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Groundwater from a diesel fuel-contaminated site in Vienna, Austria, was treated in pilot-scale subsurface flow constructed wetlands. The study aims at quantifying the contribution of biodegradation to the total removal of diesel compounds by means of compound-specific isotope analysis (CSIA). This innovative approach requires a constant isotope fractionation during the microbial transformation reaction which leads to an enrichment of the heavy isotopes, i. e. 13C and 2H, in the remaining pollutant. Filter material and/or groundwater was incubated in laboratory microcosms and the aerobic degradation of n-decane, which was chosen as model compound for diesel hydrocarbons, was monitored. Isotope fractionation was absent in water saturated microcosms because only minor n-decane biodegradation took place. During n-decane biodegradation in moist filter material, on the other hand, small but variable isotopic fractionation factors were found. The different experimental set-ups give indications how mass transfer limitations of hydrophobic molecules might mask isotopic fractionation and the consequences for field applications of CSIA are discussed in detail.

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Hager, Melanie
Hager Melanie, born 1986/02/01. Education: Environmental engineering and water management, terminated 2016/04/27 at the University of Applied Life Sciences, Vienna.Master Thesis: ´Determination of the 13C/12C and 2H/1H isotopic fractionation factor during microbial degradation of decane: a microcosm study´

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