Ex situ stimulated bioremediation of a soil contaminated with oil pollutants: the dynamics and the efficiency of biodegradation of saturated and aromatic hydrocarbons

The aim of this research was to investigate the overall dynamics and the efficiency of biodegradation of saturated and aromatic compounds – constituents of the oil pollutant, during ex situ bioremediation of the polluted soil. The effect of natural biodegradation was investigated in a parallel set of samples of the same soil which was not subjected to the processes of stimulation (bioaugmentation, biostimulation and aeration). During the period of six months, the biodegradation process caused a gradual and prominent degradation of phenanthrene, dibenzothiophene, fluoranthene/pyrene and their alkyl homologues. Among the polycyclic aromatic hydrocarbons (PAHs), distributions and abundances of benz(a)anthracene/chrysenes and triaromatic steroids were the least affected by biodegradation. n-Alkanes and isoprenoids remained low in abundances during and until the end of the experiment, indicating that the availability, rather than the biodegradability, was responsible for removal of these compounds. In the set of the samples exposed to the stimulated bioremediation, within the homologue series of phenanthrenes, dibenzothiophenes and fluoranthene/pyrenes, higher alkylated homologues were more degradable than the lower ones. Additionally, lower alkylated homologues were more degradable than their parent molecules. These results are opposite to those described in the literature and indicate that a proper choice of bioremediation conditions can influence biodegradation sequences of the compounds present in the pollutant. Furthermore, these results showed that the extent of biodegradation in the samples exposed to stimulation was much higher than in the samples where only natural biodegradation occurred, pointing that the stimulated biodegradation is much more efficient process than the natural biodegradation