A regression analysis model was developed to examine the reliability and the acceptability of the sun-dried and room-dried Azadirachta indica leaves for the remediation crude oil contaminated soil in Niger Deltal, Nigeria. An experimental approach was used to monitor the concentration of the total petroleum hydrocarbon (TPH) degradation that was enhanced in the presence of the microbes in the reactor. A regression analysis was performed to evaluate the reaction behavior microbes in reactor for the remediation of the TPH in the presence of sun-dried and room-dried A. indica leaves in sandy and loamy soils contaminated with 100 ml of crude oil. The physicochemical properties of control loamy soil was as; pH (6.75), electric conductivity (10.36 μS/cm), total oxygen (2.99%), total Nitrogen (0.091%), potassium (36.82942%), phosphorus (15.36%) and total bacteria (2.15×102 cfu/g). Whereas, these values were as pH (6.82), electric conductivity (21.48 μS/cm), total oxygen content (1.18%), total nitrogen (0.036%), potassium (24.03681%), phosphorus (5.18%) and total bacteria count (1.86×102 cfu/g) for sandy soil. The inoculant was prepared by blending sun-dried and room-dried A. indica leaves. The blended A. indica leaves in 50 to 100 g range were applied on the polluted soils for 35 days and significant reduction in contaminating agents was observed. The highest remediation was observed in soils treated with 100 g room dried A. indica leaves. A 96% remediation recorded in sandy soil treated with 100 g room dried A. indica leaves as TPH depleted from 35818.69 mg/kg to 1349.109 mg/kg and 92% reduction was observed in loamy soil treated with 100 g dried A. indica leaves and TPH depleted from 48508.92 mg/kg to 3977.739 mg/kg. The regression model developed was successfully employed to predict TPH remediation behavior, which can be applied to monitor remediation of contaminated soil.
Bioaugmentation with zeolite-immobilized bacterial consortium OPK results in a bacterial community shift and enhances the bioremediation of crude oil-polluted marine sandy soil microcosms
