Bioremediation of diesel oil-contaminated soil using native hydrocarbon-degrading bacterial strains under microcosm study.

In gas stations, leaks occur as a result of fuel supply, storage and transport. These leaks are particularly expensive to remediate if site closure is required for conventional ex situ treatments. Here, we evaluated the effectiveness of soil decontamination by less costly techniques of ‘bioremediation’, which can be performed in situ. We compared natural attenuation (i.e., maintaining soil hydration) with ‘successive biostimulation’ (nutrient addition) alone or combined with ‘successive bioaugmentation’ of contaminated soil via the addition of degradative microorganisms. Initially, 34 bacterial strains were isolated from soil with historical diesel contamination removed from a gas station in southern Brazil. A group of 5 strains was then selected to form the ‘consortium’used in bioremediation experiments, based on diesel oil (B5) biodegrading ability (measured using tetrazolium chloride reduction), biosurfactant production (rhamnolipid quantification and emulsification index) and species identification (16S rRNA sequencing).CO2 evolution demonstrated no significant difference in soil microbial activity between treatments. The increase in the heterotrophic microorganism population in contaminated soil was not altered by any of the bioremediation strategies, while the population of degrading microorganisms increased in all treatments. The degradation of hydrocarbons was monitored by analysis total petroleum hydrocarbon (TPH). Within the experimental period of 60 days, the initial TPH concentration in the contaminated soil (133 mg kg soil-1) was reduced by 84% via natural attenuation, 90% by bioaugmentation/biostimulation, and 91% by biostimulation alone, showing that the treatments displayed positive effects on biodegradation, with a substantial reduction in TPH levels.