Microbial Growth in Diesel Fuel


You do not have a bug problem, you have a water problem. Bugs are everywhere but no water no life. It is that simple. Free water is the single most destructive contaminant in any fuel system and bugs are only one of it's results
Howard L. Chesneau
Fuel Quality Services, Inc.
​Microbes Must be Eradicated 

Microbial colonies can proliferate in any fuel tank. All they need is food (fuel) and water to grow. Warm weather and the presence of biofuels will accelerate this process. Once these microbes have gained a foothold in your fuel tank, they can be hard to eliminate. The first step, of course, is to diagnose the problem and its severity.

Microbial contamination varies in appearance, but looks very different from typical dirt. Most people don't realize they have a problem with their system until they experience filter plugging. By this time the situation is far more severe than just a few microbes. 

One easy indicator may be found in your used fuel filters. Open up a clogged filter, if it is coated with stinky, slimy, black filth; then you probably have a microbe problem. ​One ASTM test method for diagnosing microorganisms in fuel is described in ASTM D7463-08. This test detects the presence of Adenosine Triphosphate (ATP) in fuel and fuel/water mixtures. ATP is an energy-bearing molecule found in all living cells. If ATP is present, it means that micrboes are living in your diesel tank. The test helps estimate the concentration of microorganisms, which is useful in diagnosing a microbial problem, validating the effectiveness of the treatment, and for ongoing monitoring of your fuel supply. The advantages of this test method are that it is fast and easy. The user can do it and see the results in about 10 minutes. 

Other tests that can be done by users may be more complex and require several days before producing results. It should be noted that regardless of the test method you choose, one sample may not provide the complete picture. The best way to get a good idea of the severity of any biological problem is to take samples from more than one location and at a variety of different depths. This is especially true when tank design makes it difficult to examine areas where there is water. Depending on the size of your fuel investment, you may wish to call in an expert or purchase a commercially available kit to do the testing yourself. A quick search for "microbial growth test kit" will yield a number of options.

Microbes are everywhere. But when they have acclimated to your fuel system, half-measures will probably not eliminate the problem. If you don't remove the system's free water and substantially reduce the active colony, they will simply grow back. You never truly sterilize a fuel system, but you can reduce and control biological activity to a level where it is not a problem. Numerous good biocides are available for proactive use. DO NOT USE what many call "maintenance dosing". These are usually sub-lethal and actually make things worse. A better proactive strategy is to periodically treat the system with a kill dose. The time frame for this can be determined by a systematic testing program to determine how frequently your system gets re-infested. Also, it is very important to institute a vigorous water removal program. This alone will significantly reduce future contamination issues. 

For bad infestations, we recommend a multi-step process: 

    1. Drain the tank of all free water.
    2. Use a high dose of a reputable biocide to "shock" the contaminated tank
    3. ​Follow this with a thorough "man down" tank cleaning, scouring the sides
      and bottom to remove all remnants.
    4. Prevent reoccurrence by using a periodic kill dose of biocide on a regular
      basis to protect a clean system.
    5. Install a highly efficient filter system at the outlet of your tank and/or at
      your dispenser to ensure that microbes (alive or dead) are not passed along
      into your equipment where they can quickly clog your onboard filters and
      form engine deposits

Be sure to follow dosing instructions carefully and retest your tank periodically, to be sure that your anti-microbial regimen is working. Some equipment operators choose to skip the tank cleaning step due to downtime, cost considerations or the inability to physically enter the tank. In this case, be aware that you may load up a large quantity of filters with dead microbes before the tank flushes itself out. Microbes cannot reproduce without water. If your tank is properly maintained and contains no free water, then microbes will not grow.