Biomedical subjects

M Elimelech

Publications and source records attributed to M Elimelech.

10 recordsLinked to original sources

PubMed2005

Effect of ferric oxyhydroxide grain coatings on the transport of bacteriophage PRD1 and Cryptosporidium parvum oocysts in saturated porous media.

To test the effect of geochemical heterogeneity on microorganism transport in saturated porous media, we measured the removal of two microorganisms, the bacteriophage PRD1 and oocysts of the protozoan parasite Cryptosporidium parvum, in flow-through columns of quartz sand coated by different amounts of a ferric oxyhydroxide. The experiments were conducted over ranges of ferric oxyhydroxide coating fraction of lambda = 0-0.12 for PRD1 and from lambda = 0-0.32 for the oocysts at pH 5.6-5.8 and 10(-4) M ionic strength. To determine the effect of pH on the transport of the oocysts, experiments were also conducted over a pH range of 5.7-10.0 at a coating fraction of lambda = 0.04. Collision (attachment) efficiencies increased as the fraction of ferric oxyhydroxide coated quartz sand increased, from alpha = 0.0071 to 0.13 over lambda = 0-0.12 for PRD1 and from alpha = 0.059 to 0.75 over lambda = 0-0.32 for the oocysts. Increasing the pH from 5.7 to 10.0 resulted in a decrease in the oocyst collision efficiency as the pH exceeded the expected point of zero charge of the ferric oxyhydroxide coatings. The collision efficiencies correlated very well with the fraction of quartz sand coated by the ferric oxyhydroxide for PRD1 but not as well for the oocysts.

Animals↗

PubMed2004

The role of endocrine disrupters in water recycling: risk or mania?

The widespread occurrence of endocrine disrupting chemicals (EDCs), such as steroid hormones, in secondary wastewater effluents has become a major concern in the water recycling practice. This paper investigates the risk of steroid hormone breakthrough during nanofiltration membrane filtration in water recycling applications. The results indicate a dynamic equilibrium between adsorption and desorption of steroid hormone with regard to the membrane. This equilibrium can be pH dependent and there is a possibility for release of steroid hormones at high pH during membrane cleaning procedures or erratic pH variations. Increase in water recovery can severely increase the hormone breakthrough concentration. The results also indicate a possibility of accumulation of steroid hormones in the NF membrane, followed by subsequent release.

Adsorption↗

PubMed2001

A novel two-dimensional model for colloid transport in physically and geochemically heterogeneous porous media.

A two-dimensional model for colloid transport in geochemically and physically heterogeneous porous media is presented. The model considers patchwise geochemical heterogeneity, which is suitable to describe the chemical variability of many surficial aquifers with ferric oxyhydroxide-coated porous matrix, as well as spatial variability of hydraulic conductivity, which results in heterogeneous flow field. The model is comprised of a transient fluid flow equation, a transient colloid transport equation, and an equation for the dynamics of colloid deposition and release. Numerical simulations were carried out with the model to investigate the colloid transport behavior in layered and randomly heterogeneous porous media. Results demonstrate that physical and geochemical heterogeneities markedly affect the colloid transport behavior. Layered physical or geochemical heterogeneity can result in distinct preferential flow paths of colloidal particles. Furthermore, the combined effect of layered physical and geochemical heterogeneity may result in enhanced or reduced preferential flow of colloids. Random distribution of physical heterogeneity (hydraulic conductivity) results in a random flow field and an irregularly distributed colloid concentration profile in the porous medium. Contrary to random physical heterogeneity, the effect of random patchwise geochemical heterogeneity on colloid transport behavior is not significant. It is mostly the mean value of geochemical heterogeneity rather than its distribution that governs the colloid transport behavior.

Colloids↗

PubMed2000

Transport of Iron Oxide Colloids in Packed Quartz Sand Media: Monolayer and Multilayer Deposition.

The transport and deposition dynamics of hematite (alpha-Fe(2)O(3)) colloids in packed quartz sand media are investigated. Column transport experiments were carried out at various solution ionic strengths, colloid concentrations, and flow velocities. A colloid transport model was proposed that includes the dynamics of blocking as well as multilayer deposition that takes place at high ionic strengths where particle-particle interactions are favorable. Blocking dynamics in the model are described by either Langmuirian adsorption (LA) or random sequential adsorption (RSA). Two important model parameters-the particle-matrix collision efficiency and the ionic strength dependent blocking (excluded area) parameter-are estimated from the colloid breakthrough curves using a nonlinear optimization procedure. The collision (attachment) efficiency for particle-particle interactions, on the other hand, was determined independently from colloid aggregation rate measurements. At very low ionic strength, only monolayer deposition is observed and the RSA model gives a better description of the experimental data than the LA model. At higher ionic strengths, multilayer deposition becomes significant and both models yield comparable results. Calculated maximum surface coverages at low ionic strengths were in good agreement with experimentally observed values obtained by scanning electron microscopy. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Coupled Influence of Colloidal and Hydrodynamic Interactions on the RSA Dynamic Blocking Function for Particle Deposition onto Packed Spherical Collectors.

The influence of electrostatic double-layer and hydrodynamic interactions on random sequential adsorption (RSA) of colloidal particles onto packed spherical collectors was investigated using inverse analysis of colloid breakthrough data obtained from well-controlled particle deposition experiments. Deposition experiments were carried out using monodisperse aqueous suspensions of positively charged latex colloids and packed columns of negatively charged uniform glass beads for different combinations of ionic strength, particle size, and approach velocity. From the experimental particle breakthrough data, the initial particle deposition rates and the virial coefficients of the dynamic blocking function based on RSA mechanics were determined. The magnitudes of the virial coefficients were observed to increase from the hard sphere values with increasing flow rates and decreasing ionic strengths of the background electrolyte. Particle size also plays a significant role in governing the deposition dynamics. The deviation from the hard sphere RSA behavior becomes more prominent for larger particles. Copyright 2000 Academic Press.

Journal Article↗

PubMed1999

Concentration Polarization of Interacting Solute Particles in Cross-Flow Membrane Filtration.

A theoretical approach for predicting the influence of interparticle interactions on concentration polarization and the ensuing permeate flux decline during cross-flow membrane filtration of charged solute particles is presented. The Ornstein-Zernike integral equation is solved using appropriate closures corresponding to hard-spherical and long-range solute-solute interactions to predict the radial distribution function of the solute particles in a concentrated solution (dispersion). Two properties of the solution, namely the osmotic pressure and the diffusion coefficient, are determined on the basis of the radial distribution function at different solute concentrations. Incorporation of the concentration dependence of these two properties in the concentration polarization model comprising the convective-diffusion equation and the osmotic-pressure governed permeate flux equation leads to the coupled prediction of the solute concentration profile and the local permeate flux. The approach leads to a direct quantitative incorporation of solute-solute interactions in the framework of a standard theory of concentration polarization. The developed model is used to study the effects of ionic strength and electrostatic potential on the variations of solute diffusivity and osmotic pressure. Finally, the combined influence of these two properties on the permeate flux decline behavior during cross-flow membrane filtration of charged solute particles is predicted. Copyright 1999 Academic Press.

Journal Article↗

PubMed1998

Effect of Interparticle Electrostatic Double Layer Interactions on Permeate Flux Decline in Crossflow Membrane Filtration of Colloidal Suspensions: An Experimental Investigation.

A systematic study on the effect of electrostatic double layer interaction on permeate flux decline and deposit cake formation in crossflow membrane filtration of colloidal suspensions is reported. Three monodisperse silica suspensions with diameters of 47, 110, and 310 nm were used as model colloids, and a tubular zirconia membrane with an average pore diameter of 20 nm was used as a model membrane. The magnitude and range of the electrostatic double layer interactions were controlled via changes in solution ionic strength and pH. The coupling between colloidal interactions and hydrodynamic forces was investigated by changing the transmembrane pressure and particle size. The results indicate that the rate of flux decline is strongly dependent on solution ionic strength and, to a much lesser degree, on solution pH (for the investigated pH range 6.1-10.0). Variations in flux decline rate with solution ionic strength are especially significant as the particle size decreases. Particle cake thickness, permeability, and porosity generally increased with a decrease in solution ionic strength for a given particle size. For given physical and chemical conditions, the cake layer porosity increased with decreasing particle size, while cake permeability decreased with decreasing particle size. These trends are consistent with the increased importance of double layer repulsive forces in controlling the cake layer structure as the solution ionic strength and particle size decrease. Pressure relaxation experiments indicated that the particle cake layer is reversible, implying no irreversible deposition (attachment) of silica colloids onto the zirconia membrane surface. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

Gravity-Induced Coagulation of Spherical Particles of Different Size and Density

We consider a dilute homogeneous suspension of rigid spherical particles with different size and density in a motionless Newtonian fluid. These particles are moving under gravity at low Reynolds and Stokes numbers (negligible fluid and particle inertia) and high Peclet numbers (negligible Brownian diffusion). Doublets are formed when two particles in relative motion are brought into contact by the action of the attractive van der Waals force. Trajectory calculations for particles with different densities indicate that as the reduced density ratio increases above unity, the percentage of particles captured on the front hemisphere decreases, and this generally results in smaller collision efficiencies. Furthermore, in contrast to the case of particles with equal density, a maximum of the collision efficiency occurs for a particle size ratio smaller than unity. Above a critical value of the reduced density ratio, the occurrence of a closed region of relative trajectories confines the capture sites mostly to the "rear" hemisphere of each particle. As the reduced density ratio increases above the critical value, this region grows larger and the collision efficiency may be estimated by a closed-form asymptotic solution. Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗

PubMed1997

Kinetics of Permeate Flux Decline in Crossflow Membrane Filtration of Colloidal Suspensions.

A series of well-controlled membrane filtration experiments are performed to systematically investigate the dynamic behavior of permeate flux in crossflow membrane filtration of colloidal suspensions. Results are analyzed by a transient permeate flux model which includes an approximate closed-form analytical expression for the change of permeate flux with time. The model is based on a simplified particle mass balance for the early stages of crossflow filtration before a steady-state flux is attained, and Happel's cell model for the hydraulic resistance of the formed particle cake layer. The filtration experiments demonstrate that permeate flux declines faster with increasing feed particle concentration and transmembrane pressure and with a decrease in the particle size of the suspension. It is also shown that crossflow velocity (shear rate) has no effect on permeate flux at the transient stages of crossflow filtration. Pressure relaxation experiments indicate that the particle cake layer is reversible, implying no irreversible deposition (attachment) of particles onto the membrane surface or the accumulated (retained) particles. The experimental results are shown to be in very good agreement with the theoretical predictions, thus verifying the validity of the model for the transient permeate flux in crossflow filtration and the underlying assumptions in the derivation of the model. Copyright 1997 Academic Press.

Journal Article↗

PubMed1997

Surface Element Integration: A Novel Technique for Evaluation of DLVO Interaction between a Particle and a Flat Plate

A novel method, the surface element integration (SEI), is developed to determine the van der Waals and electrostatic double layer interactions between a particle and an infinite flat plate from the corresponding interactions per unit area between two infinite flat plates. Comparison with the Hamaker expression for nonretarded van der Waals interaction reveals that the new technique gives the exact interaction energy between a spherical particle and a flat plate. Available analytical expressions for the electrostatic double layer interaction energy between two infinite flat plates, based on the linearized Poisson-Boltzmann equation, are used in SEI to obtain the sphere-flat plate interaction energy. These sphere-flat plate interaction energies determined using SEI are compared with the corresponding interaction energies obtained from a detailed numerical solution of the Poisson-Boltzmann equation based on finite element analysis. The comparisons reveal that SEI scales the flat plate interaction to the corresponding sphere-flat plate geometry exactly, while the scaling based on the conventional Derjaguin approximation technique grossly overpredicts the interaction energy for small particles and low electrolyte concentrations. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗