Efficient bioremediation of crude oil contaminated soil by a consortium of in-situ biosurfactant producing hydrocarbon-degraders

Abstract

Soil contamination by crude oil is a common occurrence during accidental spills, transportation, or refining processes. Bioremediation as an environmentally friendly and cost-effective approach is interesting for treating hydrocarbon-contaminated sites via natural microorganisms to break down or transform the hydrocarbons into less toxic substances. However, the bioremediation process is time-consuming due to the low accessibility of cells to hydrocarbon contaminants in soil. Applying hydrocarbon degraders with the capability to produce biosurfactants during the hydrocarbon degradation pathways could significantly handle the problem. In this study, a bacterial consortium consists Roseomonas aestuarii, Pseudomonas oryzihabitans, Pantoea agglomerans, and Arthrobacter sp. was evaluated for crude oil removal from the aqueous environment and soil microcosm. To examine the effect of supplementary biosurfactants in the bioremediation process, surfactin and rhamnolipid (ratio 1:1) were used at a concentration of 1000 ppm. Our findings indicate the consortium has high potential in removing saturated hydrocarbons from aqueous (removal yield = 96.16% after 9 days) and soil (removal yield = 64.65% after 120 days) environments. The consortium had a significantly higher removal efficiency than the single-cell treatments, possibly due to the species' synergistic effect. The GC-MS analysis confirmed a uniform removal of different molecular weight hydrocarbons by the consortium from soil. However, adding supplementary biosurfactants showed a slight modification in the consortium's performance after 120 days in soil microcosms (removal yield for saturated hydrocarbons was 65.97%). This study showed the potential application of this in-situ producing biosurfactant consortium for bioremediation purposes.

Keywords: Bioavailability; Bioremediation; Soil microcosm; Surfactin. Rhamnolipids; Synergistic effects.

Fig. 1

Residual of crude oil during the biodegradation processes in aqueous environment. Uninoculated Erlenmeyer flasks are considered as control. BS: Treatments supplemented with 1% of the isolated biosurfactants at a concentration of 1000 ppm.

Fig. 2

Biodegradation yield of crude oil from aqueous environment by degrading bacteria after incubation at 28 ± 0.5 °C and 150 rpm for 3 days (A), 6 days (B), and 9 days (C). Uninoculated Erlenmeyer flasks are considered as control. BS: treatments supplemented with 1% of the isolated biosurfactants at a concentration of 1000 ppm. Duncan’s multiple range test was used to compare the means with a P < 0.05. The difference between means with common letters is not statistically significant.

Fig. 3

Biodegradation rate of crude oil from aqueous environment by degrading bacteria after incubation at 28 ± 0.5 °C and 150 rpm for 3 days (A), 6 days (B), and 9 days (C). Uninoculated Erlenmeyer flasks are considered as control. BS: treatments supplemented with 1% of the isolated biosurfactants at a concentration of 1000 ppm. Duncan’s multiple range test was used to compare the means with a P < 0.05. The difference between means with common letters is not statistically significant.

Fig. 4

Temporal variation of TPH during the bioremediation process in soil microcosms. Un-inoculated Erlenmeyer flasks are considered as control. BS: Treatment supplemented with 1% of the biosurfactants.

Fig. 5

Biodegradation yield and rate of crude oil by bacterial consortium after incubation in soil microcosms at greenhouse conditions for 30, 60, 90, and 120 days. Uninoculated soil microcosms are considered as controls. BS: treatments supplemented with isolated biosurfactants at a concentration of 1000 ppm. Duncan’s multiple range test was used to compare the means with a P < 0.05. The difference between means with common letters is not statistically significant.

Fig. 6

Chromatograms of the remaining saturated hydrocarbons in the soil environment after 120 days of treatment. Control (a), Consortium (b), and Consortium & BS (c). Also, the representative pot samples from the soil microcosms are presented.