| dc.description.abstract | The aim of this study was to investigate the effects of biosurfactants and organic
matter amendments on the bioremediation of diesel contaminated soil.
Two strains of Pseudomonas aeruginosa with the ability to produce biosurfactant
were isolated from a water and soil sample in Co. Sligo. The first strain, Isolate A,
produced a biosurfactant which contained four rhamnose containing compounds,
when grown in proteose peptone glucose ammonium salts medium with glucose as
the carbon source. Two of the components were identified as rhamnolipid 1 and 2
whilst the other two components were unidentified. The second strain, Isolate GO,
when grown in similar conditions produced a biosurfactant which contained only
rhamnolipid 2.
The type of aeration system used had a significant effect on the abiotic removal of
diesel from soil. Forced aeration at a rate of 120L 02/kg soil/ hour resulted in the
greatest removal. Over a 112 day incubation period this type o f aeration resulted in
the removal o f 48% o f total hexane extractable material. In relation to bioremediation
of the diesel contaminated sandy soil, amending the soil with two inorganic nutrients,
KH2PO4 and NÜ4N03, significantly enhanced the removal of diesel, especially the «-
alkanes, when compared to an unamended control.
The biosurfactant from Isolate A and a biosurfactant produced by Pseudomonas
aeruginosa NCIMB 8628 (a known biosurfactant producer), when applied at a
concentration of three times their critical micelle concentration, had a neutral effect
on the biodégradation o f diesel contaminated sandy soil, even in the presence o f
inorganic nutrients. It was deduced that the main reason for this neutral effect was
because they were both readily biodegraded by the indigenous microorganisms.
The most significant removal of diesel occurred when the soils were amended with
two organic materials plus the inorganic nutrients. Amendment of the diesel
contaminated soil with spent brewery grain (SBG) removed significantly more diesel
than amendment with dried molassed sugar beet pulp (DMSBP). After a 108 day
incubation period, amendment of the diesel contaminated soil with DMSBP plus
inorganic nutrients and SBG plus inorganic nutrients resulted in 72 and 89% removal
of diesel range organics (DRO), in comparison to 41% removal of DRO in an
inorganic nutrient amended control. The first order kinetic model described the
degradation of the different diesel components with high correlation and was used to
calculate Vi lives. The V2 life, of the total «-alkanes in the diesel was reduced from 40
days in the control to 8.5 and 5.1 days in the presence of DMSBP and SBG,
respectively. The V2 life o f the unresolved complex mixture (UCM) in the diesel
contaminated soil was also significantly reduced in the presence o f the two organics.
DMSBP and SBG addition reduced UCM V2 life to 86 and 43 days, respectively,
compared to 153 days in the control. The component of diesel whose removal was
enhanced the greatest through the organic material amendments was the isoprenoid,
pristane, a compound which until recently was thought to be nonbiodegradable and
was used as an inert biomarker in oil degradation studies. The V2 life of pristane was
reduced from 533 days in the nutrient amended control to 49.5 and 19.5 days in
DMSBP and SBG amended soils. These results indicate that the addition o f the
DMSBP and SBG to diesel contaminated soil stimulated diesel biodégradation,
probably by enhancing the indigenous diesel degrading microbial population to
degrade diesel hydrocarbons, whilst the addition o f biosurfactants had no enhanced
effect on the bioremediation process. | en |
