U(VI) Bioreduction with Emulsified Vegetable Oil as
the Electron Donor – Model Application to a Field Test
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Abstract
We
amended a shallow fast-flowing uranium (U) contaminated aquifer
with emulsified vegetable oil (EVO) and subsequently monitored the
biogeochemical responses for over a year. Using a biogeochemical model
developed in a companion article (Tang et al., <i>Environ. Sci.
Technol.</i> <b>2013</b>, doi: 10.1021/es304641b) based
on microcosm tests, we simulated geochemical and microbial dynamics
in the field test during and after the 2-h EVO injection. When the
lab-determined parameters were applied in the field-scale simulation,
the estimated rate coefficient for EVO hydrolysis in the field was
about 1 order of magnitude greater than that in the microcosms. Model
results suggested that precipitation of long-chain fatty acids, produced
from EVO hydrolysis, with Ca in the aquifer created a secondary long-term
electron donor source. The model predicted substantial accumulation
of denitrifying and sulfate-reducing bacteria, and U(IV) precipitates.
The accumulation was greatest near the injection wells and along the
lateral boundaries of the treatment zone where electron donors mixed
with electron acceptors in the groundwater. While electron acceptors
such as sulfate were generally considered to compete with U(VI) for
electrons, this work highlighted their role in providing electron
acceptors for microorganisms to degrade complex substrates thereby
enhancing U(VI) reduction and immobilization