Microorganisms aqueous corrosion

Production of polymers contributes to pollution during synthesis and after use. A polymer produced by microorganisms is already a commercial product (Biopol). Unfortunately, however, cellular synthesis remains limited by the cost of downstream processing and the fact that the synthesis is aqueous-based, and it is impossible to perform the synthesis in the absence of a solvent. Recent research describes an enzyme-catalyzed polymer synthesis in which there is no solvent. This bulk polymerization mirrors conventional synthesis but eliminates the needs for extremes of temperature and corrosive acid catalysts. This represents the first rapid and efficient synthesis of polyesters from bulk polymerization under ambient conditions with very low concentrations of a biocatalyst (Chaudhary et al., 1997). 

Biofilm Control. Biofilms, often referred to as slime, occur on the surface of aqueous environments and are caused by a complex accumulation of microorganisms. Biofilms are usually considered undesirable, as they are frequently associated with odors, infections, fouling, and corrosion, but they can be beneficial under some circumstances such as the treatment of wastewater. 

Just as bulk electrolyte chemistry does not necessarily define the conditions at the metal surface under a film of microorganisms, direct counts of organisms present in the bulk aqueous environment have tJso been found to indicate little of relevance to predicting their influence on corrosion. This is because it is the organisms right at the metal surface that influence corrosion, and those organisms multiply so rapidly on the surface that a low density of organisms in the bulk quickly becomes irrelevant. 

In aqueous environments, microorganisms may influence the electrochemical environment and, consequently, corrosion rates and/or the susceptibility of metals to localized pitting corrosion in several ways. However, aU known cases of microbiologically influenced corrosion of metals can be attributed to known corrosion mechanisms, which are briefly summarized below. 

As already stated, MIC of metallic materials does not involve any new form of corrosion. The mechanisms involved in the biodeterioration of materials have already been given in detail. The main ways in which microorganisms may enhance the rate of corrosion of metals and/or the susceptibility to localized corrosion in an aqueous environment are given below in relation to known corrosion mechanisms (for each case some examples are also given) ... 

There are large numbers of reported case histories of MIC on stainless steel in water and aqueous waste systems. They are related to different industrial applications such as freshwater storage and circulation systems in nuclear power plants [103, 113,116,142] and cooling water systems in chemical process industries [117,118]. There are basically three cases (a) crevice corrosion under unexpected deposits, (b) sensitivity of pitting and crevice corrosion to trace of H2S, and (c) crevice corrosion in natural seawater. Most of these reports are not well documented concerning the microorganisms involved in the process. However, some general features are... 

Aqueous-based metalworking fluids of all types contain chemicals which, together with the water present, provide excellent nutrient sources for microorganisms. These organisms, if allowed to proliferate, can cause odors, deterioration of the fluid, and corrosion of machines and parts. 

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