Transport of plastic particles in natural porous media under freeze-thaw treatment: Effects of porous media property.

Freeze-thaw (FT) cycles would alter physical and chemical properties of soil and thus influence the transport of plastic particles (one type of emerging contaminant with great concerns). This study was designed to investigate the effects of FT treatment on the mobility of plastic particles (nanoplastics as representative) in columns packed with natural soils (i.e. loamy sand and sandy soil, quartz sand employed as comparison). We found that FT treatment of different types of porous media would induce different transport behaviors of plastic particles. Specifically, FT treatment of quartz sand did not affect plastic particles mobility. While FT treatment of loamy sand and sandy soil increased plastic particles transport. The increased pore sizes and disintegration of small soil particles from soils (the detached soil would serve as mobile vehicle for the transport of plastic particle) led to the facilitated mobility of plastic particles in two types of soils after FT treatment. The presence of preferential flow paths induced by FT treatment also drove to the enhanced mobility of plastic particles in sandy soil with FT treatment. This study clearly showed that the mobility of model plastic particles in two types of natural soils was greatly enhanced by FT treatment.

Efficient adsorption of Selenium(IV) from water by hematite modified magnetic nanoparticles.

Selenium (Se) could enter the environment through different anthropogenic sources, posing potential health risk. The removal of trace Se(IV) from water by hematite coated magnetic nanoparticle (MNP@hematite) under different solution conditions was investigated through batch experiments. The adsorption capacity of Se(IV) by MNP@hematite was 25.0 mg/g.100 µg/L of Se(IV) could be rapidly decreased to below 10 µg/L by 0.1 g/L of MNP@hematite in 10 min. MNP@hematite could effectively remove Se(IV) in a wide pH range from 4 to 9. Se(IV) could form inner-sphere complex with MNP@hematite. Thus, the presence of chloride, nitrate, and sulfate (concentration of each anions <10 mM) did not affect the removal of Se(IV); whereas, carbonate (10 mM), silicate (1 mM), and phosphate (0.1 mM) yet reduced the adsorption efficiency by competing adsorption sites. Humic acid and alginate (up to 6 mg/L) did not have obviously influence on the removal of Se(IV). MNP@hematite particles were able to simultaneously remove Se(IV) and Sb(III) at trace level very efficiently in 10 min. The magnetic adsorbent can be easily recycled and regenerated in 10 mM NaOH for 15 min. In five consecutive cycles, the adsorption and desorption efficiencies were over 97% and 82%, respectively. MNP@hematite could be employed as effective adsorbent for Se(IV) removal from water.

Effect of bacteria on the transport and deposition of multi-walled carbon nanotubes in saturated porous media.

The influence of bacteria on the transport and deposition behaviors of carbon nanotubes (CNTs) in quartz sand was examined in both NaCl (5 and 25 mM ionic strength) and CaCl2 (0.3 and 1.2 mM ionic strength) solutions at unadjusted pH (5.6-5.8) by direct comparison of both breakthrough curves and retained profiles in both the presence and absence of bacteria. Two types of widely utilized CNTs, i.e., carboxyl- and hydroxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH and MWCNT-OH, respectively), were employed as model CNTs and Escherichia coli was utilized as the model bacterium. The results showed that, for both types of MWCNTs under all examined conditions, the breakthrough curves were higher in the presence of bacteria, while the retained profiles were lower, indicating that the co-presence of bacteria in suspension increased the transport and decreased the deposition of MWCNTs in porous media, regardless of ionic strength or ion valence. Complementary characterizations and extra column tests demonstrated that competition by bacteria for deposition sites on the quartz sand surfaces was a major (and possibly the sole) contributor to the enhanced MWCNTs transport in porous media.

Influence of sulfate and phosphate on the deposition of plasmid DNA on silica and alumina-coated surfaces.

The influence of sulfate and phosphate on the deposition kinetics of plasmid DNA on solid surfaces was examined at a constant 300mM ionic strength in both NaCl-Na2SO4 and NaCl-NaH2PO4-Na2HPO4 mixing solutions with varied sulfate and phosphate concentrations at pH 6.0 by utilizing a quartz crystal microbalance with dissipation (QCM-D). Two representative solid surfaces, both silica and alumina-coated surfaces, were concerned in this study. To better understand the effects of sulfate and phosphate on plasmid DNA deposition, QCM-D data were complemented by diffusion coefficients and zeta potentials of DNA as a function of examined solution conditions. The presence of sulfate and phosphate in solutions decreased the deposition efficiencies of plasmid DNA on both silica and alumina-coated surfaces. Moreover, the deposition efficiencies decreased with increasing concentrations of sulfate/phosphate. With sulfate/phosphate ions present in solutions, the deposition kinetics of plasmid DNA on both silica and alumina-coated surfaces were mainly controlled by classic Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions.