Soil Porous Media Research Articles

Effect of biochar on microplastics penetration treatment within soil porous medium under the wetting-drying cycles and optimisation of soil-biochar mixing format

Plant-based biochar was demonstrated promising capability in adsorbing microplastic particles (MPs) within soil porous mediums. However, biochar's function in mitigating MPs' vertical penetration during wetting-drying cycles, typical of seasonal precipitation and evaporation, remains uncertain. Furthermore, few studies have investigated the structures of how biochar combines with soil. This study conducted column tests to assess the MPs retention capabilities of soil-biochar porous media under saturated and wetting-drying conditions. The water retention and hydrophilic properties were investigated to elucidate the impact of wetting-drying cycles. Additionally, different biochar-soil structures were compared to optimise the structural design. Without biochar, wetting-drying cycles resulted in 8.74 % more MPs escaping from samples. However, incorporating 15 % biochar led to only around 2 % more MPs in effluent. Biochar significantly enhanced soil's MP absorption capacity and mitigated the negative effects of wetting-drying cycles. Biochar's alveolate morphology provides ample adsorption sites and creates complex flow paths. The hydrophilic groups of biochar and capillarity by micropores facilitated slower water release during drying, preventing crack propagation and flush on MP particles. This effect was more pronounced with higher biochar content and lower porosity. Moreover, layer structure was found to improve MPs removal, benefiting the long-term performance and management of the biochar functional layer.

On the electrokinetic remediation of Pb-contaminated soil: A coupled electro-transport-reaction modelling study based on chemical reaction kinetics

The accumulation of lead (Pb) in soil resulted from industrialization and urbanization poses a threat to human health and the ecosystem. This study proposes a mathematical model for Pb migration and transformation in soil porous media, aiming to guide the design of electrokinetic remediation schemes for Pb-contaminated soils. To improve the validity of the model, the chemical reactions considered in the model are all based on chemical reaction kinetics, which were usually overlooked for model simplification. The model quantitatively describes various physical and chemical processes of Pb at the soil-pore fluid interface and in the pore fluid, including diffusion, electromigration, electroosmosis, electrolytic water reaction, precipitation, adsorption/desorption, protonation/deprotonation reaction, and water self-ionization reaction. The numerical results show that the pH value is a key factor affecting the distribution of Pb in the soil and determining the removal efficiency of Pb. The effects of different enhancement methods on Pb concentration distribution and removal efficiency were evaluated with this model. It was found that placing a cation exchange membrane at the cathode boundary while using 0.01 M nitric acid as anode electrolyte can effectively improve Pb removal efficiency from 3.9% to 93.6%. The developed model can be used to guide the design of the enhanced electrokinetic remediation schemes.

Migration characteristics of oil pollutants into soil pores influenced by surface wettability

ABSTRACT Pore-scale modeling plays an indispensable role in unveiling the migration mechanism of oil pollutants into the water-saturated soil. Navier Stokes equations and conservation of mass, coupled with the phase field method, are employed to investigate the effect of soil wettability on oil pollutants migration into the soil porous media. The results show that the oil-water interface in the migration process does not advance evenly in three wetting states. When the model system is in oil-wetting state, oil pollutants obviously migrate at a higher speed. Through monitoring the evolution of oil front location and analyzing the velocity distribution vertical to the flow direction at the central axis of the model, the channel corresponding to the peak velocity is the dominant flow channel for the oil pollutants. This study will have the potential ability in obtaining the pore-scale migration regulation of oil pollutions as well as more accurately predicting the pollution range.

An experimental study on the determination of dispersion coefficient in layered soils

Abstract Dispersivity is a measurable parameter in soil porous media that is used for studying the transport of contaminants to groundwater. The value of this parameter depends on various factors, including the kind of porous media (homogeneous or heterogeneous), flow velocity, initial contaminant concentration, travel distance, and sampling method. A physical model with dimensions of 0.10 m in width, 0.80 m in height, and 1.10 m in length was constructed to investigate the effects of these parameters on the dispersivity value. The stratified soil used consisted of three 20-cm-thick layers containing fine-grained, medium-grained, and coarse-grained soil. Sodium chloride solutions with electrical conductivity values of 10, 14, and 19 dS/m were used as the contaminants. Flow was forced through the layered heterogeneous soils at three discharge velocities of 17.58, 22.02, and 26.18 × 10−5 m/s. The point and mixed sampling methods were used. The results indicated that the soil dispersivity values in layered heterogeneous soils and homogeneous soil were influenced by contaminant concentration, flow velocity, and travel distance. Moreover, the dispersivity values obtained by point sampling were lower than those obtained using the mixed sampling method, and the mean dispersivity value in the layered heterogeneous soils was lower than that of the homogeneous soil.

Development of an Ontology-Based Knowledge Network by Interconnecting Soil/Water Concepts/Properties, Derived from Standards Methods and Published Scientific References Outlining Infiltration/Percolation Process of Contaminated Water

The present work deals with the development of an Ontology-Based Knowledge Network of soil/water physicochemical & biological properties (soil/water concepts), derived from ASTM Standard Methods (ASTMi,n) and relevant scientific/applicable references (published papers—PPi,n) to fill up/bridge the gap of the information science between cited Standards and infiltration discipline conceptual vocabulary providing accordingly a dedicated/internal Knowledge Base (KB). This attempt constitutes an innovative approach, since it is based on externalizing domain knowledge in the form of Ontology-Based Knowledge Networks, incorporating standardized methodology in soil engineering. The ontology soil/water concepts (semantics) of the developed network correspond to soil/water physicochemical & biological properties, classified in seven different generations that are distinguished/located in infiltration/percolation process of contaminated water through soil porous media. The interconnections with arcs between corresponding concepts/properties among the consecutive generations are defined by the relationship of dependent and independent variables. All these interconnections are documented according to the below three ways: 1) dependent and independent variables interconnected by using the logical operator “depends on” quoting existent explicit functions and equations; 2) dependent and independent variables interconnected by using the logical operator “depends on” quoting produced implicit functions, according to Rayleigh’s method of indices; 3) dependent and independent variables interconnected by using the logical operator “related to” based on a logical dependence among the examined nodes-concepts-variables. The aforementioned approach provides significant advantages to semantic web developers and web users by means of prompt knowledge navigation, tracking, retrieval and usage.

Research on image recognition method of rock and soil porous media based on dithering algorithm

Rock-soil mass is a kind of material with complex internal structure, and its macro-mechanical response and failure process are influenced by internal microscopic composition and structure. Based on the research results of digital image technology in quantitative aspects of internal structure of rock and soil, a method for segmentation of rock and soil pore images based on dithering algorithm and statistical method for multiple parameters of pores is proposed in this paper. The result of verification shows that the pore recognition method proposed in this paper is reliable, can obtain the pore distribution and related parameters quickly and effectively, which has certain academic value and research significance.

How crucial is the impact of calcium on the reactivity of iron-organic matter aggregates? Insights from arsenic

Environmental iron-organic matter (Fe-OM) aggregates play a major role in the dynamic of pollutants. Nowadays, there is a lack of information about the control exerted by their structural organization on their reactivity towards metal(loid)s and in particular, the impact of major ions, such as calcium. The sorption capacity of mimetic environmental Fe-OM-Ca aggregates was investigated relative to the Fe/organic carbon (OC) and Ca/Fe ratios using As as a probe. It was shown that Fe speciation is the key factor controlling the reactivity of Fe-OM-Ca aggregates regarding the high affinity of Fe(III)-oligomers towards As and the high sorption capacity of ferrihydrite-like nanoparticles. Moreover, when it occurs at high concentration, Ca competes with Fe for OM binding leading to an increase in the amount of ferrihydrite-like nanoparticles and binding site availability. As a consequence, Ca not only impacts the ionic strength but it also has a dramatic impact on the structural organization of Fe-OM aggregates at several scales of organization, resulting in an increase of their sorption capacity. In the presence of high amounts of Ca, Fe-OM-Ca aggregates could immobilize pollutants in the soil porous media as they form a micrometric network exhibiting a strong sorption capacity.

Biomechanics of Surface Runoff and Soil Water Percolation

In this study, the complex interaction of surface runoff with the biomechanics of soil water transport and heat transfer rate is theoretically investigated using a mathematical model that relies on the two phase flows of an incompressible Newtonian fluid (stormwater) within the soil (porous medium) and on the soil surface (runoff). The flow and heat transfer characteristics within the soil are determined numerically based on Darcy-Brinkman-Forchheimer model for porous medium coupled with the appropriate energy equation while analytical approach is employed to tackle the model for interacting surface runoff stormwater. The effects of various embedded biophysical parameters on the temperature distribution and stormwater transport within the soil and across the soil surface together with soil-runoff interface skin friction and Nusselt number are display graphically and discussed quantitatively. It is found that an increase in surface runoff over tightly packed soil lessens stormwater percolation rate but enhances both soil erosion and surface heat transfer rate.

The failure of using equilibrium adsorption of fosthiazate onto montmorillonite clay particles to predict their cotransport in porous media as revealed by batch and column studies

Adsorption of fosthiazate onto montmorillonite clay particles (MPs) and cotransport of fosthiazate and MPs in sand and soil porous media were investigated for the understanding of the influence of MPs on transport of fosthiazate in subsurface environments. The adsorption of fosthiazate onto MPs was first examined by batch experiments and described by isotherm equations. Then, column experiments were conducted to investigate cotransport of fosthiazate and MPs in sand or soil porous media. Finally, the distribution of fosthiazate between colloidal (i.e., MPs) and solution phases during their cotransport in the porous media was compared to that in the batch experiments. The isotherms for the fosthiazate adsorption were well fitted by Freundlich equilibrium model. The adsorption was endothermic and spontaneous, which was attributed to electrostatic attraction of the electronegative groups (phosphate ester) on the fosthiazate at the positively charged sites on the MPs. Almost complete breakthroughs were observed for the fosthiazate in sand porous media due to lack of positive surface charges for the adsorption. The addition of MPs did not enhance the retention of fosthiazate, i.e, by attachment of the MPs associated with fosthiazate, because the attachment rate of MPs on the sand surfaces was much greater than the adsorption rate of fosthiazate. However, the MPs remained in the pore water causing a distribution of fosthiazate between the colloidal and solution phases. Such distribution was dependent on MP concentration and collector property (i.e., sand or soil) and was different from that in batch experiments. Our study was the first to unambiguously show that the equilibrium adsorption cannot be used in transport models to predict the mobility of MP-associated organophosphorus pesticide fosthiazate due to greater attachment rate of MPs on soil collectors than adsorption rates of the pesticide on the MPs.

Quantify the Pore Water Velocity Distribution by a Celerity Function

Celerity and velocity of subsurface flow in soil porous medium are intimately linked with tracer transport, while only few current studies focused on their relations. This study conducted theoretical analyses based on a pore bundle model, under which celerity in unsaturated flow is equivalent to maximum velocity. Furthermore, under 3 models Brooks-Corey model and unmodified and modified Mualem-van Genuchten models, we used a celerity function to derive breakthrough curves aiming to quantify the advective tracer transport for 5 typical soil textures. The results showed that the celerity under near-saturated conditions can be 5 up to 100 times larger than the saturated hydraulic conductivity, and a small volumetric fraction (<15%) of pores contributed more than half of the specific discharge. First arrival time and extensive tailing of the breakthrough curves were controlled by maximum velocity and velocity distribution, accordingly. As the kinematic ratio in the Brooks-Corey model remained constantly for each specific soil, we used it to quantify the ratio of maximum tracer velocity over average tracer velocity. We also found that a bimodal soil hydraulic function (for a dual-permeability model) may result in similar soil hydraulic conductivity functions for different parameter sets, but their celerities are different. The results showed that the proposed celerity function can assist in investigating subsurface flow and tracer transport, and the kinematic ratio could be used to predict the first arrival time of a conservative tracer.

Simulations of coupled non-isothermal soil moisture transport and evaporation fluxes in a forest area

Abstract This study focuses on the quantification of non-isothermal soil moisture transport and evaporation fluxes in vegetated area. A one-dimensional numerical model is developed by integrating a multi-phase flow model with a twolayer energy-balance model. The non-isothermal multi-phase flow model solves four governing equations for coupled air, vapour, moisture, and heat transport in soil porous medium. The two-layer energy balance model estimates evaporation fluxes from transpiration, interception, and soil surface. The model was implemented to an oak forest area in Missouri, USA. For model calibration and validation, measurements of energy fluxes, soil moisture, and soil temperature were used. The proposed model is compared with a simple model that couples the Penman-Monteith equation with the Richards’ equation. The results indicate that the simple model underestimate the total evaporation rate. On the contrary, the proposed model includes a more detailed description of energy transfer, which could improve the accuracy in estimating evaporation rates. The proposed model could be a promising tool to quantify the energy and moisture fluxes in a soil-vegetation-atmosphere continuum in vegetated area.

Numerical Simulation of Multiphase Flow Pollutants during Migration Process in Buried Oil Pipeline Leakage

Considered influence of buried pipeline leakage of crude oil pollutants multiphase flow migration phenomenon effects, numerical model was established to buried pipeline road multiphase leak process simplified for two-dimension problem, numerical simulation was used with the CFD software FLUENT on buried pipeline leakage of crude oil pollutants migration process caused pollution problem, calculation simulation was carried out in the two species workers condition of one phase flow and multiphase flow buried pipeline leakage of pollutants around earth temperature field, the speed field and the distributions of oil/water phase in the soil porous media. Analysis the comparison of results indicated that: 1) the affected region of temperatures spread above the buried oil pipeline was more slowly than either side of the rate of diffusion;2) During the buried pipeline leakage early, except the maximum of velocity near the leakage mouth, the other penetration regional velocity of leakage crude oil are very low.

The Analysis of Crude Oil Nature’s Impact on Oil Pipeline Underground Divulging Pollutant Migration

The oil pipeline burying divulging pollutant was taken as the object of study in this paper, the heat transfer and mass transfer process of which in the soil porous medium were carried by the numerical analysis. The oil phase change for multiphase flow leakage process for buried pipelines for oil, gas and water in the low temperature was considered, and the impact on multiphase leakage process of high and low viscosity of the oil phase viscosity properties was analyzed. It cited multiphase pipeline leak by using Fluent at different times during the course of the earth temperature field , the oil / water phase distribution , surface temperature, and the results showed that : there existed a big difference between the multiphase flow leakage process surface temperature changes and porous medium heat and mass transfer processes with the conditions of high viscosity and low viscosity conditions . Therefore, the impact of the physical properties on buried oil pipeline leak process at low temperatures is great.

Quantitative Assessment of LNAPL Retention in Soil Porous Media

The presence of hydrocarbon contaminants in the vadose zone is a serious hazard for environment quality. Moreover, there is an urgent need for accurate and reliable knowledge of the hydraulics of hydrocarbon contaminants in porous media to enhance efficiency of NAPLs remediation methods. The objective of this study was to quantitatively assess the hydraulic properties of different porous media with petroleum, kerosene, diesel fuel, and gasoline. The related retention curves were then experimentally obtained. Parameters of the soils retention curves were obtained based on van Genuchten (1980), Brooks-Corey (1964), and Campbell (1974) retention models. The accuracy of models was then assessed by some statistics. The results indicated that, in most cases, air entry value was significantly increased in a petroleum retention curve despite the fact that it was decreased for other NAPLs. The pore size distribution parameters (i.e., n, m, λ, and 1/b) of diesel fuel, kerosene, and gasoline did not change considerably compared to water retention curve. The Leverett (1941) scaling function was adopted to scale soil-fluid retention curves data in two-phase systems. The results indicated that, except for a silty clay medium and petroleum, the Leverett (1941) J-function could scale the LNAPL retention curves based on the water retention curve data.

Studies of the Small Leakage in Buried Gas Pipeline under the Condition of Soil Properties

Analyzing the characteristics of the gas diffusion in soil porous media, and using proper coefficient to correct the calculation model of aerial pipeline leakage,with which to establish the diffusion model of buried gas pipeline. Combined with the mass conservation equation, fick diffusion equation and relative diffusion coefficient equation to build three-dimensional steady-state diffusion model. Then using dimensionless analysis method to calculate the diffusion equation. Through example analysis to research gas concentration fluctuations with the change of buried depth, aperture size, soil properties. Get the rule of small aperture leakage under the condition of different soil properties and rainfall, and it can be used as reference basis for scientific positioning and adopting emergency measures.

LABORATORY EVALUATION OF PHYSICO-CHEMICAL VARIATIONS IN BENTONITE UNDER ELECTROKINETIC ENHANCEMENT

When the traditional ground improvement techniques are not practical for a particular situation, alternative technology, such as electrokinetic (EK) soil treatment can be considered. EK treatment method involves applying a low direct current (DC) or a low potential gradient to arrays of electrodes inserted in the low permeable soils simulating migration of electricity, pore water, ions and charged particles across the soil, hence modifying the physicochemical, mechanical and engineering properties of the soil. This study investigates the effects of EK treatment on conductance phenomena and physico-chemical changes of bentonite at different intervals under total applied voltage of 10V subjected to specific types of anode enhancement solutions. The cumulative electroosmotic flow and electric current through the sample was measured for 15 days of treatment. The specimens were also tested for moisture content, pH and undrained shear strength variations over different time periods of 3, 6, 9, 12 and 15 days showing good correlations between the soil parameters. across the soil. The combined effects of these processes together with various geochemical reactions alter the chemical composition of the soil porous medium and hence modify the physicochemical properties of the soil during the EK

Laboratory Assessment of Kaolinite and Bentonite under Chemicalelectrokinetic Treatment

Electrokinetic treatment uses low intensity direct electric current or a low electric potential difference, to improve the engineering properties of subsurface soils while having minimum disturbance to the surface. This study aims to investigate the effects of chemical-electrokinetic treatment on properties of two types of clay soils at different intervals under the coupled Chemical, Hydraulic and Electrical (CHE) gradient. “Chemical-electrokinetic treatment” refers to improvement of soil with electrokinetic together with addition of chemical enhancement solution. The enhancement solutions used in this study are hydrated lime and saline solution. The combined effects of these processes together with various electrochemical and geochemical reactions would change the chemical composition of the soil porous medium, hence modifies the properties of the soil. The experiments were conducted in the laboratory using stainless steel electrodes under total applied voltage of 30 V for period of 15 days. Two types of fine-grained soils, kaolinite and bentonite, were used as they possess different mineralogy and geotechnical properties. The cumulative electro-osmotic flow and electric current flow through the soil samples were measured for period of 15 treatment days. Subsequently the specimens were tested for moisture content, pH and Atterberg Limit variations and the results have been reported. Test results revealed that there is a potential of developing this technique to improve engineering properties of finegrained soils, in particular to stabilise and improve soft soils for infrastructure management and constructions.

A Review of Electrokinetic Treatment Technique for Improving the Engineering Characteristics of Low Permeable Problematic Soils

The use of electrokinetic (EK) treatment which is a comparatively new methodology is being investigated in some parts of the world as a viable in situ soil remediation and treatment method. The principles of EK treatment method involve applying a low direct current or a low potential gradient to electrodes inserted in the low permeable soils that cannot readily drained. The transportation of charged species across the soil involves several complex mechanisms such as electrolysis, electro-osmosis, electro-migration and electrophoresis. This technique can also be applied/enhanced by introducing desirable non-toxic chemical compounds such as lime or cement solutions to the soil by introducing them at the appropriate electrode. The combined effect of these processes together with various geochemical reactions alters the chemical composition of the soil porous medium and thereby alters the physicochemical properties of the soil. Although the technology has been approved to be practical in many laboratory bench scale experiments and small-scale pilot field tests, complicated features such as many electrochemical reactions and soil contaminant interactions are still not fully understood, therefore there is a need for further research to be conducted for a better understanding of physicochemical changes in problematic soils and efficiency of this newly developed technology.

Numerical Simulation of Crude Pipeline Using Moisture-Heat Coupled Thermal Equation

Temperature plot is crucially important for numerical simulation of high waxy crude pipeline because of its non-Newtonian behavior at low temperature. As the fluid temperature drops below than the wax appearance temperature, the viscosity of the crude increases dramatically. Thus the needed pressure has a possibility to reach the maximum allowable pressure and cause a potential risk for the pipeline itself. To avoid this, numerical simulation of the temperature plot along the pipeline is necessary in order to obtain accurate information. However, as the temperature governing equation is a non-linear equation and the soil temperature field is also being involved. It is required to solve the surrounded soil temperature field. In the paper, the governing equation for one dimensional crude pipeline and the new moisture-heat equation for the soil (porous medium) are presented and the iteration algorithm to solve this coupled equation is given. With the algorithm and the coupled heat-moisture equations, the numerical results are obtained and have a very precise coincidence with the experimental results. Then a reliability based method is used to evaluate the flow safety of one pipeline in China. With the presented model and obtained results, the flow safety evaluation results show that the safety of the crude pipeline is assured in the test cases.

Colloid Deposition and Release in Soils and Their Association With Heavy Metals

Colloid transport in subsurface has received considerable attention recently because mobile colloids can facilitate the transport of heavy metals in soils to contaminate groundwater. Many studies on colloid mobility in the subsurface consider soils as well-defined porous media. Though similar in many aspects, soils are different from well-defined porous media. The authors emphasize the impacts of soil properties on soil-colloid deposition, release, and association with heavy metals to provide an overview of colloidal dynamics in natural soils. The electrical double layer and Derjaguin-Landau-Verwey-Overbeek (DVLO) theories are summarized in Section II as theoretical bases for further discussions of colloid dynamics in soils, and their interactions with heavy metals. After discussions of theory developments and experimental results on the characteristics of soil colloids in Section III and soil porous media in Section IV, the authors compares the deposition of colloidal particles in well-defined porous media with that in natural soils in Section V. In Section VI, processes that affect colloid release in soils are summarized and theories of ion transfer processes in soils during colloid release are reviewed and discussed. Finally, the authors give a brief overview of the adsorption and precipitation of heavy metals to soil colloidal particles and their influences on colloid surface charge development in Section VII. The authors conclude with remarks on the importance of colloid deposition and release in soils and their association with heavy metals.