•This paper presents the high efficiency of gas supply and mass transfer in water using MNBs.•The ozone MNBs technique was applied for in situ groundwater remediation of an organics-contaminated ...site.•Ozone MNBs show considerable advantages in contaminant cleanup and time efficiency.•Ozone MNBs potentially represent an innovative technology for in situ remediation of organics-contaminated groundwater.
Ozone is widely used for water treatment because of its strong oxidation ability. However, the efficiency of ozone in groundwater remediation is limited because of its relatively low solubility and rapid decomposition in the aqueous phase. Methods for increasing the stability of ozone within the subsurface are drawing increasing attention. Micro-nano-bubbles (MNBs), with diameters ranging from tens of nanometres to tens of micrometres, present rapid mass transfer rates, persist for a relatively long time in water, and transport with groundwater flow, which significantly improve gas concentration and provide a continuous gas supply. Therefore, MNBs show a considerable potential for application in groundwater remediation. In this study, the characteristics of ozone MNBs were examined, including their size distribution, bubble quantity, and zeta potential. The mass transfer rate of ozone MNBs was experimentally investigated. Ozone MNBs were then used to treat organics-contaminated water, and they showed remarkable cleanup efficiency. Column tests were also conducted to study the efficiency of ozone MNBs for organics-contaminated groundwater remediation. Based on the laboratory tests, field monitoring was conducted on a trichloroethylene (TCE)-contaminated site. The results showed that ozone MNBs can greatly improve remediation efficiency and represent an innovative technology for in situ remediation of organics-contaminated groundwater.
The soil freezing characteristic curve (SFCC) represents the constitutive relationship between sub‐zero temperature and unfrozen water content in soil. It governs the hydrologic and mechanical ...behaviors associated with freezing soil. Numerous studies have investigated the mechanisms of soil water freezing and attempted to predict SFCC using soil water characteristic curve (SWCC) and Clapeyron equation. However, limited attention has been given to the physical disparities between adsorbed and capillary water during freezing, including variations in pressures and water‐ice interfaces. In this study, we present a novel theoretical model for predicting SFCC. The model determines the freezing point by calculating the chemical potential of soil water and ice with their respective pressures, thus capturing the distinctions in freezing behaviors between adsorbed and capillary water. All model parameters possess clear physical interpretations, and the model solely relies on the SWCC as input. The validity of the proposed model was confirmed through experimental measurements involving the water phase diagram, SWCCs, and the corresponding SFCCs of sandy, silty, and clayey soils. The model exhibits strong capabilities in predicting SFCC regardless of the soil type and outperforms the conventional method in predicting the SFCC of soil with high adsorbed water content. Model analyses were performed to investigate the effects of individual pore size, soil type, and initial water content on the freezing process, revealing the distinct contributions of adsorption and capillarity in soil water freezing. This study elucidates the mechanisms underlying soil water freezing, offering a theoretical framework for the analysis and prediction of frozen soil behaviors.
Plain Language Summary
The freezing point of soil water is lower than that of free water, and the relationship between sub‐zero temperature and unfrozen water content is soil freezing characteristic curve (SFCC). The unfrozen water content is important for the physical processes in soil. Soil water content comprises adsorbed water and capillary water. They are retained in soil by different physical mechanisms, that is, adsorption and capillarity. As a result, they exhibit distinct freezing behaviors. However, the freezing of adsorbed water has been overlooked in many studies. This work established a theoretical SFCC model based on the chemical potential equilibrium between pore water and ice. The model can describe the freezing of adsorbed and capillary water and only requires the soil water characteristic curve (SWCC) as input. Experimental water phase diagram, SFCCs, and SWCCs validated this model. The model can predict the SFCC of various soils and is superior to the conventional method in predicting the SFCC of soils with high adsorbed water content. The clear physical mechanism in the model enables the analysis of the effects of pore sizes, soil types, and initial water content on unfrozen water content. This work provides a useful tool to predict frozen soil behaviors.
Key Points
A theoretical soil freezing characteristic curve (SFCC) model considering the physical disparities between adsorbed and capillary water is established
The model exhibits advantages in predicting the SFCC of soils with high adsorbed water content
The model can illustrate the effects of soil types and initial water contents on SFCC
Naphthalene, as one of the representative polycyclic aromatic hydrocarbons, widely exists in contaminated sites and is a potential threat to human health due to its high mobility in soil. The ...interaction between naphthalene and clay minerals is of great significance to the environmental behavior of naphthalene and the design of remediation technology. In this study, montmorillonite and kaolinite were selected as representative clay minerals. Naphthalene adsorption behavior on mineral surfaces and water-wet kaolinite surfaces was investigated using molecular dynamics (MD) simulation. The interaction energy was calculated to represent the interaction between naphthalene and soil fractions, and the relative concentration and density distribution of naphthalene was analyzed to describe the distribution of naphthalene on the clay surfaces. The self-diffusion coefficient of naphthalene was obtained to represent its mobility under different water content. The electron density calculation was performed to reveal the different adsorption behavior of naphthalene on different surfaces of kaolinite. The simulation results show that montmorillonite had a stronger interaction with naphthalene due to larger electrostatic interaction energy compared to kaolinite, and naphthalene distributed more intensively on the montmorillonite surface. With regards to kaolinite, naphthalene tended to be absorbed on the alumina octahedral surface rather than the silicon tetrahedral surface due to the weak hydron bond interaction. The results indicate that water impeded the adsorption of naphthalene, and the optimal initial thickness of water film, which was 10 Å, was put forward for the application of thermal remediation technology. Furthermore, the average interaction energies between water and mineral surfaces largely depended on the water content, and the competitive adsorption between water and naphthalene only occurred under absorbed and bound water conditions. Overall, the knowledge of naphthalene–soil fractions interaction gained in this study is critical to the understanding of the environmental behavior of naphthalene and the reference for remediation technology.
Spurred by the advanced technologies, mainly including horizontal drilling and hydraulic fracturing, shale gas exploration has grown significantly over the past few decades. Upon exposure to the ...aqueous fracturing fluids in the high temperature and high pressure subsurface, the mechanical properties of shales such as elasticity, hardness, and strength usually deteriorate, a phenomenon termed “shale softening”. As a complex, multiphase, and multiscale material, shale is prone to the change in its mechanical properties upon exposure to fracture fluids. It is generally agreed that shale softening has great impact on the design and operation of shale gas exploration and the long-term gas production. This paper provides a critical review of the observed, phenomenological behavior of shale softening, and summarizes the currently recognized potential or hypothesized underlying mechanisms. The former includes: (1) reduction in fracture conductivity and hence the rate of gas production; (2) degradation of mechanical properties and reservoir fracability; (3) creep and long-term damage to the shale formations. The latter consists of clay-fluid interactions, electrical double layer (EDL) repulsion, solid mineral dissolution, short-term unloading, and long-term creep. However, to date, the dominant mechanisms controlling shale softening for a rock with known mineralogical compositions and the chemistry of fracturing fluids still remain unresolved. Our preliminary investigations suggest that the dominant mechanism depend on shale's compositions. Therefore, knowledge of the mineralogy of a shale is proposed as an essential requirement for the development of a framework for probing the mechanisms of shale softening. It is expected that such a newly proposed framework can practically facilitate the design and operation of shale gas exploration and help achieve stable gas production over an extended duration.
•The observations and phenomenological behavior of shale softening were summarized.•A framework for explaining mechanisms of shale softening was proposed.•The observations and behavior of softening were validated by preliminary tests.•A research methodology of shale softening behavior and mechanisms was provided.
The efficiency of ozone for the treatment of organics contaminated wastewater is limited by its slow dissolution rate and rapid decomposition in the aqueous phase. Micro-nano-bubbles (MNBs) are a ...novel method to prolong the reactivity of the ozone in the aqueous phase, thereby accelerating the treatment of the contaminant. In this study, the effects of pH and salinity on the treatment efficiency of ozone MNBs were examined. The highest efficiency was observed in weak acidic conditions and an increase in salinity enhanced the treatment efficiency significantly. Furthermore, the treatment of highly saline industrial wastewater as well as multi-contaminant groundwater containing persistent organics were also investigated. Treatment using ozone MNBs had a considerable effect on wastewaters that are otherwise difficult to treat using other methods; hence, it is a promising technology for wastewater treatment.
Soil–water retention curve (SWRC) describes the relationship between soil matric potential and soil water content, which is recognized as the most important constitutive function for unsaturated soil ...that governs many hydrological and mechanical properties, such as fluid flow, hydraulic conductivity, chemical transport, and soil freezing and thawing, etc. Soil–water isotherm (SWI) measured from vapor adsorption technique captures the SWRC at medium to high matric potential range, where three physical mechanisms of soil–water retention (SWR) with distinct free energy levels are involved: adsorption on external particle surface, adsorption in interlamellar space, and capillarity. So far, there is not a single SWI model that can take all three mechanisms into full consideration in full matric potential range. Here a closed‐form SWI model is formulated as the mathematical sum of three independent SWIs, which are external sorptive SWI, internal sorptive SWI, and capillary SWI; each corresponds to one of the aforementioned SWR processes. The generality and effectiveness of the proposed model are experimentally validated through a suite of 21 soils, covering all common soil types with plasticity index (PI) of 4–132. The proposed SWI model shows excellent performance as it nearly perfectly (R2 > 0.99) fits both the adsorption isotherm and the desorption isotherm for each soil, validating the generality of the model. The external specific surface area (SSA) obtained from the external sorptive SWI correlates well with that determined from the classic Brunauer–Emmett–Teller equation, while the internal SSA obtained from the internal sorptive SWI also coincides with that measured independently; both further confirm the capability of the proposed SWI model to distinguish between external surface adsorption and interlamellar adsorption.
Core Ideas
A soil water isotherm model was developed to describe water adsorption on both external and interlamellar surfaces.
The generality of the proposed model was validated by extensive experimental data.
The model can separate soil–water isotherms into external adsorption, internal adsorption, and capillarity.
•A theoretical SFCC model for saline soil is proposed and validated.•The unfrozen water content during two phase transition stages is well predicted.•Eutectic temperature is related to the initial ...solute concentration and saturation.
Soil freezing characteristic curve (SFCC) characterizes the relationship between liquid water content and temperature in frozen soils, which is of significance in simulating the heat, moisture, and solute migration process in the hydrological cycle in cold regions. Soil freezing process of saline soils includes various stages including ice or salt crystallization and ice-salt eutectic. However, most SFCC models ignored the eutectic stage. Based on the framework of chemical potential equilibrium, a theoretical model is developed considering the ice-salt eutectic phenomenon in this study. The model can well predict the change in unfrozen water content in various stages for both low and high initial concentrations from the soil–water characteristic curve (SWCC). The applicability and accuracy of the model are well verified by the published data of the measured phase diagrams of bulk salt solution and SFCCs for different types of soils. The effects of soil type, initial solute concentration, and initial water content on soil freezing process and eutectic temperature are further analyzed using the theoretical model, which is in agreement with reported experimental results. The work provides a comprehensive view to understand the freezing characteristic of saline soils.
Human papillomavirus vaccination and cervical screening are lacking in most lower resource settings, where approximately 80% of more than 500 000 cancer cases occur annually. Visual inspection of the ...cervix following acetic acid application is practical but not reproducible or accurate. The objective of this study was to develop a "deep learning"-based visual evaluation algorithm that automatically recognizes cervical precancer/cancer.
A population-based longitudinal cohort of 9406 women ages 18-94 years in Guanacaste, Costa Rica was followed for 7 years (1993-2000), incorporating multiple cervical screening methods and histopathologic confirmation of precancers. Tumor registry linkage identified cancers up to 18 years. Archived, digitized cervical images from screening, taken with a fixed-focus camera ("cervicography"), were used for training/validation of the deep learning-based algorithm. The resultant image prediction score (0-1) could be categorized to balance sensitivity and specificity for detection of precancer/cancer. All statistical tests were two-sided.
Automated visual evaluation of enrollment cervigrams identified cumulative precancer/cancer cases with greater accuracy (area under the curve AUC = 0.91, 95% confidence interval CI = 0.89 to 0.93) than original cervigram interpretation (AUC = 0.69, 95% CI = 0.63 to 0.74; P < .001) or conventional cytology (AUC = 0.71, 95% CI = 0.65 to 0.77; P < .001). A single visual screening round restricted to women at the prime screening ages of 25-49 years could identify 127 (55.7%) of 228 precancers (cervical intraepithelial neoplasia 2/cervical intraepithelial neoplasia 3/adenocarcinoma in situ AIS) diagnosed cumulatively in the entire adult population (ages 18-94 years) while referring 11.0% for management.
The results support consideration of automated visual evaluation of cervical images from contemporary digital cameras. If achieved, this might permit dissemination of effective point-of-care cervical screening.
Different types of soil water, such as bound water and capillary water, have distinct effects on the physicochemical and engineering properties of soils, particularly unsaturated clayey soils. ...Therefore, it is crucial to develop an accurate and physically meaningful experimental method for identifying and quantifying these components. This study pioneers the use of a multi-step kinetic model to identify and quantify different soil water components across a wide range of relative humidity (RH) using thermogravimetric analysis (TGA) data. To validate the determined kinetic parameters (i.e., activation energy, preexponential factor, and reaction model) and the identification and quantification results of soil water components, TGA with multiple heating rates, nitrogen adsorption method, cation exchange capacity measurement, and nuclear magnetic resonance (NMR) were performed on kaolin samples equilibrated under various RH conditions. These experimental results cross-validate the superior performance of the kinetic model in determining soil water components and predicting the thermal desorption behaviors of soil water. Based on the cross-validation results, the soil water components obtained from the kinetic analysis are further identified as tightly-bound, loosely-bound, and capillary water, which exhibit variations consistent with empirical soil water isotherm models. The T2 cutoff value between bound and capillary water is determined to be 1.79 ms based on TGA and NMR results. The determined thermal kinetic parameters of different soil water components can exhibit their distinct retention mechanisms. The method and results in this study provide a new perspective on identifying different soil water components, as well as understanding the mechanism of soil-water interactions in unsaturated soils.
•A method based on thermogravimetric and kinetic analysis is developed to identify and quantify soil water components.•Kinetic model can detect tightly-bound, loosely-bound, and capillary water in kaolin.•Different soil water components exhibit distinct kinetic triplets.•Bound water content increases with humidity regardless of capillary condensation.•NMR T2 cutoff value between bound and capillary water is 1.79 ms.
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