Pressure Filtration Tests Research Articles

Nonwoven geotextiles to filter clayey sludge: An experimental study

A host of mining practices produce fine-grained mineral sludge, such as mature fine tailing from oil-sand extraction. These sludges are hard to dewater because of their high clay content and their low hydraulic conductivity. This paper describes pressure filtration tests in which eight different nonwoven geotextiles (GTXs) were used to filter high-clay-content sludges. The sludges were formulated by mixing kaolinite and silt to obtain eight different grain-size distributions (GSDs) with d50 ranging from 3 to 55 μm and clay content ranging from 0% to 38% (d < 2 μm). The sludges created for this research had the GSD and variability of real fine tailings. The results indicate that sludges can be filtered with nonwoven GTXs selected on the basis of their pore-opening size. Furthermore, calendered GTXs are more efficient in retaining particles than needle punched GTXs. In addition, only during the early stage of filtration do GTXs really influence filtering because it is at this stage that, by retaining coarser particles, they allow progressive formation of filter cake. Upon forming, the filter cake becomes the major contributor to particle retention. Finally, the sludge composition is found to be the most significant factor affecting the final state of dewatering.

Cationic starch flocculants as an alternative to synthetic polymers in geotextile tube dewatering

ABSTRACT: Polyacrylamide-based conditioners have become an essential component of the geotextile tube dewatering processes. These conditioners act as flocculants, binding fine sediments through charge neutralisation and particle bridging, resulting in faster dewatering rates and greater retention of fine sediments. Recently, however, momentum has begun to shift towards the use of sustainable materials. Natural flocculants, such as starch and chitosan, are increasingly being tested as an attractive alternative to synthetic polymers. Researchers have identified a number of natural flocculants, polysaccharides and polysaccharide derivatives in particular, as candidates for dewatering applications. In this study, the dewatering performance of four soils (sand, silt, kaolin, and natural organic soil) was evaluated with synthetic and starch-based flocculants. Dewatering performance of five cationic starch-based polymers with charge densities ranging from 0.38 to 0.94 meq/g and molecular weights ranging from 5 × 104g/mol to 5 × 105g/mol were compared with five cationic acrylamide-based polymers with charge densities that ranged from 1 to 3.05 meq/g and molecular weights that ranged from 10 × 106to 20 × 106/mol. The cationic polyacrylamides and cationic starches were selected with a wide range of charge densities and molecular weights in order to study the effect of flocculant properties on the flocculation and dewatering performance of the used soils. The optimum dose of each flocculant was determined using the jar test. Additionally, pressure filtration tests were performed to determine the dewatering rates and filter cake properties. Test results showed that the flocculants' properties, especially charge density, have a significant effect on the optimum dose. The optimum doses of the cationic starch flocculants were two to four times higher than the cationic polyacrylamide polymers. Additionally, it was found that the cationic starches were more effective in minimising the turbidity of the natural organic soils than the cationic polyacrylamides. Finally, the cationic starches allowed for a 900% increase in dewatering rate in comparison with the soil samples that were tested without flocculants.

New filtrate loss controller based on poly(methyl methacrylate‐co‐vinyl acetate)

ABSTRACTThe drilling of petroleum wells requires the use of suitable drilling fluids to ensure efficient operation without causing rock damage. Specific polymers have been used to control infiltration during drilling, to reduce operational problems. In this study, spherical microparticles of poly(methyl methacrylate‐co‐vinyl acetate) were synthesized (by suspension polymerization), characterized, and evaluated in terms of their performance in controlling filtrate loss of aqueous fluids. A filter press test with ceramic disk, simulating the rock, was used. The performance of the synthesized materials was compared with commercial polymers. It was observed that the performance of the material is directly associated with the relation between particle size and pore size of the rock specimen. Furthermore, for a suitable particle size, the rubbery characteristic of the material produces a more efficient filter cake, for filtrate control. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40646.

Determination of cake properties in ultrafiltration of nano‐colloids based on single step‐up pressure filtration test

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

Filter cake formation for slurry shield tunneling in highly permeable sand

For slurry shield tunneling projects excavated in the highly permeable soils, the slurry usually passes through the ground without forming a filter cake. As a result it may be impossible (depending on the yield strength of slurry) to built up the required support pressure which would lead to a face instability. This kind of face instability is influenced by the factors, such as the permeability of ground, the slurry pressure and the properties of slurry. How to form a thin and lowly permeable filter cake efficiently and quickly on the tunnel face becomes a crucial engineering problem for the slurry shield tunneling in the coarse-grained and highly permeable grounds. In this paper, a new apparatus was developed to study the filter cake formation on the surface of coarse-grained sands under elevated pressure. A series of pressure filtration tests were carried out on nine different slurries and five different soils. By measuring the quantities of discharged water during the test and observing the state of filter cakes formed on the soil surface, the criteria of filter cake formation was identified. The test results indicated three different types of slurry infiltration. Correspondingly, the following three different types of filter cakes were observed: a filter cake, a filter cake with an infiltrated zone, and infiltrated zone without filter cake. It was found that the ratio between the average pore size of soil (D0¯) and the particle size for which 85% by weight of particles in the slurry (d85) may be used to classify the types of filter cake formation.

A monolithic layered nonwoven–woven geotextile for use with drainage geocomposites in coal combustion residual projects

A layered monolithic filter consisting of a nonwoven needlepunched and a woven monofilament geotextile is presented in this paper. The two geotextiles are mechanically bonded in a needlepunching process to produce a hybrid geotextile on a commercial scale. The fuzzy woven side of the geotextile, resulting from the needlepunching process, is ideally suited for lamination to a geonet, although a standalone filter application is also possible. Filter press tests on the geotextile against a fly ash slurry of 500% yielded a retention efficiency of 99.6%. Gradient ratio values of 1.0–1.5 and hydraulic conductivity ratio values of 0.5–1.0 were obtained against fly ash and FGD gypsum from four power plants. Four field basin tests were performed under the CCRs wherein effluent parameters of total suspended solids, total dissolved solids, turbidity, conductivity and pH were monitored with time. The field tests showed that the fly ash and FGD gypsum contained in the test basins were not migrating with time.

Dewatering and Utilization of Fly Ash Slurries Using Geotextile Tubes

About one billion metric tons of coal ashes are produced annually around the world, among which 700 million tons are fly ash wastes that must be disposed of. The practice of wet fly ash disposal has increased environmental concerns due to fly ash leachate, ground water contamination, and the limitation of pond capacity. Therefore, alternatives to the current disposal methods should be addressed. Geotextile tube dewatering is an efficient dewatering method that can decrease the volume of fly ash slurry and at the same time provides containment of dry fly ash. In this study, pressure filtration tests were conducted to evaluate the dewatering performance of Class C fly ash with seven woven geotextiles having a wide range of hydraulic properties. Anionic polymer flocculant was used to evaluate the effect of polymer conditioning on dewatering performance. In addition, the increase in filter cake strength due to flocculants was evaluated. Lastly, chemical analysis of the effluent was performed to quantify the concentration of contaminants present in the geotextile tube effluent. The results of this study indicate that hydraulic properties of the geotextile do not have a significant effect on the dewatering performance of fly ash. It was found that polymer conditioning significantly increased the strength of the filter cake, making fly ash filled geotextile tubes suitable for use in geotechnical engineering applications. It was also found that geotextile tube dewatering does not retain fly ash trace elements that can leach out with effluent, meaning that proper safety measures must be taken in fly ash reutilization projects.

Hydraulic and chemical evolution of GCLs during filter press and oedopermeametric tests performed with real leachate

The solid waste decomposition inside a municipal solid waste (MSW) landfill may be enhanced by liquid addition in order to reach landfill stabilization in a reduced period of time as compared to dry-tomb landfills. This liquid addition provides an increased leachate volume and its specific chemical composition leads to fear a degradation of the hydraulic properties of the bottom liner system, especially the mineral part. In this study, the impact of four fluids on the chemical and hydraulic properties of three geosynthetic clay liners (GCLs) currently used in landfill bottom liner systems is evaluated using swelling tests, filter press tests and oedopermeameter tests. Each permeability test is associated to chemical analysis of the fluids before and after contact with the bentonites. The four fluids are two real leachates, a sewage slurry and a leachate from a green waste repository. The three GCLs contain either natural sodium bentonite or sodium-activated calcium bentonite.Filter press results and swell index tests reveal a larger impact on the permittivity of the bentonite of leachates as compared to the other fluids. Oedopermeameter tests lasted one year; they show a variable impact, either negative or positive, of the real leachate on the hydraulic conductivity of the GCLs. Specific conditions, such as pre-hydration, limit the impact of leachate on the hydraulic conductivity. Whatever the method used to determine the permittivity of bentonite or of the GCL, the natural sodium bentonite is less impacted by the fluids than the sodium-activated calcium bentonites.

Design parameters for geosynthetic dewatering tubes derived from pressure filtration tests

ABSTRACT: Geosynthetic tubes are increasingly being used for dewatering projects processing many different types of sludge, such as dredged materials, industrial and sewage sludge. Although there is still a lack of reliable design procedures, especially with respect to determination of the time needed for the dewatering of sludge inside a geosynthetic tube, a variety of scientific publications have applied pressure filtration tests to determine the one-dimensional filtration and consolidation characteristics of various combinations of sludge and geotextile filters. A series of pressure filtration tests were conducted on different combinations of dredged materials and geotextile filters to observe the benefits and limitations of the method with respect to geotextile tube dewatering. In this paper the application possibilities and derived values of pressure filtration tests are discussed. The main limitations could be detected for those derived values that are dependent on the test set-up. Each of the research institutes that has published on pressure filtration testing used a different apparatus. Thus the dependence of the derived results on the specific test set-up limits both the analysis itself, and the comparability of results. In particular, the value of filtration efficiency, which has frequently been used by researchers, proved to be of little significance in describing a filtration project.

Determination of cake filtration characteristics of dilute suspension of bentonite from various filtration tests

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 αav of the filter cake and the applied filtration pressure p. The logarithmic plots of αav vs. Δpc 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 αav and Δpc 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.

粒子・液体系分離における膜濾過工学の展開

One of the critical issues limiting the successful application of membrane filtration for treatment of drinking water and wastewater is typically membrane fouling of contaminants caused by pore clogging of the membrane and cake layer formation on the membrane surface during filtration. The present article delineates the importance of the electrostatic interactions of charged particles on the properties of a filter cake formed in membrane filtration. Additionally, a method is introduced for determining the compressibility of the filter cake based on a single constant pressure filtration test. This article describes theoretical derivation of a generalized characteristic form of classical blocking law, which had been most extensively used in the analysis of pore clogging of the membrane. In addition, the combined model of pore blocking and cake formation is discussed. Moreover, the development of an accurate model to explain the behavior of the irreversible pore clogging of the membrane, which will not fully recover by the simple physical backwashing, will become increasingly important, in order to establish efficient membrane-based water treatment technologies. It is finally shown that hybrid membrane filtration combined with the other separation methods proves to be useful in water treatment.

Determination of Pressure Dependence of Permeability Characteristics from Single Constant Pressure Filtration Test

The single constant pressure filtration test for dilute colloidal dispersions has been newly developed for easily determining the pressure dependence of the permeability characteristics such as the average specific cake resistance. The method made use of the gradual variation of the effective pressure drop across the filter cake with time generated by using the filter medium with a high medium resistance. The correlations between the average specific cake resistance and the effective pressure were obtained from the flux decline data. The data of the flux decline behavior obtained for the various values of the slurry concentration, applied pressure and medium resistance were largely merged by the normalized form of the reciprocal filtration rate vs. the filtrate volume. The validity of the method was confirmed not only for slurries of bentonite, Hara-Gairome clay, and polymethyl methacrylate (PMMA), but also for nanoparticle colloids of bovine serum albumin (BSA) and silica sol.

Ultra-fine coal flocculation using dual-polymer systems of ultrasonically conditioned and unmodified flocculant

Despite the progress in chemical engineering, efficient dewatering of ultra-fine coal (<150 μm) from slurries is still one of the biggest challenges in coal-mines. This process consists of two consecutive steps: suspension flocculation and sludge filtration. Unfortunately a sort of paradox appears in this situation. On the one hand large flocs are desired in order to fast and efficiently separate solid particles from the suspension, on the other hand large and porous flocs have worse dewaterability characteristics than small and tight ones. In this paper solution to this problem is proposed. In order to create large and tight aggregates a dual-polymer system was used using unmodified and sonicated flocculant. The flocculation process was investigated on a special apparatus for on-line particle size distribution (PSD) measurements consisting of the laser particle sizer, baffled mixing tank with turbine mixer and peristaltic pump. Moreover, pressure filtration tests were made. Presented results proved that ultrasonically conditioned polymers could be an attractive alternative for standard dual-polymer systems. The application of polymer blends resulted in accelerated aggregation kinetics, whereas sequential addition allowed the system to obtain slightly larger aggregates. In high overdose region a synergistic effect was found – the size of aggregates was larger than in case of unmodified polymer optimal dosage both for sequential addition and polymer blend cases. Finally, enhanced dewaterability characteristics of received sludge were obtained.

Method Developed for Quantitative Analysis of Inclusions in Solidified Aluminum Ingots

A deep-etching method was used to determine inclusions in solidified direct chill cast aluminum ingots. The technique was developed to allow easy quantification of the amount and size distribution of inclusions over billet lengths and cross sections. A pressure filtration (Prefil) test also was used to verify molten alloy cleanliness during casting, and the results of these measurements then were compared. The amount and distribution of nonmetallic inclusions were analyzed, as determined using a NaOH deep-etching method over billet lengths and cross sections. A higher inclusion count was observed at both billet ends, with more inclusions located nearer the billet section centerline. Furthermore, the inclusion density in the radial direction at every distance along the billet length was distributed inhomogeneously. Differences were observed between Prefil samples taken at different casting stages. The Prefil curves and metallographic analysis of Prefil residue obtained from melt samples, at an early casting stage or before degassing, indicate more oxides than in a melt sample taken under steady-state casting conditions. A reasonable correlation was established between the number of inclusions in the molten alloy (measured using Prefil and LiMCA) and the etch pits on deep-etched surfaces of billet cross sections.

Impact of a synthetic leachate on permittivity of GCLs measured by filter press and oedopermeameter tests

Geosynthetic clay liners (GCLs) are used in landfill liner applications due primarily to their low hydraulic conductivity to water. The low hydraulic conductivity of GCLs comes from the structure of the clay in the bentonite. However, the interaction between clay and aggressive liquids may alter the structure of the clay and, thus, result in an increase in the hydraulic conductivity of the GCL. This paper presents the results of a project aimed at evaluating the impact of a synthetic leachate on the structure of four different bentonites used in the manufacturing of GCLs. The preparation of bentonite dispersions increased the interaction between the bentonites and the various liquids. The hydraulic properties of the dispersions also were tested using filter press tests to obtain flow curves. Results of these tests were correlated with the cationic concentration, electrical conductivity and pH of the dispersions, swell indexes of the bentonite extracted from the GCLs, and permittivities of the intact GCLs determined in oedopermeameter tests. The results showed that one bentonite was more sensitive to the synthetic leachate than the other bentonites. For example, the permittivities of the more sensitive bentonite based on the oedopermeameter tests and filter press tests were respectively 2.11 × 10 −8 s −1 and 5.6 × 10 −8 s −1, whereas the permittivities for other bentonites, including a natural sodium bentonite and two sodium-activated calcium bentonites, were respectively 5.7 to 6.5 × 10 −9 s −1 and 3.2 to 3.5 × 10 −8 s −1. The filter press test served as a quick and easy-to-use test to compare the performance of the various bentonites in containing a given liquid. However, the oedopermeameter test or direct permeation test is preferable to filter press tests or fluid loss tests for evaluating the long-term impact of a liquid on a bentonite.

Assessment of rheological methods for a correlation to sludge filterability

To achieve good dewaterability, the conditioning process should create sludge flocs providing a porous cake during compression but also a high resistance to erosional stresses. This suggests that sludge’s rheological characteristics, some of which (like the yield stress or the storage modulus) represent its network strength, should be related to the material’s dewatering properties. Previous efforts to verify such a correlation—which would allow prediction of full scale dewaterability—have not provided strong correlations. In this work, commonly accepted rheological and dewatering tests were applied to conditioned sludges. Correlations were seen between different rheological parameters, particularly yield stress and specific energy, but not between rheological and filterability properties. Even using high pressure filtration tests, which should reflect the sludge’s responses to normal and shear stresses, results were related to the measured rheological properties only in an indirect manner: a threshold shear strength is required beyond which further strength confers no improvement in filterability. Thus, common rheological tests are unlikely to provide useful information regarding full scale filterability.

Swell index, oedopermeametric, filter press and rheometric tests for identifying the qualification of bentonites used in GCLs

ABSTRACT: Geosynthetic clay liners (GCLs) are used in landfill liner applications and there is a need for a better control of the properties of the bentonite in the GCL received on site, particularly in the European context where a wide variety of bentonites can be encountered. This paper presents the results of a project aimed at a rapid identification of the nature of the bentonite in a given GCL. The interaction between the bentonite and the fluid was increased by producing dispersions then testing its structure within a few hours with filter press tests and flow curves. The results of those tests were compared with swell index tests, electrical conductivity values and oedopermeametric tests. Eight GCLs were studied. Two of these GCLs contained natural calcium bentonites; they presented poor swelling properties and high permittivities. The dispersions had a low viscosity and their filtration under pressure led to large amounts of filtrate. A further two GCLs contained natural sodium bentonites and the remaining four contained sodium-activated calcium bentonites. Their permittivities, swell indices and filtrate masses were similar; however, their rheometrical behaviours were different due to a difference in the values of electrical conductivity. Thus it seems that electrical conductivity measurements and rheological tests can provide a good and fast way of identifying the nature of the bentonite contained in GCLs.

Effect of polymer conditioning on dewatering characteristics of fine sediment slurry using geotextiles

Results from laboratory investigations for evaluation and enhancement of the dewatering performance of fine silt slurry are presented. These experiments were conducted with and without polymer conditioning of the slurry. One type of soil and five types of geotextile were used. The optimal dewatering conditions were investigated using one woven geotextile. An innovative methodology is proposed for determining optimal dewatering considerations using a combination of simple bench-scale tests (jar sedimentation test, jar test, and pressure filtration test). The current state of practice utilises a trial-and-error approach heavily dependent on operator judgement, and ignores the role of the geotextile and the simulation of field mixing conditions. The proposed methodology provides a rational method to determine the optimal dewatering conditions in terms of dewatering time and amount of piping under anticipated field conditions. This novel approach guides the selection and evaluation of candidate polymers, which can be further evaluated in greater detail using pilot-scale tests. It is demonstrated that considerable enhancement can be achieved in the dewatering performance through polymer conditioning. Based on the results of this investigation, it is demonstrated that optimal dewatering conditions (maximum filtration efficiency and minimum dewatering time) can be arrived at with the methods proposed here.

Solid inclusion cakes formed during pressure filtration tests of liquid aluminum alloys

Abstract Liquid metal quality has been an important topic for aluminum alloys in both industry and academic circles. Pressure filtration, or pre-concentration techniques have been among the principal methods of measuring the contents of solid inclusions. In this work, the mutual relationships between the main variables related to liquid metal quality, filter medium, filtration process, and the formed filter cake are effectively established, based on the classic filtration theories of cake mode combined with the quantitative metallurgy of the filter cake. For the first time the specific cake resistance, formation and growth dynamics of filter cakes can be quantitatively calculated. This progress will significantly help to quantitatively understand the filtration behavior during the detection of liquid metal quality. A typical example is illustrated in this work.

New Analyses of Pressure Filtration Curves of Al Alloys: A Case Study

There has been an increasing tendency to determine liquid metal quality using pressure filtration methods such as Prefil Footprinter tests. The scientific understanding of this method, however, is emerging only recently with the introduction of derivative methods. Based on the investigation of flow behavior over the pressure filtration test, classic filtration theory has been successfully applied to understand the filtrate weight versus filtration time curve. The “clean” and “effective” resistance of filter medium, overall filtration resistance, cake resistance, pressure loss and distribution can be quantitatively calculated now. In the present work, a typical weight versus time curve from the Prefil Footprinter test of a cast Al-Si alloy is analyzed and discussed in details. The method developed in the work can provide new insights into the filtration behavior.