Bioremediation of Oil-Contaminated Soils by Stimulating Indigenous Microbes

Abstract

Abstract Two oil-contaminated sites were bioremediated by stimulating indigenous microbes by tilling, liming, and fertilizing; the hydrocarbon contents were reduced by 84% in 7 weeks at one site and by 83% in 56 weeks at the other site. The process was monitored by measuring the most probable number (MPN) of oil-degrading microbes and the total petroleum hydrocarbon (TPH) concentration in soils. Bioremediation occurred at MPNs of 105 to 106 cells g−1 soil, mean water-holding capacities of 54–82% and mean soil pH values of 4.75–5.97. The initial control TPH concentrations remained unchanged at the end of the study at both sites. Bioremediation was not required at depths greater than 6 in except at one location; tilling at 18 in was necessary and remediation took 19 weeks longer than the surface remediation of 56 weeks. As revealed by gas chromatographic analyses of soil extracts before and after bioremediation, the diversity and amounts of hydrocarbons were substantially reduced during bioremediation. There were 10 oil-degrading bacteria isolated from the sites, representing the following genera: Alcaligenes, Actinomyces, Bacillus, Citrobacter, Corynebacterium, Enterobacter, and Pseudomonas.