Effects of Oil Dispersants on the Transport of Oil Contaminants and Photolysis/Photocatalysis of Oil-Related PAHs
Type of DegreePhD Dissertation
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Petroleum is the largest energy source consumed in the US today. Routine oil exploration, transportation, refining, and consumption process result in the release of a large amount of oil into marine environments. Oil spills also frequently occur due to accidental well blow-outs or tanker spills, and oil dispersants are used as common countermeasures for mitigating such oil spills. Unfortunately, there is no quick and low-cost way to measure dispersant concentration in seawater; the effects of oil dispersants on the sediment-associated transport of oil in marine environments are also not well known. Furthermore, the effects and mechanisms of dispersants on the photolysis of oil contaminants still need to be studied. In addition to accidental spills, a large amount of oil-contaminated wastewater has been produced by the petroleum industry, which are highly toxic, and these wastes should be properly treated. In the first part of this study (Chapter 2), a new method based on surface tension measurement was developed to determine the Corexit EC9500A concentration in seawater. The method can accurately analyze Corexit EC9500A in the concentration range of 0.5−23.5 mg/L. Minor variations in solution salinity, pH, and dissolved organic matter had negligible effects on the measurements. This simple, fast, economical method offers a convenient analytical method for quantifying complex oil dispersants dissolved in seawater. In the second part of this study (Chapter 3), the effects of three model oil dispersants (Corexit EC9527A, Corexit EC9500A and SPC1000) on the settling of fine sediment particles, as well as particle-facilitated distribution and transport of oil components in sediment-seawater systems were investigated. All three dispersants enhanced the settling of sediment particles (the nonionic surfactants, Tween 80 and Tween 85, play key roles in promoting particle aggregation). Yet, the effects varied with environmental factors (pH, salinity, dissolved organic matter, and temperature). Notably, total petroleum hydrocarbons, PAHs and alkanes in the sediment phase were dramatically increased in the presence of Corexit EC9527A. In the third part of this study (Chapter 4), the effects of oil dispersants on the photodegradation of anthracene and 9,10-DMA were studied under simulated solar light. All three tested dispersants promoted the photodegradation rate of tested PAHs. Kerosene, span 80 and tween 85 are the key dispersant components that promote the photodegradation rate. The dissolved oxygen plays different roles in the photodegradation of anthracene and 9,10-DMA. The photodegradation pathway of anthracene and 9,10-DMA showed no difference in the presence or absence of a dispersant. The dispersant components undergo photodegradation under solar light. In the fourth part of this study (Chapter 5), a new class of platinum-deposited anatase/hexa-titanate nanotubes (TNTs) were prepared, and the effects of Pt form, i.e., reduced state of Pt(0) and oxidized state of Pt(IV), on photocatalytic activity were compared. The materials showed higher phenanthrene degradation rate than TiO2 (P25). Both mechanisms of the enhanced photocatalytic activity were studied. Furthermore, the nanotubes can be separated through gravity-sedimentation, and reused in multiple cycles of operations without loss in the photocatalytic activity.