Geochemical
and Microbiological Characteristics during
in Situ Chemical Oxidation and in Situ Bioremediation at a Diesel
Contaminated Site
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Abstract
While
in situ chemical oxidation with persulfate has seen wide
commercial application, investigations into the impacts on groundwater
characteristics, microbial communities and soil structure are limited.
To better understand the interactions of persulfate with the subsurface
and to determine the compatibility with further bioremediation, a
pilot scale treatment at a diesel-contaminated location was performed
consisting of two persulfate injection events followed by a single
nutrient amendment. Groundwater parameters measured throughout the
225 day experiment showed a significant decrease in pH and an increase
in dissolved diesel and organic carbon within the treatment area.
Molecular analysis of the microbial community size (16S rRNA gene)
and alkane degradation capacity (<i>alkB</i> gene) by qPCR
indicated a significant, yet temporary impact; while gene copy numbers
initially decreased 1–2 orders of magnitude, they returned
to baseline levels within 3 months of the first injection for both
targets. Analysis of soil samples with sequential extraction showed
irreversible oxidation of metal sulfides, thereby changing subsurface
mineralogy and potentially mobilizing Fe, Cu, Pb, and Zn. Together,
these results give insight into persulfate application in terms of
risks and effective coupling with bioremediation