Microbial-induced corrosion (MIC) occurs in wastewater structures. This corrosion is harmful, as it attacks and weakens the concrete and the embedded steel. Biofilms are created by microorganisms called thiobacillis bacteria. These biofilms metabolize hydrogen sulfide gas (H2S) and generate sulphuric acid (H2SO4). Sulphuric acid is a potent diprotic acid (provides 2 hydrogen ions for each molecule). So how do you combat it?
Anti-microbial Admixtures
Admixtures are specific components added to a concrete mix to enhance the mix and help the structures last longer. Anti-microbial admixtures interrupt the cell membrane of the Thiobacillus bacteria. Once the membrane is interrupted, it will die. Since the cell can no longer live on the surface, hydrogen sulfide gas cannot be converted to sulphuric acid. Without the creation of acid, there is no concrete deterioration. Although it is difficult to prove its presence, the admixture will spike proteins and impale bacteria.
Coatings that Prevent Microbial-Induced Corrosion
One of the ways to prevent microbial-induced corrosion is coatings. Many coatings resistant to acid attack can be used to prevent concrete deterioration in a MIC environment. It does, however, need to be properly applied. Proper application and conditions can be ensured in a factory environment, and uncertainties with field application can be eliminated. Proper surface preparation, controlled temperatures, accurate measurements of mix components, and application thickness are all important. Once completed, the coating must be checked for continuity via a spark or holiday test.
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