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Diesel Digest: Frequent use of biocides negates its effectiveness

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Diesel Digest: by Capt. Jeff Werner

For most engineers and captains, the gospel when topping off a diesel tank is to mix the required quantity of the additive Biobor JF into the fuel tank along with the fuel.

According to the manufacturer’s label, this additive is a biocide. By definition, that bottle contains a chemical agent that kills all life forms by poisoning when used in sufficient concentration or duration.

That is a sobering thought since many captains and engineers don’t wear neoprene gloves and eye protection when adding those toxic chemicals into the fuel tank.

Biocides have been used for years in tanks to kill and prevent the proliferation of harmful fungi, bacteria and yeasts in fuel. Although biocides serve their purpose when applied properly, there are several reasons why biocides are not always the best option when it comes to effective fuel management.

According to PAN Germany, biocides “can often contain substances of concern with allergic, ecotoxic, carcinogenic, developmental neurotoxic or endocrine disrupting properties”. Additionally, those exposed can experience severe skin irritation and burns, allergic reactions, liver damage, and serious eye irritation and problems.

Not only are biocides toxic to humans, they also pose an environmental risk. Microbiocides, which target microbes and are used in many common fuel biocides, have been shown by the U.S. Environmental Protection Agency to be toxic to aquatic life, including fish and ducks. If a fuel tank leaks into a waterway, it can cause harm to the surrounding environment. However, if that fuel was also treated with biocide, the negative effects to wildlife would be compounded.

Frequent use of biocides in a fuel tank can cause the bacteria and microorganisms within the tank to build up a resistance. Just as humans and animals develop a resistance to antibiotics, microbes found within tank ecosystems can follow suit. This means that repeated use of a biocide in a fuel tank might render it ineffective.

The primary concern with biocides is they treat a symptom of the overall problem, and that treatment is only temporary. In a tank where there is sludge and microbial contamination there is water. The mere presence of water in fuel creates a breeding ground for harmful contaminants. Microbes live in the water and feed off the fuel. Since microbes produce asexually, it only takes one viable spore or cell to cause a problem. This microbial growth creates colonies that will cover the tank in slime.

Treating a tank with biocide will kill the microbial contamination and temporarily stop the proliferation of sludge. But the bottom of the tank will stay covered in sludge that will clog fuel filters. Instead of treating a tank solely with biocide, use a fuel polishing system to perform dialysis on the diesel fuel to obtain and maintain optimal fuel quality by following these steps:

  • Suction out the layer of sludge at the bottom of the fuel tank.
  • Suction out all of the water sitting at the bottom of the tank.
  • Using a multistage filtration system, cycle the fuel in the tank with successive passes through finer and finer disposable filters. Begin with a 25-micron filter, and then switch to a 10-micron filter. The final pass should be through a 3-micron filter. For many engines, filtering down to 3 microns will be sufficient. However, for newer high-pressure common rail diesel engines, it is advisable to filter out contaminants down to 2 or 1 microns in diameter to limit damage to the injector system. These filters should also have water block capabilities to remove any entrained water from the fuel.
  • Treat the fuel with a broad-spectrum fuel additive and combustion catalyst such as AXI’s AFC-705. It contains surfactants and dispersants that break down and dissolve sludge and organic debris clinging to the walls and baffles of the fuel tank. This type of additive will keep fuel in a stable, optimal condition for months.

Biocides have their use in a yacht’s fuel management program. They should be used sparingly and safely, and only when large amounts of microbial contamination are present in the tanks. A visual inspection inside the tank or of a fuel sample will quickly confirm a heavy contamination situation.

Rather than reaching for the biocide when bunkering fuel, use a broad-spectrum fuel additive instead to immediately treat any organic contaminants mixed in with the new diesel. Finish up by completely polishing all the fuel in the tank as soon as practical.
Capt. Jeff Werner is a 25-year veteran of the yachting industry as a captain on private and charter yachts, both sail and power, and a certified instructor for the RYA, MCA, USCG and US Sailing. He also owns Diesel Doctor (MyDieselDoctor.com). Comments are welcome below.

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