A bench-scale aerobic microbial degradation study of soil contaminated with Saudi Arabian crude oil was conducted. The effects of nutrient additions and seeding with naturally-occurring microorganisms were evaluated, through comparison of results from a control reactor, a second reactor with nutrients, and a third reactor with nutrients and seed microorganisms. A separate weathering experiment was conducted under identical environmental conditions for evaluation of abiotic weathering losses of crude oil.
The total petroleum hydrocarbon (TPH) content of soil contaminated with crude oil was measured as a function of time. During the five-week evaluation period, a TPH reduction of 60 to 70% was observed for the nutrient evaluation. Based on the weathering tests, approximately 17% of the TPH loss was attributed to abiotic losses.
For the specific environmental conditions, crude oil, seawater, and soil evaluated, the addition of nutrients stimulated the biodegradation of crude oil over the test period. Due to the availability of indigenous bacteria, seeding with naturally-occurring bacteria did not improve the rate of TPH loss.
The role of microorganisms in the degradation of organic materials is well established. Both natural and engineered in situ biodegradation processes play a significant role in alleviating environmental problems associated with organic pollution. In spite of this confidence, the in situ biodegradation of certain organic contaminants is difficult to verify due to the relative degree of both microbiological and abiotic contributions to contaminant loss. This problem is of particular concern when considering appropriate remediation and impacts of accidental crude oil spills.
This research focused on bench-scale laboratory studies to evaluate the interaction of a selected imported crude oil with the seawater and soil conditions representative of the Gulf of Mexico shoreline. Due to declining supplies and production of domestic crude oil, foreign crude is imported into the U.S. in increasing volumes to meet energy demand (Beck, 1992). This work focused on imported crude oil due to the magnitude of current crude oil volumes imported into the United States via super tankers. The specific objectives of the study were to evaluate the in situ biodegradation of crude oil in soil under controlled aerobic conditions. Additional tests were conducted to evaluate abiotic weathering of the crude oil, which measured volume, mass, and compositional changes caused by environmental exposure, but unrelated to biological activity. The study was not a case history of any accidental crude oil release or environmental contamination.