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Hunkeler, Daniel

Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur.e ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/142
_
0000-0003-3525-9736

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  • Publication
    Accès libre
    Comments on “Analytical modelling of fringe and core biodegradation in groundwater plumes.” by Gutierrez-Neri et al. in J. Contam. Hydrol. 107: 1–9
    (2010)
    Hunkeler, Daniel 
    ;
    Höhener, P
    ;
    Atteia, O
    In this comment, we revisit equations concerning the analytical solutions presented by Gutierrez-Neri and co-workers for reactive transport for a pollutant undergoing core and fringe degradations. We state that a correction needs to be made in Eq. (9) of the work of Gutierrez- Neri et al. in order that the equation follows closely previous work published by J. Bear (in 1-D) and P.A. Domenico (in 3-D). Furthermore we derive alternative solutions for Eqs. (13)–(16) which separate more clearly the first-order reaction and the instantaneous reaction. It is shown that the corrected solution agrees better with the results from the numerical model than the previous solution. An improvement is also made by giving a solution which avoids negative concentrations. Furthermore, the corresponding solution for the electron acceptor reacting with the pollutant is given.
  • Publication
    Accès libre
    Engineered and subsequent intrinsic in situ bioremediation of a diesel fuel contaminated aquifer
    (2002)
    Hunkeler, Daniel 
    ;
    Höhener, P
    ;
    Zeyer, J
    A diesel fuel contaminated aquifer in Menziken, Switzerland was treated for 4.5 years by injecting aerated groundwater, supplemented with KNO3 and NH4H2PO4 to stimulate indigenous populations of petroleum hydrocarbon (PHC) degrading microorganisms. After dissolved PHC concentrations had stabilized at a low level, engineered in situ bioremediation was terminated. The main objective of this study was to evaluate the efficacy of intrinsic in situ bioremediation as a follow-up measure to remove PHC remaining in the aquifer after terminating engineered in situ bioremediation. In the first 7 months of intrinsic in situ bioremediation, redox conditions in the source area became more reducing as indicated by lower concentrations of SO24‾ and higher concentrations of Fe(II) and CH4. In the core of the source area, strongly reducing conditions prevailed during the remaining study period (3 years) and dissolved PHC concentrations were higher than during engineered in situ bioremediation. This suggests that biodegradation in the core zone was limited by the availability of oxidants. In lateral zones of the source area, however, gradually more oxidized conditions were reestablished again, suggesting that PHC availability increasingly limited biodegradation. The total DIC production rate in the aquifer decreased within 2 years to about 25% of that during engineered in situ bioremediation and remained at that level. Stable carbon isotope analysis confirmed that the produced DIC mainly originated from PHC mineralization. The total rate of DIC and CH4 production in the source area was more than 300 times larger than the rate of PHC elution. This indicates that biodegradation coupled to consumption of naturally occurring oxidants was an important process for removal of PHC which remained in the aquifer after terminating engineered measures.
  • Publication
    Accès libre
    Intrinsic bioremediation of a petroleum hydrocarbon-contaminated aquifer and assessment of mineralization based on stable carbon isotopes
    (1999)
    Bolliger, C
    ;
    Höhener, P
    ;
    Hunkeler, Daniel 
    ;
    Häberli, K
    ;
    Zeyer, J
    This study presents a stepwise concept to assess the in situ microbial mineralization of petroleum hydrocarbons (PHC) in aquifers. A new graphical method based on stable carbon isotope ratios (δ13C) was developed to verify the origin of dissolved inorganic carbon (DIC). The concept and the isotope method were applied to an aquifer in Studen, Switzerland, in which more than 34,000 liters of heating oil were accidentally released. Chemical analyses of ground water revealed that in this aquifer locally, anaerobic conditions prevailed, and that PHC mineralization was linked to the consumption of oxidants such as O2, NO3- , and SO42- and the production of reduced species such as Fe2+, Mn2+, H2S and CH4. However, alkalinity and DIC balances showed a quantitative disagreement in the link between oxidant consumption and DIC production, indicating that chemical data alone may not be a reliable assessment tool. δ13C ratios in DIC have been used before for bioremediation assessment, but results were reported to be negatively influenced by methanogenesis. Using the new graphical method to display δ13C data, it was possible to identify anomalies found in methanogenic monitoring wells. It could be shown that 88% of the DIC produced in the contaminated aquifer originated from microbial PHC mineralization. Thus, the new graphical method to display δ13C ratios appears to be a useful tool for the assessment of microbial hydrocarbon mineralization in a complex environment.
  • Publication
    Accès libre
    Engineered in situ bioremediation of a petroleum hydrocarbon-contaminated aquifer: assessment of mineralization based on alkalinity, inorganic carbon and stable carbon isotope balances
    (1999)
    Hunkeler, Daniel 
    ;
    Höhener, P
    ;
    Bernasconi, S
    ;
    Zeyer, J
    A concept is proposed to assess in situ petroleum hydrocarbon mineralization by combining data on oxidant consumption, production of reduced species, CH4, alkalinity and dissolved inorganic carbon (DIC) with measurements of stable isotope ratios. The concept was applied to a diesel fuel contaminated aquifer in Menziken, Switzerland, which was treated by engineered in situ bioremediation. In the contaminated aquifer, added oxidants (O2 and NO−3) were consumed, elevated concentrations of Fe(II), Mn(II), CH4, alkalinity and DIC were detected and the DIC was generally depleted in 13C compared to the background. The DIC production was larger than expected based on the consumption of dissolved oxidants and the production of reduced species. Stable carbon isotope balances revealed that the DIC production in the aquifer originated mainly from microbial petroleum hydrocarbon mineralization, and that geochemical reactions such as carbonate dissolution produced little DIC. This suggests that petroleum hydrocarbon mineralization can be underestimated if it is determined based on concentrations of dissolved oxidants and reduced species.
  • Publication
    Accès libre
    Petroleum hydrocarbon mineralization in anaerobic laboratory aquifer columns
    (1998)
    Hunkeler, Daniel 
    ;
    Jörger, D
    ;
    Häberli, K
    ;
    Höhener, P
    ;
    Zeyer, J
    The anaerobic biodegradation of hydrocarbons at mineral oil contaminated sites has gathered increasing interest as a naturally occurring remediation process. The aim of this study was to investigate biodegradation of hydrocarbons in laboratory aquifer columns in the absence of O2 and NO¯3, and to calculate a mass balance of the anaerobic biodegradation processes. The laboratory columns contained aquifer material from a diesel fuel contaminated aquifer. They were operated at 25°C for 65 days with artificial groundwater that contained only SO24¯ and CO2 as externally supplied oxidants. After 31 days of column operation, stable concentration profiles were found for most of the measured dissolved species. Within 14 h residence time, about 0.24 mM SO24¯ were consumed and dissolved Fe(II) (up to 0.012 mM), Mn(II) (up to 0.06 mM), and CH4 (up to 0.38 mM) were produced. The alkalinity and the dissolved inorganic carbon (DIC) concentration increased and the DIC became enriched in 13C. In the column, n-alkanes were selectively removed while branched alkanes persisted, suggesting a biological degradation. Furthermore, based on changes of concentrations of aromatic compounds with similar physical–chemical properties in the effluent, it was concluded that toluene, p-xylene and naphthalene were degraded. A carbon mass balance revealed that 65% of the hydrocarbons removed from the column were recovered as DIC, 20% were recovered as CH4, and 15% were eluted from the column. The calculations indicated that hydrocarbon mineralization coupled to SO24¯ reduction and methanogenesis contributed in equal proportions to the hydrocarbon removal. Hydrocarbon mineralization coupled to Fe(III) and Mn(IV) reduction was of minor importance. DIC, alkalinity, and stable carbon isotope balances were shown to be a useful tool to verify hydrocarbon mineralization.
  • Publication
    Accès libre
    222Rn as a Partitioning Tracer To Detect Diesel Fuel Contamination in Aquifers: Laboratory Study and Field Observations
    (1997)
    Hunkeler, Daniel 
    ;
    Hoehn, E
    ;
    Höhener, P
    ;
    Zeyer, J
    The use of 222Rn, a naturally occurring radioactive isotope, was investigated as a partitioning tracer to detect and quantify the amount of non-aqueous-phase liquids (NAPLs) in contaminated aquifers. Diesel fuel was chosen as a model NAPL. The diesel fuel-water partition coefficient for 222Rn was 40 ± 2.3, in bottles containing diesel fuel and water at 12 °C. In water-saturated quartz sand contaminated with diesel fuel, the 222Rn emanating from the sand partitioned between diesel fuel and water as expected based on this partition coefficient. In a column containing uncontaminated quartz sand, the 222Rn activity in infiltrated water increased from <0.2 to 4.9 kBq m-3, and in a subsequent column containing diesel fuel-contaminated quartz sand, the 222Rn activity in the water phase decreased to 3.3 kBq m-3. This decrease corresponds to what has been predicted using a mathematical model. At a contaminated field site, the 222Rn activity of groundwater decreased by about 40% between monitoring wells upgradient of the contaminated zone and monitoring wells within the contaminated zone. On the basis of this decrease, the average diesel fuel saturation was estimated using the mathematical model. The calculated diesel fuel saturation was in the range of that found in excavated aquifer material.
  • Publication
    Accès libre
    Bioremediation of a diesel fuel contaminated aquifer: simulation studies in laboratory aquifer columns
    (Elsevier, 1996)
    Hess, A
    ;
    Höhener, P
    ;
    Hunkeler, Daniel 
    ;
    Zeyer, J
    The in situ bioremediation of aquifers contaminated with petroleum hydrocarbons is commonly based on the infiltration of groundwater supplemented with oxidants (e.g., O2, NO ‾3) and nutrients (e.g., NH+4, PO34‾). These additions stimulate the microbial activity in the aquifer and several field studies describing the resulting processes have been published. However, due to the heterogeneity of the subsurface and due to the limited number of observation wells usually available, these field data do not offer a sufficient spatial and temporal resolution. In this study, flow-through columns of 47-cm length equipped with 17 sampling ports were filled with homogeneously contaminated aquifer material from a diesel fuel contaminated in situ bioremediation site. The columns were operated over 96 days at 12°C with artificial groundwater supplemented with O2, NO ‾3 and PO34 ‾. Concentration profiles of O2, NO ‾3, NO ‾2, dissolved inorganic and organic carbon (DIC and DOC, respectively), protein, microbial cells and total residual hydrocarbons were measured. Within the first 12 cm, corresponding to a mean groundwater residence time of < 3.6 h, a steep O2 decrease from 4.6 to < 0.3 mg 1-1, denitrification, a production of DIC and DOC, high microbial cell numbers and a high removal of hydrocarbons were observed. Within a distance of 24 to 40.5 cm from the infiltration, O2 was below 0.1 mg 1-1 and a denitrifying activity was found. In the presence and in the absence of O2, n-alkanes were preferentially degraded compared to branched alkanes. The results demonstrate that: (1) infiltration of aerobic groundwater into columns filled with aquifer material contaminated with hydrocarbons leads to a rapid depletion of O2; (2) O2 and NO ‾3 can serve as oxidants for the mineralization of hydrocarbons; and (3) the modelling of redox processes in aquifers has to consider denitrifying activity in presence of O2.