ON THE TRANSPORT AND FATE OF BIOSOLID COLLOIDS IN POROUS MEDIA

Land application of biosolids is a common practice widely employed throughout the United States. Studies have shown that biosolids contain significant amounts of colloidal materials, whose mobility in porous media may contribute to the facilitated transport of contaminants through the soil profile and into regional waterways. There is special interest in the potential impact of nano-scale colloids, given their size and reactivity. To better understand the fate of environmentally-released biosolid colloids, this study examines the contributions of physical hydrodynamics and geochemical heterogeneities to the transport behavior of nano-scale aluminum oxide colloids in porous media. The initial breakthrough of nano-scale Al₂O₃ closely followed that of the nonreactive tracer. The effluent concentration of Al₂O₃ then exhibited steady state behavior with a plateau at a relatively small fraction of the injection concentration, suggesting strong, irreversible attachment/adhesion. Following this concentration plateau, the effluent concentrations began to rise, suggesting a change in the magnitude of nano-particle attachment/adhesion that resulted in increased nano-particle mobility. The sustainability of common agricultural practices as well as surface and groundwater resources can be greatly affected by leaching of organic and inorganic compounds commonly found in biosolids (e.g., pharmaceuticals, heavy metals, and PBDEs). An accurate understanding of the processes that mediate colloid transport in porous media is key to addressing and solving such issues.