Filtration of engineered nanoparticles in carbon-based fixed bed columns

Widespread applications of engineered nanoparticles (ENPs) have raised concerns over their occurrences in the environment. In this work, laboratory experiments and mathematical modeling were conducted to determine whether carbon materials could be used to remove 3 ENPs: silver nanoparticles (AgNPs), carbon nanotubes (CNTs), and titanium dioxide (NTiO₂) from water. Hickory chips biochar (HC) and activated carbon (AC) were used and the two carbons were modified with iron impregnation to enhance their affiliation to the ENPs. Results from batch sorption experiments showed that all the carbon sorbents could sorb the ENPs in aqueous solutions and the iron modification improved their sorption ability. When the carbons were packed in sand columns, however, the unmodified carbon showed little removal efficiency to the ENPs, no better than the sand media. Similarly, the columns enabled with iron-modified carbons had better filtration ability to the ENPs, particularly to NTiO₂ and AgNP. Among all the carbons, the iron-modified biochar was the best in filtering all the ENPs. Simulations from a model based on the advection-dispersion equation matched the filtration and transport of ENPs in the columns well. The DLVO theory also accurately described the interaction between the ENPs and the carbon materials. Findings from this study indicate that biochar, particularly after modification, can be used as a low-cost filter material to remove ENPs from water.