Impact of Photooxidation and Biodegradation on the Fate of Oil Spilled During the Deepwater Horizon Incident: Advanced Stages of Weathering

While the biogeochemical forces influencing the weathering of spilled oil have been investigated for decades, the environmental fate and effects of “oxyhydrocarbons” in sand patties deposited on beaches are not well-known. We collected sand patties deposited in the swash zone on Gulf of Mexico beaches following the Deepwater Horizon oil spill. When sand patties were exposed to simulated sunlight, a larger concentration of dissolved organic carbon was leached into seawater than the corresponding dark controls. This result was consistent with the general ease of movement of seawater through the sand patties as shown with a ³⁵SO₄^2– radiotracer. Ultrahigh-resolution mass spectrometry, as well as optical measurements revealed that the chemical composition of dissolved organic matter (DOM) leached from the sand patties under dark and irradiated conditions were substantially different, but neither had a significant inhibitory influence on the endogenous rate of aerobic or anaerobic microbial respiratory activity. Rather, the dissolved organic photooxidation products stimulated significantly more microbial O₂ consumption (113 ± 4 μM) than either the dark (78 ± 2 μM) controls or the endogenous (38 μM ± 4) forms of DOM. The changes in the DOM quality and quantity were consistent with biodegradation as an explanation for the differences. These results confirm that sand patties undergo a gradual dissolution of DOM in both the dark and in the light, but photooxidation accelerates the production of water-soluble polar organic compounds that are relatively more amenable to aerobic biodegradation. As such, these processes represent previously unrecognized advanced weathering stages that are important in the ultimate transformation of spilled crude oil

Molecular tools to track bacteria responsible for fuel deterioration and microbiologically influenced corrosion

<div><p>Investigating the susceptibility of various fuels to anaerobic biodegradation has become complicated with the recognition that the fuels themselves are not sterile. Bacterial DNA could be obtained when various fuels were filtered through a hydrophobic teflon (0.22 μm) membrane filter. Bacterial 16S rRNA genes from these preparations were PCR amplified, cloned, and the resulting libraries sequenced to identify the fuel-borne bacterial communities. The most common sequence, found in algal- and camelina-based biofuels as well as in ultra-low sulfur diesel (ULSD) and F76 diesel, was similar to that of a <i>Tumebacillus</i>. The next most common sequence was similar to <i>Methylobacterium</i> and was found in the biofuels and ULSD. Higher level phylogenetic groups included representatives of the Firmicutes (<i>Bacillus</i>, <i>Lactobacillus</i> and <i>Streptococcus</i>), several Actinobacteria, Deinococcus-Thermus, Chloroflexi, Cyanobacteria, Bacteroidetes, Alphaproteobacteria (<i>Methylobacterium</i> and Sphingomonadales), Betaproteobacteria (Oxalobacteraceae and Burkholderiales) and Deltaproteobacteria. All of the fuel-associated bacterial sequences, except those obtained from a few facultative microorganisms, were from aerobes and only remotely affiliated with sequences that resulted from anaerobic successional events evident when ULSD was incubated with a coastal seawater and sediment inoculum. Thus, both traditional and alternate fuel formulations harbor a characteristic microflora, but these microorganisms contributed little to the successional patterns that ultimately resulted in fuel decomposition, sulfide formation and metal biocorrosion. The findings illustrate the value of molecular approaches to track the fate of bacteria that might come in contact with fuels and potentially contribute to corrosion problems throughout the energy value chain.</p> </div

Assessment of Biofouling and Corrosion Risk in Tanks Storing B20 Biodiesel

<p>The introduction of next generation renewable fuels to the current infrastructure potentially poses new challenges with regard to biofouling and biocorrosion. In an effort to increase energy independence, the US Department of Defense has mandated the use of next generation alternative fuels. The risk to fuel infrastructure was unknown upon the introduction of B20 (20 percent biodiesel and 80 percent conventional diesel). Three in-ground storage tanks reported as experiencing varying degrees of fouling containing B20 were selected for this study. This work represents a comprehensive attempt to measure the biodeterioration and biofouling of B20 biodiesel and the associated corrosion risk for exposed infrastructure. This knowledge will be used to monitor these activities in service, predict suitable targets for mitigation and assess the efficacy of any mitigation activities deployed.</p

Impact of Organosulfur Content on Diesel Fuel Stability and Implications for Carbon Steel Corrosion

Ultralow sulfur diesel (ULSD) fuel has been integrated into the worldwide fuel infrastructure to help meet a variety of environmental regulations. However, desulfurization alters the properties of diesel fuel in ways that could potentially impact its biological stability. Fuel desulfurization might predispose ULSD to biodeterioration relative to sulfur-rich fuels and in marine systems accelerate rates of sulfate reduction, sulfide production, and carbon steel biocorrosion. To test such prospects, an inoculum from a seawater-compensated ballast tank was amended with fuel from the same ship or with refinery fractions of ULSD, low- (LSD), and high sulfur diesel (HSD) and monitored for sulfate depletion. The rates of sulfate removal in incubations amended with the refinery fuels were elevated relative to the fuel-unamended controls but statistically indistinguishable (∼50 μM SO₄/day), but they were found to be roughly twice as fast (∼100 μM SO₄/day) when the ship’s own diesel was used as a source of carbon and energy. Thus, anaerobic hydrocarbon metabolism likely occurred in these incubations regardless of fuel sulfur content. Microbial community structure from each incubation was also largely independent of the fuel amendment type, based on molecular analysis of 16S rRNA sequences. Two other inocula known to catalyze anaerobic hydrocarbon metabolism showed no differences in fuel-associated sulfate reduction or methanogenesis rates between ULSD, LSD, and HSD. These findings suggest that the stability of diesel is independent of the fuel organosulfur compound status and reasons for the accelerated biocorrosion associated with the use of ULSD should be sought elsewhere

GeoChip-Based Analysis of Microbial Functional Gene Diversity in a Landfill Leachate-Contaminated Aquifer

The functional gene diversity and structure of microbial communities in a shallow landfill leachate-contaminated aquifer were assessed using a comprehensive functional gene array (GeoChip 3.0). Water samples were obtained from eight wells at the same aquifer depth immediately below a municipal landfill or along the predominant downgradient groundwater flowpath. Functional gene richness and diversity immediately below the landfill and the closest well were considerably lower than those in downgradient wells. Mantel tests and canonical correspondence analysis (CCA) suggested that various geochemical parameters had a significant impact on the subsurface microbial community structure. That is, leachate from the unlined landfill impacted the diversity, composition, structure, and functional potential of groundwater microbial communities as a function of groundwater pH, and concentrations of sulfate, ammonia, and dissolved organic carbon (DOC). Historical geochemical records indicate that all sampled wells chronically received leachate, and the increase in microbial diversity as a function of distance from the landfill is consistent with mitigation of the impact of leachate on the groundwater system by natural attenuation mechanisms

Correction to GeoChip-Based Analysis of Microbial Functional Gene Diversity in a Landfill Leachate-Contaminated Aquifer

Correction to GeoChip-Based Analysis of Microbial Functional Gene Diversity in a Landfill Leachate-Contaminated Aquife