Investigating the Efficacy of Bioremediation Techniques for Crude Oil Contaminated Soils in the Niger Delta Under Field Conditions

This study investigates the efficacy of bioremediation techniques for treating crude oil contaminated soils in the Niger Delta under actual field conditions, comparing biostimulation, bioaugmentation with indigenous hydrocarbon-degrading microbial consortia, and combined approaches against a natural attenuation control in a controlled field trial at a remediation site in Rivers State, South South Nigeria. Laboratory-scale bioremediation studies have produced encouraging results for Nigerian crude oil degradation, but field-scale performance under the complex and variable conditions of actual contaminated sites has not been adequately characterised. A field trial plot was established at a site contaminated to a total petroleum hydrocarbon concentration of 15,000 to 22,000 milligrams per kilogram, divided into treatment and control plots of two-square-metre area each. Biostimulation treatments comprised regular addition of nitrogen and phosphorus nutrients to promote indigenous microbial activity. Bioaugmentation used an enriched culture of locally isolated Pseudomonas, Bacillus, and Rhodotorula species confirmed as petroleum degraders. Soil samples were collected monthly for twelve months and analysed for total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, and microbial population counts. Results show that the combined biostimulation and bioaugmentation approach achieves 71 percent TPH reduction over twelve months, significantly outperforming biostimulation alone at 52 percent and bioaugmentation alone at 49 percent. Natural attenuation achieves only 18 percent reduction in the same period. PAH degradation rates are lower across all treatments. Residual contamination levels remain above agricultural reuse standards at twelve months. Keywords: bioremediation, petroleum hydrocarbon, crude oil contamination, Niger Delta, field trial.