Biomedical Engineering Reference
In-Depth Information
a
50
50
Total lactate added
40
40
Lactate
Propionic
Formic
Pyruvic
Valeric
Butyric
Acetic
30
30
20
20
10
10
0
0
0
5
10
15
20
Time (d)
b
35
70
Total lactate added
30
60
25
50
20
40
15
30
10
20
Lactate
Propionic
Acetic
5
10
0
0
02468 0 2 4 6
Time (d)
Figure 3.3. Accumulation of VFAs during growth of SDC-9
TM
(a) or PJKS
TM
(b) cultures in a 750-L
reactor. YE (0.2%) was added as a nutrient at the beginning of the culture process.
likely due to evolution of the SDC-9
TM
culture to more efficiently ferment propionate during
several years of maintenance on lactate as a primary growth substrate.
To optimize the growth of the SDC-9
TM
consortium, it has been necessary to determine a
relationship between PCE feed rate and
Dhc
cell concentration (Schaefer et al.,
2009
). The
culture production process is complicated by the fact that the cultures are mixtures and likely
contain multiple populations of dehalogenating microbes. The primary concern is to maintain
the VC-reducing population(s) in the consortium, because VC reduction is less energetically
favorable than the other dehalogenating reactions. Hence, PCE and TCE dehalogenating
populations potentially can outcompete VC reducers if the higher chlorinated substrates are
maintained in excess. Furthermore, Cupples and colleagues (
2004
) observed that net decay in
dechlorinating microorganisms could occur in the VS culture if DCE plus VC concentrations
are below 0.7 micromolar (
m
M). In addition, with SDC-9
TM
, based on many bottle assays, the
VC dechlorination rate is 28-35% of the PCE dechlorination rate. Therefore, there is a tendency
for VC to accumulate in the reactor during high rate PCE feeding. Consequently, PCE feed
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