of 1000 mm and a diameter of 30 mm was used in conjunction with in-line coagulation. The effect of operating the fibre filter with different packing densities (105, 115 kg/m³) and filtration velocities (40, 60 m/h) was investigated in terms of silt density index (SDI₁₀), modified fouling index (MFI), pressure drop (ΔP), turbidity and molecular weight distribution (MWD). The use of in-line coagulation improved the performance of fibre filter as measured by the MFI and SDI. Regardless of filtration velocity and packing density the MFI and SDI₁₀ values remained low as did the turbidity until the end of the filtration run. The MWD analysis showed the removal efficiencies of organic materials like biopolymers, fulvic acids, low MW acids for even experiments with the highest filtration velocity (60 m/h) and lowest packing density (105 kg/m³). This pre-treatment has a small foot print as it has the capacity of operating at a very high filtration velocity.     

Stabilization of highly-loaded boron carbide aqueous suspensions

Injection molding of boron carbide (B₄C) slurries affords the production of complex-shaped personal armor. To injection mold, however, requires preparation of a well dispersed, flowable suspension with >45 vol% B₄C loadings to reduce porosity that must be removed during sintering. In the present study, the preparation of highly-loaded B₄C suspensions is investigated using zeta potential and rheological measurements, varying dispersant type, molecular weight, and amount. Of those dispersants investigated, polyethylenimine (PEI) with a molecular weight of 25,000 g/mol was found to produce suspensions with up to 56 vol% B₄C and the requisite rheological properties suitable for injection molding. A PEI concentration of 1.83 mg/m² was established as the appropriate to produce highly-loaded B₄C suspensions. The effect of a prior B₄C powder treatment (ethanol washed or attrition milled) on rheological properties of the suspensions was also investigated. The PEI was completely burned out in argon, nitrogen, and air at 450 °C.     

Dynamic cross flow filtration

The dynamic cross flow filtration with the DYNO filter is a very versatile and economic high performance filtration process especially for suspensions with critical separation characteristics. Thickening, washing and clarifying of suspensions but also a classifying sieve filtration can be performed with the DYNO filter in a continuous operation with permanently high throughput rates. The principle of the dynamic high shear filtration ensures almost ideally physical conditions for the separation process. Contrary to classical cross flow filters a repeated recirculation of the suspension is not necessary for attaining the separation target. In the DYNO filter suspensions can be highly concentrated up to the flow limit in only one filtration cycle. In most cases, the concentrate is as dry as a firm filter cake and the filtrate is crystal-clear. Sieve filtration tasks for separating of coarse grain are performed with high concentration factors of up to 1000. Thus, the coarse fraction is obtained highly concentrated.     

Effect of Pore Size and Particle Size Distribution on Granular Bed Filtration and Microfiltration

Abstract

The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.     

Laboratory cake filtration testing using constant rate

A precipitated calcium carbonate with Sauter mean diameter of 7.5 μm was filtered under conditions of constant rate and constant pressure in a comparative laboratory investigation. The specific cake resistance to filtration was found to vary between 1 × 10⁹ and 1 × 10¹¹ m kg⁻¹, depending on the applied pressure, and the corresponding filter cake volume concentrations were between 0.42 and 0.54 (v/v). The calculated specific resistance, from the particle size distribution data and the Kozeny–Carman equation is one order of magnitude lower than that measured, even though the solids were extremely robustly characterised. Practical filter testing rather than design based on size distributions is known to be essential. However, the conventional approach is to use constant pressure laboratory tests, the results presented here demonstrate that constant rate filtration is a more reliable method for data acquisition, especially when determining the filter medium resistance, and readily available laboratory equipment is adequate for use.     

Aqueous and Nonaqueous Colloidal Processing of Difficult‐to‐Densify Ceramics: Suspension Rheology and Particle Packing

Aqueous and nonaqueous colloidal processing of zirconium diboride (ZrB₂) and boron carbide (B₄C) has been investigated. The aqueous and nonaqueous ZrB₂ and B₄C suspension formulations have been optimized. The suspensions were cast into green bodies using slip casting. The correlation between the state of dispersion with the rheological properties of the suspensions and the resulting packing density was observed in both aqueous and nonaqueous processing. The attractive interactions between powder particles in water were difficult to overcome with electrical double layer or electrosteric repulsion. Reasonably low viscosity aqueous ZrB₂ suspensions up to 45 vol% solids could be prepared. It was not possible to produce low viscosity (viscosity below 1 Pa·s at shear rate of 100 s^?1) aqueous B₄C suspensions with solid content above 30 vol%. Slip casting of the weakly aggregated ZrB₂ suspensions resulted in low packing densities (~55% relative density) of the green bodies. On the other hand, dispersion of powder particles in nonaqueous media (cyclohexane and dodecane) enabled suspensions with lower viscosities and a higher maximum solid concentration (up to 50 vol%) to be prepared. The well‐dispersed nonaqueous suspensions promoted an efficient particle packing, resulting in higher green densities (64% and 62% relative density for ZrB₂ and B₄C, respectively) compared to aqueous processing. The significantly high green densities are promising to allow densification of the materials at lower sintering temperature.     

Gas holdup in pulp fibre suspensions: Gas voidage profiles in a batch-operated sparged tower

Gas holdup in a semi-batch operated slurry (pulp fibre suspension) bubble column was investigated for two pulp types (softwood and hardwood kraft pulps) over a range of suspension mass concentrations (C_m=0–9% by mass) and superficial gas velocities (U_g=0.0027–0.027 m/s). Three techniques were used: height difference between gassed and ungassed operation; pressure difference as a function column height; and electrical resistance tomography (ERT). Depending on the technique used the average, axial and radial holdup profiles could be determined. In the pulp suspensions, the ERT determined gas holdups correlated well with those determined using the differential height method. In water, the ERT determined gas holdups were significantly lower, but the agreement was significantly improved by increasing the background conductivity by adding 1 g/L salt to the water. This, however, reduced the overall gas holdup due to the effect of the electrolyte on bubble coalescence. Other differences between the three measurement techniques were attributed to limitations in the detection methods and the averaging procedures used to compare results.The presence of pulp fibres reduced gas-holdup at all gas flow rates and suspension concentrations studied and is attributed to increased bubble coalescence which increases bubble size and consequently bubble rise velocity through the suspension. Gas holdup (as determined by ERT) increased with column height. The radial gas profiles were non-uniform and more peaked than the corresponding water profiles. At low suspension concentrations this was attributed to asymmetric suspension recirculation within the column. As suspension concentration increased, channels formed in the suspension with the average void fraction leveling off to a plateau.