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The aim of this research was to investigate the overall dynamics and the efficiency ofbiodegradation 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 ofthe 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 andprominent degradation of phenanthrene, dibenzothiophene, fluoranthene/pyrene and theiralkyl homologues. Among the polycyclic aromatic hydrocarbons (PAHs), distributionsand abundances of benz(a)anthracene/chrysenes and triaromatic steroids were the least affected by biodegradation. n-Alkanes and isoprenoids remained low in abundancesduring and until the end of the experiment, indicating that the availability, rather than thebiodegradability, was responsible for removal of these compounds.In the set of the samples exposed to the stimulated bioremediation, within thehomologue series of phenanthrenes, dibenzothiophenes and fluoranthene/pyrenes, higheralkylated homologues were more degradable than the lower ones. Additionally, loweralkylated homologues were more degradable than their parent molecules. These resultsare opposite to those described in the literature and indicate that a proper choice ofbioremediation conditions can influence biodegradation sequences of the compoundspresent in the pollutant. Furthermore, these results showed that the extent ofbiodegradation in the samples exposed to stimulation was much higher than in thesamples where only natural biodegradation occurred, pointing that the stimulatedbiodegradation is much more efficient process than the natural biodegradation.

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.

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.

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.

This report documents remediation activities through completion at Site 2 and Site 4 of the Alpena Combat Readiness Training Center (CRTC) in Alpena, Michigan (Figure 1). Contaminated soils were remediated from May 1995 through August 1995 using a combination of stabilization, in-situ bioremediation, and ex-situ bioremediation technologies. Remediation activities were completed by Unico Construction Co., Inc. (the general contractor) and CCC Group, Inc. (a subcontractor) both of San Antonio, Texas. Remediation activities included