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

Abstract

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. efforts, few experimental studies have been designed to test those theoretical and conceptual approaches and to describe the aforementioned environmental factors quantitatively in relation to the microbial transport models developed. Nevertheless, it is generally accepted that bacterial transport can be described by the advection-dispersion equation with modifications to account for growth, decay, attachment, and detachment [e.g., Corapcioglu and Haridas, 1984, 1985; Taylor and Jaffe, 1990; Harvey and Garabedian, 1991; Hornberger et al., 1992; Tan et al., 1992]. Attachment refers to processes such as adsorption and straining that can cause retention of bacteria in a porous medium, and detachment refers to the subsequent dislodgment of bacteria from the surfaces. The attachment and detachment of bacteria are the most important and complex processes affecting bacterial transport and are arguably the least understood. Broadbased attempts have been made t...

Processes in microbial transport in the natural subsurface

“…Therefore, in unstructured models the biomass is a fully penetrable volumeless component which assumes that a linear relation exists between mass of substrate consumed and mass of biomass produced and that no diffusion limitations affect the transfer of substrate mass from solution into the biomass. This approach has been taken in model construction [25,144,159,162], in column studies that focus on bacterial transport [69,120] and in intermediate-scale flow cell studies that focus on active degradation and growth and coupled transport [130,169]. For instance, Macquarrie et al [162] used this approach in treating biomass involved in aerobic degradation as a volumeless species undergoing transport, with equilibrium partitioning of biomass between aqueous and attached phases.…”

“…Murphy et al [169] extend the linear reversible model to include non-linear dependence of the rate coefficients on ionic strength of solution, manifest in intermediate-scale experiments. Tan et al [120], Lindqvuist et al [69], and Saiers and Hornberger [105] all introduce the classical site-saturation limiting factor on the attachment rate coefficient, in order to account for potential depletion of available surface sites as attached microbe densities increase, which may occur when aqueous microbes cannot attach to attached microbes. Ginn [43] modeled non-Markovian (i.e., residence-time dependent) attachment/detachment kinetics apparent in experiments of McCaulou et al [165] using the exposure-time approach of Ginn [153], as described below.…”

Modeling the effects of systematic variation in ionic strength on the attachment kinetics of Pseudomonas fluorescens UPER‐1 in saturated sand columns

“…After finding certain distinct modes of transport and attachment of bacteria we modeled their behavior and calculated values for more than one attachment kinetics parameter. We extend the existing first-or second-order kinetic models [Tan et al, 1994;Lindqvist et al, 1994] to include an intermediate-order kinetics ("ripening," attachment rate increases with time), which is distinct from the other two.…”

A Mathematical Model and Analytical Solution for the Fixation of Bacteria in Biogrout

“…Adsorption and desorption are important phenomena as well, but also the pore size of the matrix, the size of the microorganisms, filtration and elimination (Matthess et al 1981(Matthess et al , 1988Fontes et al 1991;Foppen et al 2006), ionic strength of the ground water (Fontes et al 1991;Foppen et al 2006), systematic (chemotaxis) and random (tumbling) motion of bacteria (Yavuz Corapcioglu et al 1984), residence time (Johnson et al 1995), decay and growth (Yavuz Corapcioglu et al 1984;Foppen et al 2006) effect the (rate of) transport of microorganisms. Hornberger et al (1992), Johnson et al (1995) and Tan et al (1994) provide various models that consider several of these phenomena and compare the model results with experimental results.…”

“…First we present the general equation for the transport of bacteria in a fully saturated porous medium, as in for example, Tan et al (1994):…”