Biodegradation Of N-alkanes Research Articles

Biodegradation studies of selected hydrocarbons from diesel oil.

In-vitro biodegradation of aliphatic and aromatic hydrocarbons present in diesel oil by Pseudomonas fluorescens, Texaco was studied in an aqueous medium. Small aliquots of diesel oil and its aromatic fraction were incubated aerobically for periods of up to seven months and analysed by GC-MS. Biotic losses proved to be greater for aliphatic than aromatic compounds. Most biodegradation occurred within the first 20 d of incubation. The most rapid biodegradation, up to 65% in 8 d, was observed for n-alkanes (C14-C18). The same compounds were also shown to be less affected by abiotic losses. Biodegradation of n-alkanes from diesel oil and diesel oil itself showed first order kinetics for the initial incubation period. Aromatic compounds proved to be resistant to biodegradation and only phenanthrene had been degraded (30%) within 6 months.

EFFECTS OF SUBSTRATE MINERALOGY ON THE BIODEGRADABILITY OF FUEL COMPONENTS

Experiments were carried out to determine the effects of mineralogy on the biodegradability of components of a whole fuel by a soil microbial consortium. Samples of quartz sand (Fischer Sea Sand) and illite clay (API 35) were spiked with marine diesel fuel, aged, slurried, and inoculated, and concentrations of fuel components were monitored over time. To help distinguish biotic from abiotic processes, identical samples were poisoned with mercuric chloride and were run in parallel. While there was chromatographic and biomarker evidence of n-alkane biodegradation in the sand samples, illite samples showed no evidence of biogenic loss of aliphatic components. Polycyclic aromatic hydrocarbons, on the other hand, were lost equivalently on both minerals and in both cases were lost to a much greater extent than were total petroleum hydrocarbons (TPHs). These results suggest that under our experimental conditions, illite inhibited the bioavailability of some TPH components to the soil microbial consortium.

Effect of Rhamnolipid (Biosurfactant) Structure on Solubilization and Biodegradation of n-Alkanes

A study to quantify the effect of rhamnolipid biosurfactant structure on the degradation of alkanes by a variety of Pseudomonas isolates was conducted. Two dirhamnolipids were studied, a methyl ester form (dR-Me) and an acid form (dR-A). These rhamnolipids have different properties with respect to interfacial tension, solubility, and charge. For example, the interfacial tension between hexadecane and water was decreased to <0.1 dyne/cm by the dR-Me but was only decreased to 5 dyne/cm by the dR-A. Solubilization and biodegradation of two alkanes in different physical states, liquid and solid, were determined at dirhamnolipid concentrations ranging from 0.01 to 0.1 mM (7 to 70 mg/liter). The dR-Me markedly enhanced hexadecane (liquid) and octadecane (solid) degradation by seven different Pseudomonas strains. For an eighth strain tested, which exhibited extremely high cell surface hydrophobicity, hexadecane degradation was enhanced but octadecane degradation was inhibited. The dR-A also enhanced hexadecane degradation by all degraders but did so more modestly than the dR-Me. For octadecane, the dR-A only enhanced degradation by strains with low cell surface hydrophobicity.

Dibenzothiophene Biodegradation by a Pseudomonas sp. in Model Solutions

The presence of fatty acid and an n-alkane may affect the biodegradation rate of aromatic sulphur compounds such as dibenzothiophene (DBT). A fatty acid (hexadecanoic acid) may form micellar structures favouring DBT bioavailability. n-Alkanes, such as n-dodecane or n-hexadecane, form a film around the aromatic sulphur molecule as a consequence of solvation, thus increasing DBT bioavailability. The mass-transfer rate from the solid to the aqueous phase controls the DBT biodegradation rate when DBT is the only carbon source. Diffusional coassimilation and microbial hydrophobic effects are rate-limiting steps in DBT biodegradation in the presence of aliphatic compounds. Diffusion depends on the DBT concentration in n-alkane, while cometabolism is associated with different n-alkane biodegradation rates. Through the definition of biodesulphurization selectivity and biodersulphurization efficiency, our investigations have shown that a selective aerobic biodesulphurization process is possible by using an unselective biocatalyst, such as a Pseudomonas sp.

Dibenzothiophene biodegradation by a Pseudomonas sp. in model solutions

The presence of fatty acid and an n-alkane may affect the biodegradation rate of aromatic sulphur compounds such as dibenzothiophene (DBT). A fatty acid (hexadecanoic acid) may form micellar structures favouring DBT bioavailability. n-Alkanes, such as n-dodecane or n-hexadecane, form a film around the aromatic sulphur molecule as a consequence of solvation, thus increasing DBT bioavailability. The mass-transfer rate from the solid to the aqueous phase controls the DBT biodegradation rate when DBT is the only carbon source. Diffusional coassimilation and microbial hydrophobic effects are rate-limiting steps in DBT biodegradation in the presence of aliphatic compounds. Diffusion depends on the DBT concentration in n-alkane, while cometabolism is associated with different n-alkane biodegradation rates. Through the definition of biodesulphurization selectivity and biodersulphurization efficiency, our investigations have shown that a selective aerobic biodesulphurization process is possible by using an unselective biocatalyst, such as a Pseudomonas sp.

Organic geochemical indicators of dynamic fluid flow processes in petroleum basins

A variety of preliminary geophysical, geochemical, and geological observations (Anderson et al., Geophysics, 12–17, April 1991a, b; Anderson, Oil & Gas J. 85–91, 26 April 1993), along with well production data (Schumacher, AAPG Ann. Conv. Abstr., April 1993), have led to the hypothesis that fluid injection into Eugene Island Block 330 (EI-330) in the U.S. Louisiana Gulf Coast may be a continuing episodic process, with the most recent injections having occurred on short geologic time scales (10,000 yr or less). Organic geochemical evidence presented here suggests these processes may occur on very short time scales (years). A process, called “dynamic fluid injection”, was proposed to explain these observations and is envisioned as episodic pressure build-up followed by rapid escape of gas and oil through geopressure and injection into overlying reservoirs. In this contribution, gas and oil compositional data and sidewall core vitrinite reflectance data from EI-330 reservoirs were examined to determine whether they are more consistent with conventional oil and gas alteration processes versus recent dynamic fluid injection. The following EI hydrocarbon patterns are consistent with subsurface oil and gas migration-fractionation having altered the EI-330 oils at sometime in the geologic past: 1. (i) Ratios of n-heptane/methylcyclohexane ( F) plotted against those of toluene/ n-heptane ( B) for EI-330 oils lie in a region of either very high maturity or within a “migrated C7” field typical of an evaporative fractionation event. High maturity was ruled out as the cause of the high F values because ethane vs propane δ 13C values were not consistent with high maturity. Thus, the high F values are proposed to represent the “migrated C7 hydrocarbon” end of an evaporative fractionation event. In comparison, nearby South Marsh Island Block 128 (SMI-128) oils, located on the opposite side of a salt ridge, show higher gas maturities along with a tight clustering of F vs B values consistent with little or no evaporative fractionation. 2. (ii) Vitrinite reflectances are higher in sidewall cores from a fault system thought to feed these reservoirs than in samples away from the fault. 3. (iii) Biomarkers for EI-330 oils are consistent with a source from the same or very similar marine Lower Cretaceous or Jurassic source rocks of almost identical type and maturity. However, significant fractionations in percent sulfur, oil density (API gravity), and percentage of different sizes of molecules within the same compound class occur between reservoirs and fault-blocks. Other observations suggest that oil migration-fractionation processes may be occurring on short time scale (possibly as little as years): 1. (i) Consistent overproduction of oil and gas in the history of production of EI-330 reservoirs extending back to 1972. 2. (ii) Abnormally high concentrations of light C3 to C9 hydrocarbons in some EI-330 oils. The lightest n-alkanes diffuse fastest and tend to be lost as reservoirs leak over time. 3. (iii) Whole oil chromatograms show sharp well-resolved light hydrocarbon n-alkane peaks superimposed over a “humpane” type baseline typical of biodegraded oils in the shallowest GA and HB reservoirs. The presence of the highly biodegradable light n-alkanes together with the biodegraded oils is consistent with oil remigration into the shallower reservoirs. Assuming that conditions are adequate to support aerobic bacterial biodegradation in these shallow reservoirs (i.e. adequate supplies of meteoric water containing oxygen and nutrients), then the presence of highly biodegradable light n-alkanes together with heavier biodegraded oil suggests very recent (years to 100s of years) injection of the light n-alkanes into the reservoir. 4. (iv) Comparison of whole oil and C7 hydrocarbon data for EI-330 reservoirs taken in 1974, 1984 and 1988 suggest temporal changes in both light and heavy hydrocarbons for a number of wells and intervals. One consistent trend in several intervals is the appearance of enhanced concentration of C15 + n-alkanes in 1984 but not in 1974, 1988, or in the most recent sample collected in December 1993. Duplicate analyses of a number of samples collected 5 days apart appear to rule out sampling and analytical artifacts as the cause of these changes. These temporal changes, if confirmed in future research, suggest that biodegradation and reinjection of n-alkanes into some shallower and cooler EI-330 intervals is an on-going process which must be occurring on very short time scales. An extensive new drilling and sampling program was recently carried out at EI-330 in which gases, fluids, and cores were collected. Analyses are in progress; results will be used to test the viability of the “dynamic fluid injection” hypothesis vs other more conventional reservoir fractionation-migration processes.

N-alkane biodegradation by a marine bacterium in the presence of an oleophilic nutriment

Hexadecane biodegradation by a marine bacterium has been investigated in the presence of an oleophilic nutriment (INIPOL EAP 22). Hydrocarbon attack was only observed after metabolism of the fatty acids present in the fertilizer. The bacterium used up 95 % fatty acids in the first 24 hours. Hexadecane biodegradation took place after 50 h incubation and reached 40 % after 360 h.

Crude oil and hydrocarbon-degrading strains of Rhodococcus rhodochrous isolated from soil and marine environments in Kuwait

Soil and marine samples collected from different localities in Kuwait were screened for microorganisms capable of oil degradation. Both fungi and bacteria were isolated. The fungal flora consisted of Aspergillus terreus, A. sulphureus, Mucor globosus, Fusarium sp. and Penicillum citrinum. Mucor globosus was the most active oil degrading fungus isolated. Bacterial isolates included Bacillus spp. Enterobacteriaceae, Pseudomonas spp., Nocardia spp., Streptomyces spp.,and Rhodococcus spp. Among these Rhodococcus strains were the most efficient in oil degradation and, relatively speaking, the most abundant. Bacterial and fungal isolates differed in their ability to degrade crude oil, with Rhodococcus isolates being more active that fungin in n-alkane biodegradation, particularly in the case of R. rhodochrous. In addition to medium chain n-alkanes, fungi utilized one or more of the aromatic hydrocarbons studied, while bacteria failed to do so. R. rhodochorous KUCC 8801 was shown by GLC and post-growth studies to be more efficient in oil degradation than isolates known to be active oil degraders.

Evolution of hydrocarbons and bacterial activity in the marine sediments contaminated by crude oil overflow and treated

The fate of an experimental oil pollution of intertidal sediments in a sheltered beach of North Brittany (France) has been investigated over a 16-month period. Chemical treatments were applied to two of the three contaminated plots by pre-mixing oil respectively with dispersant and biodegrading agents. The physico-chemical and bacteriological characteristics of the polluted areas were followed with the purpose of identifying the limiting parameters for oil microbial degradation and the effect of treatment. The concentration of hydrocarbons in the oiled sediments did not change significantly during the experimental period. Spectrofluorimetric and chromatographic data showed that the main evolution of oil concerns the degradation of n-alkanes and the removal of light aromatics. Biodegradation of hydrocarbons occurred at a measurable rate only during the warm seasons (average temperature 18 +/- 2 degrees C) causing after sixteen months the disappearance of more than 80% of the n-alkanes fraction independently of the pollution sediment level and the chemical treatment of the experimental plots. However, the biodegradation of n-alkanes proceeded during the first months, at different rates, inversely depending on oil content in the collected samples. The main limiting factor is dissolved oxygen according to the fact that spilled oil was located at 3-5 cm depth in a poorly oxygenated zone characterized by low redox potential. Nutrients were not a limiting factor probably due to domestic and agricultural inputs in this area. A marked bacterial growth was observed two weeks after the oil spill with a relative increase in hydrocarbon degrading bacteria with respect to total heterotrophs. Degradation rates, based on C14 n-hexadecane experiments, seem to follow the same way than specific bacterial counts (plate technique). Specific bacteria are always high at the end of our 16 months' field experimentation. In the laboratory as well as in the field experiments, the same behaviour of untreated and chemically treated oil was observed in partially anaerobic sediment.