Most liquid fuel systems are susceptible to microbiological contamination, the most susceptible fuels are middle distillates including aviation kerosene, automotive and marine diesel, gas oil and heating oils.

There are currently no widely accepted limit values for microbial contamination in fuels and it is difficult establish precise correlations between numbers of microorganisms found in fuel and the impact they can have on operations and fuel quality.  This is because different types of microbes can have different impacts.  Also microbial contamination is not evenly dispersed in fuel, so the numbers detected will vary depending on where a sample is drawn from.  Fuel is generally sterile immediately after the refinery process, but as it comes into contact with water in the distribution and supply chain, it can become contaminated with low numbers of microorganisms.  Most microbial growth occurs in pockets of water which can be found in tanks and system low points, particularly if these are badly designed or poorly maintained.  The water is essential for microbial growth and the microbes feed on the nutrients in the fuel.  With physical disturbance the microbes in the water become disturbed and dispersed in the fuel.  If conditions are conducive, these microbes may potentially proliferate to high levels that may have a deleterious effect on fuel properties.

Microbial activity can produce surfactants, and these may affect the water separation characteristics of the fuel and also cause water entrainment causing failure of “clear & bright” visual appearance tests as fuel samples may display a “haze” caused by the presence of suspended.  The formation of organic acids by microorganisms may also increase acidity and hence increased the measured Total Acid Number of the fuel.  Fuel from near the bottom of tanks may also display “blackening” due to presence of corrosive sulphide produced by Sulphate Reducing Bacteria (SRB).  Silver and copper corrosivity tests may also indicate failure to meet specification due to the presence of sulphide.  However, these impacts are usually only observed in fuel which has had a close and long-term association with heavy microbial proliferation in water.  The commonest impact on fuel quality will be the particulate contamination caused by the suspension of microorganisms and their by-products in the fuel – fuel specification tests that determine particulate content by visual assessment (ASTM D4156), gravimetric assessment (e.g. IP 415), filterability (e.g. IP 387 ) or by particulate counting (ISO 4406 cleanliness code) may all be affected.

The suspended microbial particles may also have a dramatic impact on the fuels fitness for use as it can cause serious filter clogging problems for in end-user applications such as rail, haulage, buses, and both fixed and portable power generation equipment.  Please also see our Aviation and Marine pages under the Industries section of this website for more information on fuel contamination issues in these sectors.

ECHA can;

• Conduct analysis of samples of fuel from your facility, vehicle or asset in our laboratory to assess the extent of microbiological contamination. Learn more about our lab analysis service here.
• Provide on-site microbial Test Kits. ECHA’s MicrobMonitor2 is a globally recognised industry standard test (IP 613/ASTM D7978) which can be used on-site or in the laboratory by non-microbiologists for the detection of microbiological contamination in diesel fuel. Learn more about the test here.
• Conduct surveys of tanks and systems at your fuel storage facility or depot if you have a concern about microbiological contamination. Learn more about our Site Surveys here.
• Provide advice on remediation, control, monitoring strategies and best practice. Learn more about our Consultancy Services here.
• Offer comprehensive, tailored training courses on microbiological contamination of diesel fuels and oils. Learn more about our Training Courses here.