EFFECTIVENESS OF ORGANIC FERTILIZER AS A BIOSTIMULATING AGENT FOR THE REMOVAL OF NAPHTHALENE IN SOIL

Abstract

Contamination of the environment by petroleum products such as polycyclic aromatic hydrocarbons (PAHs) is inevitable due to oil production, transportation and distribution activities. The potentials of organic wastes from animal droppings as bioremediation alternative for soils contaminated with naphthalene which is a PAHwas studied. The rate of biodegradation of naphthalene was studied for a period of 28 days under laboratory condition. The result of the microbial counts for soils spiked with 200 mg/kg naphthalene was a total heterotrophicbacteria (THB) count in soil amended with organic fertilizer composted from cattle dung, goat dung, pig dung and poultry manure ranging from 3.53±0.25 to 6.97±0.24 x 10⁶ CFU/g. Unamended control soil had THB count ranging from 2.26±0.12 to 2.71±0.22 x 10⁶CFU/g while THB count inunamended autoclaved control soilranged from 1.97±0.02 to 2.22±0.01 x 10³CFU/g.The count of total hydrocarbon-utilizing bacteria (THUB) inorganic fertilizer amended soil ranged from 1.7± 0.11 to 4.6±0.18 x 10⁵ CFU/g while unamended control soil had THUB ranging from 7.8±0.12 to 9.1±0.14 ×10⁴ CFU/g and THUB count in unamended autoclaved control soil ranged from 6.2±0.01 x 10¹ to 2.22±0.04 x 10³ CFU/g. The percentage naphthalene removal in organic fertilizer amended soil was 70.8%, the percentage naphthalene removal in unamended control soil was 10.1% while the percentage naphthalene removal in unamended autoclaved control soil was 4.6% after 28 days. Evaluation of the first order kinetic model resulted in biodegradation rate constant of 0.292 day^-1 and half-life of 2.37days for organic fertilizer amendment of 30 g after 28 days of treatment while unamended control resulted in biodegradation rate constant of 0.011 day^-1 and half-life of 63.01 days and unamended autoclaved control resulted in biodegradation rate constant of 0.009 day^-1and half-life of 77.02 days. The results suggest that organic fertilizer supplementation would be effective in the remediation of naphthalene polluted soils.