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ABSTRACT
This study compared the degradation of crude oil in the clay and sandy-clay soil using NPK (15:15:15) and urea fertilizers as source of nutrients. It involved physical, chemical and microbiological analysis of the soil samples using standard analytical procedures. The potential of the microbial isolates to utilize and degrade crude oil in liquid media was evaluated by turbidity assay and estimation of residual Total Petroleum Hydrocarbon (TPH). The process parameters optimized were mechanically agitated every three days for the 36 day experiment. The effect of biostimulation on crude oil degradation in contaminated soils was investigated in seven (7) groups each for the two soil types (clay and sandy-clay soil). Residual TPH, the microbial growth measured as total heterotrophic bacteria (THB), total hydrocarbon utilizing bacteria (THUB) total Heterotrophic Fungi (THF) and total hydrocarbon utilizing fungi (THUF). Laccase, peroxidase, lipase and catalase activities as well as residual TPH where assayed every 6 days for 36 days. The results obtained from the chemical analysis for both contaminated clay soil and sandy-clay soil indicated total petroleum hydrocarbon values of 7568 mg/kg, 76011 mg/kg and 7608 mg/kg while 598 ± 3.2 mg/kg and 598 ± 3.06 mg/kg was recorded for treated clay and sandy-clay soil at the end of the 36days experiment. The result also showed that the pH of the clay and sandy-clay contaminated soil samples are 5.6 ± 0.02 and 6.5 ± 0.3 while pH for the treated clay and sand-clay soil are 6.1 ± 0.2 and 8.3 ± 0.2. The result for the total organic carbon(%)forthecontaminatedclayandsandy-claysoilare0.24±0.17and0.27±0.10while
2.59 ± 0.2 was recorded for both the treated clay and sandy clay soils. The result also indicated thattheporosityofthecontaminatedclaysoilandsandy-claysoilare0.31±0.06and0.35±
0.06 while 0.31 ± 0.01 and 0.42 ± 0.02 was recorded for treated clay and sandy-clay soils. Conclusively, amendment of oil polluted clay and sandy-clay soils with NPK (15:15:15) and urea fertilizers yield a positive effect on both clay soil and sandy-claysoil.
