Stimulated bioremediation of soil contaminated with spent engine oil using organic wastes

Abstract

In this study, the role of some organic wastes in stimulating the removal of petroleum hydrocarbon from contaminated soil was assessed. The concentration of hydrocarbon in soil before, during and after bioremediation and volume of carbon dioxide released from soil were investigated. The contaminated soil was amended with chicken droppings (CD), cow dung (CDU), and rice husk (RH) for sixty (60) days under laboratory conditions. The soil was mixed thoroughly every ten (10) days to enhance aeration, and 60% water holding capacity (WHC) of the soil was maintained to supply bacteria with adequate moisture. The initial pH value of soil was 4.7, while CD, CDU and RH had values of 6.9, 7.1 and 7.6 respectively. Water holding capacity (WHC) of contaminated soil was 15%, CD showed 31%, CDU (43%) while RH had 40.7%.The percentage of nitrogen in soil was very low (0.92%) compared to Organic carbon (10.5%), and Phosphorous (19.2mg/kg).CD showed the highest value of nitrogen (2.4%) and phosphorous (17.6mg/kg) followed by CDU with 1.7%;17.1mg/kg and 0.89%;15.21mg/kg in RH. Highest concentration of organic carbon (11.4%) was recorded in RH; CDU had 10.9% while CD was with 10.1%. Concentration of spent engine oil in soil before bioremediation was 7.525mg/g. The initial count of Hydrocarbon degrading Bacteria (HDB) in contaminated soil was 5.7x10⁵CFU/g, and species of HDB isolated from soil were Acinetobacter, Bacillus, Micrococcus, Flavobacterium, and Pseudomonas. Total petroleum hydrocarbon in soil amended with CD was reduced by 86.7%, CDU and RH treated soils showed 80.05% and 66.75% reduction respectively, while untreated soil recorded lowest reduction (46.8%) at the end of 60days period. Largest volume of carbon dioxide was evolved from soil amended with CD (15.77cm^-3).Soil treated with CDU produced 14.02cm^-3, and RH soil had 11.72cm^-3. Lowest volume (3.78cm^-3) of carbon dioxide was produced from untreated soil. This result demonstrated that these organic wastes could stimulate biodegradation of spent engine oil in the order CD>CDU>RH.