80

AEROBIC BIOREMEDIATION OF TCE-CONTAMINATED GROUND WATER: BIOAUGMENTATION WITH BURKHOLDERIA CEPACIA PR1301

A field demonstration site was designed with an injection well (IW) system which minimized dilution (0.7%) and simulated the effect of contaminated ground water passing through a biological active system. Monitoring points (4 depths/point) were installed 5 hydraulic flow days upgradient and 2, 5, 10, & 15 days downgradient from the IW. A bromide ground water tracer study was used to determine hydraulic flow, flowpath and retardation of oxygen, contaminants, and micro-organisms.

The field study was conducted in six phases: background, determined original chemical and biological parameters; optimization, determined ground water velocities, flow paths and oxygen transport; biotreatment I, PR1 was grown to high cell density (1011 cells/mL) and high TOM activity in a bioreactor and continuously added to the IW with oxygen and bromide; recovery I, the IW stabilized to the original conditions and the "clean" ground water front was monitored downgradient; and Biotreatment II, cell concentrations increased stepwise from 107 to 108 cells/mL in the IW and substrate was then pulsed into the well in an effort to maintain a cell population. Recovery II marked the end of the study and all systems were terminated.

Oxygen was retarded in the soil formation by 30 days but could not be attributed to reduced metals or microbial activity. The injection well simulated a biological trench with an average 250 ppb total CAHs moving through the system. The injected PR1 at 109 cells/mL, degraded to non-detect all contaminants in the aerobic system within 24 hours and maintained that level for 4 days (test termination). Total mass of contaminants degraded during the test period is estimated at 15.5 mg, or 94.5 mg/L/h.

The test system formed an effective removal barrier for contamination allowing clean ground water to flow downgradient of the IW. However, the soil formation plugged at this cell concentration. Biotreatment II added PR1 step-wise to the well to increase cell concentration and then glucose was pulsed in an attempt to maintain cell mass.

Total contaminants in the ground water were removed only when cell concentrations reached 108 cells/ml, but this cell concentration could not be maintained with substrate pulsing in the IW. Slight plugging was evident at 108 cells/mL, but not as severe as the first treatment. This was the first demonstration that bioaugmentation could effectively degrade CAHs using a laboratory developed strain. The injected cells did not efficiently move downgradient of the injection point.

Based on these results, CDM proposed using a bio-barrier to contain the plume. However, subsequent laboratory work has shown that an adhesion resistent microorganism of the same strain can effectively move downgradient in laboratory systems using soils from the field site. Strategies are being developed to attack source areas by injection of the microorganism at multiple locations.

Key words: aerobic, bioremediation, injection well, glucose