PNNL-13501 - Pacific Northwest National Laboratory

The additions of Ti(III), Ni(II), palladium catalyst, and
EDTA resulted in small to large decreases in the rate of
trichloroethylene dechlorination, possibly indicating
adsorption of these metals or complexes blocked access
by trichloroethylene. The addition of AQDS (electron
shuttle) resulted in a small but insignificant increase in the
trichloroethylene dechlorination rate (Figure 4).
conc (µmol/L)
10
8
6
4
initial: 1.1 ppm TCE in DI water
TCE
Summary and Conclusions
Fe(II) and Mn(II) additions to partially reduced sediment
resulted in a significant increase in trichloroethylene
dechlorination. Trichloroethylene dechlorination with the
Fe(II) addition was more efficient than Mn(II). The additions
of Ti(III), Ni(II), Palladium catalyst, and EDTA did
not enhance the rate of trichloroethylene dechlorination
by the partially reduced sediment. Because the addition
of an electron shuttle (AQDS) had only a slight positive
effect, the rate of trichloroethylene degradation is not
limited by electron transfer, so the addition of an
additional electron donor rather than a catalyst is likely
more efficient. While an Fe(II) addition is thought to be
more cost-efficient than the use of reduced sediment
alone, amending the redox treatment at the field scale
involves additional coupled hydraulic and geochemical
considerations. Because both Mn(II) and Fe(II) adsorb
strongly to natural sediments, engineered small pulse
injections with a high ionic strength or low pH would be
needed at the field scale to result in a dispersed addition
of adsorbed Fe(II) or Mn(II), as indicated by reactive
transport modeling, and could be tested in experimental
systems.
References
AQDS addition: 16.5 h
2
0
acetylene
control: half life 24.8 h
0 5 10 time (h) 15 20 25
Figure 4. Trichloroethylene dechlorination to acetylene in
the presence of reduced natural sediment with the addition
of an aqueous electron shuttle (AQDS), which resulted in a
small increase in the dechlorination rate
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Publication
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Earth System Science 253