Karakterizacija biodegradabilnosti naftnih ugljovodonika u zemljištu i bioremedijacionih procesa u toku tretmana biogomilama i površinskom obradom

Abstract

U okviru ovog istraživanja ispitani su: (1) Procesi koji se odvijaju prilikom bioremedijacije zemljišta zagađenog naftom i derivatima nafte, koje je bilo izloženo spontanim abiotičkim i biotičkim procesima degradacije u toku 8 godina, tehnikama biogomila i površinske obrade na poluindustrijskoj (pilot) skali uz optimizaciju tehnoloških parametara sa ciljem povećanja efikasnosti i efektivnosti biodegradacije ugljovodonika; (2) Uticaj starenja, koncentracije, biodsotupnosti i strukture zagađujućih materija na procese biodegradacije i biotransformacije u kontrolisanim laboratorijskim uslovima. Tokom dve godine bioremedijacionog tretmana sadržaj mineralnih ulja opao je za 52% (od 27,8 g/kg do 13,2 g/kg) i 53% (od 23,2 g/kg do 10,8 g/kg), dok je sadržaj ukupnih ugljovodonika opao za 43% (od 41,4 g/kg do 23,4 g/kg) i 27% (od 35,3 g/kg do 25,8 g/kg) u biogomili i površinskoj obradi respektivno. Efikasnost uklanjanja mineralnih ulja iz zemljišta u dva posmatrana bioremedijaciona tretmana je praktično ista. Međutim, u pogledu sadržaja ukupnih ugljovodonika u biogomili uklonjeno je dva puta više ukupnih ugljovodonika (gledajući apsolutnu količinu ukupno uklonjenih ugljovodonika). Kinetika biodegradacije mineralnih ulja i ukupnih ugljovodonika u toku tretmana u biogomili u saglasnosti je sa kinetičkim modelima lnC=lnC0-kt i lnC=lnC0-kt0,5. Kinetika biodegradacije mineralnih ulja u toku površinske obrade relativno se dobro može opisati sa dva pomenuta kinetička modela, međutim, znatno bolju korelaciju pokazao je linearni model (C=C0-kt) primenjen na prvih 92 i poslednjih 200 dana eksperimenta. Promena sadržaja ukupnih ugljovodonika u toku površinske obrade zagađenog zemljišta relativno je u dobroj korelaciji samo sa kinetičkim modelom lnC=lnC0-kt0,5. Laboratorijska ispitivanja pokazala su da biodegradabilnost i sudbina ugljovodonika u životnoj sredini jako zavise od tipa, starosti i koncentracije zagađujućih materija. Naime, u slučaju zemljišta sveže kontaminiranog dizel uljem, već pri koncentracijama od 20 mg/g uočen toksičan efekat koji je prevaziđen nakon dve nedelje tretmana kao posledica smenjenja prekomerne koncentracije rastvorenih ugljovodonika biotičkim i abiotičkim putem i adaptacije prisutne mikroflore. U slučaju većih koncentracija ovaj efekat je bio još izraženiji. Kod zemljišta kontaminiranog sirovom naftom isti efekat se javlja tek pri koncentraciji od 35 mg/g, kao posledica toga da sirova nafta sadrži manju količinu lako rastvornih ugljovodonika. Za razliku od sveže kontaminiranog zemljišta, na biodegradaciju starog naftnog zagađanja u zemljištu koncentracija nije imala uticaj, u ovakvom zemljištu respiracija je bila na veoma niskom nivou pri svim ispitivanim koncentracijama, ali ne kao posledica toksičnosti, već kao posledica činjenice da se degradabilni deo zagađujućih materija degradirao tokom procesa starenja, tako da su u zemljištu zaostali visokomolekularni teško rastvorni ugljovodonici (smole, asfaltne komponente i dr.) sekvestrovani u zemljištu. Merenja biodostupnosti ugljovodonika (ekstrakcijom sa Tween80) pokazala su da je u zemljištu sveže kontaminiranom dizel uljem i sirovom naftom i starim naftnim zagađenjem oko 95%, 85% i 40% ugljovodonika biodostupno, respektivno. Koncentracija rezidualne frakcije mineralnih ulja i ukupnih ugljovodonika dobijena nakon 48 dana laboratorijskog tretmana u skoro svim probama je veća od predviđenih, što je posledica bifaznog ponašanja ugljovodonika u zemljištu, gde se jedan deo uklanja biodegradacijom, dok drugi deo difunduje u pore zemljišta i kompleksira se sa zemljišnom organskom materijom. Količina ugljovodonika iz starog naftnog zagađenja zemljišta koja može da pređe u vodenu fazu je mala reda veličine nekoliko mg/l, međutim, u prirodnim uslovima usled spiranja ugljovodonika sa zemljišta kišom, postoji verovatnoća da ovi ugljovodonici dospeju u podzemnu vodu iznad maksimalno dozvoljene koncentracije za vodu za piće (MDK = 10 μg/l) i na taj način degradiraju njen kvalitet. Zbog nemogućnosti daljag uklanjanja zagađenja bioremedijacijom, preostala količina zagađujućih materija koja može dospeti u vodenu fazu bi trebalo da se ukloni nekim drugim remedijacionim tehnikama pre njegovog konačnog bezbednog odlaganja u životnu sredinu.

The aims of this study were to examine: (1) the processes that occur during bioremediation of soil contaminated by oil and oil derivatives, which was exposed to spontaneous abiotic and biotic degradation processes over 8 years, using pilot scale biopiles and landfarming techniques to optimise technological parameters with the aim of increasing the efficiency and effectiveness of hydrocarbons biodegradation. (2) the effect of contaminants weathering, concentration, bioavailability and structure on the biodegradation and biotransformation process under controlled laboratory conditions. Over the two years of bioremediation treatment by biopiles and landfarming, the mineral oil content decreased by 52% (from 27.8 g/kg to 13.2 g/kg) and 53% (from 23.2 g/kg to 10.8 g/kg), and the total hydrocarbon content decreased by 43% (from 41.4 g/kg to 23.4 g/kg) and 27% (from 35.3 g/kg to 25.8 g/kg), respectively. The efficiency of mineral oil removal from soil in these two applied bioremediation treatments was practically the same. However, in terms ofthe absolute amount of total hydrocarbons, twice as many total hydrocarbons were removed in the biopile. The mineral oil and total hydrocarbons biodegradation kinetics in the biopile were in good agreement with the kinetic models lnC = lnC0-kt and lnC = lnC0-kt0.5. The mineral oil biodegradation kinetics during the landfarming treatment is relatively well described with those two kinetic models, however, significantly better correlation is obtained by the linear model (C = C0-kt) applied to the first 92 and last 200 days of the experiment. The change in total hydrocarbons content during the landfarming treatment is in relatively good correlation only with the kinetic model lnC = lnC-kt0.5. The laboratory biodegradation investigation showed that hydrocarbon biodegradability and its fate in the environment strongly depend upon the structure, concentration and weathering of the hydrocarbons. Thus, in the case of diesel contaminated soil, as a consequence of its structure, i.e. the presence in a higher concentration of the soluble and toxic midrange n-alkanes, a toxic effect is detected at a diesel oil concentration of 20 mg/g, although this effect is overcome after two weeks, as a consequence of the decreasing concentration of soluble hydrocarbons in biotic and abiotic processes and microbial adaptation. This effect was more pronounced in the case of the soil withthe highest diesel oil concentration. In crude oil contaminated soil, a toxic effect was observed at a much higher hydrocarbon concentration (35 mg/g) than in the diesel oil contaminated soil, which corresponds to the fact that crude oil contains significantly less soluble hydrocarbon. In contrast to these two freshly contaminated soils, the weathered contaminated soil contaminant concentration did not have an effect on hydrocarbon biodegradation, with biodegradation in this soil actually at a low level at all concentrations, not as a consequence of toxicity, but because the degradable part of the contaminant was already degraded during the weathering process, leaving behind only highly condensed hydrophobic organic contaminants (asphaltenes, resins, etc.) sequestered in the soil. The data obtained for hydrocarbons bioavailability (by Tween80 extraction) showed that the bioavailable hydrocarbon fraction from soils freshly contaminated with diesel oil and crude and weathered oil contamination were approximately 95%, 85% and 40%, respectively. The concentration of residual mineral oil fractions and total hydrocarbons obtained after 48 days of laboratory biodegradability treatment in almost all batches was greater than predicted, as a result of the biphasic behaviour of hydrocarbons in the soil, where some were degraded or lost from the soil and some transformed into the recalcitrant fraction. The amount of hydrocarbons from the weathered soil contamination that can be transferred into the water phase is small, of the order of a few mg/l in magnitude, however, under natural conditions, due to hydrocarbons leaching by rainfall, it is possible that these hydrocarbons infiltrate groundwater above the maximum permissible concentration for drinking water (MAC = 10 μg/l) and thus degrade its quality. As it is not possible to achieve further contamination degradation by bioremediation, the remaining amount of pollutants which can be transferred into the water phase should be removed by some other remediation techniques before its final safe disposal in the environment.