Biomedical Engineering Reference
In-Depth Information
3. pH-neutralized SJCA water: 50 mL of SJCA groundwater adjusted to pH 7.0-7.2 with
NaOH. [The initial pH of SJCA groundwater was 5.65 - judged too low for JS666.]
After microcosms were prepared in duplicate, all were dosed with
cis-
DCE at a nominal
concentration of 11 mg/L (5.9
mol/bottle). Each treatment (except pure-culture controls) was
matched with an uninoculated control. Microcosms were inoculated with JS666 to achieve
roughly either “1X”
m
10
5
cells/mL.
All 1X- and 0.1X-inoculated microcosms with groundwater, whether buffered or not,
degraded all of the
cis-
DCE within 2 and 4 days, respectively (Figure
7.5
). The GW
10
6
cells/mL or “0.1X”
¼
7
¼
7
MSM
and MSM-only controls actually required
more
time to completely degrade the
cis-
DCE (data
not shown). There was no degradation in any of the uninoculated controls.
7.4.3 Titration Studies with SJCA Groundwater
Given the low pH of the native SJCA groundwater (ca. 5.6-5.9), buffer addition was
deemed necessary in the field study. Though carbonates are less expensive than phosphates,
our studies indicate that JS666 tolerates much higher concentrations (eq/L basis) of orthopho-
sphates than of carbonates. Testing indicated that 10 mM phosphate buffer (equimolar mixture
of mono-basic and dibasic forms of orthophosphate) was required to titrate SJCA groundwater
to pH 7.0. However, 20-30 mM phosphate buffer was used in the bioaugmentation field study.
Such levels are consistent with typical laboratory culture conditions and should adequately
adjust the native pH. Furthermore, the effect of the subsurface soil on the amount of phosphate
buffer that would be necessary to achieve neutral pH could not be determined; therefore,
excess buffer addition was deemed prudent.
7.4.4 Field Test
The test-plot area was installed as a pattern consisting of a 4 in. (10.2 cm) diameter injection
well (which would receive JS666 inoculation
buffer), surrounded by 2 in. (5.1 cm) diameter
monitoring wells spaced at 2-4-week travel-time intervals between adjacent wells (Figure
7.6
).
Considerably upgradient (and laterally distant also) was a control plot, consisting of a similar
injection well (which would receive buffer only), with two downgradient monitoring wells.
6
5
Uninoc GW control
GW, 1X inoc
GW, 0.1X inoc
4
3
2
1
0
0
1
2
3
4
5
6
Time (days)
Figure 7.5. cis-DCE degradation in microcosms conducted on SJCA groundwater (MW-04 S)
prior to start of field bioaugmentation study (adapted from Giddings et al.,
2010
b). Results are
for pH-neutralized (NaOH) groundwater; 1X inoculation level corresponds to 7 10
6
cells/mL.
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