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Sulphate-reducing bacteria are known to play an important role in anaerobic corrosion processes. They are often found associated with metal surfaces and their activities can be of particular economic significance in many industrial areas. The aim of this thesis was to investigate anaerobic corrosion of metals by the sulphate-reducing bacteria in the presence of mixed microbial consortia in various heterogeneous marine environments. A laboratory model system was designed, based on part of an offshore oil storage system. An extensive bacteriological analysis and comprehensive study of the consequent physicochemical parameters involved in the microbial corrosion process was carried out. Particular attention was paid to the activity of the sulphate-reducing bacteria on metal surfaces. A method was developed to measure both acid-volatile and non-acid-volatile sulphur formation, produced by the activity of the sulphate-reducing bacteria on mild steel coupons. The importance of this method is firmly stressed. Previous results involving rates of sulphate reduction estimated without considering non-acid-volatile sulphur product formation, must be interpreted with caution. A study of non-biological methods of analysing corrosion and their various limitations was carried out to assess their usefulness in determining the effect of microbial corrosion in various environments. It must be stated that no single technique can be used to study anaerobic microbial corrosion. Therefore, it is recommended that a series of tests should be utilised. These should include microbiological, chemical and metallurgical methods.

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Hydrogen gas production occurs in permeable reactive iron barriers (PRBs) due to the anaerobic corrosion of granular iron. Once produced, this hydrogen gas can have detrimental physical effects on PRB performance. Corrosion-produced hydrogen may accumulate in pore spaces within the PRB, thereby reducing the porosity and permeability. It may also escape the PRB system, representing a lost electron resource that may otherwise be used in reductive remediation reactions. In addition to these physical effects of hydrogen on PRB performance, chemical interactions between hydrogen and iron also occur. Hydrogen may become absorbed by the iron and stored as an electron resource within lattice imperfections. It may also interact with iron surfaces to influence the corrosion rate of the iron. These chemical interactions between hydrogen and iron may impact the reactivity of the iron granules and therefore affect PRB performance. Currently, the chemical effects of hydrogen on PRB performance remain largely unexplored. In this study, the effect of hydrogen on iron reactivity was investigated by considering hydrogen absorption into iron and hydrogen induced changes to iron corrosion rates. Hydrogen absorption by iron creates a stored electron resource within the iron granules. Release of this stored hydrogen from trapping sites represents an additional electron resource that may be used in contaminant degradation reactions. Therefore, improved hydrogen absorption may contribute to increased iron reactivity. Hydrogen absorption by granular irons has been largely unexplored in PRB performance investigations and the effect of hydrogen absorption on contaminant remediation remains unknown. In this study, an investigation of the factors governing hydrogen absorption by three granular irons, H2Omet56, H2Omet58 and H2Omet86 was conducted. The results demonstrated that rapidly corroding H2Omet86 absorbed hydrogen at a higher rate than the other more slowly corroding irons. The presence of an oxide film on H2Omet56 appeared to improve the proportion of hydrogen absorption compared to the bare irons. Ultrasonic treatment was explored as potential method of release of trapped hydrogen for improved iron reactivity. Ultrasonic treatment appeared to be unsuccessful at releasing stored hydrogen from trapping sites, but further investigations into different ultrasound conditions as well as other methods of hydrogen release could prove useful. Hydrogen gas may also influence iron reactivity by interacting with iron surfaces to alter the corrosion rate of the iron. This may occur by processes such as hydrogen enhanced anodic dissolution, hydrogen induced cracking, enhanced pitting susceptibility and reduction of iron oxides by hydrogen gas. In this study, the effect of hydrogen on iron corrosion rates was assessed by treating two iron materials (H2Omet56 and Connelly) under high pressures of hydrogen for 14 d, then comparing the post-treatment corrosion rates of hydrogen treated irons to the post-treatment corrosion rates of corresponding irons treated under low hydrogen pressures for the same period. The results demonstrated that the post-treatment corrosion rate of high hydrogen treated H2Omet56 iron was lower than the post-treatment corrosion rate of low hydrogen treated H2Omet56 iron. Hydrogen treatment did not appear to affect the post-treatment corrosion rates of Connelly iron. The effect of hydrogen on the corrosion rate of H2Omet56 iron may be a result of hydrogen enhanced anodic dissolution. The presence of a continuous oxide film on Connelly iron appeared to inhibit the effect of hydrogen enhanced anodic dissolution on Connelly iron corrosion rates. The effects of iron oxide reduction by hydrogen and hydrogen induced pitting corrosion were also considered.

Iron corrosion is an extremely complicated process because numerous factors such as pH, DO, temperature, inhibitor, and other various constituents in water can exert a controlling influence. The economic importance of problems that are caused by corrosion has been recognized. Therefore, the necessity of better understanding corrosion phenomenon is apparent. The effect of phosphorus, especially in oxidation states different than phosphate (+V) (e.g., PO3-3, PO2-3 and PH3 gas), on anaerobic iron corrosion was examined. Tests were conducted at pH 3, 7, and 10- 11 in a solution of 10-3 M NaCl. There was not a significant catalytic effect of phosphorus species on anaerobic iron corrosion. Higher levels of PH3 did markedly increase H2 evolution, consistent with observations of other researchers, but it is possibly due to oxidation of PH3 by iron surfaces with production of H2. Various constituents were also tested for iron corrosion in anaerobic solution [Al3+ (soluble), Al(OH)3, Cu2+, Si(OH)4, Boron, NOM, and sulfide] at pH pH 3, 7, and 10-11. None of these appeared to inhibit corrosion compared to a control. At pH 7, soluble Al3+ and Cu2+ in solution led to much higher production of H2 relative to a control. Phosphorus species had little impact on iron corrosion rates in the presence of sulfides (198 mg/L as S2-). In much of the research, recovery of H2 in the headspace was much lower than was predicated based on classic equations. This implies that some other, and as yet unappreciated, reactions are occurring in this system. However, in other instances the recovery of hydrogen was consistent with classical theory. Future work should examine the circumstances in which agreements and disagreements with classic theory occur. / Master of Science