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Hunkeler, Daniel

Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/142

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  • Publication
    Accès libre
    Application of Diagnostic Tools to Evaluate Remediation Performance at Petroleum Hydrocarbon-Impacted Sites
    (2018-9)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Madsen, E.L.
    ;
    Buscheck, Thomas
    ;
    Daniels, E.
    ;
    Kolhatkar, R.
    ;
    De Rito, C. M.
    ;
    Aravena, Ramon
    ;
    Thomson, N.
    In situ treatment technologies for petroleum hydrocarbon-impacted sites (e.g., multiphase extraction, air sparging, soil vapor extraction, or in situ chemical oxidation) usually rely on a specific chemical, microbial, or physical contaminant removal process. However, target contaminant concentrations can also vary due to other co-occurring processes (e.g. delivery of remedial fluids, natural variability), which can confound the ability to demonstrate treatment efficiency. This technical note proposes a methodology that integrates several diagnostic tools to assess treatment performance. Stable isotope methods and biomarkers were selected because they provide process-specific and, often, also compound-specific information on contaminant removal. The isotope tools include compound-specific isotope analysis that can be used to discriminate between a broad range of removal processes, and isotope analysis of oxidants and degradation end products to assess overall transformation of hydrocarbons. The biomarkers cover characteristic metabolites and functional genes on a mRNA rather than DNA level to understand biological activity more carefully. This technical note integrates information from laboratory and field studies, especially controlled-field experiments where the tools have been evaluated side-by-side for different treatment methods. A tiered approach is proposed to deploy the tools in a stepwise manner until sufficient information is obtained to confidently identify the mass removal processes of interest and demonstrate efficacy of the intended treatment mechanism. The order of tool application considers the type of information that can be gained, the level of certainty, and the ease of implementation. The objective of this technical note is to enable widespread use of these diagnostic tools with the motivation to improve the efficacy of in situ treatment systems. © 2018, National Ground Water Association
  • Publication
    Accès libre
    Diagnostic Tools to Assess Mass Removal Processes During Pulsed Air Sparging of a Petroleum Hydrocarbon Source Zone
    (2018-6)
    Bouchard, Daniel 
    ;
    Marchesi, Massimo
    ;
    Madsen, Eugen L.
    ;
    DeRito, Christoph
    ;
    Thomson, Neil R.
    ;
    Aravena, Ramon
    ;
    Barker, Jim
    ;
    Buscheck, Thomas
    ;
    Kolhatkar, Ravi
    ;
    Daniels, Eric J.
    ;
    Hunkeler, Daniel 
    During remediation of contaminated aquifers, diagnostic tools can help evaluate whether an intended mass removal process was successfully initiated and acted on specific contaminants of concern. In this study, several diagnostic tools were tested in a controlled‐release in situ air sparging experiment that focused on the treatment of target hydrocarbons (e.g., benzene, toluene, ethylbenzene, and xylenes). The tools included compound‐specific isotope analysis (CSIA), expression of functional genes (mRNA), and metabolites characteristic of aerobic and anaerobic biodegradation. Total and compound‐specific mass balances were established and used, along with traditional monitoring parameters, to validate the results from the various tools. CSIA results indicated biodegradation as the main process contributing to benzene and toluene removal. Removal process‐specific isotope shifts were detected in groundwater as well as in the system effluent gas. CSIA, metabolite, and mRNA biomarkers consistently indicated that both aerobic and anaerobic biodegradation of benzene and toluene occurred, but that their relative importance evolved over time and were related to the treatment system operation. While the indicators do not allow quantification of the mass removed, they are particularly useful to identify if a removal process has been initiated, and to track relative changes in the predominance of in situ contaminant attenuation processes resulting from remediation efforts.
  • Publication
    Accès libre
    Documentation of time-scales for onset of natural attenuation in an aquifer treated by a crude-oil recovery system
    (2015-4)
    Ponsin, Violaine
    ;
    Maier, Joachim
    ;
    Guelorget, Yves
    ;
    Hunkeler, Daniel 
    ;
    Bouchard, Daniel 
    ;
    Villavicencio, Hakeline
    ;
    Höhener, Patrick
    A pipeline transporting crude-oil broke in a nature reserve in 2009 and spilled 5100 m3 of oil that partly reached the aquifer and formed progressively a floating oil lens. Groundwater monitoring started immediately after the spill and crude-oil recovery by dual pump-and-skim technology was operated after oil lens formation. This study aimed at documenting the implementation of redox-specific natural attenuation processes in the saturated zone and at assessing whether dissolved compounds were degraded. Seven targeted water sampling campaigns were done during four years in addition to a routine monitoring of hydrocarbon concentrations. Liquid oil reached the aquifer within 2.5 months, and anaerobic processes, from denitrification to reduction of sulfate, were observable after 8 months. Methanogenesis appeared on site after 28 months. Stable carbon isotope analyses after 16 months showed maximum shifts in δ13C of + 4.9 ± 0.22‰ for toluene, + 2.4 ± 0.19‰ for benzene and + 0.9 ± 0.51‰ for ethylbenzene, suggesting anaerobic degradation of these compounds in the source zone. Estimations of fluxes of inorganic carbon produced by biodegradation revealed that, in average, 60% of inorganic carbon production was attributable to sulfate reduction. This percentage tended to decrease with time while the production of carbon attributable to methanogenesis was increasing. Within the investigation time frame, mass balance estimations showed that biodegradation is a more efficient process for control of dissolved concentrations compared to pumping and filtration on an activated charcoal filter.
  • Publication
    Accès libre
    Analytical modelling of stable isotope fractionation of volatile organic compounds in the unsaturated zone
    (Elsevier, 2011)
    Bouchard, Daniel 
    ;
    Cornaton, Fabien 
    ;
    Höhener, P.
    ;
    Hunkeler, Daniel 
    Analytical models were developed that simulate stable isotope ratios of volatile organic compounds (VOCs) near a point source contamination in the unsaturated zone. The models describe diffusive transport of VOCs, biodegradation and source ageing. The mass transport is governed by Fick's law for diffusion. The equation for reactive transport of VOCs in the soil gas phase was solved for different source geometries and for different boundary conditions. Model results were compared to experimental data from a one-dimensional laboratory column and a radial-symmetric field experiment. The comparison yielded a satisfying agreement. The model results clearly illustrate the significant isotope fractionation by gas phase diffusion under transient state conditions. This leads to an initial depletion of heavy isotopes with increasing distance from the source. The isotope evolution of the source is governed by the combined effects of isotope fractionation due to vaporisation, diffusion and biodegradation. The net effect can lead to an enrichment or depletion of the heavy isotope in the remaining organic phase, depending on the compound and element considered. Finally, the isotope evolution of molecules migrating away from the source and undergoing degradation is governed by a combined degradation and diffusion isotope effect. This suggests that, in the unsaturated zone, the interpretation of biodegradation of VOC based on isotopic data must always be based on a model combining gas phase diffusion and degradation.
  • Publication
    Accès libre
    Carbon Isotope Fractionation during Diffusion and Biodegradation of Petroleum Hydrocarbons in the Unsaturated Zone: Field Experiment at Værløse Airbase, Denmark, and Modeling
    (2008)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Gaganis, Petros
    ;
    Aravena, Ramon
    ;
    Höhener, Patrick
    ;
    Broholm, Mette M.
    A field experiment was conducted in Denmark in order to evaluate the fate of 13 volatile organic compounds (VOCs) that were buried as an artificial fuel source in the unsaturated zone. Compound-specific isotope analysis showed distinct phases in the 13C/12C ratio evolution in VOC vapors within 3 m from the source over 114 days. At day 3 and to a lesser extent at day 6, the compounds were depleted in 13C by up to −5.7‰ with increasing distance from the source compared to the initial source values. This trend can be explained by faster outward diffusion of the molecules with 12C only compared to molecules with a 13C. Then, the isotope profile leveled out, and several compounds started to become enriched in 13C by up to 9.5‰ with increasing distance from the source, due to preferential removal of the molecules with 12C only, through biodegradation. Finally, as the amount of a compound diminished in the source, a 13C enrichment was also observed close to the source. The magnitude of isotope fractionation tended to be larger the smaller the mass of the molecule was. This study demonstrates that, in the unsaturated zone, carbon isotope ratios of hydrocarbons are affected by gas-phase diffusion in addition to biodegradation, which was confirmed using a numerical model. Gas-phase diffusion led to shifts in δ13C >1‰ during the initial days after the spill, and again during the final stages of source volatilization after >75% of a compound had been removed. In between, diffusion has less of an effect, and thus isotope data can be used as an indicator for hydrocarbon biodegradation.
  • Publication
    Accès libre
    Carbon Isotope Fractionation During Volatilization of Petroleum Hydrocarbons and Diffusion Across a Porous Medium: A Column Experiment
    (2008)
    Bouchard, Daniel 
    ;
    Höhener, Patrick
    ;
    Hunkeler, Daniel 
    The study focuses on the effect of volatilization, diffusion, and biodegradation on the isotope evolution of volatile organic compounds (VOCs) in a 1.06 m long column filled with alluvial sand. A liquid mixture of 10 VOCs was placed at one end of the column, and measurements of VOC vapor concentrations and compound-specific isotope ratios (δ13C) were performed at the source and along the column. Initially, the compounds became depleted in 13C by up to −4.8‰ along the column axis, until at 26 h, uniform isotope profiles were observed for most compounds, which is expected for steady-state diffusion. Subsequently, several compounds (n-pentane, benzene, n-hexane) became enriched in 13C throughout the column. For the same compounds, a significant decrease in the source vapor concentration and a gradual enrichment of 13C by up to 5.3‰ at the source over a period of 336 h was observed. This trend can be explained by a larger diffusive mass flux for molecules with light isotopes compared to those with a heavy isotope, which leads to a depletion of light isotopes in the source. The isotope evolution of the source followed closely a Rayleigh trend and the obtained isotope enrichment factor corresponded well to the ratio between the diffusion coefficients for heavy and light molecules as expected based on theory. In contrast to diffusion, biodegradation had generally only a small effect on the isotope profiles, which is expected because in a diffusion-controlled system the isotope shift per decrease of mass flux is smaller than in an advection-controlled system. These findings open interesting perspectives for monitoring source depletion with isotope and have implications for assessing biodegradation and source variability in the unsaturated zone based on isotopes.
  • Publication
    Accès libre
    Carbon isotope fractionation during aerobic biodegradation of n-alkanes and aromatic compounds in unsaturated sand
    (Elsevier, 2008)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    ;
    Patrick Höhener
    Microcosm experiments were conducted to quantify carbon isotope fractionation during aerobic biodegradation of n-alkanes (from C3 to C10) and monoaromatic hydrocarbons in unsaturated alluvial sand. In single compound experiments with n-alkanes, the largest enrichment factor was obtained for propane (−10.8 ± 0.7‰). The magnitude of the enrichment factor decreased with increasing number of carbon atoms from propane to n-decane (−0.2 ± 0.1‰). This trend can partly be explained by the decreasing probability that a 13C is located at the reacting site in the molecule with increasing chain length. After correcting for the presence of non-reacting positions, a chain length dependence of the calculated apparent isotope effect persisted. This observation suggests that transport and binding steps before the actual reaction step become increasingly rate limiting with increasing chain length. For aromatic compounds tested individually, the enrichment factor was the largest (−1.4 ± 0.1‰) for benzene (B), followed by toluene (T) (−0.8 ± 0.1‰) and m-xylene (X) (−0.6 ± 0.1‰). Enrichment factors for BTX were systematically smaller than for n-alkanes with equivalent number of carbons, which is likely related to different biodegradation mechanisms. The study demonstrates that significant carbon isotope fractionation occurs during aerobic biodegradation of n-alkanes and aromatic compounds under unsaturated conditions and that the magnitude of isotope enrichment is linked to molecule size and molecule structure.
  • Publication
    Accès libre
    Use of stable isotope analysis to assess biodegradation of volatile organic compounds in the unsaturated subsurface
    (2007)
    Bouchard, Daniel 
    ;
    Hunkeler, Daniel 
    L’objectif premier de ce projet consiste à évaluer la faisabilité d’utiliser l’analyse isotopique spécifique à chaque composé afin de démontrer la biodégradation des hydrocarbures pétroliers dans la zone non saturée. Le premier objectif était de quantifier le facteur d’enrichissement isotopique pendant la dégradation de plusieurs composés organiques volatiles (COVs) communément retrouvés sur des sites contaminés. Ces expériences en microcosmes ont été menées avec des sédiments de sol non saturés et sous des conditions aérobiques. Les résultats ont confirmé la possibilité d’observer un enrichissement isotopique dans la fraction restante du COV en phase gazeuse. La magnitude du facteur d’enrichissement isotopique mesurée était faible pour le carbone et nettement plus élevée pour l’hydrogène. Une expérience en colonne a été réalisée pour investiguer sur le rôle possiblement joué par le processus de diffusion dans le fractionnement isotopique. Une colonne longue de 1,06 m et remplie de sable alluvial fut utilisée et une source liquide de plusieurs COVs fut placée à une extrémité. Pendant la période initiale peu après la mise en place de la source, une diminution croissante du carbone lourd 13C avec la distance était notable. Cette observation peut être expliquée par une diffusion plus rapide des molécules ne contenant que des 12C ; hypothèse par la suite confirmée par des simulations analytiques qui attribuèrent différents coefficients de diffusion aux molécules de composition isotopique différente. Par la suite, le ratio isotopique s’est uniformisé indépendamment de la distance. Cependant, quelques composés ont été affectés par un enrichissement en 13C à la source pendant que ce dernier s’épuisait de la fraction liquide. Il fut montré que l’évolution isotopique de ces composés à la source suivait une tendance dite de Rayleigh et que le ratio des deux coefficients de diffusion dû à des molécules isotopiquement différentes indique le facteur d’enrichissement. Une expérience terrain avec un dense réseau de points de prélèvement a été réalisée au Danemark dans le cadre du projet GRACOS et a procurée une chance unique d’évaluer si des tendances similaires occurrent également à plus grande échelle. L’expérience consistait à enterrer une source artificielle de fuel dans la zone non saturée d’un aquifère sableux. Telle qu’attendue, une évolution isotopique similaire à celle observée pendant l’expérience en colonne fut mesurée, avec une phase initiale d’appauvrissement en 13C avec la distance, suivie par une uniformisation du ratio, et se terminant par un enrichissement en 13C. Afin d’évaluer la contribution relative de la diffusion et de la biodégradation sur le shift isotopique plus en détail, l’évolution des concentrations et du ratio isotopique a été simulée à l’aide d’un code numérique modifié (MOFAT). Il a été possible de reproduire les tendances observées en utilisant la vitesse de biodégradation évaluée de façon indépendante ainsi que les facteurs d’enrichissement reliés à la biodégradation et à la diffusion. Finalement, en se basant sur les connaissances développées sur le fractionnement isotopique par les expériences préalables, l’évolution isotopique attendue par d’autres sources de COV ayant une géométrie différente a été simulée (par ex. : une source flottante sur la nappe phréatique). Les simulations ont démontré qu’une relation linéaire entre le ln du flux de masse et le changement isotopique peut être observée lors de diffusion des COVs en régime permanent, analogiquement à l’équation de Rayleigh. Cependant, l’enrichissement isotopique net est plus petit que le facteur d’enrichissement, ceci démontrant encore une fois l’importance de la présence d’un isotope lourd dans la molécule. En conclusion, l’étude montre que l’obtention de preuve de la biodégradation des COVs dans la zone non saturée par l’analyse isotopique est plus complexe que dans la zone saturée, car l’effet de diffusion affecte également le ratio isotopique. Cependant, sous régime permanent et aussi longtemps que le composé reste en quantité suffisante à la source, le ratio isotopique peut fournir des informations autant qualitatives que quantitatives sur le degré de biodégradation. Pendant que le shift substantiel du ratio isotopique à la source complique l’identification des tendances reliées à la biodégradation, ceci aide néanmoins à l’identification de l’étape finale de l’évolution du COV à la source., The general aim of the project is to evaluate the feasibility of using compound-specific isotope analysis (CSIA) to assess biodegradation of petroleum hydrocarbons in the unsaturated zone. The first objective was to quantify the isotope enrichment factors during biodegradation of several volatile organic compounds (VOCs) commonly found on petroleum hydrocarbon contaminated sites. These microcosm experiments were carried out with unsaturated soil sediments under aerobic conditions. The results confirmed the possibility to monitor an isotope enrichment in the remaining VOCs in the air phase. The magnitude of isotope enrichment factors was small for carbon and large for hydrogen. A column experiment was then carried out to investigate the possible role played by diffusion in the isotope fractionation of migrating VOC vapours. A 1.06 m long column filled with alluvial sand was used with a VOC source. During an initial period after source emplacement, the heavy isotope 13C became increasingly depleted with distance from the source. This observation can be explained by the faster diffusion of molecules containing 12C and was confirmed by analytical simulations that attributed different diffusion coefficients to molecules with a different isotopic composition. Later, the isotope profile levelled out and for some compounds an enrichment of 13C with distance was observed indicating biodegradation. However, some compounds were also affected by an enrichment of 13C at the source as the compounds were depleting form the source. It was shown that the source isotope evolution of these compounds followed a Rayleigh trend with the ratio of diffusion coefficients for molecules with a different isotopic composition as isotope fractionation factor. A highly-controlled field experiment conducted in Denmark as part of the GRACOS project provided a unique opportunity to evaluate if similar isotope trends also occur at the field scale. The experiment consisted of burying an artificial fuel source in the unsaturated zone of a sandy aquifer. Indeed, a similar isotope evolution as in the column study was observed with an initial depletion of 13C with distance followed by a levelling out of the isotope profile and enrichment of 13C. To evaluate the relative contribution of diffusion and biodegradation on isotope shifts in more detail, the concentration and isotope ratio evolution was simulated using a modified numerical code (MOFAT). It was possible to reproduce the observed trends using independently estimated biodegradation rates and isotope enrichment factors for biodegradation and diffusion. Finally, based on the knowledge gained on isotope fractionation with the previous experiments, the expected isotope evolution was simulated for VOC sources with different geometries (e.g. point source, floating pool). The simulations demonstrated that a linear relationship between the ln of the mass flux and the isotope changes can be observed in a diffusion controlled system under steady state conditions analogous to the Rayleigh equation. However, the slope of the relationship is smaller than the isotope enrichment factor again illustrating the importance of the diffusion isotope effect. In conclusion, the study demonstrates that assessment of biodegradation in the unsaturated zone is more complex than in the saturated zone because the diffusion process influences isotope ratios as well. However, under steady state conditions and as long as the compound does not significantly deplete, isotope data can provide qualitative and possible quantitative information on the degree of biodegradation. While the substantial shift of isotope ratios during source depletion complicates the identification of biodegradation trends, it may help to identify the final stage of the evolution of a VOC source.