With development of agriculture and industry, new kinds of emerging contaminants, such as Polystyrene nanoparticles (Nano-PS), get in contact with the groundwater, which threaten local water supplies. As a result, the fate and transport of Nano-PS in the saturated porous media have become an important research subject in the field of hydrology and environmental science.
However, only little is known about the mobility and transport mechanisms of Nano-PS within the porous stratum. In order to illuminate the mechanism, variability in pore size distribution and structures, non-uniform flow velocities, different geochemical settings within soils (e.g. pH, redox conditions or ionic strength) or shifts in microbial communities are factors that are considered in our lab experiments.
Material and Methods
Nano-PS (diameter 30 nm) and quartz sand (diameter 0.21–0.30 mm) were purchased from Sigma-Aldrich Co.. Quartz sand was dry-packed into glass columns. Each column contained approximately 12 g sand and average porosity of 0.41. The columns were operated in an upward direction using syringe pumps. The columns were equilibrated by DI water at a flow rate of 3 ml/h followed by background electrolyte solution. At last, the Nano-PS solution was injected.
Results and Conclusions
The results clearly show that pH exerts significant influence on transport of Nano-PS in saturated porous media. In general, at higher pH, Nano-PS more easily flew out from the sand column. For example, the ratio of effluent Nano-PS concentration (C) to influent Nano-PS concentration (C0) was approximately to 1 at pH 9, whereas that ratio was only 0.7 at pH 5. This obvious discrepancy can be attributed to the electrostatic interactions. At pH 9, the absolute value of zeta potential is bigger than that at pH 5 for both Nano-PS and sand. Thus, the interaction between Nano-PS and sand is weak and less amount of Nano-PS is retained in the column at high pH.