Specific Resistance Of Filter Cake Research Articles

Investigating the effects of process parameters on the filtration performance of ferric hydroxide in a continuous MSMPR reactor

Iron removal in the nickel industry is achieved by precipitation and filtration, and for enhanced process efficiency, the filtration step must be improved. A mixed-suspension-mixed-product-removal (MSMPR) reactor set-up operating at steady-state was established, simulating industrial conditions, and the effect of temperature and residence time on filtration performance of the precipitated akaganéite was investigated. Increasing the reaction temperature and residence time improved the filtration performance, where temperature had the most prominent effect, reducing the specific filter cake resistance with over one order of magnitude from 25 °C to 75 °C. However, there must be a trade-off between temperature increase and cost-effectiveness. A lower moisture content in the filter cakes was also observed with increasing residence time and temperature, which is advantageous in terms of handling of waste and for potential reuse of the iron precipitates. Elevated temperatures resulted in formation of particles with higher crystallinity, lower surface area and higher stability towards aggregation. These particle characteristics were explained by the significant decrease in supersaturation at steady-state at higher temperatures. Variation in residence times, on the other hand, did not affect the solution supersaturation but was still an important parameter on the particle characteristics, which in turn had implications on the filtration performance. The significant changes observed in specific filter cake resistance and filter cake moisture content, but not in supersaturation, with varying residence times were explained by internal rearrangements and locally induced ageing of the particles.

Filtration of kaolinite and coal mixture suspension: Settling behavior and filter cake structure analysis

The filtration of kaolinite-coal mixture suspension was investigated by settling behavior observation and filter cake structure analysis. Three-dimensional X-ray microanalysis was used to analyze filter cake structure. The settling rate and specific filter cake resistance of kaolinite-coal mixture gradually increased with the increasing content of kaolinite in suspension. A high settling rate made filter cake form quickly during filtration, which prevented water to pass through, increasing the specific filter cake resistance. Filter cake structure analysis showed kaolinite trapped fine coal particles into the gap between kaolinite flocs during filtration. The size and number of pores in the filter cake formed by a high kaolinite content mixture were smaller and fewer than that formed by a low kaolinite content mixture. A high specific cake resistance was created by a high kaolinite content mixture. This study provides a novel insight into the filtration of coal slurry in coal mining and cleaning processes.

Combined filtration and oxalic acid leaching for recovering phosphorus from hydrothermally carbonized sewage sludge

Hydrothermal carbonization is a promising pretreatment for the energetic utilization of municipal sewage sludge. However, the carbonized slurry must be dewatered and the valuable compound phosphate recovered. This article reveals a new approach of combined slurry filtration and subsequent phosphate leaching using oxalic acid (18–72 g l−1) in a single apparatus for the first time. A slurry of hydrothermally carbonized sludge was filtered, washed, leached twice with oxalic acid and washed again. A thorough characterization of the filtration performance and the process products was conducted. The suspension is difficult to filter, but the permeability of the filter cake increases during acidic leaching. The specific filter cake resistance of (4.5 ± 2.2) · 1015 m−2 indicates poor filterability of the hydrochar slurry. 41–83% of phosphate and sodium are leached from the hydrochar, while all other investigated inorganics are leached to a lower extent. 12–31% of iron, calcium and manganese are removed from the hydrochar. The relative contents of carbon, hydrogen and oxygen increase in the residual hydrochar after leaching. After leaching, oxalic acid accounts 10.5–16.9% of the dry hydrochar due to adsorption and poor cake washing. Co-leached calcium, bivalent iron and magnesium precipitate from the leachate as oxalate salts. In conclusion, combined filtration and phosphate leaching enables efficient phosphate removal and generates an ash-reduced hydrochar for energetic utilization. However, to enable its technical application, the filtration performance and system integration need to undergo further development.

Factors influencing backwashing operation in the liquid phase after cake filtration

The separation of solids from process streams takes place in almost every process plant. In particular, cake-forming filtration in the liquid environment is advancing as a widespread method of separating low-concentration suspensions from their solids content and offers energy advantages over other separation principles. In addition to the actual separation performance, the filter fabrics must be regularly replaced or regenerated. The reason for this is the growing resistance because of the increasing filter cake thicknesses. Considering the reduction of disposable products, the regeneration of the fabrics is an interesting possibility to reduce costs and to guarantee a stable process control. This can be achieved by means of filter cake discharge. In the course of this regeneration, the filter cake should be discharged as completely as possible so that the fabric reaches the required initial filtrate flow of the previous filtration cycle again.Investigations concerning cake discharge have shown that the regeneration step can be divided into different discharge mechanisms (complete, partial, resuspended) which result in different cleaning qualities. In the context of this study, backwashing processes with different backwashing parameters (pressure, cake thickness) as well as different particle shapes and their influence on the regeneration quality of filter fabrics are presented and discussed.The focus of this work is the investigation of the backwashing process “cake discharge” as a subsequent and necessary step in cake-forming filtration. Within the scope of this study, a test setup was designed which allows the variation of different process variables and tissue-particle combinations. The experimental setup is kept simple and allows easy reproduction of experiments. The aim is the integrated consideration of the influencing variables on the regeneration quality. The variables cake thickness, particle shape and backwash pressure were investigated within the scope of this study.A significant influence of backwash quality on the examined multifilament filter fabric for particle systems ≤20 µm can be attributed to the particle shape and filter cake thickness. Here, a good regeneration quality can be achieved after exceeding a defined filter cake resistance. This depends significantly on the specific filter cake resistance and thus determines the required cake thickness. Particle systems which, due to their shape and size, have a lower specific cake resistance therefore require a higher cake thickness for a good cleaning result. As a rule of thumb, the absolute filter cake resistance can be estimated with ≥4 ∙ 1010 m−1. A possible influence of the backwash pressure was investigated and can be denied in the range of 0.1–2 bar. The necessary backwash volume in l/m2 was constant over this pressure range. Only the regeneration time decreased, which, relative to the filtration time, is considered insignificant.

Regulation of precoating filtration process based on SERS detection technology

The factors affecting a precoating filtration process and its regulation are studied through lab scale and pilot scale tests combined with surface-enhanced Raman spectroscopy. In the classic filtration process, the diatomite filter aids are introduced for precoating to regulate the specific resistance of the filter cake during the filtration process. This approach solves the fast termination of filtration caused by the rapid increase of the specific resistance of filter cake in classic filtration process. Moreover, surface-enhanced Raman spectroscopy is introduced to detect the trajectory of the filter particles moving with the filtrate in different precoating. The key factors, such as median particle size, thickness, and suspension mass concentration of precoating in the filter aids, are determined using lab scale and pilot scale tests. This study provides a foundation for industrial application of precoating filtration processes.

Compression and filtration characteristics of yeast-immobilized beads prepared using different calcium concentrations

ABSTRACTYeast cells were immobilized on calcium alginate beads prepared using different calcium concentrations. The compression properties of the immobilized beads (e.g., softness index and retardation time for compression) were strongly affected by the calcium concentration. The effects of the bead properties on filtration characteristics, such as cake porosity, specific cake filtration resistance, cake compression creeping effect and cake compressibility, were analysed using a dead-end filtration system. The filtration curve of yeast-immobilized beads had an “S” shape, similar to that of soft gel particles. The cake compression behaviour and variation in cake properties were directly reflected on the curve trend. The Voigt in the series model was employed to describe variation in cake porosity with time during a compression. The yeast immobilization increased the bead softness; therefore, the porosity of a cake formed by yeast-immobilized beads was lower than that formed by pure calcium alginate beads. The cakes formed by yeast-immobilized beads possessed a high compressibility of approximately 1.0 and a high softness index of approximately 1.5. The beads prepared using lower calcium concentrations had higher softness, shorter retardation times for compression, higher cake compressibility, lower cake porosity and higher specific cake filtration resistance. The results demonstrated that immobilizing yeast cells on calcium alginate beads is beneficial for retaining higher yeast activity than that of freely suspended yeast. However, the activity levels of yeast immobilized using different calcium concentrations were nearly the same after 3 h. Therefore, using high concentrations of calcium for yeast immobilization is beneficial for improving yeast activity and filtration characteristics.

Impact of pulsed electric field and preheating on the lime purification of raw sugar beet expressed juices

This work discusses the effects of pulsed electric field (PEF) and preheating on the lime purification of raw sugar beet expressed juices. The PEF pre-treatment was applied to sugar beet cossettes before their pressing at 20°C with the PEF strength and duration of respectively E=600V/cm and tPEF=10ms. Alternatively, cossettes were preheated at 80°C for 10min before pressing to produce the thermal juice.A lime-carbonation process was applied for the purification of raw expressed juices. The influences of lime quantity (varied from 0 to 15kg/m3) on the filterability and the quality of juices were investigated. It was shown that the filtration kinetics of cold PEF juice is faster than that of thermal juice leading to lower values of filtration coefficient Fk and specific filter cake resistance α. Analysis showed that thin juices obtained after purification of PEF juices presents better qualitative characteristics than those obtained from thermal expressed juices. For instance, at the optimal lime quantity (10kg/m3), the purified PEF juice was less coloured (540 vs. 1360IU), less turbid and had less proteins and colloids leading to a higher juice purity (0.961 vs. 0.945) comparatively to the purified thermal juice.

Filtration of core–shell colloids in studying the dewatering properties of water-swollen materials

The properties of filter cakes formed by the deposition of suspended particles play important roles in numerous filtration applications. As the properties of suspensions of biological/organic origin differ markedly from classical filtration properties derived from inorganic suspensions, organic polymer particles with core–shell morphology have been synthesized and applied in dead-end filtration experiments. These particles, with a dense polystyrene core and a water-swollen gel-like poly(acrylic acid) shell, have been made with varying shell–core volume ratios and particle sizes. Filtration results show that the specific filter cake resistance is more dependent on the volume fraction of the shell than on particle size, and that the filter cakes exhibit pressure-dependent compressibility with a linear correlation with shell volume fraction. Furthermore, the primary consolidation of the filter cakes was investigated and linked to the particle properties, again exhibiting dependency on both shell fraction and applied pressure.

Cross-Flow Microfiltration of Bacillus Subtilis Broths under Various Culture Times

Bacillus subtilis broths under different culture times are filtered in a cross-flow microfilter. The operating condition effects, such as cross-flow velocity, transmembrane pressure, and broth culture time, on the filtration flux, cake properties, and extracellular polymeric substances (EPS) transmissions are discussed thoroughly. The culture broths contain B. subtilis cells and EPS which is characterized as polysaccharides (hydrocarbons) and proteins. An increase in broth culture time leads to higher concentrations of cells, soluble and extractable EPS. The total protein to polysaccharide concentration ratio in the broths is ca 0.2. However, the soluble polysaccharide concentration is 10-fold higher than that of soluble proteins. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. However, the impact of cross-flow velocity is more significant. The filter cake resistance formed by B. subtilis cells and EPS flocs plays the most important role in determining the overall filtration resistance. The mass and average specific filtration resistance of cake can be estimated using a force balance model and empirical equations. The cake structure and thickness are analyzed using SEM. A thicker and more compact cake may be formed under longer broth culture time. Most soluble polysaccharide and protein molecules have the opportunity to penetrate through the cake and membrane into the filtrate because the solute transmissions are measured as high as 0.75–1.0. The influences of operating conditions on the polysaccharide and protein transmissions are negligible. Therefore, to enhance filtration flux by increasing transmembrane pressure or cross-flow velocity is beneficial to improve separation efficiency, especially by increasing cross-flow velocity.

Enzymatic hydrolysis suspension cross-flow diafiltration using polysulfone hollow fiber module

Glucose and enzyme in a high concentration enzymatic hydrolysis suspension were separated using hollow fiber cross-flow diafiltration. The operating condition effects on the filtration performance are discussed. Over 86% of the enzymes were retained using a 10kDa polysulfone membrane. Most glucose molecules penetrated through the membrane into the filtrate. The major filtration resistances are due to the cake formation on the membrane surface and enzyme blocking in the membrane pores in addition to the appreciable virgin membrane resistance. The cake mass is correlated with the drag force ratio tangential to the filtration directions and the average specific cake filtration resistance is expressed as a power-function of the transmembrane pressure with a cake compressibility of 0.3. The empirical equation related the resistances due to internal membrane fouling to the operating conditions established by conducting experimental data regression. The filtration flux can be estimated accurately by substituting the results calculated using the empirical equations into the basic filtration equation. An increase in cross-flow velocity or transmembrane pressure leads to higher filtration flux. The filtration flux increases ca 2-fold as the cross-flow velocity increases from 0.3 to 1.5m/s under a transmembrane pressure of 60kPa. The filtration flux increases over 3-fold as the transmembrane pressure increases from 20 to 100kPa. Two kinds of modified operating methods are used to improve the filtration flux. A pulse feeding method may increase the filtration flux by 25%, while the step-increase pressure method improves the filtration flux by over 34%. Forming a thin cake under low pressure in the early filtration period has great potential to significantly mitigate membrane pore blocking and enhance filtration flux.

The effect of operating conditions on resistance parameters of filter media and limestone dust cake for uniformly loaded needle felts in a pilot scale test facility at ambient conditions

Resistance parameters are essential for the prediction of pressure drop in bag filters. The reported values for limestone dust differ in magnitude and also depend on operating parameters. In this work, experimental data is provided from a pilot scale pulse-jet regenerated bag filter test facility for three types of needle felts using air and limestone dust at ambient conditions. Results reveal that specific resistance of filter media is independent of velocity while the specific resistance of filter cake increases linearly with filtration velocity. Residual pressure drop is almost constant, independent of upper pressure drop limit. The cake resistance at constant velocity fits to a second degree polynomial whereas it increases linearly with the velocity. A linear relation is reported here for all the cases. The resistance of filter cake decreases at higher upper pressure drop limit.

Influence of operating parameters on cake formation in pilot scale pulse-jet bag filter

Bag filters are commonly used for fine particles removal in off-gas purification. There dust laden gas pervades through permeable filter media starting at a lower pressure drop limit leaving dust (called filter cake) on the filter media. The filter cakeformation is influenced by many factors including filtration velocity, dust concentration, pressure drop limits, and filter media resistance. Effect of the stated parameters is investigated experimentally in a pilot scale pulse-jet bag filter test facility where lime stone dust is separated from air at ambient conditions. Results reveal that filtration velocity significantly affects filter pressure drop as well as cake properties; cake density and specific cake resistance. Cake density is slightly affected by dust concentration. Specific resistance of filter cake increases with velocity, slightly affected by dust concentration, changes inversely with the upper pressure drop limit and decreases over a prolonged use (aging). Specific resistance of filter media is independent of upper pressure drop limit and increases linearly over a prolonged use.

Microfiltration characteristics of Bacillus subtilis fermentation broths

The microfiltration characteristics of Bacillus subtilis broths under different culture conditions were studied. In the no medium addition culture condition the major component in the broth was sole B. subtilis cells. The filtration curve of dt/dv vs. v (reciprocal of filtration flux vs. filtrate volume) can be divided into three regions. After a short relaxation time the tangent slope increases drastically. This implies that significant cell deformation and cake compression occurs in the second region. The average specific cake filtration resistance will reach the maximum value at the filtration curve inflection point. The cake compressibility gradually decreases in the third region because most solid compressive pressures are depleted by the formed compact cake. In the medium addition culture condition the B. subtilis cells and extracellular polymer substances (EPS) flocs concentrations in the broth increase markedly with culture time. The filtration curve tangent slope increases continuously during the entire filtration period because of the highly compressible cake. All proteins in the extra-cellular polymeric substances are retained by the filter cake and membrane during a filtration, while most polysaccharides have the opportunity to penetrate into the filtrate when the culture time exceeds 1 day. Polysaccharide rejection increases with increasing filtration pressure for the 1-day culture broth. However, the filtration pressure has a trivial effect on the polysaccharide rejection for longer culture times. The filter cake resistance formed by B. subtilis cells and EPS flocs plays an important role in determining the overall filtration resistance. A longer culture time and lower filtration pressure are beneficial for protein/polysaccharide separation using microfiltration.

The Role of Polysaccharide on the Filtration of Microbial Cells

The role of polysaccharide on the “dead-end” microfiltration of microbial cells is studied. Yeast and blue dextran are used as typical samples of microbial cells and polysaccharide, respectively. The filter cake becomes more compressible in the early periods of filtration and exhibits much higher filtration resistance when dextran molecules co-exist in the cake structure. A cake compression mechanism is proposed to explain the pressure effects on the cake structure and filtration resistance. For the two-component cakes, the dextran molecules deform easily even under a pressure as low as 30 kPa, while significant yeast deformation is observed when pressure is higher than 100 kPa. It is attributed to the depletion of most solid compressive pressures by deformed dextran molecules. The cake porosity data indicate that the cake compressibility is higher under low filtration pressure, and blue dextran plays a significant role on the cake structure and occupies a considerable volume in the cake. A resistance model is also derived for understanding the relationship between the average specific cake filtration resistance and filtration pressure. The cake filtration resistance is determined by the effective volume fraction of each component in cake and nearly the same as that of blue dextran under low pressure.

Effect of gel particle softness on the performance of cross-flow microfiltration

The gel particle softness effect on cross-flow microfiltration performance is studied. Three kinds of soft gel particles with a similar size distribution but different softness and compression behaviors were prepared and used in these experiments. The particle softness is the most important factor affecting the pseudo-steady filtration flux compared to the other operating variables in the conditions of this study. A filter cake formed by softer particles is compressed into a more compact structure, consequently, resulting in higher filtration resistance and lower filtration flux. The particle deposition probability is analyzed using a force balance model. An increase in particle softness leads to lower particle deposition probability as well as lighter cake mass due to the drastic flux decay. The cake compression during filtration is described using the Voigt in series model. The cake porosity suddenly decreases and the specific cake filtration resistance drastically increases in the early filtration period. The skin cake layer formation in that period plays the most important role in determining the cross-flow microfiltration performance. The cake mass and average specific filtration resistance calculation results using the proposed methods agree fairly with the available experimental data.

Effect of air-sparging on the cross-flow microfiltration of microbe/protein bio-suspension

The effect of air-sparging on the performance of cross-flow microfiltration of microbe/protein bio-suspension is studied. A yeast/BSA binary suspension is separated using a two-parallel-plate cross-flow microfilter. The pseudo-steady filtration flux, cake properties and BSA rejection under various operating conditions are measured and discussed. The filtration flux increases with increasing filtration pressure, suspension and air velocities. The cake mass is significantly reduced by sparging air bubbles due to the increase in wall shear stress; however, this impact becomes trivial when air velocity exceeds 0.04 m/s. The average specific cake filtration resistance increases with increasing air velocity in a bubble flow, while suddenly decreases when the flow pattern changes to a slug flow. A drastic increase in BSA rejection is found as air bubbles are sparged into the filter channel. An increase in air flow velocity leads to higher BSA rejection especially in a slug flow regime. Taking filtration flux and BSA rejection into account, the BSA mass flux transported into filtrate decreases with increasing air velocity. Although sparging air bubbles can effectively enhance filtration flux, it is helpless for the separation of BSA from yeast cells. The results also indicate that the fluid flow pattern plays an important role in determining the filtration performance. The cake mass and BSA rejection in different flow regimes can be modeled using a force balance model for particle deposition and the standard capture equation for depth filtration, respectively.

Selective deposition of fine particles in constant-flux submerged membrane filtration

The selective deposition of fine particles in a constant-flux submerged microfiltration system is studied. The effects of operating conditions, such as filtration flux, injected air flow rate and air bubble size, on the particle deposition probability, cake mass and average specific cake filtration resistance are discussed. Smaller particles have more opportunity to deposit onto the membrane surface. The particle size distribution in the filter cake increases with increasing the filtration flux or bubble size, but with decreasing the injected air flow rate. The external forces exerted on the depositing particles are analyzed based on hydrodynamics and DLVO theory. The drag forces due to suspension flow, permeate flow, and bubble flow play the major role in determining the particle stability on the membrane surface. Interparticle forces are dominant for submicron particles, while gravitational force increases its weight as particle size exceeds 5 μm. A force balance model is used for estimating the particle deposition probability. An increase in filtration flux or a decrease in air flow rate leads to higher particle deposition probability, heavier cake, or lower average specific cake filtration resistance. The deposition probability is higher by injecting bigger bubbles under a specified air flow rate due to the lower bubble generation frequency. Consequently, a decrease in bubble size causes to lighter cake but higher average specific filtration resistance. The validities of the model predictions for particle deposition probability, cake mass and average specific filtration resistance are demonstrated by experimental data.

Effects of Air-Sparging on the Filtration Flux and Cake Properties in Cross-Flow Microfiltration of Size-Distributed Fine Particles

The effect of air-sparging on the performance of cross-flow microfiltration of size-distributed fine particles is studied. The filtration flux and cake properties under various air velocities are measured and discussed. A higher air velocity leads to a lighter cake due to the higher shear stress acting on the membrane surface, especially under a bubble flow regime. However, the decrease in deposited particle size causes higher average specific cake filtration resistance as well as lower pseudo-steady filtration flux. A force balance model is employed to grasp the particle deposition on the membrane surface. The drag forces due to fluid flows play a major role in determining the particle deposition probability. The interparticle forces are dominant for submicron particles, while the inertial lift and gravitational force increase the weights for those particles larger than 10 µm. The occurrences of a minimum deposited probability for 0.2–0.3 µm particles and a maximum value for ca 2 µm particles can be reasonably explained by the force analysis. The particle size distribution in the filter cake, cake mass, average specific cake filtration resistance, and filtration flux can be estimated satisfactorily using theoretical models. In cross-flow microfiltration using a sample including submicron and micron particles, the filtration flux may be increased by sparging a few air bubbles. Air sparging is more effective in enhancing the filtration flux under lower suspension and air velocities due to the particle size effect. However, the flux-enhanced effectiveness decreases with increasing air velocity under bubble flow and becomes negative under a slug flow regime.

Effects of porous gel particle compression properties on microfiltration characteristics

Three kinds of porous gel particles with different compression properties were prepared and used in “dead-end” filtration experiments. Incorporating the conventional cake compressibility index, two additional parameters for particle compression, retardation time and softness index, are introduced to discuss the porous gel particle viscoelastic compression behaviors and filtration characteristics, including the variations of filtration flux, cake mass, cake porosity, water inside the particles and specific cake filtration resistance during filtration. A cake compression mechanism including four stages is proposed to explain the filtration curve trend for d t / d v vs. v for different gel particles. The concave trend in the compression stage is more obvious for gel particles that exhibit longer retardation time or a smaller particle softness index, or under lower filtration pressure. The variation in cake porosity during compression can be described using a Voigt in series model. Cake mass (including dry solid and the internal water) decreases quickly in the early filtration stage because of the rapid percolation of particle internal water, and then increases gradually after the cake compression retardation time due to the formation of new cake layers. A power relationship between the average specific cake filtration resistance and filtration pressure can be regressed. However, the specific cake filtration resistance value varies with time due to both cake and particle compression. A long compression retardation time or a high particle softness index implies that the particles possess high elastic and deformable natures. Consequently, the particles will form an extremely compact and high resistance cake. These effects become trivial when the compression parameters exceed the critical values. In conclusion, the compression behaviors of cakes formed by soft particles can be well interpreted using the relationships between cake compressibility and particle compression properties, such as the retardation time and softness index.

Effect of gas–liquid flow pattern on air-sparged cross-flow microfiltration of yeast suspension

Effect of gas–liquid flow pattern on the performance of air-sparged cross-flow microfiltration of yeast suspension is studied. The pseudo-steady filtration flux and the cake properties under various operating conditions are measured and discussed. The shear stress acting on the membrane surface and the critical condition for particle deposition are analyzed theoretically based on hydrodynamic models. The cake mass is markedly reduced by increasing the wall shear stress. However, the average specific cake filtration resistance increases with increasing the wall shear stress due to more compact cake structure. The increase in the average specific filtration resistance of cake due to air-sparging is more significant in bubbly flows. Consequently, the filtration flux will be increased by air-sparging due to the cake reduction in slug flow microfiltration. However, a contrary result is obtained for bubbly flows due to the drastic increase in the average specific filtration resistance of cake. Therefore, a microfiltration operating under slug flow is more effective to enhance the filtration flux by air-sparging. In addition, the proposed model provides a method to quantitatively relate the filtration flux to operating parameters. The relationships are also strongly dependent on the gas–liquid flow pattern.