Diesel Bug is the term used to describe the microbes, usually a cocktail of bacteria and fungi, that can grow within a diesel fuel tank. It doesn’t grow in every fuel tank – many fuel users may never encounter it – but if conditions are right and it does get established, it can be a very serious problem. The risk of diesel bug infection has increased since the widespread introduction of Ultra Low Sulphur Diesel (ULSD) and the corresponding reduction of sulphur in diesel – sulphur is poison to most bacteria and fungi.
It starts as water starts to accumulate in a fuel tank. Water being heavier than diesel oil, it sinks to the bottom of the tank. The microbes then start to gather at the interface between the water and the fuel. Living in the water layer, they start to draw nutrients from the fuel and begin to multiply. Their growth rate can depend upon conditions, such as ambient temperature, but as they grow they start to form clumps of bio-mass – this biomass, which often has the appearance of brown slime, is very efficient at blocking fuel filters.
In extreme cases of infestation, the bug can spread around the fuel system and storage tank and start to form a bio-film. This is where layers of billions of microbes attach themselves to fuel tank walls and other surfaces. This can be a further problem because some microbes excrete acids which will quickly erode the fuel tanks walls.
Whilst diesel bug is not a new phenomenon – it’s been a known problem in the marine industry for many years – the changes to fuel formulations now make it a risk for anyone storing diesel, or gas oil, for long periods of time. This makes it a particular concern for applications such as standby generators, fire pumps etc.
There are a number of steps you can take to inhibit the growth of diesel bug, including improved fuel handling techniques, using fuel additives and biocides and fitment of diesel fuel polishing systems.
If you would like advice on how to ensure your fuel is bug free, contact the IPU fuel experts – firstname.lastname@example.org