Biogenic sulfide corrosion
Biogenic Sulfide Corrosion is a bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

lly mediated process of forming hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 gas and the subsequent conversion to sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 that attacks concrete and steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 within wastewater
Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

 environments. The hydrogen sulfide gas is oxidized in the presence of moisture to form sulfuric acid that attacks the matrix of concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating.

Fresh domestic sewage entering a wastewater collection system contains an abundance of sulfates, SO42-. In the absence of dissolved oxygen and nitrates, these sulfates are reduced by sulfate reducing bacteria (SRB), identified primarily from the obligate anaerobic species Desulfovibrio
Desulfovibrio is a genus of Gram negative sulfate-reducing bacteria. Some species of Desulfovibrio are capable of transduction. Desulfovibrio species are commonly found in aquatic environments with high levels of organic material, as well as in water-logged soils, and form major community members...

, to form H2S via a complex pathway of biochemical reactions.

Once the H2S gas diffuses into the headspace environment above the wastewater, a sulfur oxidizing bacteria (SOB), primarily genus Thiobacillus aerobic bacteria, which colonize on pipe crowns, walls, and other surfaces above the waterline in wastewater pipes and structures, metabolize the H2S gas and oxidize it to H2SO4. This oxidizing process can take place where there is an adequate supply of hydrogen sulfide gas greater than 2 ppm, high relative humidity, and atmospheric oxygen.
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