Experiments were designed to answer the following questions: Are issues for storing alternative fuels in contact with natural seawater different from those experienced with petroleum-based fuels? Does initial oxygen concentration in the seawater and fuel phases affect biodegradation? What roles do the differences in seawater compositions (chemical and microbiological) play in the degradation of alternative fuels and the resulting corrosion? Under typical conditions, seawater in contact with petroleum-based (JP5JP5, F76 and ultra-low sulphur diesel) and alternative (camelina-derived JP5, algal-derived F76 and fatty acid methyl ester [FAME]) fuels stored with uncoated carbon steel became anaerobic within days due to oxygen consumption by corrosion reactions and aerobic respiration. Sulphides, produced by anaerobic sulphate-reducing bacteria, and chlorides were co-located in corrosion products in both the seawater and fuel phases. In general, higher sulphide levels were associated with alternative fuels when compared with their petroleum-based counterpart. Transient oxygen influenced both metabolic degradation pathways and resulting metabolites. Catechols, indicative of aerobic degradation, and typically aerobic bacteria persisted after three-month exposures. Detection of catechols suggested that initial exposure to oxygen resulted in their formation. Transient exposure to oxygen resulted in higher proportions of Firmicutes, Deltaproteobacteria (primarily sulphate-reducing bacteria), Chloroflexi, and Lentisphaerae in seawaters exposed to fuels than the original seawater. Relative proportions of sequences affiliated with these bacterial groups varied with fuel. Despite the dominance of characteristically anaerobic taxa, sequences for the key enzyme of an aerobic hydrocarbon-degradation enzyme (alkane monooxygenase) were obtained following PCR amplification. Two different seawaters, Coastal Key West, FL, and Persian Gulf seawaters, representing an oligotrophic and a more organic- and inorganic mineral-rich environment, were used to evaluate the effect of seawater properties on biodegradation and corrosion. The original microflora of the two seawaters were similar with respect to major taxonomic groups but with markedly different species. After exposure to FAME diesel, the microflora of the waters changed dramatically, with Clostridiales (Firmicutes) becoming dominant in both seawaters. Despite low numbers of sulphate reducing bacteria in the original seawaters and after fuel exposure, sulphide levels and corrosion increased markedly due to microbial sulphate reduction in the presence of Key West seawater, but to a lesser extent with Persian Gulf seawater.
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