Microbially influenced corrosion sulfur

The choice of the appropriate material is decisive for resistance against microbially influenced corrosion. This means that before the choice of material can be made, what kind of impacts is has to resist needs to be considered. Microbial influencing factors must also be considered. Accordingly, in the presence of volatile sulfur compounds, e.g., in sewage pipelines, it is recommended not to use materials like unprotected concrete which may be destroyed by the end product of the microbial degradation process (in this case, sulfuric acid formed by Thiobacilli). Another example would be the choice of a stainless steel or of an alloy that cannot be attacked under the conditions of a biofllm and the complex metabolic processes occurring underneath it. If, for instance, a material has to be chosen for static reasons, this material has to be protected by a coating or a liner made of an inert material. All these examples are based on the consideration that all attack factors have been identified by a complete inventory. 

In many cases, microbially influenced corrosion can be reduced or even completely prevented by adopting adequate constructive measures. This is exemplified below for a sewage pipeline system. If the atmosphere above the sewage contains a large quantity of volatile sulfur compounds like H2S, then if concrete pipes must be used, they should be protected with an inert material that cannot be attacked by the microbially formed... 

In brackish and wastewater systems, microbially influenced corrosion (MIC) can occur, especially in systems where equipment has been idle for extended periods. A 6% molybdenum alloy offers protection from manganese-bearing, sulfur-bearing, and generally reducing types of bacteria. Because of its resistance to MIC, Alloy 25-6Mo is being used in the wastewater piping systems of power plants. 

Depending on the bacteria and soil conditions which can be described appropriately as an extremely heterogeneous system, these transformations may be assimilatory or dissimilatory metabolic functions. Based on the recent field surveys and laboratory studies, the bacterial-environmental interactions, with reference to the cycles of sulfur and other elements, in corrosion on buried pipes are shown as Figure 1. This Figure demonstrates that microbiologically influenced corrosion (MIC) results from the activities of a microbial community. 

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