Two different set of soil samples were collected near Kaduna Refining and Petrochemical Company Limited (KRPC), a Subsidiary of Nigerian National Petroleum Corporation (NNPC) Kaduna. The first set of samples labelled (D) was obtained from areas where diesel from the refinery spilled into the environment and the second set of samples labelled (P) was collected from areas where petrol leaked and spilled into the environment. The pH of the soil was found to be 5.9 and 6.2 for D and P samples respectively. The cation exchange capacity (CEC) was higher in sample P than in sample D (32.0 and 30.0 mmol/kg of soil respectively). P has high concentrations of cations ( Ca2+, Mg2+, K+ and Na+ with concentration values 3.6, 1.17, 0.50 and 0.22 mol/kg respectively) because of its high CEC while sample D with a lower CEC has a lower concentration of cation (Ca2+, Mg2+, K+ and Na+ with concentration values 1.20, 0.27, 0.25 and 0.17 mol/kg respectively). The oil (contaminant) was extracted in dichloromethane and a GC-MS analysis was run to determine the nature (composition) of the oil and the concentration of the contaminant was determined using gravimetric method. Results revealed that the total concentration of the contaminant (oil) before treatment was 398 g/kg and 194 g/kg for sample D and P respectively. The GC-MS results obtained showed that in both samples (D and P) linear and branched alkanes(n-Tetratetracontane, 3,6-Dimethyldecane, n-Pentadecane, 2-Bromodecane, n-Heptadecane etc. and n-Tetradecane, 2-Bromododecane, n-Octadecane, 14-Methyl-8-hexadecenal etc. respectively) were the main contaminants. Bioremediation was initiated and examined by applying separately fertilizer (F), bacteria inoculation (B), emulsifier (E) on the contaminated soil and by combining bacteria inoculation and fertilizer (B and F), fertilizer and emulsifier (F and E), bacteria inoculation and emulsifier (B and E) also a combination of bacteria inoculation, emulsifier and fertilizer (B,E and F) on both sample D and P . Bioremediation was determined by weight lost method throughout the 28days of treatment and the trend of degradation is thus: (B, E and F) > B > ( B and E ) > (B and F) > (E and F) > E > F. Results obtained showed that treatment with B,E and F combined together yielded the highest percentage of oil degradation (97%, and 95% for samples P and D respectively), followed by B (96% and 81% for samples D and P respectively). This finding suggests that Bacillus sp is a viable microbial strain for bioremediation of oil-contaminated soil when biostimulated by adding fertilizer combined with emulsification (B, E and F). The percentage of oil degraded in sample P and D are almost the same (97 and 95% respectively) and there is significant difference (P < 0.05) in the trend of degradation for D and P this may be because, even though the samples contained oil (contaminant) with almost the same composition but differ in the number of carbon chain and other physical factors like density, viscosity etc.
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