Bioremediation of Soils Contaminated with Diesel Using Bio-stimulation Method in the Bioreactors of Vermicompost and Activated Sludge

Background and There are several methods for removing oil contaminations from the polluted environments. Bioremediation could be considered as one of the best and most practical methods in the removal of oil contaminations. The aim of this research was to determine the bioremediation efficiency for soils contaminated with diesel by the biological stimulation of bioreactors containing vermicompost and activated sludge.
In an experimental study, the soil samples were collected from an area which was free of any oil pollution and 5 reactors containing one kilogram of soil were contaminated with diesel at the mass concentration of 1%. Two reactors were mixed with vermicompost at 15% and 20% mass concentrations and two reactors were mixed with activated sludge at 5% and 10% mass concentrations. Additionally, one control reactor was used to control the process. The pH of the reactors was between 7.5 and 8 and the C:N:P ratio was 100:5:1. The amount of TPH was measured at seven retention times within three months with two repetitions. The total removal of petroleum hydrocarbons (TPHs) was evaluated by GC-FID device.
The highest removal efficiency of TPH (40.24%) was observed in bioreactors containing vermicompost at a 20% mass concentration. In this reactor, the highest percentage of removal was observed in lighter hydrocarbons (50.49%). In reactors containing activated sludge, the average percentage of TPH removal was 32% which was observed in the reactor containing the 10% concentration of sludge. In this reactor, the highest percentage of removal (44.86%) was also observed in lighter hydrocarbons.
Vermicompost and activated sludge can be used in the bioremediation of soils contaminated with diesel. In current study, the performance of vermicompost was found to be more efficient. Also, the results showed that by increasing the concentration of biological modifiers, the removal rate would increase.