Intrinsic biodegradation of diesel fuel in an interval of separate phase hydrocarbons |
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| Institution: | 1. Macromolecular Materials and Lignocellulosic Fibers Group, Center of Research on Science and Technology of BioResources, São Carlos Institute of Chemistry, Trabalhador São Carlense Ave, 400, 13566-590 São Carlos, SP, Brazil;2. São Carlos Institute of Physics, University of São Paulo, Trabalhador São Carlense Ave, 400, 13566-590 São Carlos, SP, Brazil |
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| Abstract: | Emerging acceptance of the limitations of separate phase product recovery has spawned interest in the intrinsic alteration of residual separate phase petroleum products. In this study the geochemical changes in a continuous core through soil containing a separate phase diesel fuel #2 (SPD) in contact with groundwater are investigated. Chemical heterogeneities are shown to exist which can be attributed to weathering, particularly intrinsic biodegradation. The results show that the aliphatic hydrocarbon content is reduced and the δ13C ratio of the aliphatic hydrocarbons increased from top to bottom in the core. Both changes are thought to be due to preferential biodegradation of (isotopically lighter) n-alkanes. A slight increase in the relative abundance of shorter chain n-alkanes (<n-C17) was also observed. The distribution of the dominant aromatic hydrocarbons (C0–C3 alkyl-naphthalenes) is remarkably consistent throughout the core, although naphthalene is depleted below the oil–water interface. In spite of low oil saturation (S0), little or no evidence of biodegradation is noted at the uppermost boundary of the SPD. However, intrinsic biodegradation is evident approximately 0.3 m above the oil–water interface in spite of higher S0. The extent of the chemical changes attributable to biodegradation (described above) gradually increases below the oil–water interface, eventually reaching a maximum at the bottom of the SPD profile (～1.2 m below the interface) where S0 is again reduced. The relatively higher level of biodegradation observed at and below the oil–water interface may be attributed to the reduced S0 in this zone. An estimate of the mass reduction in diesel fuel between the uppermost and bottommost parts of the core is calculated to be 23% (by weight), due predominantly to the biodegradation of n-alkanes. |
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