hydrocarbon utilizing bacteria in soil contaminated with spent engine oil, as an alternative to inorganic fertilizers was investigated. Two types of agro-wastes were used for biostimulation of hydrocarbon degraders in soil contaminated with 10% w/w spent engine oil. 100g w/w each of plaintain and banana agro-wastes were supplemented and mixed with spiked soil. The rates of biodegradation of the oil were studied for a period of 70 days under laboratory conditions. The physiochemical property of agro-waste, total heterotrophic bacteria count, hydrocarbon-utilizing bacterial counts, percentage net loss and biostimulant efficiency were observed. The results of the total heterotrophic bacterial count (THBC) and hydrocarbon utilizing bacterial (HUB) counts were observed to be higher in plantain peels treatment option (38×107 and 41×106 cfu/g) than banana peels treatment options (29×107 and 29×106 cfu/g), and when compared with control (2.9×107 and 2.2×106 cfu/g) throughout the 70 days of bioremediation study. The study showed higher THBC and HUB counts at day 28 and day 42. Plantain peels treatment showed higher percentage of degradation (93.5%) and biostimulant efficiency (32.4%) than banana peels treatment with 84.11 and 24.9% respectively. Half-life for plantain peels treatment, banana peels treatment and unamended soil were 21.521, 24.146 and 43.043 day-1 respectively. These organic materials are widely available as wastes in the environment; hence, they can serve as “waste-to-environmental cleanup”.
Key words: Biostimulation, agro- wastes, spent oil, petroleum hydrocarbons, bio-stimulant efficiency, bioremediation, half-life.