A Kinetic Approach to Modeling Mobile Bacteria‐Facilitated Groundwater Contaminant Transport

Abstract

Mobile bacterial particles can act as carriers and enhance the transport of hydrophobic contaminants in groundwater by reducing retardation effects. Because of their colloidal size and favorable surface conditions, bacteria act as efficient contaminant carriers. When such carriers exist in a water-saturated porous medium, the system can be thought of as three phases: an aqueous phase, a carrier phase, and a stationary solid matrix phase. Contaminant may be present in either or all of these phases. In this study, a mathematical model based on mass balances is developed to describe the simultaneous transport and fate of a biodegradable contaminant and bacteria in a porous medium. The Monod model describes the relation between the growth rate of bacteria and concentration of the contaminant which serves as a growth substrate. The bacterial decay is assumed to be a first-order reaction. The mechanisms of bacterial mass transfer between aqueous and solid matrix phases, and contaminant mass transfer between aqueous and bacterial phases are represented by kinetic models. Governing equations are nondimensionalized and solved to analyze the bacteria-facilitated contaminant transport. The model is compared with a similar model obtained with local equilibrium assumption to understand the characteristics of kinetic and local equilibrium descriptions. Results show that the contaminant transport as well as bacterial transport can be described by local equilibrium assumption when Damk6hler numbers are larger than 10. Significant sensitivities to model parameters, particularly bacterial growth rate and influent bacterial concentration, were observed. The numerical results of the bacteria carrier effect match favorably with experimental data reported in the literature. Bacteria are colloidal-sized particles and naturally exist in groundwater aquifers. They carry negative charge in most natural systems [Harden and Harris, 1953]. In addition, since their density is near unity, they tend to form stable colloidal suspensions [Marshall, 1986]. Changes in groundwater chemistry caused by contaminant migration or changes in groundwater velocity can cause the detachment and mobilization of indigenous subsurface bacteria. Furthermore, introduction of exogenous bacteria in a bioremediation operation can enhance the transport of contaminants. Harvey et al. [1989] reported that larger microorganisms within bacterial size range migrate more rapidly through aquifer sediment than do smaller microorganisms. Smaller microorganisms should contact and therefore sorb to the solid matrix surface with greater frequency because of their higher rates of diffusional motion. Bacterial surfaces have hydrophobic chai'acteristics depending on their surface constituents, which enable hydrophobic substances to adsorb on their surfaces. Canton et al. [1977] reported that hydrophobic contaminants adsorb on the bacterial surface and can also desorb to some extent. In a review paper, Baughman and Paris [1981] concluded that sorption of organic solutes occurs on...

A dual-porosity theory for solute transport in biofilm-coated porous media

“…Finally, Eqs. (12) and (13) can be simplified and the resulting set of macroscopic equations is the following:…”

“…The assumption that the reactive phenomena do not prevail over the convective and diffusive processes, i.e., Da Ac 6 Pe A and Da Ax 6 Pe A ; is required to overcome this difficulty. These closure fields are used to evaluate the effective parameters of the macroscopic equation, according to the following expressions, which are derived by the injection of the closure assumptions (12) and (13) in the unclosed macroscopic equations (10) and (11). …”

“…Indeed, for the generally accepted orders of magnitude of the pore-scale Péclet number, in the range 0.01-100, and of the Damköhler number, lower than 10, the local-equilibrium model fails (see the comparison with experimental data of [7] or [8]. As an alternative, limitations by diffusion are considered between the microbial and bulk aqueous phase in microcolony models [9,10], while, in biofilm models [11][12][13][14], both external and internal mass transfer limitations are accounted for. These non-equilibrium models differ mainly by the assumption adopted for the geometrical description of the biomass.…”

Modeling Floodplain Filtration for the Improvement of River Water Quality

“…The retardation factor does not affect the spatial distribution of the organic matter concentration at steady state (Kim and Corapcioglu, 1996). The organic matter in river waters is somewhat recalcitrant; however, if captured in soil it can have enough time to be biodegraded due to the extended contact time with the biomass in the soil, which can increase biodegradability of the organic matter.…”

Evolution of fracture permeability due to co-colloidal bacterial transport in a coupled fracture-skin-matrix system

“…Thus, the presence of colloids and formation of fracture-skin can significantly affect the efficiency of the geothermal reservoir, as they have direct influence on the fracture permeability variation between the injection and production well, resulting from the aperture and pressure variation in the reservoir. Many numerical models have been developed for bacteria facilitated contaminant transport in porous media (Corapcioglu and Haridas, 1984;Corapcioglu and Kim, 1995;Kim and Corapcioglu, 1996;Sen et al, 2005;Kim, 2005Kim, , 2006 but very few studies have analyzed the same in the fractured media. Recently Natarajan and Suresh Kumar (2011b) developed a numerical model for bacteria facilitated contaminant transport in a coupled fracture-matrix system.…”