Advanced numerical modeling of flow and reactive transport in porous systems
Final Report Abstract
One of the major foci of the project work was the evaluation of tank experiments aimed at the determination of transverse dispersion by numerical simulation. First, the accuracy of a commonly used parameter estimation approach, which employs an analytical solution of the 2D advection-dispersion equation to fit the laboratory measurements, was assessed by performance of synthetic tank experiments, where all the parameters (porosity, hydraulic conductivity, longitudinal and transverse dispersivity, etc.) are known a priori. The synthetic measurements were evaluated by inverse analytical modelling. On average, errors in estimated transverse dispersivities were less than 10 %, which proves that the evaluation of tank experiments by analytical modelling yields good parameter estimates. Sensitivity analyses then were performed to study the influence of hydraulic and transport parameter variations on the experimental observations. Based on these results, the numerical model was used to suggest an improved tank set-up which was applied in a new set of laboratory experiments in homogeneous and heterogeneous media and at different flow velocities. A unique parameter set could be calibrated to closely fit the measured concentration data by numerical modelling of all experiments. The second major focus of our work was the model based evaluation and interpretation of reactive transport experiments performed by TP4 (Meckenstock). For this purpose, the OpenGeoSys reactive transport code (OGS) was enhanced by implementation of isotope fractionation as a new reaction class in OGS and the MPI-parallelization of the kinetic reaction kernel in order to increase the computational efficiency of the code. Our work was specifically aimed at a 75 day experiment in a homogeneous tank which started with degradation of toluene, which was later replaced by a mixture of unlabelled and deuterium-labelled ethylbenzene isotopologues, by the aerobic strain Pseudomonas putida F1. Later, the anaerobic denitrifying and hydrogen isotope fractionating strain Aromatoleum aromaticum EbN1 was inoculated, in order to study the competitive aerobic/anaerobic degradation of ethylbenzene. Simulated and measured ethylbenzene and oxygen concentrations showed a good agreement for the aerobic degradation phase, while the evaluation of the aerobic/anaerobic phase with competitive biodegradation proved to be more intricate. Especially, the simulated isotopic patterns were very sensitive on the assumed initial distribution of the A. aromaticum EbN1 biomass at the beginning of the aerobic/anaerobic phase. Ethylbenzene concentrations and isotope patterns predicted by the numerical model match the measurements quite well for the first half of the aerobic/anaerobic phase. A distinct increase in biodegradation dynamics later on, however, was not captured well by the model prediction. These observations suggest that biodegradation during the first half of aerobic/anaerobic phase follows a different dynamics than in the second half, which so far could not be modelled satisfyingly. It is hypothesized that the observed amount of biodegradation during the first half is mainly due to the inoculated biomass, while the increase in biodegradation in the second half probably results from a notable augmentation of the injected biomass, which takes a few days to come into effect.
Publications
- (2009). Enhanced biodegradation by hydraulic heterogeneities in petroleum hydrocarbon plumes. J. Cont. Hydrol., 105 56–68
Bauer, R.D., Rolle, M., Bauer, S., Eberhardt, C., Grathwohl, P., Kolditz, O., Meckenstock, R.U., Griebler, C.
- (2010). Design and evaluation of bench-scale tank experiments for the quantification of transverse dispersion using numerical simulations. In: Schirmer, M., Hoehn, E., Vogt, T.: Proceedings of the Groundwater Quality Conference, 13-18.06.2010, Zürich, Switzerland, 255-258. IAHS Publ. 342, Wallingford, UK
Ballarini, E., Bauer, S., Eberhardt, C., Rolle, M., Grathwohl, P., Beyer, C.
- (2011). Modelling of biodegradation and isotope fractionation of petroleum hydrocarbon plumes in 2D bench-scale tank experiments. Geophysical Research Abstracts Vol. 13, EGU2011-1572
Ballarini, E., Bauer,. S., Bauer, R.D., Griebler, Beyer, C.
- Interpretation of hydrocarbon plume biodegradation in 2D bench-scale tank experiments by reactive transport modelling. ModelCare 2011, Leipzig, Germany
Beyer, C., Ballarini, E., Bauer,. S., Bauer, R.D., Griebler
- Numerical simulation of bench-scale tank experiments to quantify transverse dispersion. ModelCare 2011, Leipzig, Germany
Ballarini, E., Bauer, S., Eberhardt, C., Beyer, C.
