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Kinetic Model of Gas Bubble Dissolution in Groundwater and Its Implications for the Dissolved Gas Composition
journal contribution
posted on 2003-02-26, 00:00 authored by J. Holocher, F. Peeters, W. Aeschbach-Hertig, W. Kinzelbach, R. KipferBubble-mediated mass transfer is of major importance for
the gas exchange between soil air and groundwater.
The presence of entrapped air bubbles in the upper, quasi-saturated aquifer zone can crucially affect the interpretation
of atmospheric trace gas concentrations in groundwater
and associated fluids as well as intrinsic and enhanced
bioremediation procedures that rely on the actual
dissolved gas content of gases such as oxygen or nitrogen.
To describe the bubble-mediated gas exchange in detail,
a kinetic multi-species model for dissolved gas transport in
a porous medium including inter-phase mass transfer
with entrapped gas bubbles was developed. It takes into
account changes in the entrapped gas bubble sizes resulting
from the mass exchange and therefore allows the
quantification of mass transfer between bubbles of any
gas composition and flowing or stagnating water in a substrate
column. Considering the dissolution of entrapped air
bubbles, the resulting concentrations of dissolved atmospheric
gases significantly exceed their solubility equilibrium
concentrations. The temporal evolution of the composition
of this excess gas is controlled by the solubility and the
molecular diffusivity of the gases considered, by the flow
conditions, and by the physical properties of the aquifer
such as the ratio of entrapped air to water in the pore space.
In the case of noble gases in a through-flow system,
solubility differences appear to be more important for the
composition of the gas excess than the differences
between molecular diffusivities.
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bioremediation proceduresKinetic Modelgas exchangesolubility differencesgas transportsoil airpore spacegas contentmass exchangetrace gas concentrationsentrapped gas bubblesmass transferentrapped airflow conditionssubstrate columnGas Bubble Dissolutionentrapped air bubblesaccount changesgas compositionsolubility equilibrium concentrationsentrapped gas bubble sizes
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