Rapid filtration measurement of dewatering design and optimization parameters
TL;DR: In this paper, a mathematical framework exists for the dewatering of suspensions using three parameters: the compressi®e yield stress P, the y () hindered settling function r, and a solids diffusi®ity D.
Abstract: To characterize and optimize the compressi®e dewatering of suspensions, rapidly determinable material parameters are required. A mathematical framework exists for char() acterization of dewatering using three parameters: the compressi®e yield stress P , the y () ( ) hindered settling function r , and a solids diffusi®ity D .An ew®ariation on traditional constant pressure, batch filtration tests is described along with a computer-controlled filtration apparatus that enables complete characterization of a suspension with respect to dewatering in a matter of hours. The testing methods are ®alidated experimentally on flocculated zirconia suspensions along with calculation of the material dewatering parameters. Application of the calculated parameters to modeling of a real filtration test shows excellent agreement. Practical implications of the modeling are also discussed.
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TL;DR: In this paper, physical conditioners, such as polyelectrolyte, the physical conditioner and sludge colloids may lead to the formation of a homogeneous mixture of the solids with strong and porous structure.
318 citations
TL;DR: Time has come to incorporate established mathematical techniques into environmental engineering, and wastewater treatment modelling in particular, and to use proven reliable and consistent simulation models, by combining classical concepts with results from applied mathematics.
128 citations
TL;DR: The new approach is demonstrated to be robust relative to traditional methods such as specific resistance to filtration analysis and has an in-built integrity check and the data indicate that the volatile solids parameter is a strong indicator of the dewatering behaviour of sewage sludges.
124 citations
TL;DR: A new mathematical model for continuous sedimentation-consolidation processes of flocculated suspensions in clarifier-thickener units is formulated and its convergence to a weak solution that satisfies an entropy condition is proved.
Abstract: The chief purpose of this paper is to formulate and partly analyze a new mathematical model for continuous sedimentation-consolidation processes of flocculated suspensions in clarifier-thickener units. This model appears in two variants for cylindrical and variable cross-sectional area units, respectively (Models 1 and 2). In both cases, the governing equation is a scalar, strongly degenerate parabolic equation in which both the convective and diffusion fluxes depend on parameters that are discontinuous functions of the depth variable. The initial value problem for this equation is analyzed for Model 1. We introduce a simple finite difference scheme and prove its convergence to a weak solution that satisfies an entropy condition. A limited analysis of steady states as desired stationary modes of operation is performed. Numerical examples illustrate that the model realistically describes the dynamics of flocculated suspensions in clarifier-thickeners.
121 citations
Cites result from "Rapid filtration measurement of dew..."
...Moreover, the sedimentation-consolidation model is equivalent to the suspension dewatering theory employed in [2, 28, 52, 67], and other works by the same group of authors....
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TL;DR: In this article, a method is presented to estimate the hindered settling function (R(ϕ) from batch-settling tests for solids volume fractions between the initial volume fraction and the volume fraction at which the suspension forms a continuously networked structure, known as the gel point.
Abstract: The hindered settling function R(ϕ) is a material function that quantifies the interphase drag of colloidal suspensions for all solids volume fractions ϕ. A method is presented to estimate R(ϕ) from batch-settling tests for solids volume fractions between the initial solids volume fraction, ϕ0, and the solids volume fraction at which the suspension forms a continuously networked structure, ϕg, known as the gel point. The method is based on an analytic solution of the associated inverse problem. Techniques are presented to address initialization mechanics observed in such tests as well as experimental noise and discrete data. Analysis of synthetic and experimental data suggests that accurate estimates of R(ϕ) are possible in most cases. These results provide scope for characterization of suspension dewaterability from batch-settling tests alone. © 2005 American Institute of Chemical Engineers AIChE J, 2005
103 citations
References
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TL;DR: In this paper, issues concerning powder consolidation methods compatible with the colloidal approach and issues associated with other powder processing steps, viz., densification and microstructural control, are presented with regard to research directions leading to more reliable ceramics.
Abstract: Issues concerning powder consolidation methods compatible with the colloidal approach and issues associated with other powder processing steps, viz., densification and microstructural control, are presented with regard to research directions leading to more reliable ceramics.
1,110 citations
TL;DR: In this paper, the concentration or consolidation of suspensions of fine particles under the influence of a gravitational field has been analyzed and a constitutive equation is suggested for irreversibly flocculated suspensions undergoing consolidation which embodies the concept of a concentration-dependent yield stress Py(ϕ).
Abstract: The concentration or consolidation of suspensions of fine particles under the influence of a gravitational field has been analysed. The rate and extent of consolidation depends upon a balance of three forces, the gravitational driving force, the viscous drag force associated with flow of liquid in the sediment and a particle or network stress developed as a result of direct particle–particle interactions. In the case of colloidally stable suspensions, this particle stress is the osmotic pressure of the particles; in the case of flocculated or coagulated suspensions, it is the elastic stress developed in the network of particles. A constitutive equation is suggested for irreversibly flocculated suspensions undergoing consolidation which embodies the concept of a concentration-dependent yield stress Py(ϕ). This is then used to analyse the sedimentation behaviour of flocculated sediments and to derive expressions for the initial sedimentation rate. The initial rate of change of sediment height with time in a uniform gravitational or centrifugal field is given approximately by: [graphic ommitted] where B=Δρgϕ0H0/Py(ϕ0), u0 is the sedimentation rate of an isolated particle, ϕ0 is the initial (uniform) volume fraction of solids, r(ϕ0) is a dimensionless hydrodynamic interaction parameter, Δρ is the difference in density between solid and liquid, g is the gravitational or centrifugal acceleration and H0 is the initial sediment height. The theory accounts correctly for the equilibrium consolidation behaviour of strongly flocculated suspensions, and preliminary experimental data suggest that it is not inconsistent with their dynamic behaviour. The estimation of the yield stress Py(ϕ) from a batch centrifuge experiment is also described.
403 citations
"Rapid filtration measurement of dew..." refers background in this paper
...At this stage, the structure of the network will collapse, irreversible particle consolidation will occur, and the local volŽ .ume fraction will increase Buscall and White, 1987 ....
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TL;DR: In this paper, the consolidation behavior of flocculated alumina suspensions has been analyzed as a function of the interparticle energy, and it has been shown that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range.
Abstract: The consolidation behavior of flocculated alumina suspensions has been analyzed as a function of the interparticle energy. Consolidation was performed by a centrifugal force field or by gravity, and both the time-dependent and equilibrium density profiles were measured by a gamma-ray absorption technique. The interparicle energy at contact was controlled by adsorbing fatty acids of varying molecular weight at the alumina/decalin interface. We found that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range. The most weakly flocculated suspension showed an essentially incompressible, homogeneous density profile after consolidation at different centrifugal speeds. We also found a significant variation in the maximum volume fraction, φm, obtained, with φm∼ 0.54 for the most strongly flocculated suspension to φm∼ 0.63 for the most weakly flocculated suspension. The compresive yield stresses show a behavior which can be fitted to a modified power law. In this paper, we discuss possible correlations between the fitting parameters and physical properties of the flocculated suspensions.
194 citations
TL;DR: In this article, the shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction, and the links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
Abstract: The shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction. Over a range of volume fractions, yield stresses, τy, elastic moduli, the strain delimiting the extent of the linear elastic response, and compressive yield stress, Py, are well described by power-law functions of volume fraction, while the role of interparticle attractions can be accounted for by expressing these mechanical properties as (ϕ/ϕg − 1)n, where ϕg captures the strength of particle attractions and n the microstructure. The links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
167 citations
TL;DR: In this paper, a two-stage pressure filtration process of compact formation and then consolidation is considered, and the rheological formulation appears at first examination to be significantly at variance with the conventional engineering approach.
Abstract: From the development of a compressional rheology of a flocculated suspension, a number of separation processes have been modeled. With respect to the two-stage pressure filtration process of compact formation and then consolidation, the rheological formulation appears at first examination to be significantly at variance with the conventional engineering approach. The present model may be reconciled to the early engineering model. Moreover, the filtration parameters extracted from experiments can be related to the more fundamental rheological parameters, r({phi}), the hindered settling factor, which is a function of solids volume fraction {phi}--it takes into account hydrodynamic interactions between local particles, which increase the drag forces. Useful estimates of the compact bed formation resistance and the formation time are provided as a function of applied pressure. The initial time dependence of the consolidation ratio on the elapsed consolidation time is not found to be a square root behavior as suggested by the conventional modeling.
115 citations
"Rapid filtration measurement of dew..." refers background in this paper
...Ž . rV r , and this will be denoted R here.p Since the overall dewatering process depends on both comŽ .pressibility and permeability Landman et al. 1995 derived a Ž ....
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...Landman et al., 1995 ....
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