Abstract:
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In the last few years, enhanced in situ denitrification has gained a lot of interest as a reliable bioremediation
option to remove nitrate from groundwater. However, denitrification modelling in the subsurface
environment is less developed than in other fields like wastewater treatment, due to the complexity
of describing microbial processes in natural systems and the lack of proper kinetic and stoichiometric
parameters.
In this study, a mathematical model describing nitrate, oxygen and organic carbon consumption coupled
with the growth and decay of a heterotrophic microbial population was developed. The model has
the aim of explaining experimental data that was obtained in microcosm batch tests containing groundwater
and subsoil from a nitrate-contaminated aquifer stimulated with glucose as an external carbon
source.
The most sensitive parameters (heterotrophic maximum growth rate, decay rate constant and initial
heterotrophic biomass concentration) were calibrated by experimental data fitting. Two experimental
designs, a single dentrification test and a fedbatch-operation test, were performed in order to calibrate
these parameters. The fedbatch-operation experiment, consisting of four consecutive pulses of nitrate
and a carbon source, resulted in a more appropriate calibration of model parameters than the single
denitrification test, based on the practical identifiability study. Parameter confidence intervals were calculated
by means of the Fisher Information Matrix (FIM). Results indicated that the model, with the
optimal estimated parameters, could properly fit experimental data. The presented model constitutes a
first approach for modelling enhanced denitrification in aquifer systems. |