International Journal of Environmental Bioremediation & Biodegradation. 2014, 2(2), 84-92DOI:
Abstract: Heavy metals are high density metallic chemicals that are potentially toxic at low concentrations and present a danger to human and environmental health. This study was conducted to ascertain the efficiency of microorganisms present in animal wastes in bioremediation of heavy metals present in spent engine oil contaminated soil. Spent engine oil impacted soil was excavated from a mechanic workshop in Ugbowo, Edo State, Nigeria and transported to the laboratory in a plastic container. Air dried spent engine soil samples were homogenized and measured into four plastic buckets used as test cells (1 kg each) and mixed thoroughly with poultry manure in a soil to manure ratio of 80% weight of soil to 20% weight of manure, 70% weight of soil to 30% weight of manure and 60% weight of soil to 40% weight of manure and labeled as PL 20%+SEOCS (Poultry Litter + Spent Engine Oil Contaminated Soil), PL 30%+SEOCS and PL 40%+SEOCS and CONTROL respectively. The study lasted ten (10) weeks and analytes were obtained on a weekly basis for soil pH, microbial counts, and heavy metals analysis. Results obtained indicate that pH was 6.9 in control soil initially while it ranged from 8.1 (Week 1 PL 20% +SEOCS) to 8.4 (Week 7 PL 20% SEOCS) for the treatment categories. The differences in pH between treatment categories and control were not statistically significant (P<0.05). Initial soil moisture content was 2% which was improved after watering to 17.8% (lowest) in PL 30%+SEOCS and 18.4% (highest) in PL 40% +SEOCS. Moisture content in control sample was 18.9%. The difference moisture content in all treatment categories were not statistically significant (p<0.05). Microorganisms identified in poultry litter and spent engine oil contaminated soil were; Pseudomonas Spp, Enterococcus Spp, Micrococcus Spp, Corynebacterium Spp, Arthobacter Spp, Klebsiella Spp, Acinetobacter Spp, Bacillus Spp, Penicillum Spp, Sachoromyces Spp, Mould and Trichoderma Spp. Heavy metal analysis indicate that Arsenic (mg/kg) in the control sample had 2.73% reduction, compared to 26.6%, 32.5% and 41.17% for PL 20%+SEOCS, PL 30%+SEOCS and PL 40%+SEOCS, respectively. Barium in the control sample had 6.28% reduction compared to 35.9%, 11.1% and 64.21% for PL20%+SEOCS, PL 30% +SEOCS, and PL 40%+SEOCS respectively. There was no significant difference between PL 30%+SEOCS and control while reduction in PL 20%+SEOCS and PL 40% +SEOCS was significantly different from control (P<0.05). Cadmium in the control sample had a drop of 25% while PL 20%+SEOCS, PL 30%+SEOCS and PL 40% +SEOCS had <0%, 38% and 33.3% reduction respectively. Cadmium reduction in the treatment categories was not significantly different from the control. Chromium in the control sample had 20% reduction while there was 26%, 58.06% and 46.57% reduction in the PL 20%+SEOCS, PL 30% +SEOCS and PL 40%+SEOCS respectively, there was a significant reduction in the concentration of Chromium. Cobalt in the control sample reduced by 5.86%; it had reduction of 53.3%, 56.0% and 61.4% in PL 20%+SEOCS, PL 30% +SEOCS and PL 40%+SEOCS respectively. Reductions in all treatment categories were significantly different from the control (<0.05). Lead (mg/kg) in the control reduced by 2.70% while in the treatment categories, PL 20%+SEOCS, PL 30%+SEOCS and PL 40%+SEOCS, had 15.3%, 24.06% and 34.5% reduction respectively. There was a significant reduction in the concentration of Lead (P<0.05) when compared with the control. The research findings indicate that bioremediation using growing microorganisms present in contaminated soil and animal wastes can reduce the concentration of heavy metals in soil. The research can further be implemented in a pilot scale study and subsequently on spent oil contaminated sites.