ABSTRACT
Crude oil contamination has always been a serious issue in Nigeria. It involves contamination of various media such as soil, water, and air. In order to prevent destruction of the ecosystem, it is important that these media undergo a thorough treatment process. One approach to restore contaminated soil is the application of inorganic nutrients. In this study the physicochemical properties, microbiological analyses and enzymes assay of the soil samples were done using standard analytical procedures. The effect of bio-stimulation on crude oil degradation in contaminated soil was investigated in six treatment groups involving crude oil contamination with or without treatment with NPK and urea fertilizers;3000 ppm contaminated, 5000 ppm contaminated, 8000 ppm contaminated, 3000 ppm with NPK and urea treatments, 5000 ppm with NPK and urea treatments, 8000 ppm with NPK and urea treatments. Microbial growth was measured as total heterotrophic bacteria, total hydrocarbon utilizing bacteria, total heterotrophic fungi and total hydrocarbon utilizing fungi. Laccase, peroxidase, lipase, and catalase activities as well as residual TPH were assayed every 6th day for 36 days. The results obtained indicated that there was significant increase in water holding capacity, moisture content, bulk density in the treated soil; while total organic carbon, electrical conductivity increased significantly in contaminated soil, but soil porosity, total nitrogen, and total available phosphorus were higher in uncontaminated soil. THB and THUB increased significantly from day 0 to day 18 in the treated soil while THF and THUF significantly increased from day 0 to day 12 in the soil treated with urea and NPK. Laccase activity increased significantly in the contaminated soil treated from day 0 with maximum values obtained at day 18 followed by sharp decrease. Peroxidase activity increased significantly from day 0 to day 12 in the treated contaminated soil after which a decrease followed. Catalase activity increased from day 0 and peaked at day 12 across the treatment group. Lipase activity in the crude oil contaminated soil subjected to treatment increased significantly from day 0 to day 24. The total petroleum hydrocarbon (TPH) obtained were significantly different (P <0.05) from the control when compared to the untreated. There was a significant decrease in soil TPH treated with NPK and urea. The results obtained from this findings shows that combination of urea and NPK and C:N:P ratio adopted lowered the TPH content.
