Bioremediation Efficacy of Hydrocarbon-Degrading Bacteria in Crude Oil-Contaminated Soils of Rivers State, South South Nigeria

This study evaluates the bioremediation efficacy of indigenous hydrocarbon-degrading bacteria in reducing total petroleum hydrocarbon levels in crude oil-contaminated soils of Rivers State, located in Nigeria's South South geopolitical zone. Biological remediation using indigenous microbial communities represents the most environmentally sustainable approach for managing the pervasive crude oil contamination affecting agricultural and wetland soils in the Niger Delta, yet controlled bioremediation experiments with quantitative performance data from Rivers State soils are limited. Using a controlled field microcosm design, 12 experimental bioremediation plots of 4 by 4 metres were established on contaminated farm soils in Ogba-Egbema-Ndoni local government area. Three bioremediation treatments (biostimulation with NPK nutrients, bioaugmentation with an enriched hydrocarbon-degrader consortium, and combined biostimulation plus bioaugmentation) were compared against an unmanipulated contaminated control and an uncontaminated reference. Total petroleum hydrocarbon (TPH), polycyclic aromatic hydrocarbon (PAH), and bacterial population monitoring were conducted at 30, 60, 90, and 120 days. Soil toxicity was assessed by earthworm avoidance bioassay at each sampling point. Findings revealed that combined biostimulation plus bioaugmentation achieved the greatest TPH reduction (74% in 120 days), compared to biostimulation alone (58%) and bioaugmentation alone (42%). PAH reduction paralleled TPH trends. Earthworm avoidance was significantly reduced in treated plots by day 90, indicating measurable toxicity reduction. Hydrocarbon-degrader counts peaked at 30 days in augmented plots before stabilising. The study recommends combined bioremediation as the preferred approach for Rivers State petroleum-contaminated farmland restoration. Keywords: bioremediation, crude oil, hydrocarbon-degrading bacteria, Rivers State, TPH.