Bioremediation Technologies for
Decontamination of Chlorinated Organics and Petroleum-Impacted Sites
Donald E. Damschen Dr. Lee Chee Chow
Christine P.C. Lim
Bioremediation uses naturally occurring microorganisms to degrade
various types of wastes. Like all living creatures, microbes need
nutrients, carbon, and energy to survive and multiply. Such organisms
are capable of breaking down organic contaminants to obtain food and
energy, typically degrading them into simple organic compounds, carbon
dioxide, water, salts, and other harmless substances. This technology
has been proven to work on diverse waste streams, especially petroleum
hydrocarbons, and more recently on recalcitrant chlorinated solvents.
Bioremediation has been shown to be an efficient and cost-effective
treatment method for the cleanup of contaminated soils. As such, it has
become one of the most promising technologies to consider in remediating
contaminated sites in North America. In this paper, we highlight three
different decontamination studies in North America that successfully
used bioremediation to reduce petroleum hydrocarbon and chlorinated
solvent concentrations to acceptable regulatory levels.
Petroleum Hydrocarbon Site: A former #6 fuel oil underground storage
tank existed at a Central California winery, located in a desert
climate. The fuel oil was used in the boiler operation at the winery.
Over time, the fuel oil leaked through the wooden storage tank.
Approximately 6,000 cubic yards of contaminated soil were impacted. The
soil was excavated, removed and spread out on an adjacent 4-acre field.
Twelve treatment cells were marked and constructed, each containing 500
cubic yards of soil one foot deep.
After treatment cell construction, soil sampling and chemical
analysis was conducted to determine the initial petroleum-hydrocarbon
concentration, pH, and moisture content.
Chlorinated Solvent Sites:
MATERIALS & METHODS
Petroleum Hydrocarbon Site: Soil samples were collected and analyzed
using standard methods and State of California certified laboratories.
Petroleum hydrocarbon concentrations were determined using EPA Methods
418.1 and 8015M (diesel standard). Moisture contents and pH were
determined using Methods D2216-92 and 9045, respectively. Toxicity
Characteristic Leaching Procedure (TCLP) analyses were determined using
State of California Leaking Underground Fuel Tank Field Manual methods.
BioWorld Waste Treatment products consisting of bioenhancement liquid
nutrients, vitamins, minerals and other compounds and selected,
naturally occurring hydrocarbon digesting microorganisms were added to a
4,000 gallon water truck and evenly applied to the treatment cells. This
procedure was repeated on a monthly basis during three summer months.
Mechanical discing of the cells was conducted to provide soil mixing and
aeration. Water was added to maintain reasonable moisture content in the
Chlorinated Solvent Sites:
RESULTS & DISCUSSION
Petroleum Hydrocarbon Site: The contaminated soil consisted primarily
of sandy loam. Initial petroleum hydrocarbon concentrations in the cells
ranged from 2,260 to 4,680 mg/kg or parts per million (ppm) with an
average of 3,200mg/kg (ppm). Initial moisture content and pH were 9.3%
and 8.0, respectively.
After 1 month of treatment and prior to the second scheduled
treatment, soil sampling and chemical analysis was conducted. The
petroleum hydrocarbon concentration in the cells ranged from 940 to
2,600 mg/kg with an average of 1,820 mg/kg, or a 43%
Additional treatments, soil sampling, and chemical analysis indicated
steady reduction in the total petroleum hydrocarbon (TPH) concentration.
After 11 months the average TPH concentration was reduced to
approximately 125 ppm. The target level for closure was 100 ppm.
This is shown graphically in Figure 1.
When breaking down long-chain petroleum hydrocarbons using
bioremediation, problems with recalcitrant organics can occur. We
encountered interference with the infrared method (418.1) for
determining the TPH concentrations. This method is non-specific for
petroleum hydrocarbons since it measures the absorbance of the
carbon-hydrogen stretch. Any compound containing carbon-hydrogen bonds,
such as fatty acids and other break down products, will be included in
the 418.1 analysis. To overcome this challenge, the gas
chromatography-flame ionization detector (GC-FID) method (8015M) was
used with diesel fuel as the standard. This gave better resolution since
peak heights could be directly viewed and measured.
Using the GC-FID method, the analyses indicated a broad hump of
unresolved substances at the end of the diesel range. This generally
occurred at a carbon chain length of 25 or greater. These residues
appeared to be stable, non-reactive, non-water soluble and
non-biodegradable. Since the final TPH concentrations measured were
slightly higher than the target level for closure, the question arose as
to whether the residual substances remaining represented an
environmentally acceptable endpoint. In order to answer this question,
the leachability potential of the residual soil material was evaluated.
Toxicity Characteristic Leaching Procedure (TCLP) extractions and
analyses were completed to simulate the addition of winery wastewater to
the residual soils.
The TCLP results indicated that 0.8 to 1.7% of the TPH as Diesel
present in the soil had the potential to leach out by using aggressive
extraction methods. These results agree favorably with the extensive
research indicated in the Gas Research Institute report. Effective
bioremediation can reduce hydrocarbon concentrations to levels where
they no longer pose a threat to human health or the environment. Based
on these findings, the regulatory agencies granted closure of the site.
Chlorinated Solvent Sites:
US EPA, Understanding
Bioremediation, EPA/540/2-91/002, February 1991.
US EPA, Bioremediation:
Innovative Pollution and Treatment Technology, EPA/640/K-93/002,
"Bioremediation on a Big Scale", Environmental Protection,
July 1995, pp. 15-16.
State of California Department
of Health Services, "Biological Remediation of a Fuel
Contaminated Soil Site in Carson, California", March 1990.
Hardy, John J., and Mabbula,
Sunand, "Close a Site for $3,000", Soils, March 1994, pp.
Baker, Katherine H. and Herson,
Diane S., Bioremediation, McGraw-Hill Inc., 1994.
State of California Water
Resources Control Board, Leaking Underground Fuel Tank Field Manual,
Gas Research Institute,
"Environmentally Acceptable Endpoints in Soil - Draft
Report", April 1995.
1. FUEL OIL BIOREMEDIATION RESULTS
PETROLEUM HYDROCARBON CONCENTRATIONS
(All concentrations are
mg/kg or ppm)