Gotowa bibliografia na temat „Extraction des contaminants volatils des sols”

Soil vapor extraction (SVE) technology has strong potential value in the decontamination of soils dominated by volatile contaminants. In this paper, in order to evaluate in detail the influence of the main factors on the efficiency of SVE, L9(34) orthogonal tests and response surface analysis were carried out using a self-developed one-dimensional SVE system model. A first-order kinetic reaction model was also employed to analyze the relationship between pollutant concentration and time. The thermal reaction unit of SVE technology with a scale consistent with the soil column of the indoor test was simulated using COMSOL simulation software. The obtained results indicate that the most important factors affecting the performance of SVE are time, temperature, and contaminant concentration, while the influence of the extraction flow rate is not significant. A first-order kinetic reaction model can be used to predict the half-life of contaminant concentrations. Combined with the desirability function, the optimal conditions for the removal of ethylbenzene from soil were: time 180 min, temperature 20 °C, extraction flow 6000 mL/min, and contaminant concentration 2%. The developed numerical model, 3D-SVE, nicely simulates laboratory findings. These results can provide ideas to improve the efficiency of SVE.

Many metal-contaminated soils originate in old abandoned industrial sites. One of the problems encountered in the reclamation of soils lies in the selection of the decontamination techniques. Few data are available to predict the efficiency of the extraction of metals from the contaminated soils. Moreover, a signifiant part of the contamination is often found as particles. These can be extracted from the soils by means of mineralurgical separation techniques. A trial and error procedure is often used for selecting the technique and the procedure parameters. The purpose of this study is to develop a method of mineralogical characterization for the identification and localisation of the metal contamination so as to allow a more enlightened choice of the mineralurgical treatments. Besides the identification of the contaminant particles, the method takes into account the distribution of contaminants, which can be found on the surface of the particles or included within the volume of the particle, the average proportion and the size of the contaminants in the contaminated particles, and the association of the iron oxide contaminant. The frequency of appearance of the particles depending on the different categories of the method guides the choice of the treatment technologies to be used so as to optimize the extraction of contaminant particles.Key words: metals, contamination, soils, lead, mineralurgical techniques, mineralogy.[Journal translation]

Hydroxyapatite (HA) microspheres of diameter <70 μm have been synthesized by solgel processing. The starting sols were prepared by ultrasonic mixing of concentrated solutions of calcium acetate (1.7M) with 85% H3PO4, followed by emulsification in dehydrated 2-ethyl-1- hexanol. Drops of emulsion were solidified by extraction of water with this solvent. The final thermal treatment was a 2 h soaking in air at 900°C. Properties such as hydraulic resistance and sedimentation rate, which are important for application in ion-exchangers, were superior for our prepared microspheres in comparison with irregularly shaped commercial HA. Adsorption of the following metals was investigated: U, Zn, Fe, Cu, Ni, Co, Cd, Pb, Mn, Al, Cr, As, Sb, Bi and Mo. Retention was ≈100% for of all the metals studied when pH > 3–4. On average, ≈1/20 moles of metal reacted with 1 mole of HA. Adsorbed metals could be desorbed with efficiencies of 60–90%. In addition, nuclear-waste-saturated beds of HA could be transformed to insoluble ceramics by thermal treatment. The cost of producing HA microspheres was estimated to be comparable to current prices of irregularly shaped commercial hydroxyapatite powders. For radioactive contaminants such as U, for which resorption need not be considered, porous monoliths were produced by use of industrial reagents. The retention capacity was determined to be 30 mg of U per 1 mg of monolith.

L’extraction sous pression réduite est l’une des techniques de dépollution envisageables lorsqu’il y a contamination d’un sol par des composés organiques volatils (COVs). Cette technique consiste à créer une dépression dans le sol et induire un écoulement contrôlé d’air qui entraînera les contaminants volatils dans la phase gazeuse extraite. Les objectifs de ce travail peuvent se résumer de la façon suivante : - caractérisation de la méthode la plus adaptée à déterminer les deux composantes, horizontale et verticale, de la perméabilité à l’air. - étude de l’évolution de la perméabilité à l’air du sol en fonction du degré de saturation de celui-ci en liquides. - vérification de la validité ou non de l’utilisation des colonnes unidirectionnelles dans le dimensionnement des systèmes d’extraction en se basant sur l’atteinte d’une vitesse critique de l’air au sein des pores du sol. Pour accomplir ces objectifs, un pilote d’essai a été conçu et réalisé, plusieurs expériences ont été effectuées et des modèles de la littérature ont été utilisés. Les résultats obtenus ont montré que la méthode la plus adaptée à la détermination de la perméabilité à l’air du sol est celle mettant en œuvre un régime stationnaire sans couverture à la surface du sol, Et que les résultats obtenus dans une colonne unidirectionnelle concernant la vitesse critique ne peuvent être extrapolés à l’échelle du terrain comme il se fait actuellement
Soil Vapour Extraction (SVE), which includes gas extraction and/or gas injection, is the primary method used to remove volatile organic compounds (VOCs) from unsaturated subsurface porous media. The widespread use of SVE is due to its above ground simplicity of operation and proven ability to remove contaminant mass inexpensively relative to competing technologies. The objectives of this study may be summarized as follow: - Characterisation of the more appropriate method to determine horizontal and vertical soil air permeability components. - Study of the evolution of soil air permeability as a function of liquids saturation degree. - Verification of the validity or not of the use of unidirectional columns in extraction systems design based on attainment of a critical pore-gas velocity. To accomplish these objectives, a laboratory pilot was designed and realised, a series of experimental tests was conducted and literature models have been used. Results showed that the more appropriate method to determine soil air permeability is the one which involve stationary state in an open soil and that results obtained with a unidirectional column related to critical air velocity can not be extrapolated to field scale as it's currently done

L'extraction sous pression réduite est un procédé de traitement des sols pollués par des composés organiques volatils. Son principe repose sur la mise en circulation d'un flux gazeux traversant le sol par l'application d'une dépression de quelques centaines de millibars. Une étude paramétrique menée sur un sol réel artificiellement pollué par du trichloréthylène a montré que le débit du flux gazeux n'a qu'une faible influence sur les rendements d'extraction des polluants à cause de mécanismes de transfert limités cinétiquement. L'humidité du sol a une influence négative sur l'efficacité du traitement parce qu'elle restreint la porosité du sol disponible au passage du gaz d'extraction. Les essais menés sur un sol issu d'un site pollué par des solvants chlorés ont permis de mettre au point une méthodologie destinée à tester la faisabilité technique du traitement. Cette méthodologie permet d'identifier et de limiter les risques d'échec de la réhabilitation de sites pollués. Les résultats montrent que l'usage de ce procédé n'était pas adapté au traitement du sol testé dans cette étude du fait de la présence de graisses pour laquelle les solvants chlorés ont une forte affinité
Soil vapour extraction is a treatment process for soils polluted by volatil organic compounds. Its principle relies on the circulation of gaseous flow in soil by the application of a depression of some hundreds millibars. A parametrical study has been led on a soil artificially polluted by trichlorethene. It shows that the gaseous flow rate has a slight influence on pollutants extraction yield. This is due to rate limited mass transfer processes. Soil moisture plays a negative role on treatment efficiency because of the reduction of the porosity available for the gas circulation. Tests have been performed on a soil polluted by a complex mixture of organic pollutants to elaborate a methodology of technical feasibility assessment. This methodology aims at identifying and limiting risks of site rehabilitation failure. Tests results show that soil vapour extraction was inadequat to treat the soil tested in this study because of the strong affinity between a dense organic phase (grease) and chlorinated solvents

Le travail de cette thèse concerne l'étude expérimentale, la modélisation et la simulation numérique de la dépollution par venting et SVE des sols pollués par des hydrocarbures légers. Une première partie contient une étude bibliographique de l'interaction des polluants avec le sol, les applications industrielles de ces deux techniques et des techniques de modélisation du suivi de la dépollution. La deuxième partie est constituée de la présentation des montages et techniques opératoires utilisés pour le suivi de la dépollution sur des pilotes de laboratoire. La troisième partie présente les résultats obtenus sur des sols pollués par des composants de carburant automobile seuls ou en mélange avec des conditions opératoires (débit gazeux, pression d'extraction, temps de vieillissement de la pollution). L'accord entre l'expérience et la modélisation (chiffré par des facteurs de concordance) est bon ce qui permettra d'utiliser les techniques de calcul mises au point pour une optimisation des conditions de dépollution
The work of thesis relates to experimental study, modelling and numerical simulation of depollution by venting and SVE of the soils polluted by light hydrocarbons. The first part contains a bibliographical study of pollutants interaction with the soil, of industrial applications of these two techniques and of the modelling techniques used for the follow-up of depollution. The second part is made up of the presentation of the equipments and procedures used for the follow-up of depollution on laboratory pilots. The third part presents the results obtained on soils polluted by components of automobile fuel alone or in mixture with the variation of the operating conditions (gas flow, extraction pressure, ageing of pollution). The agreement between the experimental and modelling (quantified by the factors of agreement) is good, which will allow the use of the developed techniques of calculation for an optimisation of the depollution conditions

O presente trabalho teve por objetivo apresentar e discutir um caso de identificação e remediação emergencial de compostos orgânicos voláteis, oclusos em camada arenosa do Terciário da Formação São Paulo, em decorrência do vazamento de tanques de combustíveis de um posto de serviços. A técnica de remediação adotada para o caso consistiu na extração in situ dos vapores do solo e no tratamento dos mesmos por adsorção em filtros de carvão ativado (SVE - soil vapor extraction). Os processos de seleção, projeto, implantação, operação e descomissionamento da tecnologia SVE seguiram as metodologias indicadas pela literatura, adaptadas às condições locais. O acompanhamento da eficiência da remediação foi baseado na quantificação inicial dos hidrocarbonetos totais de petróleo leves presentes no subsolo, através das técnicas de cromatografia gasosa e espectrometria de massa, e na medição em campo das concentrações de voláteis e dos respectivos teores de explosividade. O resultado da campanha laboratorial apresentou fortes indícios de que a contaminação local fosse proveniente do combustível gasolina e indicou a ocorrência do composto benzeno em concentrações superiores aos limites adotados como referência. As leituras realizadas em campo mostraram rápido declínio das concentrações de voláteis e dos teores de explosividade com a operação da tecnologia SVE, indicando baixa ocorrência de fatores limitantes do transporte de massa no local. Corroborou com tal hipótese, o fato das metas de remediação terem sido atingidas com poucas trocas de ar, parâmetro retro-analisado a partir de dados de ensaios geológico-geotécnicos. Assim, concluiu-se que, para áreas com características semelhantes à estudada, a tecnologia SVE pode ser eficiente como medida de remediação de voláteis e redução dos riscos de explosividade.
This work aims to present and to discuss a case study of identification and emergency remediation of volatile organic compounds, occluded in a sand layer of the São Paulo Tertiary Formation, as a result of the leakage of fuel tanks of a service station. The adopted remediation technique was in situ soil vapor extraction (SVE) and offgas treatment for adsorption in activated carbon filters. Selection, design, commissioning, operation and shutdown processes of SVE technology followed literature methodologies, which were adapted to local conditions. Remediation efficiency monitoring was based on the initial quantification of light total petroleum hydrocarbons in the subsoil, through gas chromatography and mass spectrometry techniques, and on measurement of the volatile concentrations and respective explosive contents in the field. The result of the laboratorial campaign presented strong indications that the local contamination proceeded from combustible gasoline and it indicated the occurrence of benzene in concentrations higher than the adopted reference. Field measurements showed fast decline of the volatile concentrations and explosive contents with the SVE technology operation, fact that indicated low occurrence of mass transfer limitations in the place. The fact that remediation goals were achieved with few air exchanges, parameter back-analyzed from geologicgeotechnical tests, contributed to reinforce such hypothesis. Thus, SVE technique can be considered efficient for volatile remediation and explosive risks reduction, for areas with characteristics similar to the studied one.

Surface and subsurface releases of organic chemicals have resulted in widespread contamination of groundwaters and soils. Frequently, such chemicals are introduced into the subsurface as nonaqueous-phase liquids (NAPLs), which are only slightly miscible with water. These organic liquids tend to migrate downward through the unsaturated soil zone, displacing the pore gases under the action of gravitational forces. During its migration, a portion of the NAPL will become entrapped in the soil pores due to capillary forces, creating zones of persistent contamination in the soil matrix. Organic liquid saturation in such zones may range from approximately 4% to 10% of the pore space (Wilkins et al., 1995). This entrapped NAPL may serve as a long-term source of contamination to the aqueous and gaseous pore fluids through subsequent dissolution and volatilization. Soil vapor extraction (SVE) has evolved over the past decade as an attractive in situ remediation technology for unsaturated soils contaminated by entrapped volatile organic compounds (VOCs). This technology involves the induction of gas flow within the porous medium to enhance volatilization of entrapped contaminants (Hutzler et al., 1989). Based upon the success of a number of feasibility studies and the ease of implementation, SVE remediation technologies are currently employed at approximately 18% of Superfund sites (Travis and Macinnis, 1992). An extensive review of the literature pertaining to SVE and related technologies is given in Rathfelder et al. (1995). Although widely implemented, SVE systems are typically designed and installed with limited understanding of the processes that control their effectiveness. Clearly, the performance of SVE will be strongly influenced by contaminant volatility and effective gas-phase permeability (Pedersen and Curtis, 1991). Relatively little is known, however, about the physical and chemical processes that control contaminant vapor-phase mass transfer. The SVE systems characteristically exhibit large initial VOC recovery rates, followed by a rapid decline in effluent gas concentrations to a persistent low level (e.g., Crow et al., 1987; DiGiulio, 1992). Furthermore, a temporary increase in the produced gas organic concentration has often been observed following SVE shutdown periods (McClellan and Gilham, 1992). Such behavior suggests the presence of mass transfer limitations.

Heated Soil Vapor Extraction (HSVE) is a technology that has been used successfully to clean up subsurface soils at sites containing chlorinated solvents and petroleum hydrocarbons. The costs have been extremely high due to the large amount of energy required to volatilize high molecular weight polycyclic aromatic hydrocarbon (PAH) compounds present in the soil matrix. One remediation contractor states that hydrocarbons are oxidized in situ by achieving temperatures in the &gt;1000 F range near the heaters [1]. A critical question is whether the volatile portion of manufactured gas plant (MGP) hydrocarbons (VOCs) can be stripped out at lower temperatures such that the remaining contaminants will be unavailable for transport or subsequent dissolution into the groundwater. Soil remediation by heated soil vapor extraction system is a relatively new technology developed by Jay Jatkar Inc. (JJI) along with the University of Wisconsin-Milwaukee [2]. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. The process developed by JJI, consists of a heater/boiler that pump and circulates hot oil through a pipeline that is enclosed in a larger-diameter pipe. This extraction pipe is vertically installed within the contaminated soil up to a certain depth and is welded at the bottom and capped at the top. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. Our previous studies had removed higher boiling compounds, such as naphthalene, etc., to a non-detectable level. Thus, the current technology is very promising for removing most of the chemical compounds; and can also remove these boiling compounds from the saturated zone. Gas chromatography (GC) is utilized in monitoring the relative concentration changes over the extraction period. Gas chromatography-mass spectrometry (GC-MS) assists in the identification and separation of extracted components. The experimental research is currently being conducted at the University of Wisconsin-Milwaukee. The objectives of this study are to identify contaminants and time required to remove them through HSVE treatment and provide data for computation fluid dynamics CFD analysis.

Heated Soil Vapor Extraction (HSVE) is a technology that has been used successfully to clean up subsurface soils at sites containing chlorinated solvents and petroleum hydrocarbons. The costs have been extremely high due to the large amount of energy required to volatilize high molecular weight polycyclic aromatic hydrocarbon (PAH) compounds present in the soil matrix. One remediation contractor states that hydrocarbons are oxidized in situ by achieving temperatures in the &gt;1000 F range near the heaters [1]. A critical question is whether the volatile portion of manufactured gas plant (MGP) hydrocarbons (VOCs) can be stripped out at lower temperatures such that the remaining contaminants will be unavailable for transport or subsequent dissolution into the groundwater. Soil remediation by heated soil vapor extraction system is a relatively new technology developed at the University of Wisconsin-Milwaukee [2]. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. The process developed at UWM, consists of a heater/boiler that pump and circulates hot oil through a pipeline that is enclosed in a larger-diameter pipe. This extraction pipe is vertically installed within the contaminated soil up to a certain depth and is welded at the bottom and capped at the top. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. Our previous studies had removed higher boiling compounds such as naphthalene, etc., to non-detectable level. Thus, the current technology is very promising for removing most of the chemicals compounds; and can also remove these high boiling compounds from the saturated zone. Gas chromatography (GC) is utilized in monitoring the relative concentration changes over the extraction period. Gas chromatography-mass spectrometry (GCMS) assists in the identification and separation of extracted components. The experimental research is currently being conducted at the University of Wisconsin-Milwaukee. The objectives of this study are to identify contaminants and time required to remove them through HSVE treatment and provide data for computation fluid dynamics CFD analysis.