PRODUCTION AND HANDLING OF DEHALOCOCCOIDES BIOAUGMENTATION CULTURES - Bioaugmentation for Groundwater Remediation - page 100

rates are adjusted to prevent accumulation of PCE, TCE or cis -DCE while maintaining a
residual VC concentration in the medium of ~1 mg/L (16 m M). The PCE feed rates for the
SDC-9 TM consortium have been optimized after evaluating the results from multiple large-
scale production runs and bottle assays. The relationship between Dhc cell numbers and PCE
feed rate is best described by the following equation: Dhc concentration (cells/L) ¼ 6.77

10 11 + [8.40 10 11 L)] (R 2

0.999) (Vainberg et al., 2009 ).
Dehalogenation of chloroethenes by SDC-9 TM also is affected by culture pH, with little or
no dehalogenation below pH 5.6 and above pH 9.0 (Figure 3.4 ; Vainberg et al., 2009 ). In another
experiment, the effect of elevated pH on TCE dechlorination activity was studied by incubating
SDC-9 TM culture in groundwater at pH 9.9 for 1 day at 15 C, and then reducing the pH to 7.0
before measuring TCE degradation activity. This short incubation at pH 9.9 resulted in the loss
of 99% of TCE degradation activity of the SDC-9 TM consortium. Both reductive dehalogena-
tion and fermentation of the growth substrates used to grow the cells consumes considerable
amounts of alkalinity (McCarty et al., 2007 ). The pH of the medium in the Shaw 4,000-L reactor
decreases from an initial pH of 7.4 to approximately 6.1 during the first 30 days of cell growth
(Figure 3.5 ). Because the culture is fed sodium lactate, however, adding NaOH to control pH
could reduce growth rates due to an excess of sodium ions in the reactor. Analysis of PCE
dechlorination with added sodium chloride (NaCl) to RAMM medium to a final total dissolved
solid (TDS) concentration of 1,000 mg/L showed that elevated level of TDS reduced dechlori-
nation rates, especially for cis -DCE and VC (Figure 3.6 ). Therefore, instead of adding NaOH to
control pH, the reactors are sparged periodically with nitrogen (N 2 ) to remove dissolved CO 2
from the culture medium. This approach sufficiently regulates the medium pH to allow
completion of the culture production (Figure 3.7 ). The duration of sparging affects the extent
of pH increase and typically sparging for 10-15 min allows the pH to increase 0.3-0.4 Standard
Units (SU) (Figure 3.8 ). Sufficiently high rates of growth and substrate dehalogenation are
sustainable in the reactors, provided the pH is maintained above 6 SU.

PCE feed rate (mg/h ¼

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

5.1 5.5 5.8 6 6.3 6.7 7 7.4 8 8.5 9 9.5

pH

Figure 3.4. Effect of pH on PCE dehalogenation by SDC-9 TM . There was no measurable activity at
pH 5.1. Values represent the mean of triplicate samples, and error bars represent one standard
error of the mean.