Solid Compressive Pressure Research Articles

Dead-end forward osmosis as an alternative for deep sludge dewatering: Evaluation method and characteristics analysis

Sludge deep dewatering technologies that are effective and energy-saving are urgently required. Forward osmosis (FO) technology was recently used for dewatering sludge. However, the final moisture content was too high—above 95.0%—to meet the treatment and disposal requirements. In this study, a novel dead-end forward osmosis (DEFO) technique was proposed and verified for deep dewatering of excess sludge. In DEFO, the feed side is in dead-end mode, while the draw side is in cross-flow mode. Further, when 30.8 g/L excess sludge, 2.0 M NaCl draw solute, 3.0 cm/s cross velocity on the draw side, and 3‰ cationic polyacrylamide dosage was used, the moisture content of the filter cake was as low as 69.2%, equating to 90.0% sludge reduction. A proposed evaluation model for DEFO sludge dewatering behavior includes critical characteristics, such as water flow osmosis resistance and water permeability coefficient of the FO membrane. The sludge dewatering process continued regardless of whether the filter cake broke. In contrast to the conclusions endorsed in traditional dead-end pressure filtration, the DEFO filter cake exhibits an abnormal structure with a dense upper cake and a loose structure for the lower cake, resulting in a permeable filter cake. The photographs, moisture content distribution, and filter cake frozen scan verified this. The solid compressive pressure and hydraulic pressure in the DEFO filter cake were negligible, resulting in low water flow resistance of the filter cake. These findings provide further insights into the use of DEFO technology for deep sludge dewatering.

Evaluation of Consolidation Behavior by Combined Membrane Filtration and Stepped Cake Compression

AbstractA 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.

Consolidation behaviour of thick suspension in centrifugal dewatering with and without supernatant

This study proposes an analytical method considering the consolidation behaviour in centrifugal dewatering of compressible filter cake. The main focus is on the consolidation behaviour after the disappearance of the supernatant in centrifugal dewatering of thick suspension. Solving the consolidation equation under the boundary condition proposed in this study, which represents the no flow rate due to the stable meniscus at the cake surface, it is possible to describe the shrinkage of the cake after the disappearance of the supernatant. Moreover, the analytical results show that, after the disappearance of supernatant, the meniscus at the cake surface plays an important role on the drastic increase of the solid compressive pressure near the surface and it has been clarified that the shrinkage of the cake mainly occurs near the surface.

Local and average filtration properties of kraft softwood lignin

The extraction of lignin from black liquor is of interest in order to increase the overall material yield when producing paper pulp by the kraft process. The extracted lignin can be used either as a solid biofuel or a potential alternative raw material to fossil oil for the production of various green chemicals and high valuable products such as carbon fibres. The LignoBoost process is a new approach in which the kraft lignin extracted reaches a high level of purity. In this study, the local and average dead-end filtration properties during dewatering of a softwood lignin extracted from black liquor using the LignoBoost process were investigated; the material was also characterized. It was found that the investigated lignin was an easy to filter material that formed weakly compressible filter cakes in the solid compressive pressure range of 0.03 to 1.5 MPa. The concentration of the lignin slurry did not influence the filtration properties; the resulting cakes final heights were in the industrial size range. Moreover, the two different filter media used yielded similar results. Semi-empirical relationships were fitted successfully to the experimental local data and a good estimation of the average filtration properties was also obtained using the relationships fitted parameters. This indicates a good agreement between the local and average experimental data.

High-level deliquoring of activated sludge by ultrahigh-pressure expression combined with flocculation

The efficient deliquoring process has been developed for achieving high-rate and high-degree deliquoring of municipal excess activated sludge, which exhibits relatively low dewaterability. In the method developed, low-pressure filtration combined with flocculation led to high-rate deliquoring of sludge due to the formation of large flocs. Subsequently, ultrahigh-pressure expression combined with water permeation through the filter cake which promoted the re-dispersion of flocs in the cake resulted in high-degree deliquoring of the cake. It should be noted that the moisture content in the compressed cake was finally reduced to 31wt% by expression operation under action of an ultrahigh pressure of 15MPa. This extremely low value of the cake moisture content implies that the liquid contained within the microorganism cells was partially removed by the mechanical pressure when the ultrahigh pressure is applied to the cake in the course of expression. The relation between the equilibrium porosity in the compressed cake and solid compressive pressure was empirically represented by a power function. The kinetics of ultrahigh-pressure expression such as the time variation of the moisture content in the compressed cake was accurately described by combining the multi-stage creep model with the modified Terzaghi model describing the primary consolidation.

고액분리 통합이론에서 pd의 역할: 간섭침전, 케이크 여과, 압착에서 케이크 두께를 중심으로

To know the role of `the solid compressive pressure to the first solid layer of a cake, ` in the `unified theory on solid-liquid separation`, we analyzed extremely compressible cake formed with floc for the following three operations with our new concepts. First, the role of was studied in calculating the sediment thickness of floc, and in calculating the cake thickness in cake filtration performed with floc sediment. Second, we calculated the expression procedure using . Finally, the influence of on cake thickness in hindered sedimentation, and on the calculation of the procedure of hindered sedimentation was verified. Thus the possibility of application of `unified theory on solid-liquid separation` and the importance of was verified. Through these processes, new theoretical definitions of the cake filtration, expression and hindered sedimentation was established.

Evaluation of low-pressure compressibility and permeability of bentonite sediment from centrifugal consolidation data

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.

Analysis of Combined Electroosmotic Dewatering and Mechanical Expression Operation for Enhancement of Dewatering

This article presents an efficient approach for the analysis of combined electroosmotic dewatering (EOD) and mechanical expression (ME) using the Terzaghi-Voigt combined model by considering creep deformation of the material. The EOD-ME process enhances dewatering because it combines the advantage of electroosmosis and mechanical dewatering, resulting in reduced void ratio compared to individual operation. The basic differential equation based on the model is solved analytically by assuming that both an electroosmotic pressure gradient E pg and a modified consolidation coefficient C e of the material are constant, resulting in the equation of solid compressive pressure in the material as a function of time and position. The analysis also leads to the equation of the average consolidation ratio U c, which is a measure of the progress of dewatering; this equation can describe well the empirical results under various conditions. The proposed approach can clearly explain the relationship of the driving forces of individual mode of operation. The large water content of semisolid bentonite–water mixture can effectively be reduced by the EOD-ME combined operation analyzed in this research.

Analysis of Gravity Filtration Behaviors of Waterworks Sludge Based upon Sedimentation Tests

Both gravity filtration experiments under constant pressure conditions and gravity sedimentation experiments were conducted using the municipal waterworks sludge. It was clarified from the theoretical analysis that the effect of sedimentation on the filtration rate was noticeable for the sludge used in this study. The local specific flow resistance at various sludge concentrations was determined by the sedimentation velocity method. The local porosity was related to the local solid compressive pressure by the sedimentation equilibrium method. The decline behaviors in the filtration rate in gravity filtration accompanied by sedimentation were well evaluated only from the sedimentation data based upon the sedimentation velocity method and the sedimentation equilibrium method.

Determination of filtration characteristics of yeast suspension based upon multistage reduction in cake surface area under step-up pressure conditions

The step-up pressure filtration experiments of yeast suspension were conducted by using a specially designed filter equipped with a cylinder in which the inner cross-sectional area decreases with the height in stages. The filtration characteristics such as the average porosity and average specific filtration resistance for a variety of filtration pressures were accurately determined from only one test by measuring the variation with time of the filtrate volume in the step-up pressure experiment on the basis of the sudden reduction of the filtration area in the filter cake surface. The relations obtained from step-up pressure filtration experiments were fairly consistent with those from a series of constant pressure filtration experiments. The compression-permeability cell data representing the local values of the porosity and specific filtration resistance as functions of the local solid compressive pressure were evaluated based upon the data of the average values of the porosity and specific filtration resistance thus obtained. It is expected that the method is distinctly efficient as an alternative to the conventional compression-permeability cell measurements.

A New Method for the Theoretical Analysis of Electroforced Sedimentation Using Terzaghi‐Voigt Combined Model

In this article a new method for the theoretical analysis of electroforced sedimentation (EFS) by use of the Terzaghi‐Voigt combined model is presented. Zinc oxide and a mixture of zinc oxide and KC‐flock are used as experimental materials. Both the electro‐osmotic pressure gradient E pg and the modified consolidation coefficient C e of the materials are assumed to be constant. The analytical solution can explain the solid compressive pressure distribution with time and position. The progress of electroforced sedeimentation can be represented by an average consolidation ratio U c as in mechanical expression. Variations of the effectiveness of EFS with the percentage of KC‐flock in the mixture, electric current density, and total solid volume per unit cross‐sectional area are investigated. EFS is best applied for materials with permanent charge.

Multiphase flow models in quantifying constant pressure dead-end filtration and subsequent cake compression: 2. Concentrated slurry filtration and cake compression

Separation of liquid from concentrated slurry is a significant process in laboratory and engineering applications. In an earlier paper (X.M. Wang, S. Chang, P. Kovalsky, T.D. Waite, Multiphase flow models in quantifying constant pressure dead-end filtration and subsequent cake compression. 1. Dilute slurry filtration, J. Membr. Sci., in press), we investigated the applicability of the Smiles and Tiller multiphase flow models to description of the filtration behavior of dilute yeast slurries and here extend the analysis to consideration of concentrated slurries. Smiles’ and Tiller's models are employed to quantify dynamic filtration behavior while a numerical technique derived from Smiles’ method is utilized for cake compression stage characterization. The numerical method for Smiles’ model for concentrated slurry filtration is the same as that for dilute slurry, while an iteration step is added to the method for Tiller's model. The results obtained indicate that the Smiles and Tiller models are equivalent in quantifying filtration behavior and cake structure of concentrated slurry and reveal that the cake structure and the ensuing filtration behavior are affected by the initial slurry solid fraction. The cake formed from slurry with a higher initial solid fraction tends to have a lower average solid fraction and a lower average specific resistance than is the case for lower initial slurry solid fractions. The variance of superficial liquid velocity through the cake during concentrated slurry filtration is much more significant than is the case during dilute slurry filtration suggesting that caution should be exercised in employing the conventional filtration model in concentrated slurry filtration data analysis. During the compression stage, the compression rate is relatively constant at the beginning then drops sharply before adopting a relatively stable value at longer times. Concomitantly, the solid compressive pressure of the upper surface of the cake increases slowly at the beginning, quickly after that and then slowly again.

Analysis of constant-current electro-osmotic dewatering of various solid–liquid systems by considering the creep deformation

A constant-current electro-osmotic dewatering (EOD) of various solid–liquid systems is analyzed using the Terzaghi–Voigt combined model by considering the creep deformation of the material. Electro-osmotic dewatering experiments under constant electric current density of bentonite clay, KC-flock, zinc oxide and some of their mixtures are carried out. The basic differential equation based on the model is solved analytically by assuming that both electro-osmotic pressure gradient E pg and modified consolidation coefficient C e of the material are constant. The solution can explain the time course of changes in solid compressive pressure distribution. The theory can also explain the final moisture distribution of the material. The progress of electro-osmotic dewatering can be represented by an average consolidation ratio U c as in mechanical expression. Both C e and E pg increase with an electric current density i. A larger C e leads to a higher dewatering rate; a larger E pg results in a higher solid compressive pressure distribution in the material. It is found that the amount of creep deformation depends upon the dewatering rate; the faster the dewatering rate, the larger the creep deformation, i.e., the creep deformation is more remarkable when a higher current density is applied to the material. The effectiveness of EOD can be represented by the relative difference of the initial and final void ratios. Variations of the effectiveness of dewatering with the material composition, electric current density i, preconsolidation pressure p s1 and total solid volume per unit cross-sectional area ω 0 are investigated. It is found that higher composition of charged material and higher current density show improved dewatering. For higher ω 0, slight increase in effectiveness of dewatering is observed. For significant decrease of preconsolidation pressure, a relatively small increase in the effectiveness is observed. Therefore, among these, the material composition and current density are the main EOD parameters that can be used to determine the feasibility of EOD as efficient solid–liquid separation process.

The preparation and filtration characteristics of Dextran–MnO 2 gel particles

Different kinds of Dextran–MnO 2 gel particles are prepared in different conditions, depending on variables such as the molecular weight of dextran and formation temperature. Some physical properties and filtration characteristics of these gel particles are measured and discussed. Although the mean sizes of these gel particles are very close to each other, their filtration characteristics are far different due to their mechanical strength and compressibility. A typical filtration curve of gel particles can be divided into three regions, and a retardation cake compression during the filtration can be observed from the curve. The particle formation temperature has a trivial effect on their mechanical strength. An increase in formation temperature leads to only a slight decrease in particle size. On the other hand, gel particles are formed by using dextrans with three different molecular weights – 70,000 (sample A), 500,000 (sample B) and 2,000,000 Da (sample C) – and are used in filtration experiments. The results show that the molecular weight of dextran plays a major role in determining particle mechanical strength; the sequence of particle hardness is sample B > sample A > sample C. The dynamic analysis method proposed by Hwang and Hseuh [K.J. Hwang, C.L. Hseuh, J. Membr. Sci. 214 (2003) 259] is employed to estimate the local cake properties in a filter cake, e.g., solid compressive pressure, porosity and specific filtration resistance. Because sample C has the highest compressibility, it constructs a cake with the lowest porosity and the highest specific filtration resistance; and consequently, the lowest filtration rate. Although the mechanical strength of sample B is higher than that of sample A, its wider particle size distribution results in lower cake porosity and higher filtration resistance, as well as a lower filtration rate. It could be said that the filtration rate decreases with an increase in the molecular weight of dextran.

On the Measurement and Evaluation of Pressure and Solidosity in Filtration

New test filtration equipment has been constructed that makes simultaneous measurement of local solid compressive pressure and local solidosity possible. Four materials were used to evaluate the new equipment. In this equipment the solidosity was measured with resolution of 1 mm in height (i.e. in the direction of the liquid flow). The experimental error was estimated to be 0.005–0.04 m 3 m −3 , depending on the properties of the slurry. Constitutive relationships for solidosity, permeability and specific filtration resistance were estimated and an overall good fit was obtained. Furthermore, it was found that the average specific filtration resistance based on the classical filtration equation could differ by as much as 20% compared to corresponding values based on local measurements.

The role of Pi, Po, and Pf in constitutive equations and new boundary conditions in cake filtration

The constitutive equations proposed by Tiller and Shirato were analyzed and a new constitutive equation originating from the sediment thickness was proposed. A new boundary condition of the filter cake based on the solid compressive pressure of the first solid layer,p f , was also proposed. Accurate average specific cake resistances at various pressures and the thickness of cake were calculated with the new constitutive equation and boundary conditions. The influence ofp f on the cake thickness and average porosity was studied theoretically. Using three constitutive equations, it was proved that the compressibility n obtained from filtration results instead of CPC (compression-permeability cell) of very compressible cake could not have an exact value.

Microfiltration of Deformable Submicron Particles.

The mechanism of microfiltration of deformable submicron particles is studied. Experiments of “dead-end” cake filtration were carried out using pseudomonas suspensions. The effects of operating conditions on the filtration performance are discussed. The results show that the filtration rates increase with increasing filtration pressure, while decrease with the increase of suspension concentration. A model for cake formation is developed based on force analysis. The flux of particle deposition and the packing porosity of the formed cake can then be obtained using the proposed model. Based on the continuity equation of compression and Kozeny equation, a numerical program is established for simulating the local porosity, specific filtration resistance, and solid compressive pressure in a filter cake. The simulated values of average porosity and average specific filtration resistance of cake agree with the experimental data. It can be found that a skin layer controlling the filtration rate will form next to the membrane surface in a microfiltration of deformable submicron particles. Although the thickness of skin layer is only 10%, its filtration resistance is about 90% of the whole cake. Most compression of cake occurs at the beginning of filtration. Increasing the suspension concentration increases the particle flux of back diffusion; therefore, a thinner and more compact cake will construct under a given filtration pressure

フロートを用いたヌッチェ型真空ろ過試験による圧縮透過特性の推算

Vacuum filtration tests of Korean kaolin slurry were conducted under various filtration pressures using a nutsche equipped with a floating disk. The floating disk was used to determine the filtrate volume by its displacement. The average porosity of filter cake was obtained based on the principle of sudden reduction of filtration area during filtration. Compression-permeability cell data such as the local specific filtration resistance and the local porosity were evaluated as functions of the local solid compressive pressure on the basis of vacuum filtration data. The expression characteristics of slurry under relatively large expression pressure conditions were well evaluated based on the compression-permeability cell data determined from the vacuum filtration data under low pressure conditions. In addition, an approximate method has been developed for obtaining the permeability data on the basis of expression data.

Final Moisture Distribution in Materials after Electro-Osmotic Dewatering.

The final states of materials after electro-osmotic dewatering are investigated. Based on our theory, the liquid pressure near the anode becomes negative if the materials are negatively charged. This negative pressure is offset by the positive solid compressive pressure arising from the force balance, resulting in a decrease in the local moisture content of the material. This propagates from the anode to the cathode until the pressure flow cancels out the electro-osmotic flow in any layer of the material. This paper explains the moisture distribution of the material at the end of the dewatering process. It is also shown that reversing the polarity of the electrodes results in a further decrease in the moisture content of the material.

Methods to determine the relationship between cake properties and solid compressive pressure

Abstract This paper summarized the methods used to determine the relationship between cake properties and solid compressive pressure. The dynamic simulation method proposed by Lu and Hwang (Mechanism of cake formation in constant pressure filtration, Separation Technol. 3 (1993) 122–132) is modified by considering the variation of the pressure drop across the septum and specific surface area of particles. The importance of the accuracy of the value of ϵi is also examined, and the effects of the operating condition, such as pressure and slurry concentration, are also discussed. The results of the obtained relationships between ϵ vs. Ps and α vs. Ps for different compactness materials through the proposed dynamic simulation method give the results very close to the corrected CP Cell test data. To compare the reliability of the obtained local cake properties vs. Ps by various methods, the results obtained for different compactness materials are used to predict the performances of the constant pressure filtrations. The results of the dynamic simulation can give the best prediction with an average deviation around 4%, while the corrected CP Cell test data may give an average deviation around 5%, and the uncorrected CP Cell data gives an average deviation around 10%.