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Section 4: Pollutant behaviour on field sites |
Groundwater Protection & Restoration Research Unit, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK
The transport of contaminants through aquifers is a complex issue affected by advection, dispersion, sorption and biodegradation. Biodegradation is the only process which allows the contaminant mass naturally to be physically reduced. Due to the quantity of contaminated sites and the expense of remediation schemes it is essential to understand the natural attenuation provided by biodegradation. Modelling of the biodegradation processes provides not only the means to a fuller understanding of a plume's development but also the facility to test potential remediation schemes. A two-tier classification system is presented which summarizes the current literature regarding the modelling of biotransformations in saturated porous media. The first relates to the treatment of the physical microbial setting and the second tier relates to the reaction approach. The physical setting tier is discussed in the context of biofilms. The basic theory and various types of biofllm are summarized while discussing the evidence for and against the necessity of representing biofilms in biotransformation models. The techniques implemented to model biofilms are summarized, including the limitations and previous and potential applications. The reaction tier constitutes four sections: first-order decay models, instantaneous reaction models, Monod kinetic models and Michaelis—Menton kinetics. For each of the reaction approaches a physical and mathematical description is provided with an explanation of its relevance for the modelling of biotransformations. An approach for selecting the appropriate modeling techniques is illustrated for a contaminated site.
