Mobilization and Transport of Natural and Synthetic Colloids and a Virus in an Iron Oxide-Coated Sewage-Contaminated Aquifer

By Joseph N. Ryan, Menachem Elimelech, Rebecca A. Ard, and Robin D. Magelky

ABSTRACT

To examine the dependence of colloid transport and mobilization on chemical perturbations, we injected colloid-mobilizing agents, synthetic tracer colloids, and a virus into a geochemically heterogeneous aquifer. The transport of mineral (silica and silica-coated metal oxide) and biological (viruses) colloids were related to the surface properties of the colloids and aquifer grains (as measured by zeta potential). The extent of ferric oxyhydroxide surface coverage measured by electron microprobe and estimated by the collision efficiencies for the viruses agreed well. Increases in pH were most effective in mobilizing colloids (both natural and synthetic) and viruses because increases in pH above the pH_pzc were most effective in reversing the charge of the ferric oxyhydroxide coatings. In most cases, the transport of mobilized colloids was limited by the advance of the colloid-mobilizing agent (e.g., decrease in ionic strength, anionic surfactant concentration, reductant concentration). A new class of tracer colloids, silica-coated metal oxides, were developed to test the dependence of colloid transport on colloid size.