Degradability of n-alkanes during ex situ natural bioremediation of soil contaminated by heavy residual fuel oil (mazut)

Abstract

It is well known that during biodegradation of oil under natural geological conditions, or oil pollutants in the environment, degradation of hydrocarbons occurs according to a well-defined sequence. For example, the major changes during the degradation process of n-alkanes occur in the second, slight and third, moderate level (on the biodegradation scale from 1 to 10). According to previous research, in the fourth, heavy level, when intensive changes of phenanthrene and its methyl isomers begin, n-alkanes have already been completely removed. In this paper, the ex situ natural bioremediation (non-stimulated bioremediation, without addition of biomass, nutrient substances and biosurfactant) of soil contaminated with heavy residual fuel oil (mazut) was conducted during a period of 6 months. Low abundance of n-alkanes in the fraction of total saturated hydrocarbons in the initial sample (identification was possible only after concentration by the urea adduction technique) showed that the investigated oil pollutant was at the boundary between the third and the fourth biodegradation level. During the experiment, an intense degradation of phenanthrene and its methyl-, dimethyl- and tri-methyl-isomers was not accompanied by the removal of the remaining n-alkanes. The abundance of n-alkanes remained at the initial low level, even at end of the experiment when the pollutant reached one of the highest biodegradation levels. These results showed that the non-stimulated biodegradation of some hydrocarbons, despite their high biodegradability, had not proceeded completely to the end, even at final degradation stages. Under the condition of reduced availability of some hydrocarbons, microorganisms tend to opt for the less biodegradable but more accessible hydrocarbons.