Sulfate reducing bacteria (SRB)
Sulphate-reducing microorganisms (SRM) are bacteria (SRB) and archaea that obtain energy through anaerobic respiration, by "breathing" sulphate rather than molecular oxygen (O2) under anaerobic (oxygen-free) conditions.
Sulphate-reducing bacteria can be traced back 3.5 billion years and are considered among the oldest forms of microorganisms on Earth. Certain SRB species can tolerate temperatures exceeding 90°C and pressures of over 100 bar.
SRB’s main nutrients are simple organic acids and molecular hydrogen (H2) from decomposing natural organic matter. These nutrients are oxidised, and sulphate (SO42-) is reduced to sulphide (hydrogen sulphide, H2S). The H2S produced by SRB can have a disastrous impact. It contaminates gas and oil, promotes the precipitation of ferrous sulphide (which can subsequently plug injection wells), and is one of the leading causes of microbiologically influenced corrosion (MIC).
Effective control of SRB can prevent the formation of H2S, extend the operational life of the system, and greatly reduce the incidence of microbiological issues.
Hydrogen sulphide (H2S) occurs naturally in many of the world’s crude oils. It is also formed during the refining process through the degradation of sulphur-containing compounds at high temperatures. Globally, the average sulphur content of crude oils processed at petroleum refineries continues to rise.
Refineries and storage facilities, such as tank farms, are likely to encounter problems related to the handling of crude oils, intermediates and refined products that contain or generate H2S.
Heavy oils, including crude oil, residual fuel and gas oil, typically have high concentrations of H2S. This is particularly a concern when these products are to be stored for an extended period or transported. Moreover, while safety remains the primary concern, H2S, can create additional challenges for these facilities.
|Odor||Faint rotten egg|
|0.003 - 0.02 ppm||Clearly detectable by smell|
|3 - 10 ppm||Very unpleasant smell|
|20 - 100 ppm||Distinct smell of rotten eggs|
|50 - 100 ppm||Stinging pain in eyes and irritation of respiratory organs|
|100 - 200 ppm||Sedation of olfactory sense|
|250 - 500 ppm||Fluids in lungs, cyanosis, bloodstained cough, pneumonia|
|500 - 1000 ppm||Stop for respiration, immediately collapse, death organ|