Biocorrosion

Corrosion is a destructive result of an electrochemical reaction between a metal or metal alloy and the environment. In corrosion, the electrons are transferred from zero-valent metal to an external electron acceptor, causing the release of the metal ions into the surrounding medium and the deterioration of the metal. Microorganisms are known to induce corrosion, the unwanted degradation of metals. The deterioration of metals or metal alloys due to microbial activity is termed biocorrosion, microbially-induced corrosion, or microbiologically-influenced corrosion (often shortened as MIC). The electrochemical nature of corrosion remains valid for biocorrosion and biocorrosion is not one distinct type of corrosion, but the term is used to describe corrosion resulting from the metabolic activity of microorganisms within biofilms at metal surfaces or close to the surface. Microorganisms induce corrosion through several mechanisms, the most significant being through local changes in the electrochemistry at the metal-solution interface under the microbial biofilm. The metabolic activity of microorganisms attached to the surfaces and the properties of the biofilm are essential factors when considering the possibility of biocorrosion. The conditions under the biofilm may differ remarkably from the surrounding environment and thus, create micro-environments where the corrosion is locally increased. Microbes can accelerate several types of corrosion mechanisms such as general corrosion and localized corrosion, the latter including pitting and stress corrosion cracking. Different corrosion mechanisms may occur simultaneously contributing to total corrosion rate at different magnitudes. Microorganisms identified on corroding surfaces encompass a wide range of species with a vast range of metabolic properties. Microbial metabolites that may induce the corrosion of metals and metal alloys include sulfide, organic and inorganic acids and volatile compounds such as hydrogen, hydrogen sulphide, carbon dioxide, or ammonia, and additionally, microorganisms may directly consume electrons from metals.

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