BIOREMEDIATION POTENTIAL OF INDIGENOUS MICROORGANISMS IN HYDROCARBON CONTAMINATED SOILS OF NIGER-DELTA, NIGERIA

Abstract

Hydrocarbon contamination from long-term petroleum exploration has resulted in significant soil degradation in the Niger Delta region, Nigeria, latitudes 4°10′ to 6°20′ North and longitudes 2°35′ to 7°30′ East of the Equator. This study evaluated the biodegradation potential of indigenous microbial communities in contaminated soils of the region. Soil samples were collected from five petroleum-impacted sites showing high contamination levels, with Total Petroleum Hydrocarbon (TPH) concentrations ranging from 6,970 to 9,861 mg/kg, exceeding regulatory limits. Laboratory microcosm experiments were conducted over 60 days under four treatment conditions: Natural Attenuation (NA), Bio-stimulation (BS), Bio Augmentation (BA), and a combined Bio-stimulation–Bio-Augmentation (BS + BA) approach. Biodegradation performance was monitored using microbial counts, soil respiration (CO₂ evolution), and TPH reduction. Hydrocarbon utilizing bacteria increased from approximately 5.95 to 7.50 log₁₀ CFU/g in the combined treatment, indicating strong microbial adaptation and activity. The highest TPH removal efficiency of 83.8% was achieved under combined treatment with BS + BA, reducing TPH from 6,800 mg/kg to 1,100 mg/kg within 60 days. This was followed by BA (76.5%), BS (72.1%), and NA (38.2%), while the sterile control showed minimal reduction (5.9%). Soil respiration trends supported these results, with maximum CO₂ evolution reaching 74.5 mg CO₂/kg/day in the combined treatment. The results indicated that indigenous microbial communities can be effectively stimulated to achieve significant hydrocarbon degradation.