BIOAUGMENTATION FOR MTBE REMEDIATION - Bioaugmentation for Groundwater Remediation - page 296

5,000 g/L MTBE) and TBA also was reduced to non-

detect levels ( < 50 mg/L TBA). These studies demonstrated that overall activity of naturally-
occurring MTBE degraders could be stimulated by increasing the dissolved oxygen levels in
groundwater, albeit more slowly than the bioaugmented plots. The activity in the biostimulated
plot became comparable to the bioaugmented plot after about 240 d of operation. The short-
term performance of MC-100 bioaugmented and the biostimulated test plots are reported in
Salanitro et al. ( 2000 ).

m g/L to non-detect concentrations ( < 5 m

10.4.2 Bioaugmentation with Direct Degraders (PM1)

Another bioaugmentation study at the NBVC was performed by researchers from the
University of California Davis (Smith et al., 2005 ). These researchers generated a stable
oxygen-rich environment in two test cells, and then inoculated one of the test cells with the
PM1 isolate. They then monitored MTBE concentrations in both systems for several months.
The manner and volume of bacterial introduction was not detailed in available literature.
Surprisingly, stronger attenuation of MTBE was observed in the control (biostimulation) cell
over the 240 days that the test cells were monitored.
One important finding from this test was the discovery of naturally-occurring “PM1-like”
activity at this site. Similar sequences were found in samples from aquifers at Vandenberg Air
Force Base (approximately 90 miles north of NBVC) and in two other MTBE-impacted sites in
northern California (Kane et al., 2001 ). These results suggested that bacteria similar to PM1 are
in fact more common than initially thought, and may be present in low numbers at many sites.
Such findings may account for the common observation that MTBE biodegradation does occur
in biostumulated sites, albeit after an initial lag period, as long as the dissolved oxygen
concentrations are relatively high.

10.4.3 Bioaugmentation with Propane Oxidizers (ENV 425)

A bioaugmentation study performed by Envirogen (now Shaw Environmental, Inc.) at the
NBVC attempted the seeding of a test cell similar to those described above with bacteria
capable of cometabolic oxidation of MTBE when grown on propane. The pilot test was
conducted to determine the effectiveness of using propane and oxygen biostimulation and
bioaugmentation (by addition of a propane oxidizing strain of Rhodococcus ruber , strain
ENV425). The seeding process was a single event for this test, though no description of the
introduction method is available. Although MTBE concentrations upgradient and downgradi-
ent of the treatment system were evaluated, the concentrations of added deuterated MTBE
(d-MTBE) and iodide (a conservative groundwater tracer) were measured to evaluate biotic and
abiotic attenuation (due to dispersion) as the contaminant passed through the biological barrier.
The ratio of the groundwater tracers between downgradient transects provided evidence
concerning the relative losses of MTBE resulting from dispersion and degradation. The use
of d-MTBE provided evidence of biodegradation by tracking the generation of deuterated
daughter products. Test results showed the downgradient concentrations of d-MTBE consis-
tently increased over the 8 months of the test, and that the control plot (biostimulation) showed
an average half life of d-MTBE four times greater than the test plot (bioaugmentation)
(USEPA, 2002 ).