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A model is proposed to describe the hydromechanical behaviour of granular bentonite systems. Its formulation is based on abstracting the system as a discrete set of bentonite units, which form continuum sub-domains where homogeneous behaviour is assumed. This allows the mass balance of each unit to be characterised in an integrated way, in addition to applying advanced double porosity-based models with relative simplicity to describe its stress–strain behaviour. As a first approach, the liquid flow in the megapores between the units is approximated with an advective–diffusive continuous medium formulation. The contact between units is modelled using a strut scheme. To evaluate the scope of the model, the hydration of a granular bentonite specimen has been reproduced. Without introducing material parameters additional to those used in double porosity models, very satisfactory results have been obtained when modelling the evolution of the integrated behaviour of the whole sample (swelling pressure and total water mass increase) as well as the evolution of the distribution of water content, dry density and local vertical displacements. The model has demonstrated its consistency by maintaining the quality of the fit regardless of the significant decrease in megaporosity. In addition, the results illustrate the capability of the formulation to introduce the effect of friction and of the initial heterogeneity of the system into the model. For this reason, and although the scope of the formulation must be evaluated in a wider range of cases (non-isothermal conditions, non-negligible salinity, high porosity granular systems), the model is a tool of interest for the analysis of the homogenisation of granular bentonite systems., Se propone un modelo para describir el comportamiento hidromecánico de sistemas bentoníticos granulares. Su formulación se basa en abstraer el sistema como un conjunto discreto de unidades de bentonita, que forman subdominios continuos en los que se asume un comportamiento homogéneo. Esto permite caracterizar de forma integrada el balance de masas de cada unidad, además de aplicar modelos avanzados basados en la doble porosidad con relativa simplicidad para describir su comportamiento tensión-deformación. Como primera aproximación, el flujo de líquido en los megaporos entre las unidades se aproxima con una formulación de medio continuo advectivo-difusivo. El contacto entre unidades se modela mediante un esquema de puntales. Para evaluar el alcance del modelo, se ha reproducido la hidratación de una muestra de bentonita granular. Sin introducir parámetros materiales adicionales a los utilizados en los modelos de doble porosidad, se han obtenido resultados muy satisfactorios al modelizar la evolución del comportamiento integrado de toda la muestra (presión de hinchamiento e incremento de masa de agua total), así como la evolución de la distribución del contenido de agua, la densidad seca y los desplazamientos verticales locales. El modelo ha demostrado su coherencia al mantener la calidad del ajuste independientemente de la disminución significativa de la megaporosidad. Además, los resultados ilustran la capacidad de la formulación para introducir en el modelo el efecto de la fricción y de la heterogeneidad inicial del sistema. Por ello, y aunque el alcance de la formulación debe ser evaluado en un rango más amplio de casos (condiciones no isotérmicas, salinidad no despreciable, sistemas granulares de alta porosidad), el modelo constituye una herramienta de interés para el análisis de la homogeneización de sistemas bentoníticos granulares.

This paper evaluates the combination of electrokinetic soil flushing (EKSF) with soil vapor extraction (SVE) for the removal of four hexachlorocyclohexane (HCH) isomers contained in a real matrix. Results demonstrate that the combination of EKSF and SVE can be positive, but it is required the application of high electric fields (3 V cm−1) in order to promote a higher temperature in the system, which improves the volatilization of the HCH contained in the system. Electrokinetic transport is also enhanced with the application of higher electric gradients, but these transport processes are slower than the volatilization processes, which are the primary in this system. Hence collection of species in the electrolyte wells is negligible as compared to the compound dragged with air by the SVE but the temperature increase demonstrates a good performance. Combination of EKSF with SVE can efficiently exhaust the four HCH isomers reaching a removal of more than 90% after 15 days of treatment (20% more than values attained by SVE) but it is required the application of high electric fields to promote a higher temperature in the system (to improve the volatilization) and EK transport (to improve the dragging). 1-D transport model can be easily used to estimate the average pore water velocity and the effective diffusion of each compound under the different experimental conditions tested., Este artículo evalúa la combinación de lavado electrocinético del suelo (EKSF) con extracción de vapor del suelo (SVE) para la eliminación de cuatro isómeros de hexaclorociclohexano (HCH) contenidos en una matriz real. Los resultados demuestran que la combinación de EKSF y SVE puede ser positiva, pero se requiere la aplicación de campos eléctricos elevados (3 V cm −1) con el fin de promover una mayor temperatura en el sistema, lo que mejora la volatilización del HCH contenido en el sistema. El transporte electrocinético también mejora con la aplicación de gradientes eléctricos más altos, pero estos procesos de transporte son más lentos que los procesos de volatilización, que son los principales en este sistema. Por lo tanto, la recolección de especies en los pozos de electrolito es insignificante en comparación con el compuesto arrastrado con aire por el SVE, pero el aumento de temperatura demuestra un buen desempeño. La combinación de EKSF con SVE puede agotar eficientemente los cuatro isómeros de HCH alcanzando una eliminación de más del 90 % después de 15 días de tratamiento (20 % más que los valores alcanzados por SVE) pero se requiere la aplicación de campos eléctricos elevados para promover una temperatura más alta en el sistema (para mejorar la volatilización) y transporte EK (para mejorar el arrastre). El modelo de transporte 1-D se puede usar fácilmente para estimar el promediola velocidad intersticial del agua y la difusión efectiva de cada compuesto bajo las diferentes condiciones experimentales probadas.

The ability of helium gas displacement pycnometry to characterise the reduction of adsorbed water density with increasing bentonite water content was tested. For this purpose, after obtaining the grain density (which was assumed to be constant), an intensive campaign of 45 experiments was carried out with two bentonites for a total of 90 determinations, obtaining very consistent water density results. Furthermore, the water retention curve of one of the two bentonites was fully characterised by 95 tests with a chilled-mirror dew-point psychrometer. The water content results were used to determine the microstructural void ratio, both assuming a constant water density and considering the variation of the adsorbed water density obtained with the helium pycnometer. It was verified that with the constant value, by assuming a lower water density (1 g/cm3 ) than the experimental (values of 1.20 g/cm3 were obtained under hygroscopic conditions), higher values of microstructural void ratios are predicted, up to 15% greater for a relative humidity of 70% (0.46 instead of 0.40). For higher relative humidities the comparison loses its consistency, since the presence of capillary water cannot be disregarded, and the calculation of the microstructural void ratio is based on the assumption that the water present in bentonite is mainly in the form of adsorbed water. However, this does not compromise the analysis performed, as the results obtained for lower relative humidity values provide enough information to demonstrate the relevance of the errors that can occur when deriving models of the microstructural void ratio without taking into account the variation of the density of adsorbed water., Se probó la capacidad de la picnometría por desplazamiento de gas helio para caracterizar la reducción de la densidad del agua adsorbida con con el aumento del contenido de agua de la bentonita. Para ello, tras obtener la densidad del grano (que se suponía constante), se realizó una campaña intensiva de 45 experimentos. constante), se llevó a cabo una campaña intensiva de 45 experimentos con dos bentonitas para un total de de 90 determinaciones, obteniendo resultados de densidad de agua muy consistentes. Además, la curva de retención de agua de una de las dos bentonitas se caracterizó completamente mediante 95 ensayos con un psicrómetro de punto de rocío con espejo frío. Los resultados de Los resultados del contenido de agua se utilizaron para determinar la relación de vacíos microestructurales, tanto asumiendo una densidad de agua constante constante y considerando la variación de la densidad del agua adsorbida obtenida con el picnómetro de helio. Se verificado que con el valor constante, al suponer una densidad de agua menor (1 g/cm3 ) que la experimental (valores de 1,20 g/cm3 se obtuvieron en condiciones higroscópicas), se predicen valores más altos de las relaciones de vacío microestructurales predichos, hasta un 15% mayores para una humedad relativa del 70% (0,46 en lugar de 0,40). Para humedades relativas superiores la comparación pierde consistencia, ya que no se puede descartar la presencia de agua capilar, y el cálculo de la relación de vacíos microestructurales se basa en la suposición de que el agua presente en la bentonita está principalmente en forma de agua adsorbida. Sin embargo, esto no compromete el análisis realizado, ya que los resultados obtenidos para valores de humedad relativa más bajos proporcionan información suficiente para demostrar la relevancia de los errores que pueden producirse al derivar modelos de la relación de vacíos microestructurales sin tener en cuenta la variación de la densidad del agua adsorbida.

This article proposes an approach to ensure consistency between constitutive formulations used in double-porosity models when the macrostructural void ratio, eM, is very small. These formulations model processes of different physical natures and therefore are usually presented independently, in which case an additive decomposition is assumed, and they calculate the total strain of the system as the sum of the strains caused by each process. This independence means that when eM is reduced, the contributions considered are not always consistent. To solve this problem, soil stiffness in the proposed approach is increased when eM is reduced, and at the same time the effect on strain by macrostructural processes not linked to changes in stress is reduced. To simulate the flow, it is assumed that there is always a minimum operating value of eM that controls mass transport. This approach was applied to a practical case, and confirmed that when the effect of the stress state on microstructure behavior was taken into account, the conceptual framework initially proposed for non-negligible eM values was satisfactorily extended., Este artículo propone un enfoque para asegurar la consistencia entre las formulaciones constitutivas utilizadas en los modelos de doble porosidad cuando la relación de vacío macroestructural , e M , es muy pequeña. Estas formulaciones modelan procesos de diferente naturaleza física y por lo tanto se suelen presentar de forma independiente, en cuyo caso se supone una descomposición aditiva, y calculan la deformación total del sistema como la suma de las deformaciones provocadas por cada proceso. Esta independencia hace que cuando e M se reduce, las contribuciones consideradas no siempre son consistentes. Para resolver este problema, la rigidez del suelo en el enfoque propuesto se incrementa cuando e Mse reduce, y al mismo tiempo se reduce el efecto sobre la deformación por procesos macroestructurales no vinculados a cambios en la tensión. Para simular el flujo, se supone que siempre hay un valor mínimo de operación de e M que controla el transporte masivo. Este enfoque se aplicó a un caso práctico y confirmó que cuando se tuvo en cuenta el efecto del estado tensional sobre el comportamiento de la microestructura, el marco conceptual propuesto inicialmente para valores de e M no despreciables se amplió satisfactoriamente.

The reactive transport framework ORCHESTRA was used to implement a dual porosity reactive transport system that accounts for mechanical processes relevant for confined swelling clays at full saturation. The new implementations are based on water retention data generated by molecular dynamics simulations, and on fundamental mechanical formulations. The code predicts and fully couples porewater chemistry, exchanger population, diffusive transport, mineral reactions, volume fractions of the free and Donnan porosity domains, and swelling pressure. The chemomechanical predictions were compared with experimental measurements of swelling pressure and d-value of the clay in different chemical environments. A simulation of bentonite in contact with a constant concentration reservoir demonstrates the performance of the new model approach. It can be used to model interactions of bentonite with different groundwaters or cement and steel., El marco de transporte reactivo ORCHESTRA se utilizó para implementar un sistema de transporte reactivo de porosidad dual que da cuenta de los procesos mecánicos relevantes para las arcillas expansivas confinadas en plena saturación. Las nuevas implementaciones se basan en datos de retención de agua generados por simulaciones de dinámica molecular y en formulaciones mecánicas fundamentales. El código predice y acopla completamente la química del agua intersticial , la población del intercambiador, el transporte difusivo , las reacciones minerales, las fracciones de volumen .de los dominios de porosidad libre y de Donnan, y la presión de hinchamiento. Las predicciones quimiomecánicas se compararon con mediciones experimentales de la presión de expansión y el valor d de la arcilla en diferentes entornos químicos. Una simulación de bentonita en contacto con un yacimiento de concentración constante demuestra el rendimiento del nuevo enfoque del modelo. Puede usarse para modelar interacciones de bentonita con diferentes aguas subterráneas o cemento y acero.

This work aims to shed light on the scale-up a combined electrokinetic soil flushing process (EKSF) with permeable reactive barriers (PRB) for the treatment of soil spiked with clopyralid. To do this, remediation tests at lab (3.45 L), bench (175 L) and pilot (1400 L) scales have been carried out. The PRB selected was made of soil merged with particles of zero valent iron (ZVI) and granular activated carbon (GAC). Results show that PRB-EKSF involved electrokinetic transport and dehalogenation as the main mechanisms, while adsorption on GAC was not as relevant as initially expected. Clopyralid was not detected in the electrolyte wells and only in the pilot scale, significant amounts of clopyralid remained in the soil after 600 h of operation. Picolinic acid was the main dehalogenated product detected in the soil after treatment and mobilized by electro-osmosis, mostly to the cathodic well. The transport of volatile compounds into the atmosphere was promoted at pilot scale because of the larger soil surface exposed to the atmosphere and the electrical heating caused by ohmic losses and the larger interelectrode gap., Este trabajo tiene como objetivo arrojar luz sobre el escalado de un proceso de lavado de suelo electrocinético combinado (EKSF) con barreras reactivas permeables .(PRB) para el tratamiento de suelos enriquecidos con clopiralid. Para ello, se han realizado pruebas de remediación a escala de laboratorio (3,45 L), banco (175 L) y piloto (1400 L). El PRB seleccionado estaba hecho de suelo fusionado con partículas de hierro cerovalente (ZVI) y carbón activado granular (GAC). Los resultados muestran que PRB-EKSF involucraba el transporte electrocinético y la deshalogenación como los principales mecanismos, mientras que la adsorción en GAC no fue tan relevante como se esperaba inicialmente. No se detectó clopiralida en los pozos de electrolito y solo en la escala piloto, cantidades significativas de clopiralida permanecieron en el suelo después de 600 h de operación. El ácido picolínico fue el principal producto deshalogenado detectado en el suelo después del tratamiento y movilizado por electro-ósmosis, principalmente al pozo catódico.

The temperature effect on the microstructure deformability of compacted bentonites was assessed using a Clausius-Clapeyron type equation. To this end, vapor adsorption data obtained at different temperatures under low water content conditions was used, identifying changes in the microstructural water with changes in the microstructural void volume. The formulation proposed allows for an extension of the 2D-models used in macroscopic double-porosity approaches to a 3D surface in which temperature is explicitly considered. The results obtained were encouraging, fitting the experimental data highly satisfactorily. Therefore, the approach proposed in this study can be a key tool for characterizing the nonisothermal behavior of compacted bentonites., El efecto de la temperatura sobre la deformabilidad de la microestructura de las bentonitas compactadas se evaluó mediante una ecuación tipo Clausius-Clapeyron. Para ello, se utilizaron datos de adsorción de vapor obtenidos a diferentes temperaturas en condiciones de bajo contenido de agua, identificando cambios en el agua microestructural con cambios en el volumen vacío microestructural. La formulación propuesta permite una extensión de los modelos 2D utilizados en los enfoques macroscópicos de doble porosidad a una superficie 3D en la que se considera explícitamente la temperatura. Los resultados obtenidos fueron alentadores, ajustando muy satisfactoriamente los datos experimentales. Por lo tanto, el enfoque propuesto en este estudio puede ser una herramienta clave para caracterizar el comportamiento no isotérmico de las bentonitas compactadas.

This work proposes a formulation to simulate the swelling of compacted bentonites, focusing the analysis on the modelling of the increase of macrostructural void ratio generated by the destructuration of the microstructure under low confinement conditions. First, its formulation is described, highlighting its integration into a generalised constitutive model, which is able to describe the behaviour of compacted bentonites under very different conditions of stress, salinity and water content. After, its scope is assessed, comparing the model predictions with experimental results of free swelling tests performed under different salinity conditions. The results obtained are very satisfactory, especially considering that the proposed swelling model is based on only two material parameters. © 2021 Elsevier Ltd

Thermal load imposed on the ground by the foundations of some singular buildings may produce variations in geochemistry conditions. In soils containing soluble salts, such as gypsum, their dissolution/precipitation rates may be modified, triggering ground settlement as well as angular distortion of building foundations. This paper examines these processes for the case of the Central Storage Facility for high-level radioactive waste planned in Spain. This facility would impose a thermal load over a long period of time due to the disposal of spent nuclear fuel. A numerical model, including the equations for describing the dissolution/precipitation process, as well as the hydrogeological, thermal, chemical, and geomechanical changes in the ground caused by the construction and operation of the facilities, is proposed. The model focuses on the response of the building foundation under different hypothesis of thermal loading underneath the building. Comsol Multiphysics software was used for solving the resulting partial differential equations by the finite element method. This analysis concludes that moderate thermal loading of the ground would develop in the Case Study, with negligible mechanical effect on the foundation., La carga térmica impuesta al suelo por los cimientos de algunos edificios singulares puede producir variaciones en las condiciones geoquímicas . En suelos que contienen sales solubles, como el yeso , sus tasas de disolución/precipitación pueden modificarse, provocando asentamientos del suelo y distorsión angular de los cimientos de los edificios. Este artículo examina estos procesos para el caso de la Instalación Central de Almacenamiento de residuos radiactivos de alta actividad.prevista en España. Esta instalación impondría una carga térmica durante un largo período de tiempo debido a la eliminación del combustible nuclear gastado. Se propone un modelo numérico que incluye las ecuaciones para describir el proceso de disolución/precipitación, así como los cambios hidrogeológicos, térmicos, químicos y geomecánicos en el suelo provocados por la construcción y operación de las instalaciones. El modelo se centra en la respuesta de los cimientos del edificio bajo diferentes hipótesis de carga térmica debajo del edificio. Se utilizó el software Comsol Multiphysics para resolver las ecuaciones diferenciales parciales resultantes mediante el método de elementos finitos. Este análisis concluye que se desarrollaría una carga térmica moderada del suelo en el caso de estudio, con un efecto mecánico insignificante en la cimentación.

The water retention curve deduced with low water content data allows the modelling of the bentonite void ratio associated with the pores located inside the clay aggregates, or micropores. However, if both the water content and the microporosity continue to increase, the latter can no longer be directly obtained from the former, because, in that case, the presence of water in the pores existing between the aggregates (macropores) may not be negligible. Therefore, it is not easy to obtain experimental evidence that allows to contrast whether the model's extrapolation of the microstructural void ratio obtained under dry conditions is valid for higher water contents. This work analyses the use of data obtained from molecular dynamics models to assess the validity of such extrapolations, and defines the variables needed to compare the results from molecular dynamics and laboratory experiments. The encouraging agreement obtained contributed to the confidence in the proposed procedure, which enabled a new strategy that uses molecular dynamics data to model the macroscopic behaviour of compacted sodium bentonites.

The increasing needs for modelling of reactive transport phenomena in different areas of environmental modelling have led to the development of many numerical codes. However, many of them suffer from a lack of flexibility, which hinders the adaptation of the codes to new problems. Moreover, in many cases, changes can be done by a very reduced group of people, and often by a single person, the main developer. Implementation platforms based on multiphysics modelling removes these barriers, although until now within that programming environments has been only possible the coupling of geochemical codes to transport equations using operator splitting techniques. This paper presents the EE4MGM tool, a MS Excel worksheet, provided in supplementary material, for the edition and complete implementation of reactive transport models in COMSOL. The tool automatically generates the code needed to solve the desired reactive transport problem by selecting only which species make up the geochemical system. This way, the numerical model will be completely adapted to the idealisation to be applied, being able to choose easily and effortlessly from a wide range of different levels of conceptual complexity. The organization of data input and the equation libraries obtained for the implementation in the multiphysics COMSOL environment are first described. Afterwards, two examples, in one and two-dimensional domains, to check the utility of the tool are presented.

Electroosmotic permeability is a soil parameter that is fundamental for designing and implementing environmental remediation, dewatering, or soil stabilization processes. It presents a narrow range of variation compared to hydraulic permeability, so that in many occasions no experimental tests are carried out to determine it. Traditionally, the Helmholtz–Smoluchowski equation has been used to estimate electroosmotic permeability, despite having several drawbacks that make it difficult to apply, as it was deduced for large capillaries (unusual in clays) and its dependence on the zeta potential of the soil, difficult to measure and dependent on a wide variety of factors. The present work describes a semi-empirical formulation that allows the estimation of the electroosmotic permeability as a function of the specific surface area and the total void ratio and is based on the Donnan equilibrium and the ion hydration models. The parameters for modeling are calibrated and validated with experimental data, obtaining better results than those given by the Helmholtz–Smoluchowski model. In addition, the expected trends in the behavior of clays that can be found in the literature are obtained in a quantitative and consistent manner for different types of clays with variable water content and pore water salinity.

This work analyses the characterization of the hygric behaviour of a stone heritage material by solving the inverse problem using experimental data obtained from a water absorption by capillarity test (EN 15801). This common test is undemanding and requires relatively simple equipment as compared to other hygric characterization tests. For the solution of the direct problem of transient flow in partially saturated porous media, a computational module was developed in COMSOL Multiphysics that includes the conceptual model from the standard EN 15026. The selected material was the heritage stone of the Cuenca Cathedral, differentiating between two characteristic lithotypes: one with greater porosity and another that is more resistant, with more reduced porosity. Based on the experimental results, the intrinsic permeability and the parameters of the moisture storage function are estimated for the two lithotypes. Similarly, contrast tests were conducted to quantify the estimation error. A stochastic analysis was performed to assess if the estimated hygric parameters satisfactorily characterize the behaviour of the studied stone.

In this work, a three-month test is used to evaluate the role of electrokinetic fences in the prevention of the diffusion of herbicide in case of accidental spills of large amounts of highly concentrated products in clay soil. To do this, a mock-up (0.95 × 2.00 × 0.50 m 3 ) is used and an electrokinetic fence is placed far away from the hydraulic plume in order to mitigate the effect of the diffuse pollution caused by the spill of an important amount of 2,4-dichlorofenoxiacetic acid (2,4-D) and oxyfluorfen. The results confirm that diffusion of pollutants is important and that the presence of an electrokinetic fence can contain micellar pollutants and help to minimize the trespassing of soluble pollutants, although they cannot fully prevent this trespass. The results obtained in this work are compared to those obtained in previous works, in which fence technology with surrounding electrode placement was evaluated and important differences were pointed out; this has generated valuable data for the design of this technology.

In this work, the remediation of soil spiked with clopyralid is evaluated using two types of zero valent iron (ZVI) barriers coupled with electrokinetic soil flushing (EKSF). These barriers consist of soil merged with iron particles. In one of the tests conducted, granular milimetric iron was used, whereas in the other, iron was placed in the form of nanoparticles. The performance of this novel technology is compared to that of single EKSF technology. Tests were carried out in bench scale mockups (175 L) and they lasted one month. Over this period, soil underwent the application of an electric field of 1.0 V/cm between a row of three anodes and a row of three cathodes. Results indicate that ZVI barriers seriously affect electrokinetic flushes by preventing the mobility of pollutants to the electrode wells. However, they achieve a larger dehalogenation of clopyralid than single EKSF. There are no significant differences between the results obtained using the two sizes of ZVI and the volatilization of pollutants associated to thermal effects was almost prevented by means of capillary barriers implemented on top of the mockups. After the treatment, most of the clopyralid not removed is concentrated near the anodes wells and a very important fraction can be easily extracted by excavating a very small percentage of the soil, because the pollutant has been concentrated in very specific points during remediation. Results are significant for the design of full-scale applications for the remediation of soils polluted with soluble chlorinated hydrocarbons.

This work presents a techno-economic study of the scaling-up of the electrochemically-assisted soil remediation (EASR) process of polluted soil. Four scales have been selected for the study: laboratory, bench, pilot and prototype, with a capacity of treating a volume of soil of 1 × 10 −4 , 2 × 10 −3 , 0.11 and 21.76 m 3 , respectively. This study analyses the technical information produced by studies carried out at each scale, and informs about the fixed costs (construction of the electrokinetic remediation reactor, installation of auxiliary services and purchase of analytical equipment) and variable costs (start-up, operation and dismantling of the test) derived from running a test at each of the evaluated scales. The information discussed in based on the experience gained with many evaluations carried out over the last decade at these scales. This information can provide useful guidance for developing a scaling-up of the EASR for many researchers starting on the evaluation of this important environmental remediation technology.

This paper presents a formulation to incorporate the influence of water salinity on the swelling behaviour of a MX-80 bentonite into previously developed hydro-mechanical models that can reproduce swelling under dilute conditions. The effects of salinity on macro- and microstructural water chemical potentials were introduced. In addition, a description of solute transport was included to characterise the evolution of the system's salinity. A simplified geochemical model was adopted to idealise the geochemical complexity of bentonite. In addition, the modelling of the destructuration process that occurs during swelling was modified to account for the effect of salinity. The formulation was implemented in a multiphysics partial differential equation finite element solver, and the numerical model was used to simulate several vertical free swelling tests with feed water of different salt contents (deionised, 10, 35 and 70 g/L). The results demonstrate that even though the model can be developed further, it represents a significant improvement over models that do not account for the effects of salinity. © 2017 Elsevier B.V.

This paper presents a formulation to incorporate the influence of water salinity on the swelling behaviour of a MX-80 bentonite into previously developed hydro-mechanical models that can reproduce swelling under dilute conditions. The effects of salinity on macro- and microstructural water chemical potentials were introduced. In addition, a description of solute transport was included to characterise the evolution of the system’s salinity. A simplified geochemical model was adopted to idealise the geochemical complexity of bentonite. In addition, the modelling of the destructuration process that occurs during swelling was modified to account for the effect of salinity. The formulation was implemented in a multiphysics partial differential equation finite element solver, and the numerical model was used to simulate several vertical free swelling tests with feed water of different salt contents (deionised, 10, 35 and 70 g/L). The results demonstrate that even though the model can be developed further, it represents a significant improvement over models that do not account for the effects of salinity.

This work reports results of the application of electrokinetic fence technology in a 32 m3 -prototype which contains soil polluted with 2,4-D and oxyfluorfen, focusing on the evaluation of the mechanisms that describe the removal of these two herbicides and comparing results to those obtained in smaller plants: a pilot-scale mockup (175 L) and a lab-scale soil column (1 L). Results show that electric heating of soil (coupled with the increase in the volatility) is the key to explain the removal of pollutants in the largest scale facility while electrokinetic transport processes are the primary mechanisms that explain the removal of herbicides in the lab-scale plant. 2-D and 3-D maps of the temperature and pollutant concentrations are used in the discussion of results trying to give light about the mechanisms and about how the size of the setup can lead to different conclusions, despite the same processes are occurring in the soil.

This work evaluated water transport that occurs in a partially saturated soil of low hydraulic permeability when undergoing an electrokinetic remediation process. The soil used was a compacted kaolinite. To evaluate a wide range of possible conditions, soil with three different initial water contents (10, 15 and 20%) was used, obtaining a range of dry densities of 1300–1600 kg m−3. The tests were performed using a lab-scale setup with a soil capacity of 675 cm3 and applying different electrical potential gradients (0.5, 1, 1.5 and 2 V cm−1). The experimental results obtained were used to validate a conceptual model implemented in COMSOL. The validated model was used to conduct a detailed interpretation of the observed water transport processes and to perform a study of the hydraulic behaviour of the soil as a function of the initial conditions of compaction, water saturation and applied electrical potential gradient.

This study compares the capabilities of two numerical models that simulate the behaviour of compacted saturated MX-80 bentonite exposed to different chemical environments. Both codes have different approaches: one of them is a reactive transport model, and the other is a hydrogeomechanical model. The study shows that the combined use of both approaches provides a useful basis for designing bentonite barriers in the geological disposal of high-level nuclear waste. Although, their application is now limited to simple geometries and boundary conditions, the proposed approaches are a first step towards a fully thermo-hydro-mechano-chemical model. It is also shown that there is a need for a greater understanding of the chemomechanical coupling that occurs at the microstructural scale to achieve this comprehensive model in the future.

This work aimed to evaluate electrokinetic soil flushing (EKSF) technologies for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from spiked soils using an electrode configuration consisting of one cathode surrounded by six anodes (1c6a) and one anode surrounded by 6 cathodes (1a6c). Experiments were conducted for over one month in a bench-scale set-up (175 dm(3) of capacity) that was completely automated and operated at a constant electric field (1.0V cm(-1)). The electrical current, temperature, pH, moisture and pollutant concentration in electrolyte wells were monitored daily, and at the end of the experiments, an in-depth sectioned analysis of the complete soil section (post-mortem analysis) was conducted. Despite the geometric similarity, the two strategies led to very different results mainly in terms of water and herbicide mobilization, whereas pH and conductivity do not depend strongly on the electrode configuration. The volume of water extracted from cathodes with 1a6c is seven times higher than that of the 1c6a strategy. Herbicide was transported to the anode wells by electromigration and then dragged toward the cathode wells by electro-osmotic fluxes, with the first process being much more important. The configuration 1c6a was the most efficient and attained a transfer of 70% of the herbicide contained in the soil to flushing water in 35 days. These results outperform those obtained by the configuration 1a6c, for which less than 8% of the herbicide was transferred to flushing fluids in a much longer time (58 days).

This study analyses the effect of the scale-up of electrokinetic remediation (EKR) processes in natural soils. A procedure is proposed to prepare soils based on a compacting process to obtaining soils with similar moisture content and density to those found in real soils in the field. The soil used here was from a region with a high agrarian activity (Mora, Spain). The scale-up study was performed in two installations at different scales: a mock-up pilot scale (0.175 m3) and a prototype with a scale that was very similar to a real application (16 m3). The electrode configuration selected consisted of rows of graphite electrodes facing each other located in electrolyte wells. The discharge of 20 mg of 2,4-dichlorophenoxyacetic acid [2,4-D] per kg of dry soil was treated by applying an electric potential gradient of 1 V cm−1. An increase in scale was observed to directly influence the amount of energy supplied to the soil being treated. As a result, electroosmotic and electromigration flows and electric heating are more intense than in smaller-scale tests (24%, 1% and 25%, respectively respect to the values in prototype). In addition, possible leaks were evaluated by conducting a watertightness test and quantifying evaporation losses., Este estudio analiza el efecto del escalado de procesos de remediación electrocinética (EKR) en suelos naturales. Se propone un procedimiento de preparación de suelos basado en un proceso de compactación para obtener suelos con contenido de humedad y densidad similar a los que se encuentran en los suelos reales en campo. El suelo utilizado aquí era de una región con una alta actividad agraria (Mora, España). El estudio de escalado se realizó en dos instalaciones a diferentes escalas: una escala piloto maqueta (0,175 m 3 ) y un prototipo con una escala muy similar a una aplicación real (16 m 3 ). La configuración de electrodos seleccionada consistió en filas de electrodos de grafito uno frente al otro ubicados en pozos de electrolito. La descarga de 20 Se trataron mg de ácido 2,4-diclorofenoxiacético [2,4-D] por kg de suelo seco aplicando un gradiente de potencial eléctrico de 1 V cm - 1 . Se observó que un aumento en la escala influye directamente en la cantidad de energía suministrada al suelo que se está tratando. Como resultado, los flujos electroosmóticos, de electromigración y calentamiento eléctrico son más intensos que en ensayos a menor escala (24%, 1% y 25%, respectivamente, respecto a los valores en prototipo). Además, se evaluaron posibles fugas realizando una prueba de estanqueidad y cuantificando las pérdidas por evaporación.

In this work, an accidental spill of Fluoxyl (commercial herbicide containing oxyfluorfen) is simulated in a pilot plant with a soil volume of 70 × 50 × 50 cm 3 . The transport of Fluoxyl obtained by the free diffusion of pollution and under the application of the electrokinetic fences (EKF) technology are compared in a 34-day treatment. In addition, the temperature, conductivity, and pH are monitored daily. At the end of the experiment, a post-mortem analysis is carried out in order to obtain a 3-D distribution map of the pollutant. The results show that EKF is a good technology to remove oxyfluorfen from the soil without excavation because it is able to attain a fast transfer of oxyfluorfen to the flushing fluid used. After 34 days, the decrease in the concentration of oxyfluofen in the simulated case without any treatment is only 5.5%, whereas when EKF is applied, the removal yield is approximately 63% (60.7% of improvement vs. natural volatilization). Detailed analyses of the experimental data, the 3-D map, and recent literature suggest that the main mechanism involved for the removal is the rapid transfer of oxyfluorfen to the flushing fluid used. The results are also discussed in the context of a previous work in which the same technology has been applied for the removal of the ionic herbicide 2,4-D. A comparison allows sound conclusions to be made for future scale-up studies.

Mating disruption has proved successful against California red scale (CRS), Aonidiella aurantii Maskell (Hemiptera: Diaspididae) in Mediterranean citrus. Although mating disruption does not affect negatively the parasitism by Aphytis melinus DeBach (Hymenoptera: Aphelinidae), a CRS parasitoid introduced to the Mediterranean, there is no information regarding its potential effect on the native Aphytis species. In the present study, the effect of CRS mating disruption on the field parasitism inflicted by Aphytis spp. has been assessed and compared to a mineral oil and a control treatment. In order to confirm the effectiveness of the mating disruption we also evaluated its effect on the captures of the CRS males and on fruit infestation. Moreover, the potential role of the CRS sex pheromone as kairomone for the Aphytis species was also evaluated by comparing captures of parasitoids on sticky traps with or without pheromone. Significantly lower CRS male captures and fruit damage were registered in the mating disruption respect to the control or oil treatments indicating that mating disruption was effective. In September, when compared to the control, parasitism by Aphytis spp. was significantly lower in the mating disruption and mineral oil treatments and crucially no Aphytis chrysomphali Mercet were registered in the mating disruption treatment. Finally, while the captures of both A. melinus and Aphytis lepidosaphes (Mercet) were not significantly different between traps with or without pheromone, A. chrysomphali captures were significantly higher in traps baited with CRS pheromone. These results suggest a possible kairomonal effect of the CRS pheromone on A. chrysomphali .

Attractants and pheromones are commonly used in integrated pest management programs in crop systems. However, pheromone dispensers employed in monitoring traps and lure and kill devices are not usually well studied and attractants are released at uncontrolled rates leading to low treatment efficacies and misleading monitoring estimations. Fruit flies are pests of economic importance and monitoring is essential in order to program insecticidal treatments. Moreover, lure and kill techniques are being increasingly used, but the cost of these techniques depends on the number of required traps and, therefore, on the efficacy of the attractants. Ceratitis capitata and Bactrocera oleae are the two main fruit flies in Mediterranean countries, and the effect of different doses of trimedlure and spiroacetal on fly attraction has been studied. Results showed that a release rate over 1.28 mg/day of spiroacetal reduces B. oleae attraction and emission values over 2.4 mg of trimedlure per day did not increase C. capitata catches. Under the environmental conditions of our study, an optimum release rate for pheromone attraction in B. oleae was determined. Emission values over this optimum level reduced B. oleae attraction. However, when a parapheromone was used with C. capitata, a fruit fly of the same family, the optimum emission value was not found and higher quantities of parapheromone attracted the same number of flies. The saturation effect of high concentrations of pheromone and parapheromone is discussed., We wish to thank "Cartuja de Portacoeli" and Domingo de Guzman Orero for offering their orchards for this research, and Juan Bautista for field assistance. This research was supported by "Ministerio de Ciencia e Innovacion" project number AGL2006-13346-C02-02.

[EN] The rice striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae) is one of the most important rice pests worldwide, Rice is frequently grown in an intensive production system in areas adjacent to environmentally sensitive areas. Therefore, the use of insecticides is problematic and new techniques, including mating disruption, are being introduced. Due to the high cost of pheromones, it is essential to optimize the density of the pheromone dispensers. The main purpose of this research was to determine the minimal dosage and optimal dispenser distribution for effective mating disruption of C. suppressalis. To this end, we conducted a wide-area trial to test several dispenser densities. 31, 25 and 16 dispensers/ha during 3 years. Results were compared with a standard mating disruption treatment (51 dispensers/ha) and a standard aerial chemical treatment with tebufenozide. Treatment efficacy was determined by pheromone trap catches and crop damage assessment. The release rate of the pheromone dispensers was also quantified. The results of these trials suggest that such treatments provide effective pest control even with reduced pheromone dispenser densities. Longer-lasting dispensers with lower residual load at the end of trials will greatly improve the efficacy of mating disruption for C. suppressalis. Moreover, an important consideration is that these newly tested dispenser densities imply a significant reduction in the cost of the treatment. These results are essential in order to expand the use of mating disruption in rice crop protection. (C) 2009 Elsevier Ltd. All rights reserved.