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Cake filtration using non-woven filters has been known as a promising water pretreatment technique for decades. In this work, four types of non-woven filters with different thicknesses were fabricated by a hot-pressing technique using polypropylene fibre webs. The filters were employed to filtrate a slurry by using a vacuum cake filtration apparatus to study the performance of the filters. The excellent bonding points between fibre webs were found by scanning electron microscopy. X-ray diffraction and X-ray fluorescence analysis of the filter cake revealed the major mineral phases in the cake were calcium carbonate, calcium oxide, iron oxide, and magnesium oxide. Specific cake resistance, filter resistance, and total resistance were measured from constant pressure filtration tests to evaluate the filter with and without using a filter aid. Type D filter with the highest thickness (594.14 µm) showed the lowest total filtration resistance (5.11 × 10+11 m−1) indicating the best performance among the other types of filters. Adding the sawdust in the slurry as the filter aid reduced both cake resistance and filter resistance, resulting in a higher filtrate flow rate. The total resistance decreased by 75.1% using 3.0 g of sawdust in the cake filtration process. According to the results, the filter cake was slightly compressible, and the filter with the highest thickness had the lowest total filtration resistance indicating the best performance among the other types of filters. [ABSTRACT FROM AUTHOR]

In the present work, the fouling behavior and the corresponding specific cake resistance of polyethersulfone microfiltration membrane fouled by using different solutions (bovine serum albumin solution, sodium alginate solution, humic acid and activated sludge suspension) under different operating conditions, transmembrane pressure (TMP), concentration (C), stirred speed (ω) and temperature (T) were systematically investigated. The ensuing results showed that the proposed equation can be used to accurately calculate instantaneous specific cake resistance (α). The average specific cake resistance increased with increasing operating pressure, concentration, and stirred speed, while it decreased with increasing operating temperature. The average specific cake resistance of sodium alginate (SA) was larger and the sequence was SA>HA>BSA>AS. [ABSTRACT FROM AUTHOR]

This study aims to provide valuable new insights regarding the effect of aeration intensity on long-term self-forming dynamic membrane bioreactor (SFDMBR) performance and the associated mechanisms. Three identical SFDMBRs, with different aeration intensities (i.e., 200, 500 and 800 L/h), were operated in constant transmembrane (TMP) mode for 60 days. The best chemical oxygen demand (COD) removal performance was achieved at medium aeration intensity, owing to the enhanced COD removal contribution by the self-forming dynamic membrane (SFDM). As expected, the SFDM formation time was extended with increasing aeration intensity. Different from the initial short-term stage results, it was interestingly found that the SFDMBR operated at medium aeration intensity exhibited the best long-term filtration performance, followed in order by the SFDMBRs with low and high aeration intensity, respectively. Further analysis revealed that the governing fouling mechanism transited from biomass accumulation to the increase of specific resistance, as aeration intensity increased. The variation of SFDM-specific resistance was verified with particle size distribution (PSD) data and scanning electron microscopy (SEM) images. The long-term increasing rate of SFDM filtration resistance was consistent with both extracellular polymeric substances (EPS) content and the proteins/polysaccharides (PN/PS) ratio of SFDMs. Internal EPS production was enhanced in the thicker SFDM formed at a lower aeration intensity. [ABSTRACT FROM AUTHOR]

Improving filtration by increasing particle surface hydrophobicity. [Display omitted] • Addition of the hydrophobic reagent improved filtration rates of fine particles. • Addition of hydrophobic reagent reduced moisture content of the cakes. • Filtration may be modelled in terms of a slip occurring at the particle surface. • Slip length decreased as the effective capillary sizes increased. Fine particle filtration has been known to become progressively inefficient as the filter cake builds up owing to restricted movement of liquid through the small cavities formed in the cake. In different chemical industries, this restricts higher throughput rates and also results in higher transportation costs due to increase in moisture content. This paper discusses the influence of using a surfactant, DAH (dodecylamine hydrochloride), in enhancing the filtration rate of a finely ground particles and the reduction of moisture content in the cake. The observed enhanced filtration rate has been attributed to a reduction in the resistance to liquid flow due to the increase in hydrophobicity at the particle surface. The resulting enhanced filtration rate has been modelled by superimposing a slip velocity at the boundary of the capillaries formed in the cake. The model evaluates the cake and medium resistances by incorporating a slip length into the filtration equation which varies with the concentration of hydrophobic reagent and the effective size of capillaries. The increase in filtration rate is more pronounced for finer particle slurries. Also, it has been observed that the moisture content of the filter cakes formed was reduced. [ABSTRACT FROM AUTHOR]

This study aims to provide valuable new insights regarding the effect of aeration intensity on long-term self-forming dynamic membrane bioreactor (SFDMBR) performance and the associated mechanisms. Three identical SFDMBRs, with different aeration intensities (i.e., 200, 500 and 800 L/h), were operated in constant transmembrane (TMP) mode for 60 days. The best chemical oxygen demand (COD) removal performance was achieved at medium aeration intensity, owing to the enhanced COD removal contribution by the self-forming dynamic membrane (SFDM). As expected, the SFDM formation time was extended with increasing aeration intensity. Different from the initial short-term stage results, it was interestingly found that the SFDMBR operated at medium aeration intensity exhibited the best long-term filtration performance, followed in order by the SFDMBRs with low and high aeration intensity, respectively. Further analysis revealed that the governing fouling mechanism transited from biomass accumulation to the increase of specific resistance, as aeration intensity increased. The variation of SFDM-specific resistance was verified with particle size distribution (PSD) data and scanning electron microscopy (SEM) images. The long-term increasing rate of SFDM filtration resistance was consistent with both extracellular polymeric substances (EPS) content and the proteins/polysaccharides (PN/PS) ratio of SFDMs. Internal EPS production was enhanced in the thicker SFDM formed at a lower aeration intensity.

• Need for bioreactor temperature control for autotrophic denitrification of 320 mg/L nitrate. • A specific denitrification rate of up to 0.25 g NO 3 -N/g MLSS was achievable. • Relatively high concentration of SMPs in sulfur-based denitrification bioreactor. • Higher specific cake resistance of sulfur-driven sludge than conventional sludge. In this study, any remaining nitrate not eliminated during a biological treatment process with a low C/N ratio was effectively removed using sulfur powder in an autotrophic denitrification membrane bioreactor. Moreover, particular attention was given to investigating the potential for membrane fouling in a sulfur-based denitrification reactor, with a comparative analysis to conventional activated sludge in an aerobic membrane bioreactor. At an influent nitrate concentration of 320 mg/L, the removal efficiency reached 94–98 % within a 4-hour hydraulic retention time and at a reactor temperature of 30 °C. The sulfur-based denitrification reactor exhibited soluble microbial products concentration and specific cake resistance values of 38.3 mg/L and 1.4 × 1013 m/kg, respectively, which were 5.47 and 2.26 times higher than those of conventional activated sludge. Furthermore, it was observed that the supernatant from the sulfur-based denitrification reactor resulted in more significant fouling within the membrane surface. [ABSTRACT FROM AUTHOR]

Highlights • A novel method for the accelerated analysis of membrane fouling is introduced. • It is based on centrifugal ultrafiltration with a stepwise change of centrifugal acceleration. • The fouling resistance and the pressure dependency of specific cake resistance can be determined. • The reversibility of fouling (filter cake compression) can be evaluated. Abstract The article introduces a novel method for accelerated analysis of membrane fouling during ultrafiltration of colloids: centrifugal ultrafiltration with a stepwise change of centrifugal rotation speed. The method allows simultaneous analysis of membrane fouling for different colloidal samples in a single analytical centrifugation experiment. The analysis for determination of fouled membrane resistance, specific cake resistance and reversibility of the filter cake compression is provided. The method applicability was tested with bovine serum albumin solutions at different protein concentrations. Fouled membrane resistance as well as pressure dependency of specific cake resistance was determined in a wide pressure range of 10...450 kPa. Results obtained with the help of the proposed method were in a good agreement with those obtained using the conventional method of constant pressure dead-end ultrafiltration. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • A process comprising classification and pressure filtration steps was investigated. • Diameter of underflow spigot had a major effect on the particle size distributions. • High proportion of submicron particles resulted in high filtration resistance. • Classification prior to the filtration step reduced the required filtration area. • Up to 99% area reduction was obtained in the underflow filtration (E T = 0.7) Abstract Hydrocyclones are used in the classification of solids for instance in the mining and minerals processing industries for modifying the particle size distribution of solids, as well as for ore concentration purposes. Improvement in the filtration properties of the slurry is usually achieved as a result of the classification process when only the underflow is evaluated, owing to the coarse and narrow particle size distribution. However, overall comparisons of the filtration properties incorporating filtration of both the underflow and overflow streams have not been discussed a lot in the literature. The objective of this study is to investigate hydrocyclone classification of a calcite slurry, to evaluate the resulting pressure filtration properties of the underflow and overflow streams, and to compare the required total filtration areas for a constant solids production capacity. The results show that the average specific cake resistance depended primarily on the fine particle content of the slurry, and therefore the Kozeny-Carman equation was not suitable for the prediction of the specific cake resistance. The specific resistances of feed and underflow filter cakes were underestimated consistently. Wide particle size distribution was one of the most apparent factors reducing cake porosity. The main outcome of the comparison of the required filtration areas was that a low specific cake resistance and high solids concentration of the underflow caused the total area requirement to decrease almost in all cases, compared to the area required for the filtration of the feed slurry. Moreover, as high as 99% reduction in the total filtration area, compared to the feed slurry, could be achieved by filtering only the underflow streams, omitting the dewatering of the overflow streams. In the light of the promising results of the study, the incorporation of a classification step prior to filtration should be investigated further, e.g. in tailings treatment applications. [ABSTRACT FROM AUTHOR]

The effects of pressure and cake thickness were studied using a split-plot design for pressure filtration of a fine refuse slurry obtained from a bituminous coal preparation facility. Pressure filtration offers the potential to significantly reduce the moisture content of the fine refuse stream with the addition of little to no flocculants, thereby minimizing the volume of refuse stored in impoundments and providing a recycle water stream for use within the plant. Experimental results showed that the final cake moisture decreased with increase in pressure and decrease in cake thickness. In addition, specific cake resistances calculated for the various tests indicated an increasing trend with increasing pressure and decreasing cake thickness. With increase in cake thickness, an increase in cake moisture and the weight of solids deposited in the cake was observed. An ANOVA analysis indicated that both cake thickness and pressure significantly affected the cake moisture, while only cake thickness statistically influenced the weight of solids in the cake. A regression model was developed with an R2 value of about 0.99 to relate cake thickness, the single largest statistically significant factor, with the weight of solids in the cake. Filter capacities were calculated in terms of the solids deposited per unit time based on a product specification of 25 percent cake moisture, and it was observed that the thinnest cake had the highest filter capacity. [ABSTRACT FROM AUTHOR]

Tailings management and water recovery from mineral processing tailings which contain high amount of fine and clay materials are very important and this matter presents considerable challenge. Any improvement in disposal and tailings filtration methods requires understanding of fluid flow in the cake pores and filter media, which are affected by various parameters. In this study, the effects of physical parameters on the specific cake resistance (α), cake formation rate, moisture content, and filter cloth resistance in the filtration of iron processing plant tailings have been examined by vacuum Top-Feed Leaf method. The main parameters which investigated in this work were cloth type, solid content, pressure drop, and thickness of cake. Experiments results showed that the polypropylene type B (PP-B) cloth was suitable for filtration process, because it had the least resistance to fluid flow. Increasing solid amount from 30 percent to 60 percent, increased specific cake resistance from 96 × 10 +10 to 230 × 10 +10  kg/m and cake formation rate was also increased from 0.18 to 0.46 mm/min and αwas between 10 11 and 10 13 . Results also showed that the iron tailings had a moderate filtration capability, and based on the compressibility factor result (n: 0.56), the filter cake was compressible. This study clearly determined the action of physical parameters on dewatering mechanism and the fluid flow through the cake and cloth pores, and demonstrated the possibility of enhancing the water recycling in the industrial plant by choosing appropriate level for each parameters. [ABSTRACT FROM AUTHOR]

Filtration of fine particle slurries is known to be inefficient in most plant operations and the problem is exacerbated by the presence of even small quantities of clay minerals. This paper discusses the influence of the commonly encountered clay types, bentonite and kaolin, in the filtration of a pyritic gold ore and how the adverse effects can be mitigated by the addition of Ca 2 + ions and a hydrophobic reagent respectively, depending on the clay type. The presence of both kaolin and bentonite clays resulted in increasing specific cake resistance, filter medium resistance and final cake moisture content while effects of bentonite clay being more detrimental. The addition of hydrophobic reagent DAH (dodecylamine hydrochloride) improved the filtration rate of kaolin-containing ore. The moisture content of the filter cake was also reduced. By contrast, in the case of the bentonite-containing ore, the presence of DAH did not affect the filtration rate and the moisture content. Filtration of the bentonite-containing ore was significantly improved with the addition of Ca 2 + ions. [ABSTRACT FROM AUTHOR]

Membrane bioreactors (MBRs) are continuously being improved, but membrane fouling still causes severe problems, so effective measures to reduce fouling are imperative to minimize operational cost. Potential foulants can be found in MBR sludge flocs, but it is not known which fraction(s) that mainly influence fouling and how sludge flocs affect fouling. A standard procedure was developed to separate sludge into floc/colloid, colloid/solute, and solute fractions. The fouling properties of MBR sludge and sludge fractions were evaluated in a lab-scale MBR equipped with aerated flat-sheet membranes. The fastest flux decline took place in the solute fraction due to formation of irreversible fouling; this fraction contained foulants smaller than the membrane pore diameter (0.2 μm), causing pore blocking and/or adsorption. Flux declined more slowly in the colloid/solute fraction, where fouling was more reversible. The external fouling layer on the membrane was shown to protect it from pore blocking/adsorption. Flux decline was slowest in unfractionated MBR activated sludge. Thus, presence of sludge flocs reduced the concentration of foulant and also directly reduced the formation of an external fouling layer by shear. This may be due to surface erosion or more turbulence close to the membrane surface by sludge flocs which thereby partly removed the external fouling layer. To reduce membrane fouling, concentrations of solutes (e.g., macromolecular extracellular substances) and colloids (e.g., single cells) should be kept low and concentration of sludge flocs high. [ABSTRACT FROM AUTHOR]

A method is proposed for determining the compression-permeability (C-P) data expressed as the dependences of the local specific cake resistance and local cake porosity on the solid compressive pressure from a combined membrane filtration and stepped cake compression test. Filtration employing a membrane with a high flow resistance, which provided the pressure dependence of the average specific cake resistance, was followed by step-up compression, which gave cake porosities at several compressive pressures. On the basis of these data collected as the time variation of the dewatering volume, the compression-permeability data of bentonite slurry were evaluated. Consolidation behaviors of the filter cake and semi-solid material were accurately described on basis of the C-P data. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the membrane fouling mechanism according to the coagulant dosage in algal rich water using a ceramic membrane. The algae that were used in this experiment were Microcystis sp. of cyanobacteria, and the fouling mechanism was analyzed through irrigation and filtration resistance through a constant flow operation. The experimental results showed that the filtration resistance decreased as the coagulant dosage increased, but the irreversibility at above optimum coagulant dosage increased. Additionally, as the coagulant dosage increased, the resistance value due to cake and adsorption contamination decreased, and membrane fouling by adsorption was dominant in comparison with cake fouling and adsorption fouling. The specific cake resistance was decreased as the coagulant dosage increased. The characteristics of the cake layer according to the coagulant dosage were found to loosely form the cake layer by increasing micro-size algae as the coagulant dosage increased. The results of this experiment confirmed the membrane fouling mechanism according to coagulant dosage when the ceramic membrane filtered algal rich water.

The article is devoted to the application of analytical centrifugation for the measurement and analysis of centrifugal ultrafiltration kinetics. The model of centrifugal ultrafiltration of colloids accounting for the cake formation, compression and possible decompression is proposed. The method for the determination of filter cake properties (pressure dependency of specific cake resistance) from the results of batch centrifugal ultrafiltration experiment is presented. The method was tested for the determination of filterability of model samples: aqueous solutions of protein (bovine serum albumin) and nanoparticle suspension (Laponite RD). The pressure dependency of specific cake resistance was determined in the range of 10−500 kPa from the results of centrifugal ultrafiltration experiments at different centrifugal rotation speeds. The obtained values of specific resistance were in good correspondence with those measured in a series of reference constant pressure dead-end filtration tests. [ABSTRACT FROM AUTHOR]

Current development of analytical centrifugation methods facilitates the experimental characterization of dispersion stability and optimization of separation processes (such as centrifugation and filtration). Nevertheless, theoretical analysis of the centrifugal data remains rather complex. In addition, different side effects can influence the centrifugal process and complicate data interpretation. The present paper proposes a simple method for characterization of filterability of concentrated aggregated suspensions by centrifugal consolidation. Different experimental protocols were tested in order to reduce the influence of side effects. Selection of the optimal protocol was based on X-ray analysis of local (spatially resolved) consolidated sample structure. The multistep centrifugal consolidation with constant centrifugal acceleration ratio is suggested. Data analysis based on a single numerical solution of a basic consolidation equation yields the pressure dependency of specific cake resistance. A satisfactory correspondence (15% difference) was observed between the pressure dependency of specific cake resistance determined from the proposed multistep centrifugal consolidation, and conventional constant pressure dead-end filtration experiments for the studied concentrated aggregated kaolin suspension in the pressure range of 7.5…170 kPa. [ABSTRACT FROM AUTHOR]

Separation of dregs from green liquor is a major challenge in kraft pulp mills, and it results in compressible filter cakes with high specific cake resistance. In industrial applications, the use of lime mud as a filter aid is a practical approach to reduce the resistance of the dregs cake. However, the amount of solid waste then increases considerably, because the lime mud has to be disposed with the dregs. In this study, green liquor sludges from two different pulp mills were filtered without filter aids by using laboratory-scale pressure filters. The effect of some variables, such as the permeability of the filter cloth, the temperature of filtration, the filtration pressure, and the storage period on the filterability of the green liquor sludges was investigated. The results provide information for optimizing the process parameters to improve the filterability of the sludge. The lowest cake resistance (2.20 · 10 12 m/kg) was obtained at filtration the temperature of 80 °C. However, the higher operating temperature did not necessarily have a positive effect on the recovery of sodium (valuable element for the process) from the cake. The results showed that higher amounts of certain elements, such as Na, K and B were recovered from the dregs cake at the filtration temperature of 60 °C. It was also observed that the storage period had a negative effect on the filtration properties. In addition, elemental analysis of the filtrate and dregs cake samples showed that harmful metals, such as Al, Cd, Fe, Mn and Zn were mostly insoluble and remained in the dregs. [ABSTRACT FROM AUTHOR]

Filtration of organic slurries is important in many industries but challenging because the hydraulic resistance is high due to gel materials in the slurries. Particles with solid polystyrene (PS) core and varying amount of poly(N-isopropylacrylamide) (PNIPAM) gel surface were synthesized. At low amount of gel, the gel deformed and partly filled the cake void increasing the resistance. This was successfully fitted using a semi-theoretical model for deformable particles. At high amount of gel, the gel deformed filling the entire cake void and the resistance was dominated by the gel. During consolidation, the primary retardation time increased three orders of magnitude with gel thickness as expected as primary consolidation were dominated by the dissipation of pore water. The secondary retardation time also increased but not as pronounced as primary retardation time. Secondary consolidation was due to local compression of the gel and therefore less dependent on gel thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2241-2247, 2017 [ABSTRACT FROM AUTHOR]

During the filtration of suspended organic material, filter cakes with high specific resistances are often formed. The properties of these filter cakes differ markedly from the classical filtration properties derived from inorganic suspensions, not only by having a higher specific resistance but also by being highly compressible. These organic substances typically have a high surface charge density, due to the different functional groups on their surfaces, so a set of model particles was synthesized in which the surface charge density can be varied while keeping all other properties constant. The synthesized monodisperse particles all have a polystyrene core and varying ratios of charged ( i.e. polyacrylic acid) and uncharged ( i.e. hydroxypropyl cellulose) stabilizing polymers covalently grafted to the surface. All used particles have proven to be stable against aggregation during storage and are easily redispersed upon agitation. Aqueous suspensions of the particles were filtered in a dead-end setup at constant pressure to determine the filter cake properties. Results indicate that the specific cake resistance, cake compressibility, and cake porosity increase with the particle surface charge. Comparison with two empirical models of filter cake resistance demonstrates that particle charge is more important than is porosity, as highly charged filter cakes have resistances orders of magnitude higher than calculated, which is not the case for filter cakes of uncharged particles. DLVO theory suggests that the results cannot be explained in terms of classical double-layer effects, even in the extreme case of very small interparticle distances. Deviations from this classical behavior, arising from the confinement of charged particles by charged walls or pores, are a possible explanation, allowing the high resistances to be interpreted as increased osmotic pressure due to the distribution of counterions in the pores. Calculations indicate that osmotic pressure increases with particle charge and with decreasing porosity, but remains close to zero for uncharged particles. [ABSTRACT FROM AUTHOR]

The filtration properties of mineral slurries depend for instance on the properties of the solid particles and on the way how these particles arrange themselves when the filter cake is formed. In cake filtration applications, the focus is often on particle size instead of the shape of particle size distribution (PSD). The aim of this experimental study is to demonstrate the influence of the width of PSD on the properties of the filter cake in the pressure filtration of Ni-Cu mine tailings. Modification of PSD is performed by using a stirred media mill at various operational conditions. The results show that not only particle size should be considered when the filtration properties are evaluated: a significant reduction of the average specific cake resistance (>60%) and increase of the average porosity (almost 30%) can be achieved by stirred media grinding at optimal conditions, in spite of reducing the median particle size. On the other hand, the selection of unfavorable grinding conditions may cause substantial increase in cake resistance. Above all, the results imply that the size of particles in the coarse end of PSD should be reduced while avoiding grinding of the finest particles. This seems to be obtainable by paying special attention to the size of the grinding medium. The main outcomes of this study will help in reducing the energy consumption of dewatering of tailings to be disposed of, and recovering valuable elements from tailings deposited in ponds, requiring the use of optimized grinding circuits and solid-liquid separation operations. However, the benefits obtained in the filtration stage should overcome the increased costs caused by the installation and energy consumption of the grinding systems. This means that the demonstrated grinding method may be profitably utilized in industrial scale only when the material is easy to grind and the filtration properties can be significantly improved, or when the filtration plant is the main bottleneck of the process. [ABSTRACT FROM AUTHOR]

A series of dead-end unstirred microfiltration experiments were conducted. Impact of different operating conditions (trans-membrane pressure (TMP), temperature, and concentration) on the specific cake resistance (SCR) using yeast suspension and polyethersulfone membranes of 0.1 μm was systematically studied. The results showed that TMP, temperature, and concentration have a significant influence on the SCR. The SCR increased with the increasing concentration and TMP, while decreased with the increasing temperature. The sequence of average accumulated impact of the operating conditions on the SCR was TMP (54.6%) > temperature (−24.2%) > concentration (21.1%). The total accumulated impact of operating conditions on the SCR was 44.5%. This result provides the basis for process optimization and process modeling. [ABSTRACT FROM PUBLISHER]

The effect of reaction temperature and time on the filterability of slurries of primary sewage sludge (PSS) and synthetic faeces (SF) following hydrothermal carbonization (HTC) was investigated and optimized using response surface methodology (RSM). Filterability was shown to improve as the treatment temperature and reaction time at which the solids were carbonized was increased. The best filtration results were achieved at the highest temperature (200°C) and longest treatment time (240 min) employed here. The specific cake resistance to filtration of the carbonized solids was found to vary between 5.43 × 1012 and 2.05 × 1010 m kg−1 for cold filtration of PSS, 1.11 × 1012 and 3.49 × 1010 m kg−1 for cold filtration of SF, and 3.01 × 1012 and 3.86 × 1010 m kg−1 for hot filtration of SF, and decreased with increasing reaction temperature and time for carbonization. There was no significant difference in the specific resistance of cold and hot filtration for SF. The RSM models employed here were found to yield predictions that were close to the experimental results obtained and should therefore prove useful in designing and optimizing HTC filtration systems for generating solids for a wide variety of end uses. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1279-1290, 2015 [ABSTRACT FROM AUTHOR]

Relaxation or backwashing is obligatory for effective operation of membrane module and intermittent aeration is helpful for nutrients removal. This study was performed to investigate effects of different filtration modes on membrane fouling behavior and treatment in membrane bioreactor (MBR) operated at three modes i.e., 12, 10 and 8 min filtration and 3, 2, and 2 min relaxation corresponding to 6, 5 and 4 cycles/hour, respectively. Various parameters including trans-membrane pressure, specific cake resistance, specific oxygen uptake rate, nutrients removal and sludge dewaterability were examined to optimize the filtration mode. TMP profiles showed that MBR (8+2) with 8 min filtration and 2 min relaxation reduced the fouling rate and depicted long filtration time in MBR treating synthetic wastewater. MBR (12+3) was more efficient in organic and nutrients removal while denitrification rate was high in MBR (8+2) . [ABSTRACT FROM AUTHOR]

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead-end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869-3877, 2014 [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cake fouling is the leading cause of membrane permeability decrease when filtering mixed liquor suspension containing high suspended solid concentrations. A simple model is proposed to simulate the cake resistance evolution with time by considering a macro-scale fouling linked only to the accumulation of particles on the membrane surface. This accumulation appears as the difference between the flux of deposited particles due to the filtration and the flux of particles detached from the membrane surface due to the tangential shear stresses caused by recirculation flow in the sidestream membrane bioreactor (MBR) or gas sparging close to the membrane surface for submerged MBR configuration. Two determining parameters were then highlighted: the specific cake resistance and the 'shear parameter'. Based on these parameters it is possible to predict model outputs as cake resistance and permeate flux evolution for short-time filtration periods. [ABSTRACT FROM AUTHOR]

Highlights: [•] Results contributed the guideline optimizing the extractor’s design and operation. [•] The separation efficiency depends on the filtrate and deposited cake properties. [•] As RCF, L/S ratio and basket radius increased, the separation efficiency increased. [•] The 3 sections of filtering screen were feed, transition, and drainage section. [ABSTRACT FROM AUTHOR]

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 (5×103–5×105 Pa). 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. [ABSTRACT FROM AUTHOR]

The single step-up pressure filtration test was developed to determine the pressure dependence of average specific resistance of the cake formed in ultrafiltration of a variety of nano-colloids over a wide range of pressure drops across the cake. The values of the average specific resistance at extremely low pressures were obtained from only the flux decline data through the use of the distinct time variation of the pressure drop across the cake generated by using the ultrafiltration membrane with a high hydraulic resistance under the low filtration pressure in the first step of filtration. The values at higher pressures were obtained from the time variation of the filtration rate induced by a stepwise increase in the pressure. The correlations between the average specific cake resistance and the pressure drop across the cake were evaluated using only the flux decline data for a variety of different proteins and nanoparticles. © 2013 American Institute of Chemical Engineers AIChE J, 60: 289-299, 2014 [ABSTRACT FROM AUTHOR]

Abstract: The fouling propensity of an inorganic colloid (silica) and an organic (humic acid) and their mixture was studied in this paper. Fouling propensity was characterized as the modified fouling index (MFIUF) and specific cake resistance in dead-end UF at constant pressure. Experimental results for individual foulants demonstrated that MFIUF increased linearly with increasing particle concentration for both humic acid and colloidal silica over most of the concentration range, with deviations at the lowest concentrations. In terms of specific cake resistance, the individual foulants tended to have higher values at low concentrations that gradually declined to steady values at higher concentrations. These trends could be due to differences in cake formation and packing density with foulant flux. For the mixed foulants the presence of modest amounts of humic acid (<15mg/L) tended to reduce both MFIUF and specific resistance below that of the colloidal silica alone (50–150mg/L). This is attributed to the effect of the humic acid on silica packing density. At higher concentrations of humic acid (>20mg/L) or lower concentrations of silica the mixture MFIUF started to exceed that of the colloid alone, possibly due to interstitial humic acid effects on cake resistance. Very low adsorption of humic acid on colloidal silica was also observed using Quartz crystal microbalance with dissipation (QCM-D) and zeta potential measurements. The results confirm that knowledge of the individual MFIUFs could not be used reliably to predict the fouling potential of the mixture. [Copyright &y& Elsevier]

Abstract: In moving biofilm membrane bioreactor (MB-MBR) sponge carriers for biofilm growth were coupled with conventional submerged membrane bioreactor (C-MBR). This study compared the fouling propensity of C-MBR with MB-MBR and investigated factors affecting fouling variations in both the systems. Membrane fouling tendencies were monitored in terms of trans-membrane pressure (TMP) and the fouling characterization included membrane fouling resistances in situ and specific cake resistance (SCR) in batch filtration cell. Comparison of TMP profiles depicted prolong filtration periods in MB-MBR. Cake layer resistance (R c), pore blocking resistance (R p) as well as SCR were higher in C-MBR. The study reveals that hybrid biomass in MB-MBR creates relatively more porous cake structure in the absence of filamentous bacteria which were found in abundance in C-MBR. Filamentous bacteria were also responsible for the release of high concentration of carbohydrates in the form of soluble extra polymeric substance (EPS) contributing to higher R p in C-MBR. [Copyright &y& Elsevier]

Abstract: This paper discusses application of centrifugal consolidation technique for evaluation of the low-pressure compression–permeability characteristics of mineral sludge. The evaluation is based on analysis of consolidation kinetics and ultimate compression of the sediment measured at various centrifugal accelerations. Dependencies of the volume fraction of particles φ, specific cake resistance α and compressibility coefficient C of the sludge versus solid compressive pressure ps were estimated and compared with those obtained from dead-end filtration experiments. [Copyright &y& Elsevier]

Abstract: Various types of filtration experiments of dilute bentonite suspension were performed by using the fully automated and computer-driven experimental apparatus equipped with an unstirred batch filtration cell. The filtration tests conducted were the single constant pressure filtration test with an appreciable membrane resistance, a series of constant pressure filtration tests with the negligible membrane resistance under conditions of various filtration pressures, a constant rate filtration test, and a variable-pressure, variable-rate filtration test. The experimental data of the time variation of both the filtration rate and applied filtration pressure monitored throughout the course of filtration enabled us to evaluate the relation between the average specific cake resistance α av of the filter cake and the applied filtration pressure p. The logarithmic plots of α av vs. Δp c have roughly merged into a unique curve irrespective of the type of filtration tests. The plots were approximated by a straight line over the moderate and high pressure ranges, and approached asymptotically to a constant value as the pressure decreased. The relation between α av and Δp c was fairly consistent with the empirical equation presented by Tiller et al. and the expression presented in this paper over wide ranges of the pressure. [Copyright &y& Elsevier]

Abstract: Fouling studies with three different molecular weight cut-off (MWCO) (100kDa, 30kDa and 10kDa) membranes in regenerated cellulose were carried out in the presence of Acros humic acids (HA) at pH 3.0, 6.7 and 9.5. It was shown that the tighter membranes were less fouled compared with the higher MWCO membranes. 100kDa membrane showed the highest degree of fouling. The role of pH showed that the highest degree of fouling happened at a neutral pH (pH 6.7) and the lowest degree of fouling happened at a basic pH (pH 9.5). Effectiveness of a novel pre-treatment method was applied to the 100kDa membrane. We added in the HA solution clay particles, homemade synthetized from natural bentonite and denoted Mont-CTAB. We observed a gain in productivity of 25%. 2D-fractal dimension parameter decreased under 1.5, showing a de-organization of the cake due to clay particles in/on the cake and a specific resistance of 4.4×1011 m/kg was obtained in presence of clays versus 3.6×1014 m/kg with HA alone. Finally the development of clay assisted ultrafiltration process changes the cake morphology limiting fouling impact and it is hope that for long term experiments, formation of a gel-layer should be limited. [Copyright &y& Elsevier]

Cellulosic wastes, from sources such as low-quality cardboard and paper, are regarded as potential feedstocks for bioethanol production. One pathway from these cellulosic materials to ethanol is saccharification (hydrolysis) followed by fermentation. Saccharification is commonly performed using enzymes that are able to cleave the cellulosic structure to smaller units, preferably to glucose monomers. During the hydrolysis, mixing conditions have a considerable impact on the performance of the enzymes. Thus mixing conditions in the hydrolysis tank can also influence the downstream operations and, consequently, the overall economy of the bioethanol process. In this experimental study, four types of impeller, at different hydrolysis conditions were used. The effect of mixing on the glucose yield and on the filtration characteristics of the hydrolysate was evaluated. It was shown that not only the sugar yield depended on the mixing conditions: the effect on the solid–liquid separation step was even more significant. [ABSTRACT FROM AUTHOR]

Abstract: The effects of particle size and its distribution on permeate flux and specific cake resistance (α) of rice wine suspensions were determined. Specific cake resistance decreased as the ratio of particles having size larger than 45μm increased. For rice wine suspensions with particle sizes in the range of 1–20μm (mean diameter of 5–6μm), α increased linearly with total suspended solids concentration. The dependence of α on total suspended solids concentration was minimal when particles with size greater than 20μm were present. Specific cake resistance was independent of total suspended solids concentration when rice wine suspensions contained greater than 50% by weight of particles having size larger than 45μm. [Copyright &y& Elsevier]

Abstract: The removal of the organic matter of the swine manure liquid fraction has been carried out by an integral process based on two stages: anaerobic digestion in an expanded granular sludge bed (EGSB) reactor followed by ultrafiltration (UF) as a tertiary treatment. The lab-scale EGSB reactor was operating for 39 weeks with a hydraulic retention time (HRT) of 3.8 days; leading to a 70% tCOD removal and a biogas production of 0.15Nm3 CH4 kg−1 tCOD removed. The UF process was studied in two different geometry and configuration membrane modules: external tubular (E-T) and submerged hollow fiber (S-HF). Both lab-scale systems have been compared in terms of the filtration selectivity and productivity and the S-HF has been the most selective and productive configuration in the filtration of the EGSB effluent. The whole process (EGSB+S-HF) provides a permeate flow without solids and yields a tCOD removal around 90%. Finally this paper proposes a satisfactory model for the UF of the EGSB effluent in the S-HF module. Both the membrane intrinsic resistance (R M) and the specific cake resistance (α) have been calculated. [Copyright &y& Elsevier]

Abstract: The cake formation during filtration of a bidisperse polystyrene solution containing 3.3 and 5.7μm particles has been studied. Microfiltration membranes are used in treating feed suspensions with a wide variety of particles, of different types and sizes. These different particles determine the properties of the cake formed during operation. Using an optical system, the local properties of the cake have been determined while simultaneously following the fouling with global methods like pressure and flow measurements. The cake thickness was measured and coupled with the resistance data. A minimum cake porosity was observed at 50% number fraction of larger particles. The measured specific cake resistance is compared to a predicted specific cake resistance obtained using the Kozeny–Carman relation incorporating a correction for the bidisperse particle distribution. The Kozeny–Carman relation showed a similar trend to the experimental results, with lower absolute values. This was suggested to be due to better ordering or compaction of the cake in some regions, which resulted in lower experimental porosities in comparison to the theoretical porosities. [ABSTRACT FROM AUTHOR]

The article discusses a research on gravitational drainage of compressible particle suspensions, published in wileyonlinelibrary.com on May 12, 2010. Gravitational drainage is one of the methods being used for solid-liquid separation. In this study, the drainage time increased with feed concentration and with squared volumetric load proportionally. It notes that velocity, cake resistance and compressibility were being settled by the input parameters.

Abstract: The clarification of rough non-alcoholic beer (RNAB) and diluted malt extract (DME) was investigated in a pilot plant consisting of a tubular ceramic membrane with nominal pore diameter of 0.45μm. The results of the primary experiments show that the concentration of suspended particles in the RNAB (∼0.05kg/m3) and DME (∼0.2kg/m3) correlates proportionally to turbidity (in NTU) with the factor of 4.45×10−4 (kgm−3 NTU−1). During cross-flow microfiltration (CFMF), flux declined drastically with time due to fouling mechanisms and propensity. According to the characterizing curve of log(d 2 t/dV 2) versus log(dt/dV), fouling is initiated by penetration of aggregates through the membrane surface, followed by blocking of the pores for the first 15min of operation. Cake formation mechanism controls the fouling phenomenon above 20th minute of operation and continues until achieving a quasi-steady-state flux. The specific cake resistance of DME particles was found to change from 6.7×1014 to 36.9×1014 m/kg for the transmembrane pressures (TMP) of 52–207kPa and the compressibility factor of the cake was evaluated to be 1.027, indicating that the cake layer is highly compressible. This finding is corroborated with previous works in the literature. This explanation for the mechanisms was further verified using scanning electron microscopy (SEM), which showed a distinct cake layer with thickness of about 30–40μm on the membrane surface and no constriction of pores. The contributions of each, reversible and irreversible fouling were evaluated by comparison of hydraulic resistances after water rinsing, water backwashing and chemical cleaning of the fouled membrane. The reversible fouling including gel and stationary cake layers contributed to more than 95% of the hydraulic resistance and the remainder was attributed to irreversible fouling. The in-pore fouling contributed to 5% of irreversible fouling resistance and 0.2% of total resistance. These observations confirm that microfiltration of RNAB is controlled by formation of cake layer on the surface of the membrane and therefore hydrodynamic techniques may play a significant role in improving the performance of the operation. [Copyright &y& Elsevier]

Abstract: It is known that micellar-enhanced ultrafiltration (MEUF) is an efficient and economic process for the removal of trace metal ions and organics from aqueous media. In this work, flux decline behavior in MEUF of aqueous solutions containing trace Cu(II) (1.6–8mM) and anionic surfactants sodium dodecyl sulfate (SDS) or sodium dodecyl benzene sulfate (SDBS) was studied at 25°C in batch mode. An UF membrane that had average pore size comparable to those of Cu(II)-adsorbed micelles was adopted. All experiments were performed as a function of stirring speed (200–400rpm), solution pH (3.0–5.0), molar concentration ratio of surfactant to metal (S/M, 2.5–12.7), and applied pressure (69–345kPa). It was shown that more than 90% of Cu(II) could be removed at an S/M ratio of 12.7 and pH 5 using SDS. The blocking filtration law was used to identify the mechanism(s) of flux decline during the MEUF processes. Finally, the specific cake resistances in both SDS and SDBS systems were evaluated and compared. [Copyright &y& Elsevier]

This study covers the experimental results of the pressure filtration of fine suspensions of quartz, calcite, dolomite, and kaolin minerals carried out in the presence of borax and surfactants in the slurry. Anionic, cationic, non-ionic and amphoteric surfactants were used in the experiments, and very drastic increases were obtained in the filtration rates of all the mineral slurries. When 3 % w/w borax and 50 g/t surfactant were present in the mineral suspension, the filtration rate increased for about 15-17 times, especially for the use of dolomite filter cakes. Even with kaolin, the filtration rate increased for 2-2.5 times when these reagents were used simultaneously. It was determined that the minerals gained high negative zeta potential values, about -34 to -36 mV, in the presence of 3 % borax. The filter cakes containing particles with higher surface charges and adsorbed surfactants on their surfaces showed relatively small specific cake resistances. These cakes became incompressible and provided very high filtration rates. [ABSTRACT FROM AUTHOR]

Abstract: Nowadays, membrane biofouling remains a big challenge in application of membrane bioreactor (MBR) for wastewater reclamation. This study investigated an alternative for alleviating the membrane fouling by a combination of denitrifying granular sludge and microfiltration. The dead-end microfiltration performances of denitrifying granular sludge suspension and its supernatant were evaluated. Results showed that the permeate flux of denitrifying granular sludge was 2.35–9.4 times higher than that of suspended denitrifying sludge. It was further revealed that the superior filtration performance of denitrifying granular sludge was due to its big size, reduced surface charge and soluble polysaccharides (sPS). Microfiltration of the supernatant obtained from the suspension showed that the substances in the supernatant was mainly responsible for the membrane pore blocking in the microfiltration of denitrifying granular sludge, while the cake layer helped to remove the pore blocking-causing substances. It appears from this study that the combination of denitrifying granular sludge with membrane filtration would be an attractive alternative for high-efficiency nitrogen removal as well as for control of membrane biofouling. [Copyright &y& Elsevier]

Abstract: The performance of hybrid adsorption–membrane filtration processes can drop owing to limited adsorption capacity and increased membrane fouling. Here we compared preadsorption by carbon black (CB) nanoparticles and powdered activated carbon (PAC) on subsequent membrane fouling in the ultrafiltration of river water containing natural organic matter (NOM), using an unstirred batch setup with four cycles of filtration and backwashing. PAC was ineffective at reducing fouling although PAC enhanced removal of micromolecular NOM. CB had a high capacity to adsorb macromolecular NOM, and subsequently prevented irreversible fouling. The CB cake was more easily detachable by backwashing than the PAC cake because of structural differences. Our results demonstrate that CB mitigated irreversible fouling and reduced the deposition of transphilic NOM on the membrane surface. [Copyright &y& Elsevier]

The main objective of this work was to investigate the filterability of MBR sludge and its mixture with conventional activated sludge (CAS). In addition, the impacts of type and dose of various polyelectrolytes, filter type and sludge properties on the filterability of both MBR and Mixed sludges were determined. Specific cake resistance (SCR) measured by the Buchner funnel filtration test apparatus and the solids content of the resulting sludge cake were used to assess the dewaterability of tested sludges. The type of filter paper used in Buchner tests affected the results of filterability for MBR, CAS and Mixed sludges. SCR values and optimum polyelectrolyte doses increased with increasing MLSS concentrations in the MBR, which suggested that increase in MLSS concentrations accompanied by increases in EPS and SMP concentrations and a shift toward smaller particles caused poorer dewaterability of the MBR sludge. The significant differences observed among the filterability of CAS and MBR sludges suggested that MLSS alone is not a good predictor of sludge dewaterability. Combining CAS and MBR sludges at different proportions generally improved their dewaterability. Combining MBR sludges having typically high MLSS and EPS concentrations with CAS having much lower MLSS concentrations may be an option for full-scale treatment plants experiencing sludge dewaterability problems. Better filterability and higher cake dry solids were achieved with cationic polyelectrolytes compared to anionic and non-ionic ones for all sludge types tested. [ABSTRACT FROM AUTHOR]