What is microbial induced corrosion (MIC)?
Microbial induced corrosion primarily affects pipe, manholes and other precast concrete products used in sewer systems. Corrosion of the concrete occurs due to production of sulfuric acid by a group of bacteria known as Thiobacilli. These bacteria essentially oxidize hydrogen sulfide (H2S). The H2S is released into the headspace of sewers when a sewer pipe becomes turbulent (rough flow of sewage, as when a toilet is flushed). The H2S is produced by another group of bacteria present in sewage, known as self-reducing bacteria. Together these two groups of bacteria create a cycle. As the acid reduces the pH of the concrete, one strain of bacteria die off and are replaced by another that survive at a lower pH. The cycle perpetuates until the pH has dropped to 1 or less. The time for this to happen is based on many things including temperature, turbulence and concentration of hydrogen sulfide.
