M. Yavuz Corapcioglu

Transport and fate of microorganisms in porous media: A theoretical investigation

Abstract Bacteria and viruses found in groundwater are a proven health hazard as evidenced by the large number of outbreaks of water-borne diseases caused by contaminated groundwater. To analyze the fate of biological contaminants in soils and groundwater, we studied various transport processes including dispersion, convection, Brownian motion, chemotaxis and tumbling of bacteria. The differences between bacteria and viruses in their transport mechanisms, decay and growth kinetics have also been investigated. It has been shown that the rate of deposition terms can be incorporated by a first-order and an adsorption isotherm for bacteria and viruses, respectively. The movement of bacteria is coupled with the transport of a bacterial nutrient present in seeping wastewater.

Modeling of centrifugal filtration in unsaturated deformable porous media

Centrifugal filtration through porous matermls, under both saturated as well as unsaturated flow condmons, plays an important role in diversified fields of science and technology, such as soft physics, groundwater hydrology, sludge dewaterlng, pharmacology, and petroleum engmeenng It is of specml interest in certain industrial processes that involve fluid extraction and drying, e g , in the sugar and paper pulp industries To meet the needs to evaluate centrifugal filtraUon in all these cases, studies have been conducted leading to formulas that express relations among the many variables that describe the process Most of these studies have been expenmental ones, leading to empirical relations that describe the filtration capacity In some cases, results have been obtained by using very simple models of the filtration phenomenon Because of the nature of these investigations, each result could be apphed only to a specific case, or to a hmlted range of cases The absence of a umform methodology for the design of centrifuges has forced engineers to use pdot-scale evaluation procedures In what follows, we shall show how the theory of flmd flow through a deformable porous medmm, in the presence ofa centnfugal force, may serve as a basis for the construction of a rather general model of centrifugal filtration

Dual-porosity groundwater contaminant transport in the presence of colloids

Prior studies have shown that colloids can facilitate contaminant migration in unimodal porous media. To investigate the effect of no-flow regions on flow and contaminant transport in dual-porosity soils, we model a porous medium composed of two different homogeneous, superposed, and interacting regions: the mobile region and the immobile region. We assume that the advective-dispersive processes govern the transport of contaminant and colloids in the mobile region, while the diffusion process dominates in the immobile region. The contaminant and colloid mass transfer mechanisms between these two regions are represented by a first-order mass transfer. Colloid deposition on the solid matrix is expressed by a kinetic sorption relationship. The contaminant sorption with the solid matrix and colloidal surfaces is also incorporated into the model. Coupled with mass transfer terms, two sets of governing equations representing the fate and transport of contaminant and colloids in both the mobile and immobile regions are developed and applied to experimental data available in the literature. Numerical solutions are obtained by employing a fully implicit, finite difference scheme. The numerical results indicate that the colloidal facilitation is increased in a dual-porosity porous medium compared to a unimodal medium. The model is validated by comparing the numerical results with the experimental data available in the literature for colloid-facilitated contaminant transport in a single-porosity medium and contaminant transport in a colloid-free, dual-porosity medium. A sensitivity analysis is conducted to deduce the effect of major model parameters on contaminant transport. The analysis demonstrates that, although both the volumetric fraction of the mobile region and the mass transfer rate coefficients between the two regions have effects on the dual-porosity transport, the early breakthrough is affected mainly by the volumetric fraction of the mobile region, while the tailing is affected largely by the mass transfer rate coefficients.

Land Subsidence — A. A State-of-the-Art Review

Following a description of the phenomena of land subsidence, its main features and its occurrence in many parts of the world, the review starts with the simplest depth-porosity model and models that are based on field data and empirical relations. It then continues through models that are based on the theories and physical concepts. The first studies of these kind are the semi- infinite elastic solid models which assume the earth to behave like a homogeneous, isotropic half space with a uniform elasticity modulus. A more rigorous approach to model land subsidence includes transient flow and equilibrium equations for isothermal reservoirs. A solution of this set of coupled equations can be obtained either by full-coupling which could be quite lengthy or by partial coupling which can be separated into two subgroups: “leap frog” and “two step” techniques. In the “two-step” method, the aquifer flow equation is solved in a three or two-dimensional space and then it is assumed that the solid deformation is one dimensional and one-dimensional consolidation equations are solved for aquitards in the reservoir. The results of the flow equation are the time dependent boundary conditions of the consolidation equations. An alternative approach to explain the behaviour of aquitards is given by viscoelastic models which assume a Theological constitutive equation instead of an elastic one as employed by the “two-step” technique. Later, models using a plastic stress- strain relation, and models for horizontal displacements are also reviewed. Finally, geothermal reservoir models that require an additional energy equation are discussed.

Transport of dissolving colloidal particles in porous media

A mathematical model was developed to simulate the transport and dissolution of colloidal particles with a water-soluble component in a porous medium. The model is based on mass balance equations describing the mass transport, dissolution, sorption, capture, and release of colloids in a three-phase medium consisting of a solid matrix, an aqueous phase, and colloids. Colloid dissolution, contaminant sorption on solid matrix, and colloid capture mechanisms are represented by first-order kinetics. A numerical comparison of the model of a water-soluble component associated with fly ash–mobilized transport and transport due only to dissolved component migration indicates that the presence of colloids significantly increases the aqueous phase contaminant concentration.

THERMOELASTOPLASTIC DEFORMATION OF POROUS MATERIALS

Abstract A thermoplastic deformation theory which is based on a proposed general yield criterion and associated flow rule is presented for fully saturated nonisothermal porous materials. The theory can be applied to prediction of stresses and strains in thermoconsolidation of many engineering materials, e.g., soils, concrete, ceramics, etc.

Land Subsidence — B. A Regional Mathematical Model for Land Subsidence due to Pumping

A regional mathematical model for land subsidence and horizontal displacement resulting from pumping from an aquifer is developed on the basis of the works of Biot and Verruijt on consolidation. The regional mathematical model is obtained by integrating the equations that describe soil deformation in a three-dimensional space over the aquifer’s thickness, assuming conditions of plane excess total stress. These equations involve coupling between the equations of equilibrium of the porous medium and those of mass conservation. The resulting model yields both the aquifer compaction and the horizontal displacements, as functions of space coordinates and of time, for confined, leaky and phreatic aquifers.