Two distinctive soil samples were gotten near Kaduna Refining and Petrochemical Company Limited (KRPC), a subsidiary of Nigerian National Petroleum Corporation (NNPC) Kaduna. The first sample set, labeled (D), was from a location where diesel leaked from a refinery into the environment, and his second sample set, labeled (P), was from a gasoline leak. It was from where it leaked into the environment. The soil pH was found to be 5.9 and 6.2 for the D and P samples, respectively. The cation exchange capacity (CEC) was higher for sample P than for sample D (32.0 and 30.0 mmol/kg soil, respectively). P has a high concentration of cations (Ca2+, Mg2+, K+, and Na+ concentration values ​​of 3.6, 1.17, 0.50, and 0.22 mol/kg, respectively) due to its high CEC, whereas sample D, which has a low CEC, Density is one less. Cations (Ca2+, Mg2+, K+, and Na+ with concentration values ​​of 1.20, 0.27, 0.25, and 0.17 mol/kg, respectively). Oils (contaminants) were extracted into dichloromethane, GC-MS analysis was performed to determine the oil properties (composition), and contaminant concentrations were determined using gravimetric methods. As a result, the total contaminant (oil) concentration before treatment was found to be 398 g/kg and 194 g/kg for samples D and P, respectively. The GC-MS results obtained indicate that linear and branched alkanes (n-tetratetracontane, 3,6-dimethyldecane, n-pentadecane, 2-bromodecane, n-heptadecane , and n-tetradecane, 2-bromododecane, n-octadecane, 14-methyl-8-hexadecenal, etc.) were the major impurities. 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.

Background of the study

One of the major environmental problems in today’s world is hydrocarbon pollution resulting from activities associated with the petrochemical industry. Petroleum pollution has been a prevalent problem in Nigeria since the beginning of oil exploration and the development of the oil industry (Okoh et al., 2001). Accidental releases of petroleum products are a particular environmental concern. Hydrocarbon components are known to belong to families of carcinogens and neurotoxic organic pollutants. Currently accepted disposal methods of incineration or burial in unsafe landfills can be prohibitively expensive if the levels of contaminants are high. The detrimental impact of pollutants on the environment has increased awareness and vigilance against pollution in the Niger Delta environment. Relatively recently, Nigeria has experienced significant population growth, urbanization and industrial activity (Eze and Okpokwasili, 2010). The release of crude oil into the environment from oil spills has received worldwide attention (Millioli et al., 2009). Bioremediation, defined as a biological response to environmental abuse, continues to attract research interest worldwide (Hammer, 1993). Bioremediation has been described as using living microorganisms to break down environmental pollution. That is, technology that removes pollutants from the environment and restores the original natural environment (Sasikuma and Papmazath, 2003). The long-term goal of bioremediation design is to present cost-effective designs that reduce contaminants to the lowest reasonably and practically possible levels (ALARP). To achieve this cost-effectiveness, researchers around the world are turning their attention to using organic waste as a nutrient-limiting source for effective bioremediation (Ibiene et al. 2011).

Mechanical and chemical methods commonly used to remove hydrocarbons from contaminated sites are of limited effectiveness and can be expensive (Das and Chandran, 2011). Bioremediation is a promising technique for treating these contaminated sites because it is inexpensive and results in complete mineralization. Bioremediation essentially works on biodegradation. This is due to the complete mineralization of organic contaminants into carbon dioxide, water, inorganic compounds, cellular proteins, or the conversion of complex organic contaminants by biological agents such as microorganisms (Das and Preethy) into other simple It refers to being transformed into an organic compound, 2010). Many native microorganisms in water and soil are capable of degrading hydrocarbon contaminants.


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