Quantitative characterization of soil aggregate microstructure

Soil has a complex porous structure that plays an important role in the application of bioremediation. Bioremediation is a cost-effective technology of degrading toxic pollutants in soil and ground water to less harmful substances with microorganisms. Most of the processes developed in laboratories for effective bioremediation fail on site due to lack of understanding of the complex soil structure.; Soil is a two phase model with an aggregate phase of agglomerated soil particles and a mobile phase of ground water moving between the soil aggregates. Diffusion, sorption and biodegradation occur in the aggregates while convective transport occurs in the mobile phase. The description of these processes and their contribution to bioremediation is complicated by the heterogeneous pore size distribution and irregular pore morphology of soil, which determines the system microstructure and thus the transport of chemical and microbial components in the bioremediation process. The main objective of this thesis was to quantitatively characterize the microstructure of four soils representing a range of sand-silt-clay compositions using both experimental measurements and computer simulation techniques.; Soil aggregates were flooded with a fluorescent dye and the dye filled pore networks were imaged using a laser scanning confocal microscope to optically section each three-dimensional aggregate into a series of two-dimensional images. Pore size distribution and pore morphology were estimated from these images. The irregular pores in each two-dimensional section were modeled by their best-fit ellipses. Algorithms were developed for the connection of these elliptic fit pores in subsequent planes, enabling reconstruction of the three dimensional pore networks. Four different soils of varying composition were studied in order to establish a relationship between pore structure and soil composition. Monte Carlo simulations of the aggregate pore structure were developed and compared to the experimental pore structures to examine hypotheses regarding the relationship between soil composition and microstructure. This work provides a basis for investigating the contribution of soil aggregate pore structure to bioremediation processes.