Microbial removal of engine oil from polluted media (the case study: Hamadan City)

Discharging industrial wastes into the soil causes accumulation of pollutants, especially petroleum hydrocarbons and used engine oil, in the environment. This study was done to find some bacterial strains capable of removing the engine oil from contaminated soils. Soil samples contaminated by engine oil were collected from some polluted area of Hamadan City, and then their bacterial strains were isolated and classified on the basis of morphological keys and biochemical tests. The efficiency of these bacterial strains in removing the pollutant was evaluated in minimal salt medium (MSM) containing 1% engine oil. The optical density (OD) of the media was measured as an indicator of bacterial growth and degradation of the engine oil during day 0, 5, 10, and 15 at 600 nm wavelength. The bacterial strain responsible for the highest OD was chosen as the effective one, and the efficiency of oil removing was evaluated for this bacterial strain. In this study, eight bacterial strains called EODB1-8 were isolated. The results of the OD determination showed that the four bacterial strains caused more turbidity in the samples. The effects of time, type of bacteria, and their interaction effects were also significant in all samples. The turbidity of the samples was increased with increasing exposure time. The maximum turbidity was caused by the bacterial strain EODB4 and it was introduced as the best engine oil degrading bacterial strain. Its engine oil removal efficiency was evaluated to be 62.85% and it was identified as Pseudomonas alcaligenes using morphological keys and biochemical identification methods.