| Summary: | The indiscriminate disposal of fresh and used motor oil into the environment (land and water) is a common practice in Nigeria and this practice has contributed to its soil contamination and makes up a greater percentage of polluted ground in the world. Over the years, the contamination of auto-mechanic workshops by used oil and fresh oil has been left uncared for, Soil contaminated with fresh and used motor oil creates a serious effect on plant tissues, soil components, and its microorganisms, human and other animal health. Optimization of a biostimulation process used in the treatment of used motor oil contaminated soil has been carried out. D-optimal design of response surface methodology with one numerical factor and a categorical factor at two levels was employed to generate 10 experimental runs for the biostimulation system. The input variables of the system were palm bunch ash (a stimulant) and pollution level. The two levels of the latter factor considered were 5% and 10 % (w/w) pollution level, while the response of the system was oil and grease (O&G) removal. The biostimulation experiments were carried out according to the RSM design, and the experimental data obtained were analyzed using the quadratic model. The results of the analyses showed that the developed quadratic model was able to represent the system with both input factors affecting the system significantly since p-values for the model was found to be less than 0.05. The results also showed that O&G removal was affected by both the PBA and the pollution level. It was also observed from the numerical optimisation carried out that 100 % and 83.36 % O&G removal was attained at 5 % and 10 % pollution level respectively after ten weeks of the study. The findings of this work revealed that palm bunch ash (PBA) can be used as a stimulant for the bioremediation of used motor oil contaminated soil. Thus, its application in the treatment of oil-contaminated soil is highly recommended.
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