Corrosion by Sulpher oxidizing bacteria

Sulphur oxidisers are capable of oxidising elemental sulphur or sulphur-bearing compounds to sulphuric acid. They thrive best in environments at low pH and can produce localised sulphuric acid concentrations up to 5 wt%. In other words, these organisms have the capacity to create very extreme corrosive conditions. But you should create a wider view on their capabilities. Generally speaking, you can distinct two different types of sulphur-oxidising bacteria

  • photoautotrophs and
  • chemo- lithotrophs.

The photoautotrophic bacteria obtain their energy from sunlight for their metabolism, while in the dark they reduce carbon dioxide to organic substances with this energy. This energy is stored in the form of ATP. Chemolithotrophic bacteria obtain their energy directly from oxidation reactions.

In these reactions, oxygen will serve as an electron acceptor for aerobic bacteria and nitrates and nitrites for anaerobic bacteria. The required electrons are released during the oxidation of sulphides and the end products sulphur particles, sulphates and nitrogen gas or nitrites.

Sulphate-reducing and sulphur-oxidising bacteria can have a symbiotic relationship in changing soil conditions. This works like a cyclic process. Sulphate-reducing bacteria can grow rapidly during wet and rainy seasons, when the soil is wet and poorly aerated. The sulphur oxidisers will start to thrive when the weather starts to change and the soils dries. During this proces these SOB’s are oxidising the sulphide metabolic products to sulphuric acid, which can have extensive corrosion damage to buried metal structures as a result.

You can read a more extensive article on these underlying mechanisms

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