Sulphate-reducing bacteria (SRB)

 
 
Sulfate reducing bacteria (SRB)

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.

 
 

The presence of hydrogen sulphide in crude oils

 

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.

 
crude oil
 
 

Properties of hydrogen sulfide

 
Hydrogen sulfide 2D
Hydrogen sulfide 2D
 
 
CAS number 7783-06-4
EC number 231-977-3
Appearance Colorless gas
Odor Faint rotten egg

Other names

Dihydrogen monosulfide
Dihydrogen sulfide
Stink damp
Sulfur dihydride
Sulfur hydride
Sulfureted hydrogen

Oveview about risks of hydrogen sulfide

  • Hydrogen sulphide reacts with metal ions to form metal sulphides, which can be considered salts of hydrogen sulphide 
  • When hydrogen sulphide reacts with Fe2+, iron sulphide, a black-coloured solid, can precipitate
  • Hydrogen sulphide is highly toxic 
 

Effects on humans

Concentatiion Effect
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

 

 
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