Colloid-enhanced transport of chemicals in subsurface environments: A review

Ample published evidence demonstrates that colloidal particles can act as carriers to enhance the transport of contaminants in subsurface environments. Conventionally, soil and aquifer porous media are considered to have two phases: an immobile solid matrix and a mobile liquid. Published reports indicate that biocolloids, aluminosilicate clay minerals, and organic colloids can migrate to considerable distances during water flow in soils and aquifers. In the presence of such carriers, the system should be perceived as consisting of three phases: a stationary solid matrix phase, a carrier phase, and an aqueous phase. Particle transport through porous media has been clearly demonstrated in filtration studies, but a need exists to investigate the role of colloidal carriers upon contaminant transport in porous media and to model carrier-enhanced migration of contaminants accurately. In order to assess the potential role of colloidal carriers in facilitating chemical transport in porous media, this review was undertaken to investigate (1) the occurrence and stability of colloids in porous media, (2) the association and movement of colloids with chemicals in porous media, (3) models for the transport of colloids in porous media, and (4) models for colloid-enhanced chemical transport in porous media. In addition, suggested areas for future research are included.