The most probable number (MPN) is the number of organisms that are most likely to have produced laboratory results in a particular test. The MPN method is used to quantify the concentration of the viable microorganisms in a sample and involves inoculating decimal dilutions into tubes of a broth medium, observing results and using a standard MPN...
Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating.
This corrosion may occur where stale sewage generates hydrogen sulfide gas into an atmosphere containing oxygen gas and high relative humidity. There must be an underlying anaerobic aquatic habitat containing sulfates and an overlying aerobic aquatic habitat separated by a gas phase containing both oxygen and hydrogen sulfide at concentrations in excess of 2 ppm.
Common corrosion-causing factors resulting in biogenic sulfide corrosion in presence of oxygen in aerobic bacteria are:
Biogenic sulfide corrosion is also known as microbiologically induced corrosion.
Biogenic sulfide corrosion involves the conversion of sulfates into hydrogen sulfide, which in its gaseous form is readily detectable. Hydrogen sulfide is then oxidized into sulfuric acid by another genus of bacteria that ultimately causes corrosion.
The most prevalent odorous gas is hydrogen sulfide (H2S), a precursor to the formation of sulfuric acid, H2SO4, which causes the destruction of metal and concrete substrates and appurtenances within wastewater collection and treatment facilities.
Some sulfate-reducing bacteria produce hydrogen sulfide, which can cause sulfide stress cracking. Acidithiobacillus bacteria produce sulfuric acid; acidithiobacillus thiooxidans frequently damages sewer pipes. Ferrobacillus ferrooxidans directly oxidizes iron to iron oxides and iron hydroxides. Other bacteria produce various acids, both organic and mineral, or ammonia.
Methods of preventing biogenic sulfide corrosion include:
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