Modeling Microbial Transport and Biodegradation in a Dual-porosity System (original) (raw)

Transport of bacteria in an aquifer sand: Experiments and model simulations

Water Resources Research, 1994

Experiments were carried out to determine the breakthrough of bacteria through a saturated aquifer sand at three flow velocities and three cell concentrations. Bacteria were either suspended in deionized water or 0.01 mol L -• NaCI solution. Bacterial transport was found to increase with flow velocity and cell concentration but was significantly retarded in the presence of 0.01 mol L -• NaC1. A mathematical model based on the advection-dispersion equation was formulated to describe bacterial transport and retention in porous media. The transport equations for bacteria were solved using the finite difference Crank-Nicolson scheme combined with Newton-Raphson iterations. The best fit of the numerical model to the experimental data was obtained using the downhill simplex optimization technique to minimize the sum of the squares of deviations between model predictions and experimental data by varying three parameters. This numerical model was found to describe the experimental data very well under all the experimental conditions tested. An alternative model (also based on the advection-dispersion equation) was tested against all the experimental data sets, but it did not represent the experimental data as well as the model proposed in this paper. face materials [e.g., Bitton et al., 1974; Wollum and Cassel, 1978; Smith et al., 1985; Parke et al., !986; Tan et al., 1991]. Many environmental factors such as ionic strength and flow velocity of the soil solution and properties of the porous materials have been identified to affect microbial transport in porous media in qualitative terms [e.g., Goldshrnid et al., 1973; Bitton et al., !974; Smith et al., !978; Wollum and Cassel, 1978; Gerba and Bitton, !984; McDowell-Boyer et al., 1986; Fontes et al., 1991; Gannon et al., 1991b; Gammack et al., 1992]. Complex mathematical models have also been developed to describe bacterial transport in porous media [e.g., Corapcioglu and Haridas, 1984, !985; Taylor and Jaffe, 1990]. Despite the experimental and modeling 1Now at Centre for Environmental Mechanics, CSIRO, Canben'a, Australia.

Modeling microbial transport in porous media: Traditional approaches and recent developments

Advances in Water Resources, 2007

A substantial research effort has been aimed at elucidating the role of various physical, chemical and biological factors on microbial transport and removal in natural subsurface environments. The major motivation of such studies is an enhanced mechanistic understanding of these processes for development of improved mathematical models of microbial transport and fate. In this review, traditional modeling approaches used to predict the migration and removal of microorganisms (e.g., viruses, bacteria, and protozoa) in saturated porous media are systematically evaluated. A number of these methods have inherent weaknesses or inconsistencies which are often overlooked or misunderstood in actual application. Some limitations of modeling methods reviewed here include the inappropriate use of the equilibrium adsorption approach, the observed breakdown of classical filtration theory, the inability of existing theories to predict microbial attachment rates, and omission of physical straining and microbe detachment. These and other issues are considered with an emphasis on current research developments. Finally, recently proposed improvements to the most commonly used filtration model are discussed, with particular consideration of straining and microbe motility.

Hydraulic Behavior and Contaminant Transport in Multiple Porosity Media

Transport in Porous Media, 2001

The hydraulic behavior and contaminant transport of aquifers containing distinct families of fractures are investigated by using the multiple porosity continuum model. We consider that the conditions are such that a horizontal 2D flow takes place. By writing the continuity of mass (including exchange terms between the various families of fractures) and Darcy's law for each family of fractures, macroscopic equations for both confined and unconfined flow are obtained. A classification procedure and geometrical idealization of the individual fractures for each family is proposed which enables the calculation of the exchange coefficients. Equations for the description of the contaminant transport in the field scale for both confined and unconfined aquifer are developed. It turns out that the adequate formulation of the macroscopic equations and their sink-source term depends on whether the aquifer investigated is confined or unconfined, and also on the value of an nondimensional parameter describing the transfer process at the microscopic scale (connection Peclet number). Numerical investigation of representative problems offers some insight into the behavior of double and triple porosity aquifers.

Contaminant transport and biodegradation: 1. A numerical model for reactive transport in porous media

Water Resources Research, 1989

A new numerical solution procedure is presented for simulation of reactive transport in porous media. The new procedure, which is referred to as an optimal test function (OTF) method, is formulated so that it systematically adapts to the changing character of the governing partial differential equation. Relative importance of diffusion, advection, and reaction are directly incorporated into the numerical approximation by judicious choice of the test, or weight, function that appears in the weak form of the equation. Specific algorithms are presented to solve a general class of nonlinear, multispecies transport equations. This includes a variety of models of subsurface contaminant transport with biodegradation.

A Two Equation Model of Biologically Reactive Solute Transport in Porous Media

Transport of biologically reactive dissolved solutes in a porous medium including a biofilm phase is a complex process involving a wide variety of scales (from the bacteria scale to the aquifer heterogeneity scale) and processes (hydrodynamic, physicochemical and biochemical). The objectives of this work are 1) to derive a two-equation macroscopic model for bio-reactive transport at the Darcy-scale from the pore-scale description using the volume averaging method and 2) to compare the results of this model with those of recently developed one-equation models but confined to limited domains of application.

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

Journal of Hydrology, 1984

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 pheratic aquifers on E, coli transport influenced by preconsolidation and compressibility of soil

International Journal of Engineering & Technology, 2012

The rate of pollution on soil are the major problem of ground water contamination in the study area, the influence from preconsolidation and compressibility of soil influence on E.coli transport has been carried out. This is to determine the rate of influence on E.coli transport in pheratic aquifers, mathematical model were developed to monitor the influence on the preconsolidation and compressibility of soil on microbial transports, experimental analysis were also carried out through a standard column experimental analysis, ten samples were collected in a drilling site at interval of three metres each for several location, the effluent discharge from the lower end of the column were collected and subjected to a thorough analysis, the theoretical values were compared with experimental values, and both values compared faviourably well. This study has explained the transport of E.coli base on the level of concentration generate from aquiferious zone. The study has reveal that the expl...

Microbial transport in soils and groundwater: A numerical model

Advances in Water Resources, 1985

To serve as a tool in the long term evaluation of the risk ofaccumulation of microbial contaminants (bacteria and viruses) entering soil and groundwater, a mathematical model is developed to predict the spatial and temporal distribution of pollutant concentration. The governing equation for bacterial transport is coupled with a transport equation for the bacterial nutrient present in the seeping wastewater. The deposition and declogging mechanisms are incorporated into the model as a rate process for bacteria and as an equilibrium partitioning for viruses. While the decay is assumed to be a first order reaction and the growth of bacteria is assumed to follow the Monod equation, the model equations exhibit nonlinearity and coupling. A simplified set of equations is solved analytically to test the numerical results. Coupled numerical solutions in one and two dimensions are obtained by the Galerkin method at spatial and temporal locations of interest. Cases studied included a soil column and a horizontal two-dimensional field coupled with the one dimensional solution. For these examples, the bacteria are removed almost totally within the top 7 cm of soil with minimal risk of clogging.