Remediation of Crude Oil-Contaminated Soils Using Biochar-Amended Biostimulation: A Field Trial in Bayelsa State

Biostimulation with nutrient amendments and biochar co-application is a promising combined strategy for accelerating petroleum hydrocarbon degradation in contaminated soils, yet field-scale validation under Niger Delta conditions is lacking. This study evaluates the effectiveness of biochar-amended biostimulation for remediating crude oil-contaminated soils through a controlled field trial at a decommissioned spill site in Bayelsa State, South South Nigeria. Six treatment plots were established: control, nutrient-only biostimulation, low-dose biochar alone, high-dose biochar alone, biochar with biostimulation at low nutrient dose, and biochar with biostimulation at high nutrient dose. Sugarcane bagasse biochar was produced at 500 degrees Celsius and characterised before application. Total petroleum hydrocarbons, alkane fractions, soil microbial biomass carbon, dehydrogenase enzyme activity, and basic soil properties were monitored at 0, 45, 90, and 180 days. Results show that the combined high-dose biochar and high-nutrient biostimulation treatment achieved the greatest total petroleum hydrocarbon reduction of 76 percent over 180 days, significantly outperforming all other treatments. Dehydrogenase activity, a proxy for overall microbial metabolic activity, was highest in biochar-amended plots, suggesting that biochar's porous structure enhanced microbial habitat. Linear alkane degradation was essentially complete in biochar-biostimulation plots. Soil pH stabilisation and improved soil structure were documented as co-benefits of biochar addition. The field trial provides evidence for scaling biochar-biostimulation as a community-deployable remediation strategy for the Niger Delta. Keywords: biostimulation, biochar, crude oil, soil remediation, Bayelsa State