Yuanfang Huang

Application of DLVO energy map to evaluate interactions between spherical colloids and rough surfaces.

This study theoretically evaluated interactions between spherical colloids and rough surfaces in three-dimensional space using Derjaguin-Landau-Verwey- Overbeek (DLVO) energy/force map and curve. The rough surfaces were modeled as a flat surface covered by hemispherical protrusions. A modified Derjaguin approach was employed to calculate the interaction energies and forces. Results show that more irreversible attachments in primary minima occur at higher ionic strengths, which theoretically explains the observed hysteresis of colloid attachment and detachment during transients in solution chemistry. Secondary minimum depths can be increased significantly in concave regions (e.g., areas aside of asperities or between asperities) due to sidewall interactions. Through comparing the tangential attractive forces from asperities and the hydrodynamic drag forces in three-dimensional space, we showed that attachment in secondary minima can be located on open collector surfaces of a porous medium. This result challenges the usual belief that the attachment in secondary minima only occurs in stagnation point regions of the porous medium and is absent in shear flow systems such as parallel plate flow chamber and impinging jet apparatus. Despite the argument about the role of secondary minima in colloid attachment remained, our study theoretically justified the existence of attachment in secondary minima in the presence of surface roughness. Further, our study implied that the presence of surface roughness is more favorable for attachment in secondary minima than in primary minima under unfavorable chemical conditions.

Modeling Nitrate Leaching and Optimizing Water and Nitrogen Management under Irrigated Maize in Desert Oases in Northwestern China

Understanding water and N transport through the soil profile is important for efficient irrigation and nutrient management to minimize nitrate leaching to the groundwater, and to promote agricultural sustainable development in desert oases. In this study, a process-based water and nitrogen management model (WNMM) was used to simulate soil water movement, nitrate transport, and crop growth (maize [Zea mays L.]) under desert oasis conditions in northwestern China. The model was calibrated and validated with a field experiment. The model simulation results showed that about 35% of total water input and 58% of the total N input were leached to <1.8 m depth under traditional management practice. Excessive irrigation and N fertilizer application, high nitrate concentration in the irrigation water, together with the sandy soil texture, resulted in large nitrate leaching. Nitrate leaching was significantly reduced under the improved management practice suggested by farm extension personnel; however, the water and nitrate inputs still far exceeded the crop requirements. More than 1700 scenarios combining various types of irrigation and fertilizer practices were simulated. Quantitative analysis was conducted to obtain the best management practices (BMPs) with simultaneous consideration of crop yield, water use efficiency, fertilizer N use efficiency, and nitrate leaching. The results indicated that the BMPs under the specific desert oasis conditions are to irrigate the maize with 600 mm of water in eight times with a single fertilizer application at a rate of 75 kg N ha(-1).

Effects of Flow Velocity and Nonionic Surfactant on Colloid Straining in Saturated Porous Media Under Unfavorable Conditions

Knowledge of colloid straining mechanism in porous media is of importance for protecting groundwater from being contaminated by biocolloids (e.g., bacteria and protozoa) and by contaminants whose transport can be facilitated by mobile particles. This study examined effects of flow velocity on colloid straining in porous media under unfavorable chemical conditions. Saturated column experiments were conducted using glass beads as collector and a

Facilitated attachment of nanoparticles at primary minima by nanoscale roughness is susceptible to hydrodynamic drag under unfavorable chemical conditions.

3\,\mu \text{ m}

Analysis of the anisotropic spatial variability and three-dimensional computer simulation of agricultural soil bulk density in an alluvial plain of north China

carboxylate-modified polystyrene latex microsphere as model colloid. To unambiguously examine colloid straining mechanisms, attachment was minimized by extensively cleaning the collectors and adopting deionized water as solution. Results show that increasing flow velocity decreases colloid straining under unfavorable chemical conditions, in agreement with to theoretical finding in literature. This study additionally examined effects of nonionic surfactant (Triton X-100) on colloid straining in porous media under unfavorable chemical conditions. Results show that the addition of Triton X-100 decreases colloid straining and the decrease is enhanced by increasing the concentration of Triton X-100.

Sequential indicator simulation and indicator kriging estimation of 3-dimensional soil textures

Abstract This study theoretically investigated detachment of homoaggregates and heteroaggregates attached on the planar surfaces at primary minima during transients in solution chemistry. The homoaggregates were represented as small colloidal clusters with well-defined structures or as clusters generated by randomly packing spheres using Monte Carlo method. The heteroaggregates were modeled as microparticles coated with nanoparticles. Surface element integration technique was adopted to calculate Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energies for the homoaggregates and heteroaggregates at different ionic strengths. Results show that attached homoaggregates on the planar surface at primary minima are irreversible to reduction in solution ionic strength whether the primary spheres of the homoaggregates are nano- or micro-sized. Heteroaggregation of nanoparticles with a microparticle can cause DLVO interaction energy to decrease monotonically with separation distance at low ionic strengths (e.g., ⩽0.01M), indicating that the heteroaggregates experience repulsive forces at all separation distances. Therefore, attachment of the heteroaggregates at primary minima can be detached upon reduction in ionic strength. Additionally, we showed that the adhesive forces and torques that the aforementioned heteroaggregates experience can be significantly smaller than those experienced by the microspheres without attaching nanoparticles, thus, the heteroaggregates are readily detached via hydrodynamic drag. Results of study provide plausible explanation for the observations in the literature that attached/aggregated particles can be detached/redispersed from primary minima upon reduction in ionic strength, which challenges the common belief that attachment/aggregation of particles in primary minima is chemically irreversible.

Modeling of water and nitrogen utilization of layered soil profiles under a wheat-maize cropping system

This study investigated effects of flow velocity on attachment of nanoparticles at primary minima in the presence of surface roughness under unfavorable chemical conditions. Saturated sand-packed column experiments were conducted at 0.1 and 0.2M NaCl using 30 nm polystyrene latex nanoparticles as model colloids. Particle attachment at primary minima was unambiguously determined by removing particles attached at secondary minima through introducing deionized water and excavating the packed beds. The calculated primary-minimum attachment efficiency was found to decrease with increasing flow velocity, indicating that the fraction of a collector surface that is available for attachment at primary minima decreases with increasing flow velocity. The torque analysis, however, showed that the adhesive torque that the particle experiences at primary minima is much larger than the maximum hydrodynamic drags of a porous medium for the flow velocities used. We attributed the discrepancy to the reason that the sand surface is very rough and the roughness mainly causes the attachment in primary minima under the experimental conditions used in this study. By considering influence of surface roughness in the torque analysis, our calculations show that while particle attachment in primary minima is favored atop of nanoasperities under unfavorable conditions, the adhesive torque that the particle experiences can be greatly reduced and, thus, the attachment is susceptible to flow drag. Whereas the increase of adhesive torque by surface roughness has been widely recognized in the literature, our study indicates that the rough asperities can also decrease adhesive torques for particles attached atop of them.

Observed Dependence of Colloid Detachment on the Concentration of Initially Attached Colloids and Collector Surface Heterogeneity in Porous Media

Abstract Accurate quantification of the spatial patterns of soil organic matter (SOM) is essential for both SOM management and for the application of SOM models. The objective of this study is to determine whether elevation could be used to increase the accuracy of spatial predictions and the corresponding prediction uncertainty of soil organic matter. The sequential Gaussian simulation (SGS) and sequential Gaussian co‐simulation (SGCS) algorithms were compared with respect to the accuracy of predictions as well as to the uncertainty inherent in the spatial prediction of soil organic matter. The SGS algorithm accounted for only the SOM data. The SGCS accounted for both SOM data and intensive elevation data. The root mean square errors revealed that the more accurate simulations were those accounting for intensive elevation information by the SGCS method for the two areas compared with SGS. As regards modelling local uncertainty, SGCS performed better at modelling prediction uncertainty than SGS. In addition, the results of assessing the standard deviation confirmed that the exhaustive elevation data could be used to reduce the spatial uncertainty of SOM by SGCS compared with the SGS algorithm.