Coating platform MIC

Are methanogens causing MIC corrosion?

The answer to this question is both yes and no. Metabolic products of methanogens can lead to a decrease in conductivity, thereby leading to a lower corrosion rate. But they can also enhance the corrosion process through several modes of action.

Sulphate reducing bacteria (SRB) are in general the first group of bacteria you think about in relation to MIC, however, they are not the only species involved in MIC. One of the species that are often related to MIC, specifically in combination with SRB are the Methanogens. Methanogens are microorganisms (Archaea) able to produce methane. They prefer anaerobic conditions and there are two different classes of Methanogens, the acetoclastic methanogens which prefer to use acetate as carbon source to make methane, and the hydrogenoclastic methanogens which prefer to use hydrogen gas (H2) as energy and carbon dioxide (CO2) as carbon source to produce methane.

There is a lot of ongoing scientific research on the role of methanogens. And recent scientific evidence shows that instead of using H2 as their energy source, methanogens can also use an electrode (electrons) as a viable energy source.
This can also be the case if the potential of a metal surface is such that it can provide enough energy for the methanogens to live.

 

Sulphate reducing bacteria (SRB) in general also like anaerobic conditions but several SRB are known to be able to resist and in rare cases also consume  some oxygen. SRB in general grow by using a carbon source as energy source, for example lactate or acetate, and reduce sulphate to hydrogen sulphide (H2S). This H2S can directly cause corrosion by locally reducing the pH. Another way of growth for SRB is by using protons (H+) as electron acceptor, producing H2. This growth mechanism is mostly favourable if sufficient energy is available or if the hydrogen pressure is kept low.

When a specific group of methanogens, the so called hydrogenoclastics, are very close to the SRB they can directly consume the hydrogen gas, maintaining an extremely low hydrogen pressure for the SRB to make to conditions favourable for the SRB. In that way SRB and methanogens both benefit from the syntrophic interaction allowing them both to multiply and both to directly and indirectly damage metal structures. Within our online Masterclass, these mechanisms are explained in more detail.

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