EXACT APPROACH TO BIOSTIMULATION OF SOIL CONTAMINATED WITH SPENT MOTOR OIL USING COW DUNG AND POULTRY LITTER IN LAND FARMING MICROCOSM
Bio-stimulation of hydrocarbon contaminated soil using organic stimulants are usually based on proportion of contaminated soil rather than the concentration of contaminants (exact approach) and most studies carried out on bioremediation of hydrocarbon contaminated soil were based on basic proof of concept and not geared towards development of processes that could lead to development of a realistic large scale treatment technology. In view of the aforementioned, a study was carried out on bio-stimulation of soil contaminated with spent motor oil using cow dung and poultry litter as bio-stimulants employing the exact approach in land-farming microcosms adopting the Box-Behnken design of experiment and based on the design of experiment fourteen microcosms labeled S1 to S13 and a control labeled S14 were investigated. The oil and grease content (O&G) and the total heterotrophic bacteria count (THBC) were used to assess the extent of bioremediation. After eight (8) weeks of bioremediation, the efficiency of degradation in all microcosms (S1 to S14) varied from 68 - 90% except the control (S14) with 35%. S1 showed the highest response to bioremediation of 90% and bio-stimulant efficiency of 61%. The microbial counts increased in the first three weeks (1.18×107 – 1.02×109) corresponding to the period of fast removal of O&G in all microcosms. Based on the percentage removal of the O&G content (90%), the exact approach showed a great potential for the remediation of spent motor oil contaminated soil at contaminant load range of 6.2 – 12.5% and carbon-nitrogen molar ratio (C:N) chosen (15:1 – 10:1).