Transport of engineered nanoparticles in porous media and its enhancement for remediation of contaminated groundwater

The engineered nanoparticles (ENPs) with high reactivity are promising materials for in-situ groundwater remediation, however, their low mobility in natural porous media greatly limits their application in this area. Therefore, understanding the fate and transport of ENPs in subsurface environment and how to enhance the transport is extremely important. This review is focused on recent advances in research on fate and transport of ENPs in porous media, with respect to mechanisms and mathematical models associated with ENPs transport and strategies for transport enhancement. Results of the existing research indicate that main mechanisms associated with ENPs transport include advection, dispersion, adsorption, straining, aggregation, blocking, ripening, and size exclusion, which are affected by a combination of various factors including physicochemical properties of ENPs, porous media and aqueous phase, and the flow conditions as well. In natural soils and sediments, ENPs transport can be enhanced in the presence of polymers or mobile carriers, however, such an enhancement may still not guarantee delivery of ENPs and adequate distribution throughout the contaminated area. For successful ENPs application in groundwater remediation, it is urgent to develop more effective technology to facilitate ENPs transport in subsurface.