Biomedical Engineering Reference
In-Depth Information
Table 3.2. Multiple Culture Production Runs with Chlorinated Solvent Dechlorinating Consortia
PCE
Activity
(mg/h/g
DWT)
cis-DCE
Activity
(mg/h/g
DWT)
Date
(month/
year)
Volume
(L)
Final
OD
550
Final Dhc
(cells/L)
a
Culture
DWT (g/L)
SDC-9
TM
01/2006
550
1.3
1.4 E11
0.51
16
13
SDC-9
TM
02/2008
550
1.7
2.8 E11
0.66
22
14
SDC-9
TM
03/2008
3,200
1.6
1.4 E11
0.65
41
37
SDC-9
TM
05/2008
2,500
1.6
2.4 E12
0.59
42
39
SDC-9
TM
08/2008
2,000
1.4
1.0 E12
0.51
80
69
SDC-9
TM
07/2009
2,500
1.5
5.5 E11
0.52
88
82
SDC-9
TM
08/2009
2,500
1.5
8.6 E11
0.64
101
69
SDC-9
TM
01/2010
2,500
1.7
7.0 E11
0.57
113
79
SDC-9
TM
03/2010
2,500
1.4
9.3E11
0.55
126
107
PJKS
TM
01/2008
2,500
1.1
9.4 E11
0.41
32
14
PJKS
TM
02/2008
1,700
1.3
1.0 E11
0.50
64
45
Hawaii-05
TM
11/2007
550
1.2
1.5 E11
0.50
23
16
a
Based on qPCR assuming 1 16 S rRNA gene copy/cell
3.3.1 Factors Affecting Culture Growth
Several factors can affect the results obtained during growth of
Dhc
cultures, including
substrate type and feed rates, pH, and VFA accumulation. Growth of
Dhc
requires the presence
of a chlorinated substrate as an electron acceptor, H
2
as an electron donor, and a carbon growth
source such as acetate (Cupples et al.,
2003
;Heetal.,
2003b
;L¨ffler et al.,
2003
;Maym
´
-Gatell
et al.,
1997
). In
Dhc
consortia, the primary growth substrate (e.g., lactate) is fermented by non-
Dhc
members to H
2
and acetate that can be utilized by
Dhc
. The presence of excess H
2
, however,
can lead to substrate competition with methanogenic bacteria in the consortia that also can use
H
2
, albeit at a higher substrate threshold than
Dhc
(L¨ffler et al.,
1999
;Luetal.,
2001
;Yangand
McCarty,
1998
). Therefore, in developing a cell culturing protocol for the described cultures,
attempts were made to maintain consistent low H
2
concentrations within the reactor. The sodium
lactate feed rate used during the Shaw culturing process results in a sustained dissolved hydrogen
concentration in the reactor of
<
20 nM. During the initial batch feeding of lactate and YE added
prior to inoculation, H
2
concentrations sometimes exceed 100 nM; however, during the extended
cell culture process the H
2
concentrations are typically 3-5 nM, which is similar to the half
velocity coefficient for hydrogen previously calculated for the VS culture (7
2 nM) (Cupples
et al.,
2004
).
Fermentation of lactate also leads to an accumulation of VFAs (e.g., propionate and
acetate; Figure
3.3
) that can potentially inhibit dechlorinating organisms in a consortium.
Studies with SDC-9
TM
, demonstrated that dehalogenation of chlorinated ethenes by the culture
was not inhibited by propionate and acetate concentrations to 6,000 mg/L (82.1 and 101.6 mM,
respectively) (data not shown). Figure
3.3a
and
b
show the formation of VFAs during growth
of SDC-9
TM
and PJKS
TM
, respectively. In both cases, the VFA concentrations do not reach
inhibitory levels with the culture production protocol described here. Notably, the SDC-9
TM
culture accumulates much less propionate than the PJKS
TM
culture grown under the same
conditions. Although the reason for this lower accumulation of propionate is not certain, it is
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