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 trimethyl-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.

Dobro je poznato da se u toku biodegradacije nafte u prirodnim geološkim uslovima, ili naftnog zagađivača u životnoj sredini, degradacija ugljovodonika odigrava prema definisanom rasporedu. Na primer, glavne promene u procesu razgradnje normalnih alkana dešavaju se u toku drugog, "blagog", i trećeg, "umerenog", stupnja (na skali biodegradacije od 1 do 10). Prema dosadašnjim istraživanjima, u četvrtom stupnju, kada počinju intenzivne promene fenantrena i njegovih metil izomera, normalni alkani su već u potpunosti uklonjeni. U ovom radu u toku perioda od 6 meseci izvođena je ex situ prirodna bioremedijacija (nestimulisana bioremedijacija bez dodatka biomase, hranljivih sastojaka i biosurfaktanata) zemljišta zagađenog mazutom. Niska obilnost normalnih alkana u frakciji ukupnih zasićenih alkana u početnom uzorku (identifikacija je bila mogućna tek nakon koncentrovanja pomoću karbamida) pokazala je da je ispitivani naftni zagađivač na granici između trećeg i četvrtog stupnja biodegradacije. Tokom eksperimenta, intenzivnu razgradnju fenantrena i njegovih metil, dimetil i trimetil izomera nije pratilo uklanjanje ostatka normalnih alkana. Njihova obilnost je ostala na početnom, niskom nivou i na kraju eksperimenta kada je zagađivač dostigao jedan od najviših stepena biodegradacije. Dobijeni rezultati su pokazali da se razgradnja pojedinih ugljovodonika uprkos njihovoj visokoj biodegradabilnosti ne odigrava do potpunog kraja ni u završnim fazama degradacije. U uslovima njihove smanjene dostupnosti, mikroorganizmi se opredeljuju za teže degradabilne, ali dostupnije ugljovodonike.