Transport of two naphthoic acids and salicylic acid in soil: Experimental study and empirical modeling

International audienceIn contrast to the parent compounds, the mechanisms responsible for the transport of natural metabolites of polycyclic aromatic hydrocarbons (PAH) in contaminated soils have been scarcely investigated. In this study, the sorption of three aromatic acids (1-naphthoic acid (NA), 1-hydroxy-2-naphthoic acid (HNA) and salicylic acid (SA)) was examined on soil, in a batch equilibrium single-system, with varying pH and acid concentrations. Continuous flow experiments were also carried out under steady-state water flow. The adsorption behavior of naphthoic and benzoic acids was affected by ligand functionality and molec- ular structure. All modeling options (equilibrium, chemical nonequilibrium, i.e. chemical kinetics, physical nonequilibrium, i.e. surface sites in the immobile water fraction, and both chemical and physical nonequilibrium) were tested in order to describe the break- through behavior of organic compounds in homogeneously packed soil columns. Tracer experiments showed a small fractionation of flow into mobile and immobile compart- ments, and the related hydrodynamic parameters were used for the modeling of reactive transport. In all cases, the isotherm parameters obtained from column tests differed from those derived from the batch experiments. The best accurate modeling was obtained considering nonequilibrium for the three organic compounds. Both chemical and physical nonequilibrium led to appropriate modeling for HNA and NA, while chemical nonequi- librium was the sole option for SA. SA sorption occurs mainly in mobile water and results from the concomitancy of instantaneous and kinetically limited sites. For all organic compounds, retention is contact condition dependent and differs between batch and column experiments. Such results show that preponderant mechanisms are solute dependent and kinetically limited, which has important implications for the fate and transport of carboxylated aromatic compounds in contaminated soils

Caractérisation et modélisation géochimique de la solubilisation des éléments minéraux majeurs dans les sédiments de l’assainissement urbain.

National audienc

Effet de l'introduction d'une strate sur le transfert d'eau et de colloïdes dans un milieu sableux

L'effet de l'hétérogénéité du milieu poreux sur l'écoulement et le transfert colloïdal a été étudié en colonnes de laboratoire. Cette hétérogénéité a été créée par l'insertion de macropores artificiels de 0.9mm de diamètre et d'un géotextile dans un milieu sableux. Cette étude confirme la fonction de chemin préférentiel des macropores, dans les sols hétérogènes, pour les solutés et les particules colloïdales, favorisant ainsi le transfert de pollution en conditions saturées. L'introduction d'une strate artificielle peut réduire l'effet des macropores. La rétention colloïdale dépend du degré d'homogénéité de l'écoulement : elle diminue en présence d'un écoulement homogène et augmente quand l'écoulement est hétérogène

Identification of the artifact contribution to two urban Technosols by coupling a sorting test, chemical analyses, and a least absolute residual procedure

PurposeIn the context of urban extension, the depletion of natural resources for construction constitutes a crucial issue. Specifically, in the field of earthworks, the amounts of materials can be massive and pose the crucial problem of resource shortage. Therefore, the reuse of excavated urban soils from foundation layers as new earthwork construction materials appears to be a sustainable and promising solution. Before repurposing, a better knowledge of urban soils and their potential pollutant load is compulsory.Materials and methodsIn this paper, two soils excavated from the town of Paris are studied. After the stripping of their surface, to remove organic matter and surface pollution, the matrixes were submitted to elemental analyses using ICP-OES, C/S measurements, and XRF techniques. The elemental analyses were carried out on the whole materials, on three granulometric fractions (400m) and on the families of artifacts (i.e., construction and demolition wastes, natural gravel, industrial wastes, magnetic, and non-magnetic slags) found in the soils. The combination of elemental analyses and a least absolute residual (LAR) procedure were used to quantify artifact contributions in all granulometric fractions.Results and discussionThe soils exhibit evidence of anthropic inputs with high contents of pollutants under the forms of carbonaceous, sulfur mineral and metallic alloys. Carbonaceous and trace pollutions are concentrated in magnetic and non-magnetic slags, while sulfur and strontium pollutions are concentrated in gypsum components. In both cases, all the granulometric fractions (including whole material) can be retrieved as a combination of artifact composition, suggesting that the Technosols mainly result from the mixture of these artifacts. The amounts of natural material, gypsum components, and magnetic slags increase with the fineness of the fractions. In contrary, the amount of non-magnetic slags decrease with the fineness of the fractions and suggests that the processes of slag weathering are not similar: carbonaceous slags are more stable than iron-enriched slags.ConclusionsThe elemental analyses of granulometric fractions of soils and the artifacts using LAR analyses help in identifying the compositions of each granulometric fraction and give insight into the evolution of artifacts in the soil. These tools are also promising regarding the assessment of geo-environmental characteristics of urban soils, which in turn provides relevant information regarding management and reuse

Turbulent velocity profile in fully-developed open channel flows

The determination of velocity profile in turbulent narrow open channels is a difficult task due to the significant effects of the anisotropic turbulence that involve the Prandtl's second type of secondary flow occurring in the cross section. With these currents the maximum velocity appears below the free surface that is called dip phenomenon. The well-known logarithmic law describes the velocity distribution in the inner region of the turbulent boundary layer but it is not adapted to define the velocity profile in the outer region of narrow channels. This paper relies on an analysis of the NavierStokes equations and yields a new formulation of the vertical velocity profile in the center region of steady, fully developed turbulent flows in open channels. This formulation is able to predict time averaged primary velocity in the outer region of the turbulent boundary layer for both narrow and wide open channels. The proposed law is based on the knowledge of the aspect ratio and involves a parameter CAr depending on the position of the maximum velocity (ξdip). ξdip may be derived, either from measurements or from an empirical equation given in this paper. A wide range of longitudinal velocity profile data for narrow open channels has been used for validating the model. The agreement between the measured and the computed velocities is rather good, despite the simplification used

Impact of the volume of gaseous phase in closed reactors on ANC results and modelling.

International audienc

Rapid and accurate measurement methods for determining soil hydraulic properties: A review

International audienceAbstract The determination of soil hydraulic properties is important in several environmental sciences but may be expensive and time consuming. Therefore, during the last decades, a great effort has been made in soil sciences to develop relatively easy, robust, and inexpensive methods for soil hydraulic characterization. In this manuscript, we reviewed and discussed different infiltrometer techniques in light of the available experimental applications. More specifically, we considered the simplified falling head (SFH) infiltrometer technique and the single-ring infiltration experiment of the Beerkan type. Concerning this latter method, we considered different algorithms for data analysis: two simplified methods based on the analysis of transient (TSBI) and steady (SSBI) Beerkan infiltration data, and the Beerkan Estimation of Soil pedoTransfer parameters algorithm (BEST), that allows to estimate the soil characteristics curves, i.e., the soil water retention curve and hydraulic conductivity functions. For a given method, after dealing briefly theory and practice, available literature references were reported to account for specific applications in order to provide findings on method validation and application. With the aim to provide practical information on available tools for a simpler application of the reviewed methods, several video tutorials were reported to show i) how to conduct correctly field experiments and ii) how to calculate saturated hydraulic conductivity or soil hydraulic functions using user-friendly tools for data analysis. Finally, details on a new automated single-ring infiltrometer for Beerkan infiltration experiments (i.e., construction, assembly and field use) were presented

A Simple Correction Term to Model Infiltration in Water‐Repellent Soils

International audienceSoil water repellency can substantially alter hydrologic processes, particularly the abilityof soils to infiltrate water. Water repellency often changes through time, making it difficult to simulate infiltration behaviors of water-repellent soils using standard models. Here, we propose a simple rate-based correction term that starts with a value of zero at the beginning of the infiltration process (t = 0) and asymptotically approaches 1 as time increases, thus simulating decreasing soil water repellency through time. The correction term can be used with any infiltration model. For this study, we selected a simple two-term infiltration equation and then, using two data sets of infiltration measurements conductedin soils with varying water repellency, compared model error with versus without the added term. The correction substantially reduced model error, particularly in more repellent soils. At the same time, the rate constant parameter introduced in the new model may be useful to better understand dynamics of soil water repellency and to provide more consistent interpretations of hydraulic properties in water-repellent soils

Evaluation of pollutant transfer from a BOF steel slag used in road construction

The use of alternative materials in civil engineering, especially in road construction, is developing in order to save natural resources and to promote the re-use of wastes or industrial by-products according to sustainable development strategies. Steel production generates great amounts of by-products as steel slag (about 2.2 million tons in France in 2006). Unlike blast furnace slag which has been extensively used in cement industry, building trade and road construction, the use of Basic Oxygen Furnace slag (BOF slag) has been restrained due to insufficient volume stability and to the lack of environmental regulations. This study aimed at investigating the potential release of pollutants from a BOF slag used in a civil engineering structure (an industrial platform) and their transfer through the underlying soil, using a multi-scale approach. The BOF slag was characterised by a very alkaline pH due to the presence of free-lime (up to 6% of CaO+Ca(OH)2)) and rather high concentrations of chromium, vanadium and barium (respectively 910, 740 and 128 mgkg-1). An experimental platform has been constructed using a 0-6 mm BOF slag and percolating waters have been sampled and analysed for one year. Total chemical analysis, mineralogical analysis and batch tests according to NF EN 12457-2 standard method have been carried out in order to characterise the slag and to study the release of pollutants. Pollutant transfer through the soil has been studied using laboratory column experiments. Two different soils have been investigated: a sandy soil and a silty clay loam. The inlet solution was obtained from batch tests performed on the BOF slag used for the construction of the platform. The results of the follow up of the experimental platform showed that the pH of seepage waters was very alkaline, more than 12, and the conductivity was rather high, between 5330 and 9540 µScm-1. Except for Ba (between 1.3 and 2.25 mg L-1), the concentrations of trace elements were rather low, less than 20 µgL-1 for Cr and less than 30 µgL-1 for V. As regards batch tests, the conductivity of leachates was high, about 8000 µScm-1, and the pH value was more than 12. In the conditions of the leaching test, the release of trace elements was generally low, concentrations of Cr and V were less than 10 µgL-1. The first results obtained from column experiments seemed to indicate a good retention of vanadium by the soil, and chromium appeared more mobile. An attempt of modeling will be carried out with the CHESS model for the speciation of pollutants and with HYDRUS and PHREEQC codes for the transfer processes

Influence of Carbonation on the Microstructure and Hydraulic Properties of a Basic Oxygen Furnace Slag

Basic oxygen furnace (BOF) slag is considered as a potential alternative construction material and is used here on an experimental plot to accurately quantify the risk of pollutant release. Since pollutant release depends on flow, this initially requires characterizing BOF slag hydraulic properties. These were monitored and estimated at plot scale by carrying out water infiltration experiments and inverse numerical modeling. Monitoring the plot showed that the BOF slag studied crusted at the surface as a result of weathering processes. Numerical inversion proved that the crusted material differed from the unaltered slag in terms of water retention and hydraulic conductivity functions. Although all the data pointed to a decrease in saturated hydraulic conductivity with crusting, the trends depended on the infiltration devices used for the capillary length (tension disc vs. Beerkan). Scanning electron microscope (SEM) microanalysis of laboratory weathering cells and lysimeter measurements were monitored in parallel to study the microstructure more precisely and highlighted a reduction of porosity by clogging. On the basis of SEM observations, two conceptual models of pore reduction, based on two different pore clogging hypotheses, were applied to predict hydraulic properties. This step demonstrated that the effect on water retention and hydraulic conductivity strongly depended on the way precipitated phases form and coat grains and could explain the evolution of the transport properties observed. This study contributes to knowledge on the hydraulic properties of BOF slag and their evolution due to carbonatio