Inherent Bacterial Diversity and Enhanced Bioremediation of an Aged Crude Oil-contaminated Soil in Yorla, Ogoni Land Using Composted Plant Biomass

Aim: Inherent bacterial diversity and enhanced bioremediation of an aged crude oil-contaminated soil (ACOCS) in Yorla, Ogoni land were investigated using composted plant biomass of Eichhornia crassipes (EC), Tithonia diversifolia (TD) and Cynodon dactylon (CD) as biostimulants to enhance rate of crude oil biodegradation by autochthonous hydrocarbon utilizing microorganisms in the soil.

Study Design: An area of 50 m × 50 m was marked out in the ACOCS and EC, TD and CD (2,500 g each) were used to biostimulate 4,000g of ACOCS in situ in TPA (treatment plot A) through TPG (treatment plot G). TPA was un-amended while TPB, TPC, and TPD had EC, TD and CD added singly. TPE had EC and TD, TPF with EC and CD whereas; TPG had EC, TD, and CD combined.

Place and Duration of Study: The study was carried out in Yorla farm land in Khana L.G.A. in Rivers State. Age crude oil-contaminated soil was taken bi-weekly from each of the 7 treatment setup during the 70-day remediation study period that spanned 10 weeks (0, 14, 28, 42, 56 and 70).

Methodology: Soil samples were obtained using an auger and analyzed for their microbiological and physicochemical properties. Whole plant parts of EC, TD, and TD were collected and composted for 2 weeks before being used for biostimulation of resident crude oil-utilizing microbes.

Results: Results indicated reductions in total petroleum hydrocarbon (TPH) from 98,673 to 79,583 ppm (19% loss), 98,443 to 31,461 ppm (68% loss), 98,446 to 19,364 ppm (80% loss), 98,337 to 26,345 ppm (78% loss), 98,225 to 6,987 ppm (93% loss), 98,113 to 11,243 ppm (89% loss) and 93,867 to 1,002 ppm (99% loss) in TPA, TPB, TPC, TPD, TPE, TPF and TPG respectively. Gas chromatographic fingerprinting of ACOCS before treatment indicated the absence of n-alkanes within n-C2 to n-C8 region which is attributable to weathering processes. However, after treatment with the amendments, carbon lengths between n-C9to n-C34 were significantly (ρ >0.05) attenuated while the much heavier fractions (n-C35 to n-C45) showed a decreasing tendency for enhanced biodegradation thus, signifying their immobilization or possibility of being “lock-up” in particle pores.

Conclusion: Results suggest that composted E. crassipes, T. diversifolia and C. dactylon are potent biostimulants for enhanced degradation of residual hydrocarbons after aging of contaminated sites. These substrates could serve as potential candidates for rapid bioremediation of aged crude oil-contaminated soil hence, availing these long lost fields in for crop cultivation once again.