Rafig Azzam

Transport and deposition of stabilized engineered silver nanoparticles in water saturated loamy sand and silty loam

It is considered inevitable that the increasing production and application of engineered nanoparticles will lead to their release into the environment. However, the behavior of these materials under environmentally relevant conditions is still only poorly understood. In this study the transport and deposition behavior of engineered surfactant stabilized silver nanoparticles (AgNPs) in water saturated porous media was investigated in transport experiments with glass beads as reference porous medium and in two natural soils under various hydrodynamic and hydrochemical conditions. The transport and retention processes of AgNPs in the porous media were elucidated by inverse modeling and possible particle size changes occurring during the transport through the soil matrix were analyzed with flow field-flow fractionation (FlFFF). A high mobility of AgNPs was observed in loamy sand under low ionic strength (IS) conditions and at high flow rates. The transport was inhibited at low flow rates, at higher IS, in the presence of divalent cations and in a more complex, fine-grained silty loam. The slight decrease of the mean particle size of the AgNPs in almost all experiments indicates size selective filtration processes and enables the exclusion of homoaggregation processes.

Transport of stabilized engineered silver (Ag) nanoparticles through porous sandstones.

Engineered nanoparticles are increasingly applied in consumer products and concerns are rising regarding their risk as potential contaminants or carriers for colloid-facilitated contaminant transport. Engineered silver nanoparticles (AgNP) are among the most widely used nanomaterials in consumer products. However, their mobility in groundwater has been scarcely investigated. In this study, transport of stabilized AgNP through porous sandstones with variations in mineralogy, pore size distribution and permeability is investigated in laboratory experiments with well-defined boundary conditions. The AgNP samples were mainly characterized by asymmetric flow field-flow fractionation coupled to a multi-angle static laser light detector and ultraviolet-visible spectroscopy for determination of particle size and concentration. The rock samples are characterized by mercury porosimetry, flow experiments and solute tracer tests. Solute and AgNP breakthrough was quantified by applying numerical models considering one kinetic site model for particle transport. The transport of AgNP strongly depends on pore size distribution, mineralogy and the solution ionic strength. Blocking of attachment sites results in less reactive transport with increasing application of AgNP mass. AgNPs were retained due to physicochemical filtration and probably due to straining. The results demonstrate the restricted applicability of AgNP transport parameters determined from simplified experimental model systems to realistic environmental matrices.

Undrained shear strength of clays as modified by pH variations

The undrained shear strength of clays is an important geotechnical parameter used during construction processes. Several laboratory tests were performed on kaolinite and smectite mixed with pore fluids with different pH values. Vane shear tests were carried out and it was found that the undrained shear resistance for clays increased considerably if the pore fluid had a high or a low pH. A possible explanation could be the dissolution of Al3+ which acts as a coagulant, increasing the internal shear resistance. Geochemical computations, Al measurements and ζ-potential experiments were performed to confirm this theory. The research suggests varying the pH may make a useful contribution to soil improvement techniques.RésuméLa résistance au cisaillement non drainé des argiles est un paramètre géotechnique important utilisé en phase de construction d’ouvrages. Plusieurs essais de laboratoire ont été mis en œuvre sur des kaolinites et des smectites préparées avec des fluides de différents pH. Des essais de cisaillement au scissomètre ont été réalisés et l’on a trouvé que la résistance au cisaillement non drainé des argiles augmente considérablement si le fluide interstitiel a un pH faible ou fort. Pour un pH faible, une explication possible pourrait venir de la dissolution des Al3+ qui agissent comme des coagulants, augmentant la résistance au cisaillement. Des calculs géochimiques, des mesures de teneur en Al et de potentiel ζ ont été réalisés pour confirmer cette théorie. Les résultats de cette recherche suggèrent que le fait de faire varier le pH de l’eau interstitielle peut contribuer utilement à l’amélioration de la résistance des sols.

Quantitative assessment of intrinsic groundwater vulnerability to contamination using numerical simulations

Intrinsic vulnerability assessment to groundwater contamination is part of groundwater management in many areas of the world. However, popular assessment methods estimate vulnerability only qualitatively. To enhance vulnerability assessment, an approach for quantitative vulnerability assessment using numerical simulation of water flow and solute transport with transient boundary conditions and new vulnerability indicators are presented in this work. Based on a conceptual model of the unsaturated underground with distinct hydrogeological layers and site specific hydrological characteristics the numerical simulations of water flow and solute transport are applied on each hydrogeological layer with standardized conditions separately. Analysis of the simulation results reveals functional relationships between layer thickness, groundwater recharge and transit time. Based on the first, second and third quartiles of solute mass breakthrough at the lower boundary of the unsaturated zone, and the solute dilution, four vulnerability indicators are extracted. The indicator transit time t(50) is the time were 50% of solute mass breakthrough passes the groundwater table. Dilution is referred as maximum solute concentration C(max) in the percolation water when entering the groundwater table in relation to the injected mass or solute concentration C(0) at the ground surface. Duration of solute breakthrough is defined as the time period between 25% and 75% (t(25%)-t(75%)) of total solute mass breakthrough at the groundwater table. The temporal shape of the breakthrough curve is expressed with the quotient (t(25%)-t(50%))/(t(25%)-t(75%)). Results from an application of this new quantitative vulnerability assessment approach, its advantages and disadvantages, and potential benefits for future groundwater management strategies are discussed.

Impact of climate change on groundwater recharge in a small catchment in the Black Forest, Germany

Temporal and spatial changes of the hydrological cycle are the consequences of climate variations. In addition to changes in surface runoff with possible floods and droughts, climate variations may affect groundwater through alteration of groundwater recharge with consequences for future water management. This study investigates the impact of climate change, according to the Special Report on Emission Scenarios (SRES) A1B, A2 and B1, on groundwater recharge in the catchment area of a fissured aquifer in the Black Forest, Germany, which has sparse groundwater data. The study uses a water-balance model considering a conceptual approach for groundwater-surface water exchange. River discharge data are used for model calibration and validation. The results show temporal and spatial changes in groundwater recharge. Groundwater recharge is progressively reduced for summer during the twenty-first century. The annual sum of groundwater recharge is affected negatively for scenarios A1B and A2. On average, groundwater recharge during the twenty-first century is reduced mainly for the lower parts of the valley and increased for the upper parts of the valley and the crests. The reduced storage of water as snow during winter due to projected higher air temperatures causes an important relative increase in rainfall and, therefore, higher groundwater recharge and river discharge.RésuméLes changements du cycle hydrologique dans le temps et l’espace sont la conséquence des variations du climat. En plus des changements dans l’écoulement de surface, avec de possibles inondations et sècheresses, les variations climatiques peuvent affecter les eaux souterraines, du fait de la modification de la recharge avec des conséquences pour la gestion future de l’eau. La présente étude examine, en référence au Rapport Spécial sur les Scénarios d’Emission (RSSE) A1B, A2, B1, l’impact du changementmclimatique sur la recharge des eaux souterraines dans le bassin d’alimentation d’un aquifère fissuré de la Forêt Noire, Allemagne, dont les données sur l’eau souterraine sont clairsemées. L’étude utilise un modèle de bilan hydrique prenant en compte une approche conceptuelle pour l’échange eau souterraine-eau de surface. Les données sur le débit de la rivière sont utilisées pour le calage et la validation du modèle. Les résultats montrent des changements de recharge de la nappe, dans le temps et l’espace. Celle-ci s’est progressivement réduite en été durant le 21ème siècle. Son total annuel est affecté négativement dans les scénarios A1B et A2. En moyenne, pendant le 21ème siècle, elle est réduite principalement dans les parties basses et augmentée dans les parties hautes de la vallée et sur les crêtes. La réduction du stockage d’eau sous forme de neige en hiver, imputable à des températures de l’air supérieures prévisibles cause une importante augmentation relative des pluies et, par suite, une recharge de nappe et un débit de rivière plus importants.ZusammenfassungZeitliche und räumliche Änderungen des hydrologischen Kreislaufs resultieren aus der Variation des Klimas. Neben den Änderungen des Oberflächenabflusses mit möglichen Überschwemmungen und/oder Dürren, können sich Klimaänderungen auch auf das Grundwasser durch veränderte Grundwasserneubildungsraten auswirken, was Konsequenzen für das zukünftiges Wassermanagement haben kann. Diese Untersuchung befasst sich mit der Auswirkung der Klimaszenarien A1B A2 und B1 des Sonderberichts über Emissionsszenarien (SRES) auf die Grundwasserneubildung eines geklüfteten Grundwasserleiters im Schwarzwald (Deutschland), von dem nur begrenzt grundwasserbezogene Daten verfügbar sind. Es wird ein hydrologisches Wasserbilanzmodell mit einem konzeptuellen Ansatz für den Austausch zwischen Grund- und Oberflächenwasser gerechnet, das anhand von Abflussdaten kalibriert bzw. validiert wird. Die Ergebnisse zeigen, zeitliche und räumliche Änderungen der Grundwasserneubildung, die während des 21. Jahrhunderts in den Sommermonaten generell abnimmt. Im Mittel werden Abnahmen vor allem für die Talregionen des Untersuchungsgebiets prognostiziert, während in den höher gelegenen Regionen die Grundwasserneubildung eher zunimmt. Durch die ansteigenden Temperaturen wird während der Wintermonate weniger Wasser in Form von Schnee zwischengespeichert, so dass in diesem Zeitraum ein relativer Anstieg des Oberflächenabflusses und der Grundwasserneubildung prognostiziert wird.ResumenLos cambios temporales y espaciales del ciclo hidrológico son las consecuencias de las variaciones climáticas. Además de los cambios en el escurrimiento superficial con posibles inundaciones y sequías, las variaciones climáticas pueden afectar al agua subterránea a través de la alteración de la recarga del agua subterránea con consecuencias para el manejo futuro del agua. Este estudio investiga el impacto del cambio climático, de acuerdo con el informe especial sobre escenarios de emisiones (SRES) A1B, A2 and B1, sobre la recarga del agua subterránea en el área de una cuenca hidrográfica de un acuífero fisurado en la Selva Negra, Alemania, que tiene escasos datos de agua subterránea. El estudio usa un modelo de balance de agua considerando un enfoque conceptual para el intercambio agua subterránea–agua superficial. Los datos de la descarga del río son usados para la calibración y validación del modelo. Los resultados muestran cambios espaciales y temporales en la recarga del agua subterránea. La recarga del agua subterránea se reduce progresivamente para el verano durante el siglo 21. La suma anual de recarga de agua subterránea está afectada negativamente para los escenarios A1B y A2. En promedio, la recarga de agua subterránea durante el siglo 21 se reduce principalmente para las partes bajas del valle y se incrementa en las partes más altas de los valles y las crestas. La reducción en el almacenamiento de agua en forma de nieve durante el invierno debido a las mayores temperaturas del aire proyectadas provoca un importante aumento relativo de las precipitaciones y, por tanto, mayor recarga de aguas subterráneas y de mayor descarga de los ríos.摘要水循环的时间和空间变化是气候变化影响的结果。除了可能通过洪水或者干旱改变地表水流外,气候变化可通过改变地下水补给影响地下水及未来的水管理结果。德国山林区地下水数据稀少,根据排放情景(SRES)A1B、A2和B1的专题报道,本文调查了气候变化对该区裂隙含水层流域地下水补给的影响。本文使用考虑了地下水地表水相互作用概念化方法的水均衡模型。河水排泄数据用于模型识别验证。结果展示了地下水补给量的时空变化。21世纪地下水补给量在夏季逐渐减少。情景A1B和A2下,地下水每年补给量的影响是负面的。21世纪地下水补给量均值在山谷下游减少,在山谷上游及山顶增加。由于升高的空气温度,冬季以雪形式贮存的水减少,导致降雨量的相对增加,进而引起地下水补给量及河水排泄量的增加。ResumoMudanças temporais e espaciais do ciclo hidrológico são consequências das variações climáticas. Além de mudanças no escoamento superficial, com possíveis cheias e secas, as variações climáticas podem afetar as águas subterrâneas, através da alteração da recarga, com consequências para a gestão futura da água. Este estudo investiga o impacte da mudança do clima, de acordo com o Relatório Especial sobre Cenários de Emissões (SRES) A1B, A2 e B1, na recarga das águas subterrâneas na bacia hidrográfica de um aquífero fissurado na Floresta Negra, Alemanha, que apresenta uma escassez de dados sobre águas subterrâneas. O estudo utiliza um modelo de balanço hídrico, considerando uma abordagem concetual para as trocas água subterrânea-água superficial. São utilizados dados de descarga do rio para a calibração e validação do modelo. Os resultados mostram mudanças temporais e espaciais na recarga dos aquíferos. Durante o século XXI, a recarga das águas subterrâneas é progressivamente reduzida no verão. O montante anual da recarga subterrânea é afectado negativamente para os cenários A1B e A2. Em média, a recarga de água subterrânea durante o século XXI é reduzida, principalmente nas partes mais baixas do vale, e aumenta para a parte superior do vale e para as cristas. O reduzido armazenamento de água, sob a forma de neve, durante o inverno, devido às previstas temperaturas do ar mais elevadas, causa um importante aumento relativo da precipitação e, portanto, maior recarga de águas subterrâneas e maior caudal do rio.

Strength of soil reinforced with fiber materials (Papyrus)

Construction of building and other civil engineering structures on weak or soft soil is highly risky because such soil is susceptible to differential settlements, poor shear strength, and high compressibility. Various soil improvement techniques have been used to enhance the engineering properties of soil. Soil reinforcement by fiber material is considered an effective ground improvement method because of its cost effectiveness, easy adaptability, and reproducibility. Hence, in the present investigation, papyrus fiber has been chosen as the reinforcement material, and it was randomly included into the soil at four different percentages of fiber content, i.e., 5, 10, 15, 25% by volume of raw soil. The main objective of this research is to focus on the strength behavior of soil reinforced with randomly included papyrus fiber. Direct shear, consolidation, and displacement tests were performed on papyrusreinforced specimens with various fiber contents. The results of these tests have clearly shown a significant improvement in the failure deviator stress and shear strength parameters (c and φ) of the studied soil with a percent addition of 10% (the preferred percent). Moreover, this addition ratio reduced the displacement of the soil under loading. It can be concluded that papyrus fiber can be considered an appropriate soil reinforcement material.

Experimental study on mechanical properties of granite after freeze–thaw cycling

It is important to understand the effect of freeze–thaw cycles on the mechanical properties of rocks. In this paper, the variation of the uniaxial compressive strength, peak strain, elastic modulus and stress–strain curves of granite subjected to freeze–thaw cycles with different heating temperatures were studied experimentally and the relationships were derived. As the number of freeze–thaw cycles increases, the compressive strength and elastic modulus decrease, while the peak strain decreases. In addition, an increased temperature increases the peak strain while decreasing the compressive strength and elastic modulus. An expression for the initial damage for the adopted rock material due to freeze–thaw cycling was proposed based on the Loland model. The current research has established a solid foundation for further experimental studies on the fatigue behavior of granite after freeze–thaw cycling.

Transport of engineered silver (Ag) nanoparticles through partially fractured sandstones

Transport behavior and fate of engineered silver nanoparticles (AgNP) in the subsurface is of major interest concerning soil and groundwater protection in order to avoid groundwater contamination of vital resources. Sandstone aquifers are important groundwater resources which are frequently used for public water supply in many regions of the world. The objective of this study is to get a better understanding of AgNP transport behavior in partially fractured sandstones. We executed AgNP transport studies on partially fissured sandstone drilling cores in laboratory experiments. The AgNP concentration and AgNP size in the effluent were analyzed using flow field-flow fractionation mainly. We employed inverse mathematical models on the measured AgNP breakthrough curves to identify and quantify relevant transport processes. Physicochemical filtration, time-dependent blocking due to filling of favorable attachment sites and colloid-facilitated transport were identified as the major processes for AgNP mobility. Physicochemical filtration was found to depend on solute chemistry, mineralogy, pore size distribution and probably on physical and chemical heterogeneity. Compared to AgNP transport in undisturbed sandstone matrix reported in the literature, their mobility in partially fissured sandstone is enhanced probably due to larger void spaces and higher hydraulic conductivity.

Landslide hazard and cascading effects following the extreme rainfall event on Madeira Island (February 2010)

Heavy rainfall on February 20, 2010, triggered numerous shallow rapid landslides across Madeira Island, a Portuguese archipelago in the North Atlantic. Two days after the extreme rainfall event, a field campaign was started which involved describing and mapping a variety of landslide types and the related losses at 120 different locations throughout the Island. Most of the failures started as debris slides or avalanches at high elevations and transformed into debris flows which rushed downslope into populated coastal areas. Over half of the mapped landslides were located in the central and southern area of the island. A further 1,257 landslide locations were revealed in these areas using remote sensing data which were then assembled in a spatial database. Due to anthropogenic influences caused by urban development and population expansion, the event demonstrated the increased vulnerability of the island’s infrastructure. In order to mitigate future losses, it is important to quantify the typical preparatory factors which contribute to rainfall-induced landslides. This increases our understanding of the hazards and associated risks. The analysis shows that based on their spatial frequency, distribution and in the context of the drainage system, three main factors contribute to the triggering of the landslides due to the heavy rainfall event in February 2010: the characteristic soil type, the land cover and the slope gradient. It can now be recognized that the distribution of landslides is highly dependent on the temporal and spatial distribution of these factors. Furthermore, the anthropogenic impact on the extent of the hazard becomes obvious due to poor settlement planning and drainage system modification.

Influence of organic matter and solute concentration on nitrate sorption in batch and diffusion-cell experiments

Nitrate sorption potentials of three surface soils (soils-1-3) were evaluated under different solute concentrations, i.e. 1-100 mg L(-1). Batch and diffusion-cell adsorption experiments were conducted to delineate the diffusion property and maximum specific nitrate adsorption capacity (MSNAC) of the soils. Hos pseudo-second order model well fitted the batch adsorption kinetics data (R(2)>0.99). Subsequently, the MSNAC was estimated using Langmuir and Freundlich isotherms; however, the best-fit was obtained with Langmuir isotherm. Interestingly, the batch adsorption experiments over-estimated the MSNAC of the soils compared with the diffusion-cell tests. On the other hand, a proportionate increase in the MSNAC was observed with the increase in soil organic matter content (OM) under the batch and diffusion-cell tests. Therefore, increasing the soil OM by the application of natural compost could stop nitrate leaching from agricultural fields and also increase the fertility of soil.