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| Titel |
Modelling of biodegradation and isotope fractionation of petroleum hydrocarbon plumes in 2D bench-scale tank experiments |
| VerfasserIn |
Elisabetta Ballarini, Sebastian Bauer, Robert Bauer, Christian Griebler, Christof Beyer |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046708
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| Zusammenfassung |
| In case of the natural attenuation of an organic contaminant in porous aquifers,
biodegradation together with transverse mixing represent the main processes that determine
plume length and contaminant concentration. In order to study the interplay of biodegradation
processes in detail, aerobic and anaerobic biodegradation of ethylbenzene were investigated
in 2D bench-scale tank experiments. This set-up reduces natural complexity and allows a
spatially and temporally resolved evaluation of individual parameters and processes. Flow of
oxic and reduced groundwater through the homogeneously and heterogeneously packed
porous media was maintained by simultaneously injecting water into inlet ports and
extracting from outlet ports at the sides of the tank at a transport velocity of 1.2 m d-1. A
mixture of unlabeled and fully deuterium-labeled ethylbenzene isotopomers (ratio 3:1)
was supplied through one central inlet port, generating an ethylbenzene plume. In
the first phase of the experiment, the system was recharged with water containing
oxygen as electron acceptor and inoculated with the strain Pseudomonas putida
F1 to initiate aerobic biodegradation of ethylbenzene. Later, nitrate was added as
an additional electron acceptor and competitive degradation under denitrifying
conditions was studied after inoculating strain Aromatoleum aromaticum EbN1. The
spatial distribution of anaerobic degradation was investigated using measurements of
compound-specific stable isotope fractionation along vertical profiles at the tank
outlet.
High resolution reactive transport modelling was applied to substantiate the experimental
results and to elaborate the factors controlling biodegradation. For the numerical
evaluation of the laboratory experiments, the FEM code OpenGeoSys (OGS) was
used. OGS is a software for the simulation of thermo-hydro-mechanical-chemical
(THMC) processes in porous media that allows simulation of multi species reactive
transport, kinetic and equilibrium geochemical reactions, biodegradation reaction
following multiplicative Monod kinetics as well as stable isotope fractionation.
Sensitivity analysis showed that although an increase of water flow velocity and
sediment porosity results in higher transverse mixing, the reduced contact time between
electron donor and acceptor limits ethylbenzene degradation. Simulated and measured
ethylbenzene and oxygen concentrations showed a good agreement for the aerobic
degradation phase, while the evaluation of the anaerobic phase turned out to be more
difficult as there are uncertainties in the correct stoichiometry of the denitrification
reaction. The model results, calibrated on the stable isotope signatures, showed that
for the case of aerobic/anaerobic degradation, the reproduction of the observed
isotopic patterns is strongly dependent on the assumed initial distribution of microbial
biomass.
Key words tank experiments; numerical modelling; biodegradation; isotope fractionation. |
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