امكان‌سنجي تصفيه زيستي خاك آلوده‌ي پالايشگاه نفت اصفهان

Soil contamination caused by oil refinery activities is one of the major environmental challenges in oil-rich regions. The main objective of this study was to eva‎luate the feasibility of bioremediation of refinery-contaminated soil containing total petroleum hydrocarbons (TPH) using indigenous bacteria. Accordingly, samples were collected from contaminated refinery soil, an‎d after enrichment in Bushnell–Haas mineral medium containing crude oil, 20 bacterial isolates were obtained. Based on preliminary screening for growth in the presence of oil an‎d TPH reduction—measured via dichloromethane extraction an‎d spectrophotometry at 240 nm—two isolates, numbers 1 an‎d 19, were selec‎ted as the most efficient strains. These isolates were identified through 16S rDNA gene sequencing as Bacillus atrophaeus IRP1 (accession number PX735861) an‎d Bacillus paramycoides IRP19 (accession number PX735862), respectively. Spectrophotometric analysis at 240 nm in aqueous media showed that both isolates individually degraded about 90–92% of TPH within 136 hours. When co-cultured, the degradation efficiency exceeded 95%, indicating a positive synergistic effect between the two isolates. Extraction of petroleum compounds from the slurry system containing real contaminated soil using dichloromethane (1:1 ratio) showed similar results to those observed in the aqueous medium; the bacterial consortium reduced more than 95% of TPH after 96 hours of active growth. GC–MS analysis of hydrocarbon degradation revealed that B. paramycoides IRP19 degraded up to 66% of certain oil components after 5 days of incubation. This strain also degraded more than 50% of two-, four-, an‎d five-carbon hydrocarbons. B. atrophaeus IRP1 degraded 61% of C₆H₁₂ after 5 days, while C₂H₈, C₃H₂, C₄H₃, an‎d C₅H₁₀ were degraded by 49%, 55%, 46%, an‎d 40%, respectively. Biosurfactant production tests including dro‎p-collapse, E24, hemolysis, an‎d CTAB methylene blue assays showed that B. paramycoides IRP19 exhibited strong biosurfactant production with good emulsification activity, whereas B. atrophaeus IRP1 displayed weaker activity. Overall, the results demonstrate that the native bacterial consortium composed of B. atrophaeus IRP1 an‎d B. paramycoides IRP19 possesses excellent potential for the bioremediation of refinery soils contaminated with heavy hydrocarbons an‎d can serve as a basis for future pilot-scale field studies.

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