In Situ Bioremediation
- Laboratory testing of microbial culture MC-100 (previously referred to as BC-4) under anoxic conditions and oxygenated conditions in soils augmented with specific ether degraders
- Field test using a MC-100 microbial consortium grown with MTBE as the sole carbon source; specific MTBE removal rate of 20-30 mg/gm cells/hr; injected into test plots located within the MTBE plume; test plots were 20 ft wide and 40 ft long
- On-site oxygen generating system (Air-Aep AS-80 pressure swing adsorption system); intermittent oxygen sparging using a total of 1700L gas delivered to each plot from 4-8 times/day (started six weeks prior to MC-100 seeding to increase levels of DO in groundwater)
- Monitoring wells were screened over 5-ft intervals - 10-15 ft bgs for shallow wells; 15-20 ft bgs for deep wells
Joseph P. Salanitro
Westhollow Technology Center
3333 S. Highway 6 (P.O. Box 1380)
Houston, TX 77251-1380
Telephone: (281) 544-7552
Fax: (281) 544-8727
Paul C. Johnson
Arizona State University
Engineering Center, G-wing, Room 252
Tempe, AZ 85287-5306
Telephone: (480) 965-9115
Fax: (480) 965-0557
MTBE and TBA
- MTBE concentrations ranged from 2,000-8,000 ug/L; plume 4,000 feet (ft) long and 400 ft wide
- TBA concentrations ranged from 50-250 ug/L
Leaks from gasoline storage tanks
Purpose/Significance of Application:
Laboratory and field testing of in situ bioremediation using MC-100 to treat MTBE in groundwater
Regulatory Requirements/Cleanup Goals:
Field experiments were designed to implant high densities of MC-100 in an oxygenated biobarrier and to compare the results with those for an oxygenated zone and a control zone
- Cleanup goals for MTBE and TBA are 5 and 10-15 ug/L, respectively, as stated in State of California MCL directives.
- Addition of MC-100 (50 mg cells/L groundwater) reduced MTBE to non-detectable levels within two weeks
- Microcosms prepared with soil and oxygenated groundwater from the Port Hueneme site containing gasoline (700 mg/L) also degraded MTBE (70-80 mg/L) and BTEX (45 mg/L) to non-detect levels in 16 weeks when seeded with MC-100 at 50 and 250 mg cells/kg soil.
- DO levels in target treatment zones increased from <1 mg/L to >10 mg/L - >20 mg/L
- Oxygen plus MC-100 plot reduced concentrations of MTBE from 1,000 ug/L to < 1 ug/L and TBA from 50-250 ug/L to <10 ug/L; oxygen-only plot reduced MTBE concentrations to 10 ug/L (where DO was about 20 mg/L), but TBA was not degraded; in the control plot, the concentration of MTBE remained at approximately 1 mg/L; no TBA data were provided
Full-scale costs for in situ bioremediation of MTBE using the oxygenated biobarrier was projected by the technology provider to be about $150,000, depending on site-specific conditions.
From 1984-1985, several thousand gallons of leaded gasoline containing MTBE were released from storage tanks at the Naval exchange (NEX) gasoline station of the naval base at Port Hueneme, California, resulting in MTBE and BTEX plumes. Laboratory and field experiments of in situ bioremediation using addition of oxygen and the MC-100 culture were conducted at Port Hueneme. The MC-100 culture, which is part of the patented "BioRemedy" process developed at the Westhollow Technology Center, is marketed by Shell Global Solutions. Equilon Enterprises LLC designs and implements the process, which is expected to be commercially available in early 2000.
Laboratory testing indicated that MTBE and BTEX could be degraded with oxygen in soils augmented with MC-100. For the field tests, the DO levels in the aquifer were increased from <1 mg/L to between 10 and 20 mg/L, prior to the addition of MC-100. Results showed that the oxygen plus MC-100 reduced MTBE and TBA concentrations to < 1 ug/L and < 10 ug/L, respectively. The in situ bioremediation of MTBE using the oxygenated biobarrier was estimated by the technology provider to cost about $150,000 for a full-scale application, depending on site-specific conditions. According to the technology provider, inoculation of subsoils with specific MTBE-degraders and maintaining adequate oxygenation of the aquifer will enhance MTBE biodegradation in situ and control the MTBE plume mass from reaching potential downstream receptors. Additional benefits of inoculated barriers over oxygen-only sparged aquifers is that MTBE-degraders may not be present in many aquifers or are present in insufficient numbers to sustain MTBE degradation in plumes over long periods.