Bacterial degradation of crude oil using solid formulations of bacillus strains isolated from oil-contaminated soil towards microbial enhanced oil recovery application

Abstract

Microbial enhanced oil recovery has played a major role in enhancing crude oil recovery from depleted oil reservoirs to solve stagnant petroleum production. Most studies have focused on the use of bacteria by liquid-state fermentation, with less attention paid to solid-state fermentation. Here, we examined the efficiency of crude oil degradation using solid formulations of Bacillus strains and evaluated their feasibility for application in enhanced oil recovery. Three Bacillus strains, namely B. atrophaeus 5-2a, B. aryabhattai 6-2a and B. amyloliquefaciens 6-2c, were isolated from oil-contaminated soil samples. Two strains, 5-2a and 6-2c, secreted extracellular biosurfactants with excellent oil-displacing and emulsifying activity; their diameter of clear zone and emulsification index were 19.7–20.1 cm and 56.6–61.1%, respectively. Three bacterial formulations demonstrated high efficiency to degrade resins (max 24.18%) and asphaltene (max 56.17%), and they decreased the viscosity of crude oil to varying degrees at 40 °C (max 26.47%). The associated CO₂ and H₂ production was 33.0–36.2 mmol L⁻¹ and 61.8–68.0 mmol L⁻¹, respectively, and acid production was 1410–1560 mg L⁻¹. Bacterial formulations removed 82.32–94.50% of crude oil adsorbed on filter paper in 4 d at 40 °C. The results indicate that the three bacterial formulations are efficient in degrading and removing crude oil.