Kaolinite and illite colloid transport in saturated porous media

Natural mineral colloids facilitated transport of EE2 in saturated porous media: Effects of humic acid and conjugate form

Steroid estrogens have posed significant ecological risks to aquatic organisms due to their potent endocrine-disrupting effects. The role of natural mineral colloids in facilitating the transport of hydrophobic organic pollutants in the environment has been confirmed, but the control mechanisms of colloids on 17α-Ethinylestradiol (EE2) migration in the subsurface environment are often still not well understood. This study combined the batch sorption equilibrium experiments and dynamic transport simulations to reveal the interface interactions and co-transport characteristics between illite colloids and EE2 at both macroscopic and microscopic levels. The existing form changes of EE2 and the influence of coexisting humic acid (HA) during transport in porous media were also specifically investigated. The batch experiments demonstrated that the primary mechanisms governing EE2 sorption onto illite colloids involved surface sorption and hydrogen bonding. The coexistence of HA could load onto the surface of illite colloids, thereby enhancing the colloidal sorption capacity for EE2. Transport experiments demonstrated that the migratory ability of EE2 in silty clay was limited, but illite colloids could significantly promote its penetration, with the peak penetration content (Ct/C0) increasing from 0.64 to 0.77. In the absence of HA, EE2 primarily transported in a dissolved form, accounting for 62.86% of the total concentrations. When HA concentrations were increased to 10 mg/L and 20 mg/L, the proportion of colloidal conjugate EE2 in the effluents reached 52.13% and 54.49%, respectively. The enhanced transport of EE2 by HA was primarily attributed to the improved migration ability of illite colloids and the increased proportion of illite-EE2 conjugate, resulting in a maximum Ct/C0 value of 0.94. The validity of these results was further confirmed by employing calculations based on the Derjaguin-Landau-Verwey-Overbeek and Colloidal Filtration Theory. This study provides new insights of understanding the transport of EE2 in subsurface environment.

Removal Efficiency of Bottom Ash and Sand Mixtures as Filter Layers for Fine Particulate Matter

Permeable pavement is a technology that allows rainwater to infiltrate into the pavement. Permeable pavements not only help reduce surface runoff by allowing rainwater to infiltrate into the pavement, but also improve water quality with the filter layer that removes particulate matter pollutants. This study evaluated the particulate matter removal efficiency of bottom ash-sand mixtures as filter layers for removing fine (≤10 μm) or ultrafine (≤2.5 μm) particulate matter in the laboratory. Five filter media were tested: silica sand, bottom ash, and bottom ash-sand mixtures with 30:70, 50:50, and 70:30 ratios. The mixed filters exhibited more consistent and stable particulate matter removal efficiency over time than either the uniform sand or bottom ash filter. The 50:50 bottom ash-sand mixture demonstrated removal rates of 58.05% for 1.8 μm particles, 93.92% for 10 μm particles, and 92.45% for 60 μm particles. These findings highlight the potential of bottom ash-sand mixtures as effective filter media for removing PM10 road dust, although field validation with actual pavement systems is necessary.

Characterization and properties of Chinese red clay for use as ceramic and construction materials

This study involves the characterization and analysis of a Chinese red clay obtained from Hunan province to determine its suitability for manufacturing ceramic products. X-ray fluorescence analysis showed the clay has high silica (63.25 weight percent) and alumina (21.38 weight percent) content along with iron oxide, alkalis, and calcium acting as fluxes. X-ray diffraction (XRD) confirmed the presence of quartz, kaolinite, illite, and hematite as the major mineralogical phases. Scanning electron microscopy revealed loosely stacked, plate-shaped kaolinite particles exhibiting pseudohexagonal morphology. Particle size distribution shows a d50 of 12.7 μm and specific surface area is 21.3 m2/g. Differential thermal analysis-thermogravimetric analysis showed mass losses between 450-600°C and 950-1050°C corresponding to dehydroxylation and formation of a liquid phase, respectively. Dilatometry traced the onset of viscous flow sintering around 1000°C. Test bars produced from the clay were fired at 800°C, 900°C, 950°C, 1000°C, and 1050°C. The firing shrinkage increased from 2.5% at 800°C to 12.8% at 1050°C. Strength improved from 11.2 megapascals at 800°C to 42.3 megapascals at 1050°C due to densification and mullite formation. Hematite content caused the color to change from orange-red at 950°C to dark red at 1050°C. XRD analysis of fired specimens confirmed the presence of hematite and newly formed mullite and cristobalite phases. The results indicate the suitability of the clay for manufacturing bricks, roof tiles, and wall tiles using appropriate firing temperatures and cycles.

Solid-liquid interface adsorption of antibiotic resistance plasmids induced by nanoplastics aggravates gene pollution in aquatic ecosystems

Antibiotic resistance genes (ARGs) and nanoplastics (NPs) have been identified as emerging pollutants in water environment; the interactions between antibiotic resistance plasmids (ARPs) and NPs will influence ARG transport in sediments. Herein, the adsorption experiments of a typical ARP onto polystyrene nanoplastics (PS-NPs) in river and lake sediments were conducted to elucidate the adsorption mechanisms and the effects of environmental factors. Results indicated that the adsorption amounts of PS-NPs increased with the dosages while decreased with the particle size of sediments. Multi-layer adsorption of PS-NPs was found to exist mainly in sand and silt sediments, whereas the filling adsorption dominated in the clay. Moreover, the adsorbed PS-NPs enhanced the physisorption of ARPs in sediments through stimulating the intraparticle diffusion of ARPs induced by electrostatic force. Besides, the adsorption amounts of ARPs onto the PS-NPs decreased with the increasing pH and dissolve organic matter due to the enhanced electrostatic repulsion and competitive adsorption. The ion strength played catalytic roles by increasing the electrostatic attraction and adsorption sites of ARPs on PS-NPs. The adsorbed ARPs in sediments were closely related with the ARGs in extra/intracellular DNA of biofilms, influencing the distribution and proliferation of ARGs largely. The findings indicate that ARG-associated pollution might be enhanced by the solid-liquid interface adsorption induced by NPs, which was controlled by pH, ion strength and dissolve organic matter. This study provides supplementary insights into the roles of NPs as carriers of ARP in sediments, and advances our understanding on the risks of NP-ARG co-occurring contamination in aquatic ecosystems.

Long-Term Examination of Water Chemistry Changes Following Treatment of Cyanobacterial Bloom with Coagulants and Minerals

The abundant growth in cyanobacterial blooms poses severe ecological threats with a high risk to aquatic organisms and global public health. Control of cyanobacterial blooms involves spraying cyanobacteria removal materials, including coagulants. However, little is known about the fate of the coagulated-cyanobacteria-laden water. Here, we examined long-term changes in water quality following treatment with various coagulants and minerals for cyanobacterial removal when the coagulated cyanobacterial cells were not removed from the water. An experiment in a controlled water system tested the effects of six different compounds, one conventional coagulant, two natural inorganic coagulants, and three minerals. All tested coagulants and minerals exhibited >75% of cyanobacterial removal efficiency. However, compared to the control, higher concentrations of nitrogen were observed from some samples treated during the experimental period. After 20 months, the final total phosphorus concentration of the raw water increased 20-fold compared to the initial concentration to 11.82 mg/L, indicating significant nutrient release over time. Moreover, we observed that the decomposition of sedimented cyanobacterial cells caused the release of intracellular contents into the supernatant, increasing phosphorous concentration over time. Therefore, cyanobacterial cells should be removed from water after treatment to prevent eutrophication and maintain water quality.