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Yeast 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. ...

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 over...

The sugars produced by enzymatic hydrolysis of rice straw are separated using cross-flow diafiltration in this study. The effects of membrane type, membrane pore size, cross-flow velocity and transmembrane pressure on the filtration flux, sugar rejection, and sugar mass flux transported to the filtrate are discussed. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. When the membrane made of mixed cellulose ester (MCE) is used, over 70% filtration resistances are caused by the membrane fouling; while the resistance due to virgin membrane is dominant when regenerated cellulose (RC) membranes are used. A force balance model is applied to relate the filtration flux and filtration resistance to operating conditions. The calculated data of filtration flux based on this model agree fairly well with experimental data. In addition, a theoretical model is used to explain the sugar transmission through the cake and membrane pores. The sugar rejection coefficient decreases ...

Two polymeric membranes, PTFE and PVDF, were employed in a direct contact membrane distillation system to investigate the effects of NaCl concentration, feed temperature, and flow rate on distillate flux and NaCl rejection. The distillate flux increases with increasing the feed flow rate or temperature, PTFE membrane has a higher distillate flux than that of PVDF, and PTFE membrane also has a larger solute rejection than that of PVDF membrane. The decrease of solute rejection by PVDF membrane is owing to the membrane pore wetting, especially at high feed temperature and flow rate. The membrane fouling tests under various feed compositions show that increasing NaCl concentration from 4.5 wt% to 10 wt% or the addition of CaSO4 or BSA into NaCl solution does not cause severe fouling on the PTFE membrane. The distilled water flux recovery (FR) is about 0.96–0.97. The addition of MgCl2 or MgSO4 has a little significant fouling tendency, the distilled water FR is about 0.87–0.88.

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 ca...

Effects of geometric structure parameters of 10 mm-diameter hydrocyclones on the particle separation efficiency are studied using computational fluid dynamics (CFD). The fluid velocity profiles and particle trajectories are simulated using RFLOW software with a standard isotropic k-e turbulent model. The JIS standard CaCO3-17 particles are adopted as a particulate sample in simulations and experiments. Comparing the simulated results with experimental data, a maximum deviation about 20% in partition curves occurs for 5–10 µm particles. However, fairly good agreements for the cut-size predictions and the fish-hook phenomenon are obtained. The simulated cut-size d 50 is only 2 µm larger than that measured in experiments, while the value of d 100 can be accurately predicted. An increase in overflow diameter or a decrease in underflow diameter leads to a lower separation efficiency but a clearer separation sharpness due to lower fluid underflow rate. A short-and-wide rectangular inlet is more efficie...

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is a...

The filtration characteristics of cross‐flow microfiltration of fine particles suspended in polymeric aqueous solution are studied. Polymethylmethacrylate (PMMA) submicron particles are suspended in polyacrylamide (PAA) aqueous solution to prepare the suspensions used in experiments. Effects of operating conditions, such as cross‐flow velocity, filtration pressure, and PAA concentration, on the filtration flux and the cake properties are discussed. The results show that an increase in cross‐flow velocity or filtration pressure causes the filtration flux to be higher, but the filtration flux decreases with an increase in PAA concentration. Since the flow behavior indices of three prepared suspensions are almost the same, the average specific filtration resistance of cakes under various cross‐flow velocities and PAA concentrations remain almost constant; and then the cake mass plays a major role in determining the filtration resistance and the filtration flux. A force balance model is derived for p...

A membrane bioreactor (MBR) combines membrane separation and biological treatment, normally involving the activated sludge process, in municipal wastewater treatment. Despite excellent performance over years of full‐scale operation, the interactions between microbes and the membrane in the MBR process, which determine its design and operational criteria, remain unclear. This report reviewed research regarding how numerous process parameters impact biofouling rates and, in particular, the possible contribution of microbial products to biofouling. This study also characterized different fractions of microbial products and assessed their potential affect on membrane fouling.

The use of cross‐flow microfiltration for purification of liposome vesicles is studied. The liposomes are concentrated while the phospholipid monomers are rejected or permeated through the filter membrane during filtration. Effects of operating conditions, such as cross‐flow velocity and filtration pressure, on the filtration rate, the cake properties, the rejection coefficient of phospholipid, and the separation efficiency are discussed. The experimental results show that the filter cake formed by liposome vesicles exhibits a very high compressibility and specific filtration resistance. Cake resistance plays a major role on the overall filtration resistance. The filtration rate attenuates quickly at the beginning of filtration, due to the deposition and the compression of liposome vesicles. After a period of time, the filtration rate gradually approaches a pseudo‐steady value. An increase in applied filtration pressure causes an increase in the filtration rate at the pseudo‐steady state, the mem...

The effects of dynamic membrane formed by fine particles on the filtration rate and the rejection of macromolecules in cross-flow microfiltration are studied. Experiments were carried out using the binary suspensions prepared by polymethyl methacrylate (PMMA) particles and the Dextran macromolecules. The filtration rates, the rejections of Dextran and the cake properties under various operating conditions, such as the cross-flow velocity and the filtration pressure, are measured and discussed. The filtration rate increases with increases of the cross-flow velocity and the filtration pressure but decreases when the molecular weight of Dextran is increased. On the other hand, the rejection of Dextran increases with the increase of filtration pressure but decreases with the increase of cross-flow velocity. The standard capture equation for deep-bed filtration is adopted to relate the rejection of Dextran and the properties of dynamic membrane. The results show that the mass of the dynamic membrane is the mos...

The effects of particle size distribution on the cake properties and the performance of cross-flow microfiltration of dual-sized particles are studied. An equation based on the force analysis at the critical condition of particle deposition is derived to relate the filtration rate and the cake properties. The packing porosities of dual-sized particles under various mixing fractions are predicted theoretically in accordance with two limiting conditions, cavern and displacement effects, and are compared to the simulated results and experimental data. The results show that either the theoretical predictions or simulation results agree with the experimental data except in the region near the lowest packing porosity. There has been an overestimation on cake porosity using simulation method and an overestimation using theoretical prediction about 30% near the lowest packing porosity. The average specific filtration resistance of cake can be estimated accurately by substituting the average particle diameter base...

A method for determining the cake properties in centrifugal dewatering is proposed in this study. By substituting experimental data of cake saturation versus time into the proposed procedures, the values of capillary pressure and filter cake permeability under various cake saturations can be estimated. Two kinds of particulate samples, CaCO3 and polystyrene powder, were used in the centrifugal dewatering experiments. The results show that both cakes exist in their funicular state for most times of dewatering. The value of capillary pressure increases while the permeability of cake decreases during the course of centrifugal dewatering. The regression functions relating the capillary pressure and permeability to the cake saturation are in agreement with the empirical equations used in previous work. A program was also designed to simulate the variation of cake saturation during centrifugal dewatering. A good agreement between the simulated results and the experimental data was obtained. The optimum operatin...

Constant pressure filtration experiments of Ca-alginate gel particle, Saccharomyces cerevisiae, and polymethyl methacrylate (PMMA) were conducted to study the local properties of cake layer formation by deformable particles. Effects of particle deformation due to frictional drag and cake mass on cake compression and contact area among particles were examined. The factors that lead to the increase in filtration resistance were discussed. The dynamic analysis proposed by Lu and Hwang in 1993 was modified to analyze formation and compression of cake during cake filtration of deformable particle slurry. A thin skin layer of low porosity and high resistance was formed next to the filter medium due to severe deformation, caused by frictional drag, of the first layer. The results of this study clearly indicate that neglecting the area-contact effect among particles will lead to an overestimate of cake porosity, and neglecting the transient effect of cake compression during gel layer formation will result in an u...

Simulation of cake formation of mono-sized and dual-sized particles under gravitational sedimentation and filtration is presented. The dynamic analysis proposed by Lu and Hwang in 1993 is applied to examine the local cake properties formed under a falling head by considering the hindered settling effect of particles in the slurry and the variation of the pressure drop across the filter septum. Results of this study show that, at a given position in a cake, the solid compressive pressure reaches a maximum value and then decreases for a gravity filtration due to the decrease in the driving head. A cake constructed with dual-sized particles has a more compact structure than does one with mono-sized particles, and larger particles will form looser packing than will smaller ones for mono-sized particles. A dual-dispersed suspension with a lower fraction of large particles will result in the lowest cake porosity and the highest specific filtration resistance of cake. Comparison of the porosity distribu...

The migration and deposition of submicron particles in laminar crossflow microfiltration is simulated by integrating the Langevin equation. The effects of operating conditions on the particle trajectories are discussed. It is found that the Brownian motion of particles plays an important role in particle migration under a smaller crossflow velocity of suspension or a smaller filtration rate. Based on the simulated trajectories of particles, the transported flux of particles arriving at the membrane surface can be estimated. The particle flux increases with an increase of filtration rate and with a decrease of particle diameter; however, the effect of crossflow velocity on the particle flux is not obvious. The forces exerted on particles are analyzed to estimate the probability of particle deposition on the membrane surface. The probability of particle deposition increases with an increase of filtration rate, with a decrease of crossflow velocity, with a decrease of particle diameter, or with an i...

A theoretical model for predicting the probability of particle deposition in crossflow filtration of power law slurry is developed. The model is based on the critical angle of friction between depositing particles, which can be estimated by analyzing the forces exerted on the particles. The binding force between the particles due to polymer adsorption plays an important role in the particle deposition. The smaller the flow behavior index of the slurry is, the larger the binding force and the higher the probability of particle deposition will be. The effects of operating conditions such as the crossflow velocity of the slurry and the filtration rate on the probability of particle deposition are also discussed in depth. The calculated values of the probability of particle deposition agree fairly well with the experimental data. A program is designed to simulate the packing structure and the porosity at the cake surface. The porosity increases not only with the increase of the crossflow velocity, bu...