AthenaES™ Projects
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%.
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