Colloid Detachment from Rough Surfaces in the Environment

by Neyland, Ryan P.

Colloid detachment and mobilization can be of significant interest to those studying colloid behavior in the environment. The transport of pathogens such as viruses, bacteria, and protozoa can cause health problems in animals and humans. The transport of organics, radionuclides, and other hydrophobic contaminants can be enhanced by adsorption to mobilized colloid surfaces. Research has been done by others quantifying the detachment of colloids from smooth porous media. Real surfaces in the environment and engineered systems are rough. Glass beads were chemically roughened by procedures similar to those from Shellenberger and Logan (2002) and Itälä et al. (2001) using chromic acid and a citric acid/ammonium fluoride solution. Surface asperities were measured using Atomic Force Microscopy (AFM), and the roughness was defined by three parameters: Root Mean Square (RMS) roughness, peak to valley height (P/V height), and peak to peak distance (?). Detachment from the chemically etched porous media was measured in column tests. The controlling roughness parameter between the two batches of beads was found to be ?. A theoretical model to predict the effect of roughness on detachment was developed. Using a moment balance around the downstream point of contact, the parameters incorporated into the model were particle diameter, P/V height, and ?. The model predicted the shear required for colloid detachment in column tests. Surface roughness was found to significantly inhibit colloid detachment. VIII