Bioremediation of petroleum pollutants

Abstract

Hydrocarbon-degrading microorganisms are ubiquitously distributed in soil and aquatic environments. Populations of hydrocarbon-degraders normally constitute less than 1% of the total microbial communities, but when oil pollutants are present these hydrocarbon-degrading populations increase, typically to 10% of the community. With regard to rates of natural degradation, these typically have been found to be low and limited by environmental factors. Rates reported for pristine marine waters typically are less than 0·03 g/m 3/day. In adapted communities rates of hydrocarbon degradation of 0·5–50 g/m 3/day have been reported. Bioremediation tries to raise the rates of degradation found naturally to significantly higher rates. The two general approaches that have been tested for the bioremediation of marine oil spills are the application of fertilizer to enhance the abilities of the indigenous hydrocarbon-utilizing bacteria and the addition of naturally occurring adapted microbial hydrocarbon-degraders by seeding. Bioremediation, accomplished by the application of fertilizer to enhance the abilities of the indigenous hydrocarbon-utilizing bacteria, was successfully applied for the treatment of the 1989 Alaskan oil spill in Prince William Sound, Alaska. Seeding with adapted nonindigenous microbial hydrocarbon degraders was tested on smaller spills in Texas—such as the Mega Borg spill—but bioremediation to remove petroleum pollutants by seeding has yet to be demonstrated as efficacious in field trials. The spill of more than 200,000 barrels of crude oil from the oil tanker Exxon Valdez in Prince William Sound, Alaska, as well as smaller spills in Texas—such as the Mega Borg spill—have been treated by bioremediation to remove petroleum pollutants. The Exxon Valdez spill formed the basis for a major study on bioremediation through fertilizer application and the largest application of this emerging technology. Three types of nutrient supplementation were tested: water-soluble (23:2 N:P garden fertilizer formulation): slow-release (Customblen); and oleophilic (Inipol EAP 22). Each fertilizer was tested in laboratory simulations and in field demonstration plots to determine the efficacy of nutrient supplementation. The use of Inipol EAP22 (oleophilic microemulsion with urea as a nitrogen source, laureth phosphate as a phosphate source, and oleic acid as a carbon source) and Customblen (slow-release calcium phosphate, ammonium phosphate, and ammonium nitrate within a polymerized vegetable oil coating) was approved for shoreline treatment and was used as a major part of the cleanup effort. Multiple regression models showed that nitrogen applications were effective in stimulating the rates of biodegradation.