Transport of nonlinearly biodegradable contaminants in aquifers
This thesis deals with the transport behavior of nonlinearly biodegradable contaminants in aquifers. Such transport occurs during in situ bioremediation which is based on the injection of an electron acceptor or electron donor. The main interests in this thesis are the mutual influences of underlying processes, i.e. transport, adsorption and biodegradation, and their influence on in situ bioremediation performance. To gain insight in these influences, the processes in a homogeneous aquifer are studied. Subsequently, the effect of physical heterogeneity of an aquifer on the displacement of the biodegradable contaminant is examined.Considering a homogeneous aquifer, numerical simulations are performed to ascertain the effect of transport, adsorption and biodegradation on the displacement of the contaminant and of the electron acceptor or electron donor. In the initial phase, the developed numerical results are successfully described by first order degradation. In the final phase, the numerical results show a traveling wave behavior; the developed concentration fronts have constant front shapes and 'travel' with a constant velocity through the aquifer. This behavior is due to the balance between the steepening effect of nonlinear biodegradation and the spreading effect of dispersion. Because of this traveling wave behavior, semi-analytical solutions have been derived that satisfactorily approximate the numerical results. These semi-analytical solutions are used to assess the performance of the in situ bioremediation. If in situ bioremediation is applied to a polluted site, the electron acceptor injection concentration and the injection velocity will be the only manipulative properties. By varying these two properties, the in situ bioremediation performance can be influenced and optimized.To study a physical heterogeneous aquifer, the hydraulic conductivity is considered spatially variable and it is assumed to be a random space function. The effect of physical heterogeneity is determined using a Lagrangian stochastic approach. Results show that incorporation of physical heterogeneity leads to a spreading of the breakthrough curve of both the contaminant and the electron acceptor or electron donor. In case of a large degree of heterogeneity, i.e. a strongly heterogeneous aquifer, it is the heterogeneity which determines the shape of the breakthrough curve and not the dispersion or nonlinear biodegradation.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
| Subjects: | aquifers, biodegradation, bioremediation, contaminants, besmetters, biodegradatie, bioremediëring, watervoerende lagen, |
| Online Access: | https://research.wur.nl/en/publications/transport-of-nonlinearly-biodegradable-contaminants-in-aquifers |
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| Summary: | This thesis deals with the transport behavior of nonlinearly biodegradable contaminants in aquifers. Such transport occurs during in situ bioremediation which is based on the injection of an electron acceptor or electron donor. The main interests in this thesis are the mutual influences of underlying processes, i.e. transport, adsorption and biodegradation, and their influence on in situ bioremediation performance. To gain insight in these influences, the processes in a homogeneous aquifer are studied. Subsequently, the effect of physical heterogeneity of an aquifer on the displacement of the biodegradable contaminant is examined.Considering a homogeneous aquifer, numerical simulations are performed to ascertain the effect of transport, adsorption and biodegradation on the displacement of the contaminant and of the electron acceptor or electron donor. In the initial phase, the developed numerical results are successfully described by first order degradation. In the final phase, the numerical results show a traveling wave behavior; the developed concentration fronts have constant front shapes and 'travel' with a constant velocity through the aquifer. This behavior is due to the balance between the steepening effect of nonlinear biodegradation and the spreading effect of dispersion. Because of this traveling wave behavior, semi-analytical solutions have been derived that satisfactorily approximate the numerical results. These semi-analytical solutions are used to assess the performance of the in situ bioremediation. If in situ bioremediation is applied to a polluted site, the electron acceptor injection concentration and the injection velocity will be the only manipulative properties. By varying these two properties, the in situ bioremediation performance can be influenced and optimized.To study a physical heterogeneous aquifer, the hydraulic conductivity is considered spatially variable and it is assumed to be a random space function. The effect of physical heterogeneity is determined using a Lagrangian stochastic approach. Results show that incorporation of physical heterogeneity leads to a spreading of the breakthrough curve of both the contaminant and the electron acceptor or electron donor. In case of a large degree of heterogeneity, i.e. a strongly heterogeneous aquifer, it is the heterogeneity which determines the shape of the breakthrough curve and not the dispersion or nonlinear biodegradation. |
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