Abstract:
Continuous-flow and batch experiments were conducted with a column reactor
system containing Hanford aquifer material in order to evaluate the potential of in-situ
bioremediation of carbon tetrachloride (CT) at Hanford. The effectiveness of benzoate
and acetate as primary substrates was considered. Nitrate and sulfate were potential
electron acceptors. Transport experiments indicated the following characteristics:
porosity, 27%; longitudinal dispersivity, 11 cm; and CT retardation factor, 3.9.
Denitrification and CT transformation occurred during periods of benzoate and acetate
addition. Chloroform (CF) was detected as a product of CT transformation in all cases.
Benzoate generally induced the fastest rates of CT transformation. However, acetate was
much better at inducing denitrification. Sulfate reduction was never observed, even
during extended absences of nitrate and nitrite. The continuous-flow experiments showed
more rapid transformation near the point of injection; however, residence times were not
long enough to completely degrade CT. In batch experiments CT transformation
appeared to follow pseudo-first-order kinetics, with rates decreasing from the point of
injection. Switching from continuous-flow to batch experiments appeared to be an
effective means of determining spatial differences in microbial activity within the
column. Overall, these results indicate that the microbial population at Hanford is
capable of transforming CT in the subsurface. However, methods to control the
production of CF may be necessary before this technology can be successfully employed.
