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Microorganisms in your fuel


As the use of biofuels increases, so, too, does the proliferation of bugs in fuel.

While these microorganisms cannot live and proliferate in fossil fuel, they find their perfect environment in the molecules of water contained in fuels and especially at the interface between water and fuel.

Microbial growth is seen as characteristic sludge, formed from accumulated cellular materials, slime materials or gelatins, which may restrict fuel pipelines and filters and cause injector fouling.

These microorganisms can multiply to produce a few kilograms of biomass in a very short time.

Tanks in an engine room or other warm locations and tanks receiving distillated fuel from injectors are ideal environments to grow bugs. Fuel stored in double-bottom tanks due to lower temperatures are less prone to have bugs.

The classic way for water ingress is through air in the yacht’s tanks when the tanks are not full of fuel. Particularly in winter, air in contact with the cold walls of tanks condensates and the water produced mixes with any fuel left in the tank after the operation season.

Eliminating water either by an Alpha Laval separator or draining it out automatically eliminates bugs and the problems are solved without using chemical biocides, which in addition to being toxic are also corrosive and might be harmful to the engine.

The problem is more complicated nowadays because, especially in Europe, biodiesel (fuel made by organic products such as sunflower seeds, sugar beets or sugar cane) is mixed into fossil fuel up to 7 percent in order to reduce CO2 emissions.

Biodiesel produces CO2 as well as fossil diesel, but when the bio products grow, they absorb CO2, so the final balance is near zero. Any country actually can produce organic products to transform into biofuels.

Nevertheless, the use of biodiesel complicates the mechanical operation of separating water from the fuel and draining it out of the tanks together with bugs.

Biodiesel contains lipids and is a good environment for bugs, so the only way to kill bugs is with the use of biocides. Biocides are chemical substances that can deter or kill any harmful organism generated inside the fuel tanks.

Most biocides are made with chlorine or chemical compounds that kill bugs. There are many brands of biocides on the market that can help to kill and/or control microorganism proliferation. Not all are necessarily supposed to be injected and there are biocides with less toxicity than others and with a faster action. And one important quality that products must have is the chemical properties to dissolve the massive surge of dead bugs to avoid clogging filters.

Yacht captains and engineers have different options for their needs in the market and might get in the topic thoroughly before taking any decision regarding this issue. Your professional fuel supplier can offer advice on the proper product for your vessel and circumstances.

Silvio Rossi is managing director of Rossmare International, a fuel bunkering company based in Savona, Italy. Comments on this article are welcome at

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