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Over the past decades MIC or Microbiologically Influenced Corrosion was recognized as a separate corrosion form besides general corrosion, galvanic corrosion, crevice corrosion, pitting, intergranular corrosion, erosion corrosion and stress corrosion. Today MIC should be considered as an extra parameter, a biological element amplifying the abiotic electrochemical corrosion process. MIC refers to the influence of microorganisms on the kinetics of the corrosion processes of metals. This accelerated type of corrosion may not be associated with one specific organism but with a collection of bacteria co-existing at the same time at the same place forming a microbial consortium. The main type of bacteria generally associated with corrosion or iron or steel are sulfate reducing bacteria (SRB), Sulphur-oxidizing v-bacteria (SOB), iron-oxidizing/reducing bacteria (IOB/IRB), manganese oxidizing bacteria and bacteria secreting organic acids and extracellular polymeric substances (EPS) or slime. The classical mechanisms for microbial influenced corrosion can be reviewed as follows: 1. Metabolic production of aggressive compounds 2. Oxygen concentration cell formation 3. Acceleration of anodic or cathodic reactions by depolarization effect 4. Hydrogen embrittlement (depolarization). Ballast water discharged by ships is generally identified as a major pathway for introducing species to new environments. The effects of the introduction of new species have in many areas of the world been devastating. The upcoming IMO ballast water management convention (2004) (maybe in force this year?) will try to call a hold to this explosive situation. Today, ships exchange their ballast water in the middle of the ocean but in the future, all ships will have to install a ballast water treatment system on board to rule out these organisms effectively. One of the possible techniques is to sterilize the ballast by means of UV light. The D-2 ballast water treatment system shall have an efficacy of; • not more than 10 viable organisms per m³ ≥50 micrometers in minimum dimension, and • not more than 10 viable organisms per milliliter
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