Prevent microbial growth in fuel tanks

Prevent microbial growth in fuel tanks

On-farm fuel storage has changed a lot in recent years. Tanks have been built with improved safety and efficiency, but proper maintenance practices are necessary to protect fuel inside.

While occurrences are limited, microbial contamination of diesel fuel can create challenges such as:

  • plugged filters
  • fuel flow problems
  • injector malfunctions
  • reduced combustion efficiency
  • increased rates of corrosion

Microbial growth

Bacteria and fungus cause microbial growth. Microbial growth occurs when water is in the storage tank and the diesel fuel temperature is between 10 C and 40 C. Bacterial and fungal spores commonly found in the soil can enter the fuel tank through vents on the storage tank or through contamination during filling. Condensation of water vapour within the fuel tank creates the conditions suitable for microbial growth at the fuel-water interface near the bottom of the tank.

The microbial growth and biomass production result in what appears to be a dark slime with an appearance of algae – some have even likened it to chocolate mousse. Under severe conditions, sludge accumulates on the bottom of the storage tank.


The easiest way to prevent microbial growth is to limit the amount of water in the storage tank. Check tank bottoms for water every month initially, decreasing frequency if no water is found. Tanks should be checked for water at least twice a year.

Regularly drain water from the bottom of the fuel tank by mechanical methods or with drain plugs located at the bottom of the tank. Water leakage into underground storage tanks should also be prevented.

Equip fuel tank vents with filters to prevent bacterial and fungal spores from entering the tank. Periodic tank cleaning, maintenance and inspection should be scheduled. Treatment with an approved fuel preservative can help to control or delay the buildup of microbial growth. The frequency of fuel treatment will depend on how fast microbial growth builds up.


Remove microbial growth by manually draining or chemically cleaning the tank. The use of a biocide may be necessary in combination with high-pressure washing.

When selecting chemical treatment, consider the compatibility with the fuel and other additives, environmental impacts and potential effects to equipment fueling systems.

Fuel filters on the storage tank and on transfer tanks will prevent slime or sludge from being transferred to farm equipment. Fuel transfer piping should draw fuel from the middle third of the tank to prevent sucking up of microbial growth or water.

If you suspect microbial growth in your on-farm diesel fuel storage tanks, talk to your local Co-op Fuel Team to find out how to submit fuel samples for testing and learn about remediation options.

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