RENA of Oil-Contaminated Soils in Nigeria

Bioremediation has been used to clean up hundreds of oil spill sites in Nigeria that were contaminated as a result of oil exploration and oil production operations (20). The cleanup, which began in 1999, was developed and performed by Shell Petroleum Development Company of Nigeria. The company's preferred approach for soil and groundwater remediation programs is known as remedial enhanced natural attenuation (RENA). Liquid sludge is removed for ex situ treatment, and the residual hydrocarbon is bioremed-iated in situ. Application of the RENA process for remediation of hydrocarbon-impacted soil accelerates the natural process by using human intervention to increase access to water, sunlight, oxygen, and nutrients, i.e., in situ bioremediation based upon biostimulation of the indigenous microorganisms. The intervention involves simple tilling of the impacted soils, which aerates the soil and ensures adequate oxy gen to support aerobic hydrocarbon biodégradation. It also involves occasional addition of nutrients, water, and sometimes topsoil. These actions increase the microbial population that biodegrades petroleum hydrocarbons and provides optimized conditions for hydrocarbon metabolism by the indigenous microbial communities. Shell reports that the use of RENA is cost-effective and restores the soils and groundwaters to preoiling conditions. RENA is viewed as an environmentally friendly and natural process that has gained acceptance in the communities where it is carried out. It is simple and can be performed by local people, which aids in its acceptance. It is well suited for the tropical climate of the Niger Delta, where soils have diverse microbial populations, including naturally occurring hydrocarbon-degrading microorganisms, warm temperatures, and abundant rainfall.

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