Biocorrosion

Biocorrosion of stainless steel is caused by exopolymer-producing bacteria. It can be shown that Fe is accumulated in the biofilm [2.62]. The effect of bacteria on the corrosion behavior of the Mo metal surface has also been investigated by XPS [2.63]. These last two investigations indicate a new field of research in which XPS can be employed successfully. XPS has also been used to study the corrosion of glasses [2.64], of polymer coatings on steel [2.65], of tooth-filling materials [2.66], and to investigate the role of surface hydroxyls of oxide films on metal [2.67] or other passive films. 

Geesey, G. 0-, Lewandbwski, Z, ajjd Fleming,.- H-C, Biofaufing /Biocorrosion id In sutal fVater Systems. Lewi.v Publi sher.s lnc. Chels ea, Michigan (1993) or 4) ... 

Tiller, A. K., Biocorrosion in Civil Engineering, Cranfield Institute of Technology (1990)... 

Condenser design usually calls for thin-walled tubing with high thermal conductivity characteristics plus a high degree of resistance to biofouling and the many forms of corrosion that may occur. (These forms include crevice and pitting corrosion, biocorrosion, and erosion-corrosion). 

G. Hernandez, C. Lemaitre, G. B. G. Mecanique, J. Guezennec, and J. P. Audouard. Biocorrosion of 316 1 stainless steel modified by poison alloying elements in sea water. In Proceedings Volume. Annu NACE Corrosion Conf (Corrosion 92) (Nashville, TN, 4/27-5/1), 1992. 

This review describes our unique assay system to investigate the role of cell-free hydrogenases in anaerobic biocorrosion, which resulted in proposing a new biocorrosion model. 

We were also able to clearly demonstrate the Clostridium pasteurianum [Fe] hydrogenase 1 was a corrosive enzyme, accelerating the dessolution of iron and hydrogen production from mild steel surfaces (Bryant and Laishley 1990). We believe hydrogenases are intimately involved in the metal biocorrosion process. 

This discussion has centered on the importance of iron in regulating the cellular protein components that play crucial roles in the microorganisms ability to affect biocorrosion of metals. However, it should also be noted... 

Thus we propose a novel biocorrosion model (Fig. 18.4) (van Ommen Kloeke et al. 1995) whereby the derepressed OM cytochrome(s) remove electrons from the cathodic site on the mild steel surface and couple with... 

Figure 18.4. Proposed biocorrosion model for cathodic electron depolarization of mild steel by D. vulgaris Hildenborough. CM, cytoplasmic membrane HMC, high molecular weight cytochrome [Fe] Fl2ase, iron hydrogenase [NiFe] H2ase, nickel iron hydrogenase ETS, electron transport system.

Bryant RD, Laishley EJ. 1990. The role of hydrogenase in anaerobic biocorrosion. Can J Microbiol 36 259-64. 

Dithazolium salt (141) displays fungicidal and acaricidal activities <82JAP82l83770), and salts of the type (248) are shown to be inhibitors of biocorrosion of metals <90URP1587049). 

Corrosion is an electrochemical process whereby the oxidation of metal(s) or alloys to their (lower energy state) oxides or cations takes place, resulting in loss of mechanical or structural strength and metal wastage. Corrosion takes many forms and includes biocorrosion, which is corrosion taking place at the water-metal interface of a biofilm. 

This is a general name for a wide variety of corrosion processes that may be actively or passively influenced, or induced, by an even wider variety of microbiological organisms. The electrochemical reactions that occur always result in metal wastage, as with all other forms of corrosion the most active biocorrosion processes primarily involve sessile bacteria rather than planktonic bacteria, algae, or fungi. 

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. 

Passive biocorrosion tends primarily to promote general metal wastage under the biodeposit, which can increase the total iron levels in the recirculating cooling water, although pitting corrosion can also occur. 

It may also be difficult to distinguish between passive and active forms of biocorrosion, as they may occur at the same time biofilm accumulations on metal surfaces will naturally contain live organisms (including slime producers, sulfate reducers, and acid producers), as well as dead bacteria, excretion products, trapped particles, and perhaps oil and grease or other foulants. 

Some examples of bacterial species involved in passive biocorrosion are ... 

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. 

Quantitative assessments of damage to cooling systems as a result of biocorrosion remain difficult, posing a bigger problem than generally recognized, and deserve more attention from both operators and water treaters. 

Merely periodically varying the types of microbiocides employed or adding product more frequently is generally insufficient to provide a well-managed microbiological control program and is seldom an effective solution for biocorrosion control, and may unnecessarily increase chemical treatment costs. 

Geesey/Lewandowski/Flemming, Editors. Biofouling and Biocorrosion in Industrial Water Systems. Lewis Publishers, USA, 1990. 

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