Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 10, 2009) Includes bibliographical references.

Thesis (Ph. D.)--University of Rhode Island, 2006. / Typescript. Includes bibliographical references (leaves 126-134).

Thesis (M.S.)--Ohio University, November, 2004. / Title from PDF t.p. Includes bibliographical references (leaves 74-83).

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Microbiologically Influenced Corrosion (MIC) is a process influenced by microbial presence and their metabolic activities. This study examined the microbial effects on metal corrosion under different environmental conditions with nutrient supplements. Experiments were conducted by inserting stainless steel 304 and mild steel coupons (2.5 x 2.5 cm²) into loam soil and a simulated seawater/sediment system with various nutrient conditions (sterilized, without supplement, 5 mM NaNO₃ or NH₄NO₃). Two mild and stainless steel coupons were removed monthly and the corrosion rate was evaluated based on the weight loss. Bacterial populations were enumerated using the most probable number (MPN) technique. The presence and adhesion of microbes on mild steel coupons were examined using Scanning Electron Microscopy (SEM). The extent of the corrosion process on the surface of the metal coupons were visualized by using the Stereo Microscope. The elemental composition of the corrosion products formed on the coupon surface were determined by Energy Dispersive X-Ray analyses. Isolation and identification of aerobic microorganisms were conducted and examined for its potential in either accelerating or inhibiting corrosion. The bacterial populations present on the mild steel surface were analyzed by fluorescent in situ hybridization. Denaturing gradient gel electrophoresis (DGGE) analyses of PCR-amplified 16S rDNA fragments were conducted to determine the microbial community complexity of the biofilm. Greater weight losses of mild steel in loam soil and the seawater/sediment system with NaNO₃ (48.86 mg/g and 19.96 mg/g of weight loss, respectively after 20 weeks) were observed with total heterotrophic bacterial population presented (106.695 MPN/ml and 0.11187 MPN/ml respectively) compared to the autoclaved control (7.17845 mg/g and 0.12082 mg/g of weight loss respectively). Supplementation of 5 mM NH₄NO₃ increased the total heterotrophic bacterial population and resulted in a decrease in weight loss measurements on the stainless steel coupons (211.4 MPN/ml with a 0.01 mg/g weight loss) after 20 weeks compared to the non-autoclaved loam soil and loam soil supplemented with NaNO₃ (139.2 MPN/ml and 134.9 MPN/ml respectively with no weight loss). SEM images of the mild steel coupons confirmed the presence and adherence of bacteria on the metal surface. Stereo microscopic images displayed reddish-brown deposits and pitting on the coupon surface. Isolation, identification and sequence analysis revealed that most microorganisms were the Bacillus species. This group of microorganisms are iron-oxidizing bacteria that could also promote the corrosion process. After 20 weeks of incubation, the total SRB cell counts were lower in samples supplemented with NaNO₃ in both loam soil and the seawater/sediment system. This study also indicated that the isolated aerobic microorganisms do play a role in the corrosion process in both stainless and mild steel. DGGE analysis revealed microbial diversity in the corrosion products especially those affiliated to the bacterial phyla Firmicutes and Gamma-Proteobacteria. Fluorescent in situ hybridization analysis allowed for an overall estimation of Eubacteria and sulphate-reducing bacteria present in the biofilm formed on the surface of mild steel. The current study indicates that the addition of nitrates did not significantly reduce the rates of corrosion of both mild and stainless steel. However, it does seem that environmental conditions did pose as an important factor in the corrosion process. Therefore, further studies need to be implemented to analyze the environmental type, microbial composition and optimization of the concentration of nitrates for possible mitigation of metal corrosion. To optimize MIC prevention and control, collaboration between engineers and microbiologists proves advantageous to develop an environmentally sound and potentially cost-effective approach to control corrosion. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Microbial-influenced corrosion (MIC) has been widely recognized as a significant economic and environmental problem in the oil and gas industry. MIC can be classified into two types based on the mechanisms: the extracellular electron transfer MIC (EET-MIC) and the metabolite MIC (M-MIC). The first includes electroactive bacteria that facilitate EET, while the latter includes bacteria that secrete corrosive metabolites. Sulfate-reducing bacteria (SRB) is believed to cause EET-MIC in carbon steel, a widely used metal in the oil and gas industry. In previous electroactive bacteria studies, nanowires have been shown to facilitate EET by acting as electron mediators. This study investigates the use of magnetite nanowires as electron mediators to accelerate EET-MIC of C1020 by Desulfovibrio vulgaris. The addition of 40 ppm (w/w) nanowires to carbon steel incubated with D. vulgaris, corrosive SRB species, for seven days resulted in 45% weight loss and 57% deeper pitting of carbon steel. Furthermore, electrochemical measurements of open circuit potential, linear polarization resistance and potentiodynamic polarization were found to be parallel with weight loss and pitting results. Therefore, these findings highlight the possibility of using magnetic nanowires as an electron mediator with high efficiency and selectivity to EET-MIC for future MIC studies and applications.

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Thesis (Ph. D.)--Mississippi State University. Department of Agricultural and Biological Engineering. / Title from title screen. Includes bibliographical references.