What is Microbially Induced Corrosion (MIC) of Concrete? In a previous blog, “What are the Main Causes of Manhole Deterioration”, we highlighted various problem areas existing in manhole structures, and we mentioned Microbially induced corrosion (MIC) in passing. So, what is MIC and where does it come from? Microbially induced corrosion (MIC) can be defined as the process by which live microorganisms cause changes in the physical properties of a structural material. You may have also heard it referred to as microbially influenced corrosion, biocorrosion, or just microbial corrosion. In the case of concrete, a common material of construction for wastewater manholes, lift stations, and treatment plant structures, MIC can reduce lifespan by as much as 50%. Sulfate naturally occurs in drinking water and so it eventually ends up in the wastewater stream. Those sulfates are converted to hydrogen sulfide gas (H2S) by sulfate-reducing bacteria. This process