Application of Bioremediation Techniques for Petroleum-Contaminated Soils in Imo State, South East Nigeria

Petroleum hydrocarbon contamination from pipeline leaks and illegal oil processing in Imo State has degraded agricultural soils across communities in the state's oil-producing areas. This study evaluated the effectiveness of bioremediation techniques in restoring total petroleum hydrocarbon concentrations to acceptable levels in contaminated soils collected from three affected communities. Four treatment approaches were compared in a randomised field plot design: natural attenuation, biostimulation with nitrogen and phosphorus amendments, bioaugmentation with a locally isolated hydrocarbon-degrading bacterial consortium, and a combined biostimulation plus bioaugmentation treatment. Soil total petroleum hydrocarbon concentrations were monitored at two-week intervals over twelve weeks. Soil microbial community structure, dehydrogenase activity, and plant phytotoxicity tests using cowpea seedlings were used as supplementary indicators of remediation progress. Results showed the combined biostimulation plus bioaugmentation treatment achieved the greatest reduction in total petroleum hydrocarbons, reaching 76 percent removal efficiency by week twelve. Natural attenuation alone achieved only 28 percent reduction. Dehydrogenase activity increased progressively in all treated plots, with highest activity in the combined treatment. Cowpea germination trials confirmed reduced phytotoxicity in remediated soils. The study demonstrates the practical utility of combined bioremediation approaches for oil-contaminated soils in South East Nigeria and recommends development of a standardised bioremediation protocol for application by state environmental agencies following spill incidents. Keywords: bioremediation, petroleum contamination, Imo State, bioaugmentation, soil restoration.