Biomedical Engineering Reference
In-Depth Information
Table 5A.1 Measured Dhc Concentrations in Soil and Water Samples from a Laboratory
Bioaugmentation Column Constructed with Fort Dix, New Jersey Aquifer Materials (derived from
Schaefer et al., 2009 ).
Distance from Column Influent
(centimeter(s))
Soil (Dhc/g)
Water (Dhc/L)
10 3
0-3.5
1
8 10 7
3.5-7
84
7-10.5
< 80
5 10 7
10.5-14
< 80
14-17.5
< 80
10 7
17.5-20
<
80
1
30 times more Dhc was recovered from the box than the amount added, indicating significant
growth of the organisms in the flow cell, although the highest concentration of Dhc was
found near the injection point.
Column studies are especially useful because they allow assessment of bacterial transport
and degradation. Several column studies have been performed to evaluate microbial transport
through saturated soils. Straining, filtration processes and the formation of biofilms often
control microbial transport in soils (Ginn et al., 2002 ; Yang and McCarty, 2000 ). The ultimate
effect of these processes on transport is dependent upon microbial characteristics, porous
media properties, flow rates, and aqueous geochemical properties. For example, Fuller et al.
( 2000 ) showed that subpopulations of a microbial consortium may have a range of adhesion
properties, resulting in variable transport distances of each microbial population in soil.
Azizian et al. ( 2008 ) inoculated a continuous-flow anaerobic column constructed with
Hanford site soils to evaluate reductive dechlorination of PCE. The influent PCE (0.09 mM)
was transformed to VC and ethene within a hydraulic residence time of 1.3 days, and the Dhc
concentrations in the column ranged from about 4
10 6 cells/g near the column influent to
10 6 cells/g near the column effluent (Behrens et al., 2008 ). In work by Schaefer et al.
( 2009 ) with dechlorinating bioaugmentation cultures, Monod kinetic parameters were deter-
mined for batch cultures used to inoculate aquifers and bacteria that passed through a saturated
soil column (Schaefer et al., 2009 ). The Dhc concentrations within the column increased from
nondetectable before inoculation (at a detection limit of approximately 5
~2
10 4 cells/L) to ~10 8
cells/L after inoculation and electron donor addition, and the Dhc concentrations in the aqueous
phase were within an order of magnitude throughout the length of the column (Table 5A.1 ).
The Schaefer et al. observations also were consistent with the results of Yolcubal et al. ( 2002 )
who observed that actively growing bacteria are more prevalent in the aqueous phase than
associated with the solid phase.
These microcosm, tank and column studies provide useful insights to aid those planning
field bioaugmentation activities. The microcosm studies demonstrate that in well-mixed sys-
tems high inoculation densities (e.g., > 10 7 Dhc /L) result in fairly rapid rates of VOC dechlori-
nation as was predicted by Lu et al. ( 2006 ). The Dhc -containing cultures grow well under
ambient environmental conditions, provided sufficient electron donor and VOC electron
acceptor are present. Column and tank studies, however, suggest that the distribution of Dhc
can vary based on VOC composition and electron donor availability, and that a large proportion
of an inoculum applied may be filtered out by soils near an injection point (Behrens et al., 2008 ;
Schaefer et al., 2009 ; Sleep et al., 2006 ). Nonetheless, the Dhc are highly mobile in some aquifer
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