Microbes In Your Fuel


Why Treating Your Tank For Them Is Important

When left unattended, fuel in storage tanks can sometimes develop a dirty slime at the fuel/water interface. This is not only unsightly, but can also block tank strainers and filters. If left unchecked, it can spoil the fuel and contribute to tank corrosion.

This slime is comprised mainly of fungus microbes, and uses kerosene or diesel as its main food source. Often described as looking like “chocolate mousse,” most of the sludge is composed of one specific type of fungus called Cladosporium resinae, commonly known as “clad.” In order to grow, fungus needs water, fuel, and a temperature range of 50* Fahrenheit – 104* Fahrenheit. If any of the previous conditions are not met, fungal spores will remain dormant until suitable conditions are present.

The key to fungal control is removal of water. The low points of tanks and pipework must be drained regularly. If all water is removed, one of the essential conditions is absent, and fungi cannot grow. If fungal contamination is suspected, samples can be tested. It is important to draw samples from the fuel/water interface and the tank bottoms. Once fungi is confirmed to be present, there are several treatment methods that can be used.

One option is to steam-clean the tank thoroughly. Any small residue of fungus or dirt remaining will help the fungus to re-establish. A fungicide or biocide may then be added as a preventative measure. Fungicides and biocides work by stopping fungus and bacteria from growing in the fuel, thereby prolonging its life. These chemicals are only effective on fungus and bacteria, and will not stop other oxidation reactions from taking place. They are normally active at the water-fuel interface where the fungus and bacteria grow. If fungus is present, then a kill dose is required (as opposed to a maintenance dose, which is lower). There are a few points to remember when handling fungicides and biocides:

  • Handling and mixing is hazardous because they are poisons.
  • For a kill dose, killing the fungus can lead to a buildup of dead matter which will block filters and cause the fuel to oxidize.
  • Ideally, the fungus should be killed, and the tank then emptied and drained.
  • Maintenance doses are no more effective than regular draining-off of water.
  • Disposal of water bottoms requires special handling with regard to the environment.

Fuel treatments do have advantages, and are infinitely better than doing nothing at all. However, their many disadvantages (including hazardous handling and storage requirements) mean that most companies are simply not equipped to handle them. Moreover, biocides do not clear the whole problem. They treat the infection, but will leave the contaminate in the fuel (e.g. fungal spores). This contaminate will remain until the tank is cleared out completely, or until it is strained out by the primary filter. Clean Fuels Associates can not only treat your tank with the appropriate biocides and fungicides, but can also clean any and all tanks.