Optimization of in situ Hydrocarbon Bioremediation Protocols
Client: Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS
Project Size: $500,000
Duration: 4 years
The chemical composition of crude oil and even of refined petroleum includes hundreds
of different alkanes and aromatic hydrocarbons. Among these are the polycyclic aromatic
hydrocarbons (PAHs), which are known carcinogens. While large oil spills from ships
dramatically illustrate the disastrous effects of oil on ecosystems, the largest number
of spills occur during refueling in port and far more oil enters the environment from
terrestrial spills and run-off, with chronic effects on ecosystems and serious threats
to fresh water supplies and human health. Excavation and relocation of contaminated soils
and sediments, while inadequate, is all-to-frequently the remedial action of choice.
Alternatively, the bioremediation of petroleum compounds can occur through the diverse
of enzymatic activities within bacterial populations. These biocatalysts are ubiquitous
in the environment and their level rapidly increases in the presence of petroleum
contamination. However, complex interactions of environmental and biological factors
influence the rate and extent of hydrocarbon biodegradation by these microbial communities.
The objective of the work performed in this project was to identify the key parameters
affecting the biodegradation of hydrocarbons within a particular microcosm such that
more effective remediation is achieved.
The low aqueous solubility of PAHs and the resulting low bioavailability are
thought to significantly contribute to their persistence in the environment. The addition
of surfactants to contaminated soils has, in some cases, increased the rate and degree of
biodegradation of PAHs. The in situ production of biosurfactants offers several advantages
to the addition of chemical surfactants. Culture supernatants of a native bacterial strain
known to produce a rhamnolipid biosurfactant increases the concentrations of PAHs in aqueous
extracts of creosote-contaminated soil. A protocol for inoculating contaminated soils with
this bacterial strain and enriching the soil with a slow-release fertilizer has been developed.
This protocol was effective in establishing the surfactant-producing bacteria in microcosms
containing contaminated soil (from Popile, Arkansas) for more than 6 months despite high
levels of PCP, a wood preservative that is highly toxic to most bacteria. Augmenting the
autochthonous bacterial community in Popile soil samples with the surfactant-producing
bacterium resulted in increases in PAH concentrations in aqueous extracts of the soil.
Soil inoculated with this bacterium and fertilized with dried blood (an established
organic fertilizer) showed decreased concentrations of many PAHs relative to fertilized
but non-inoculated soil samples. After seven months of treatment, mean concentration of
several PAHs were significantly reduced by the following percentages: acenaphthene, 91%;
fluorene, 94%; phenanthrene, 98%; anthracene, 61%; fluoranthene, 60%; pyrene, 15%; benz[a]anthracene,
26%; chrysene, 63%.