Corrosion, types biocorrosion

The various types of bacteria involved in the common forms of biocorrosion may act as single species, in concert with other species, or in conjunction with other nonbiological forms of corrosion. 

Biocorrosion in well-oxygenated cooling systems can also involve other types of bacteria, such as nitrifying bacteria, which are commonly found where ammonia is present (say from refinery or fertilizer plant leaks). They are principally aerobic and oxidize ammonia to nitrate, causing serious local falls in pH that result in nitric acid corrosion. Examples are Nitrosomonas sp. and Nitrobacter sp. 

SRB have been implicated in localised pitting corrosion, commonly referred to as microbially influenced corrosion (MIC). These and other anaerobes cause biocorrosion due to production of adds and other by-products (e.g.hydrogen sulphide), that cause cathodic depolarisation of metal surfaces. SRB also cause discoloration problems and production of foul odors. They are susceptible to bioddes, and can be controlled. Many other types of anaerobes may be present in the mill system, including the common helical-shaped, motile bacteria Spirillum. These corkscrew-shaped anaerobes are often seen under the microscope swimming in deposit samples and soured stock. 

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