Bioremediation of soils saturated with spilled crude oil

Abstract

A desert soil sample was saturated with crude oil (17.3%, w/w) and aliquots were diluted to different extents with either pristine desert or garden soils. Heaps of all samples were exposed to outdoor conditions through six months, and were repeatedly irrigated with water and mixed thoroughly. Quantitative determination of the residual oil in the samples revealed that oil-bioremediation in the undiluted heaps was nearly as equally effective as in the diluted ones. One month after starting the experiment. 53 to 63% of oil was removed. During the subsequent five months, 14 to 24% of the oil continued to be consumed. The dynamics of the hydrocarbonoclastic bacterial communities in the heaps was monitored. The highest numbers of those organisms coordinated chronologically with the maximum oil-removal. Out of the identified bacterial species, those affiliated with the genera Nocardioides (especially N. deserti), Dietzia (especially D. papillomatosis), Microbacterium, Micrococcus, Arthrobacter, Pseudomonas, Cellulomonas, Gordonia and others were main contributors to the oil-consumption. Some species, e.g. D. papillomatosis were minor community constituents at time zero but they prevailed at later phases. Most isolates tolerated up to 20% oil, and D. papillomatosis showed the maximum tolerance compared with all the other studied isolates. It was concluded that even in oil-saturated soil, self-cleaning proceeds at a normal rate. When pristine soil receives spilled oil, indigenous microorganisms suitable for dealing with the prevailing oil-concentrations become enriched and involved in oil-biodegradation.

Figure 1

Dynamics of hydrocarbonoclastic microbial communities in the oil-saturated soil (OSS) and OSS diluted (with pristine desert soil: I, 1 kg OSS + 0.25 kg; II, 1 kg OSS + 0.5 kg; III, 1 kg OSS + 0.75 kg) during bioremediation. Shaded areas contain all the bacterial strains with ≤2% occurrence. For minor organisms in the shaded areas, refer to Supplementary Table S2.

Figure 2

Dynamics of hydrocarbonoclastic microbial communities in the oil-saturated soil (OSS) and OSS diluted (with pristine garden soil: I, 1 kg OSS + 0.25 kg; II, 1 kg OSS + 0.5 kg; III, 1 kg OSS + 0.75 kg) during bioremediation. Shaded areas contain all the bacterial strains with ≤2% occurrence. For minor organisms in the shaded areas, refer to Supplementary Table S2.

Figure 3

Oil-tolerance of 17 hydrocarbonoclastic isolates. (A) strains with highest tolerance; (B) strains with less tolerance.