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Benzene oxidation under sulfate reducing
conditions Mass balances, degradation rates and
isotope fractionation in columns running under
close to in situ conditions Carsten Vogt1, Stefan
Gödeke2, Hanns-Christian Treutler3, Anko
Fischer1, Holger Weiß2, Mario Schirmer4, Hans
Hermann Richnow1 Departments 1Isotope
Biogeochemistry, 2Groundwater Remediation,
3Analytical Chemistry, 4Hydrogeology carsten.vogt_at_
ufz.de
Objective Benzene is considered to be the most
resistant compound among typical alkylated
benzenes in gasoline under anoxic conditions.
Here, we proved the degradation of benzene under
sulfate-reducing conditions under close to in
situ conditions - in columns infiltrated with
benzene-containing, anoxic groundwater from a
benzene-contaminated aquifer near Zeitz
(Saxonia-Anhalt, Germany) -, using a combination
of different methods.
Field site and experimental plant
Benzene degradation in sand-filled columns
Sketch of the experimental plant at the benzene
contaminated field site in Zeitz, Saxonia-Anhalt,
Germany. Columns were filled with either coarse
sand (grain size 2 - 3.15 mm) or pumice (Eifel
volcano rock).
Isotope fractionation
Concentrations of benzene (A, B), sulfate (C, D),
hydrogen carbonate (E, F) and sulfide (G, H)
after 6, 12, 18 and 24 m flow through sand filled
columns. Data in A, C, E and G (left sided
diagrams) show compound concentrations in the
inflow and in the outlets of columns 1-4,
respectively, as a function of time. Data in B,
D, F, H show average compound concentrations (n
45, average of each data curve shown in A, C, E
and G) as a function of distance between inflow
and column outlet. For benzene degradation,
zero-order and first-order correlations were
calculated (shown in B). Mean temperatures for
the operation day 248 through 599 were 15.1C ?
Inflowing groundwater ? 6 m ? 12 m ? 18 m ?
24 m (for 2a, c, e, g)
Left picture Benzene degradation, carbon
hydrogen and sulfide production and sulfate
reduction in sand filled columns (sampled in
November 2005) Right picture Corresponding
carbon and hydrogen isotope fractionation in the
course of benzene degradation

• Results conclusions
• Benzene was degraded in both sand and
  pumice-filled columns in average zero-order rates
  of
• 8-36 µM d-1
• Electron balances strongly indicate a
  mineralization of benzene with sulfate as
  electron acceptor
• Benzene degradation in the columns was
  accompanied by isotope fractionation of carbon
  and hydrogen
• Data suggest a high potential for Natural
  Attenuation of benzene under sulfate-reducing
  conditions at the field site Zeitz

Electron balances degradation rates
Table 1
Table 2
Electron balances (Table 1, only shown for
sand-filled columns) and rates (Table 2) for
benzene oxidation under sulfate reducing
conditions in the column system, based on data
recorded from operation day 169 to 599 (see also
the picture above). Mean temperature was 15.1 C.
Mean retention times in the columns were
determined using radon as tracer.