Bioremediation of diesel contaminated soil using bacterial cocktail and organic nutrients

Abstract

Bioremediation is a process of contaminant degradation in the environment using microorganisms. Bioremediation of diesel contaminated soil was studied using bacterial cocktail and organic nutrients from cow dung and poultry droppings at interval of 21 days for a total period of 84 days. Two hundred grams (200g) of soil were weighed into clay pots polluted with 10% (w/w) diesel oil and left undisturbed for 48 hours in an open field. After 48 hours, the clay pots were inoculated with bacterial cocktail (two bacteria isolates from diesel contaminated soil), 10% (w/w) of cow dung (CD), 10% (w/w) of poultry droppings (PD) and 5% (w/w) of sodium azide (NaN3). The two bacterial isolates were identified as Micrococcus luteus trpE16 and Bacillus subtilis DNK UT 02 after screening for hydrocarbon utilization using standard methods. The counts of hydrocarbon utilizing bacteria (THB) in the amended soil ranged from 20.2×107 and 63.5×107 cfu/g while unamended soil had the least count of THB ranging between 8.4×107 and 19.0× 107 cfu/g. Soil bioremediated with bacterial cocktail (BC) + 10% (CD+PD) recorded highest total petroleum hydrocarbon (TPH) degradation of 48.76%, 56.32%, 72.89% and 96.80% at the end of days 21, 42, 63 and 84 respectively while autoclaved soil with 5% NaN3 recorded the least (10.03%, 13.38%, 14.02% and 18.42%) respectively. First order kinetic model showed that soil bioremediated with BC with 10% (CD+PD) recorded highest biodegradation rate constant of 0.2096 day-1 and half-life of 3.31 days. Statistical analysis indicated that the results obtained were significantly (P < 0.05) different during the 84 days of this study. Amendment of diesel contaminated soil with bacterial cocktail and organic wastes caused changes in the soil physiochemical properties and accelerated the rate of biodegradation in the soil. However, poultry droppings and cow dung can serve as a potential and viable biostimulant for enhanced biodegradation of diesel in soil.