DIESEL FUEL BUG

There are known to be over 20 species of fuel bugs that can contaminate your fuel storage tank. If the conditions are suitable they 'move in' and start to multiply. The fungal spores are carried by air and water, entering your fuel system via filling ports and vents. The air space above the fuel in tanks contains water vapour. The walls of the tanks are cool and the water vapour condenses on these surfaces. This water subsequently accumulates and sinks to the bottom of the tank creating an ideal environment for the growth of the most common of fungi "Cladisporium resinae".
Once in a fuel supply this contamination can exist virtually undetected and wait for the right conditions for growth. They can double their numbers every 20 minutes and one single spore can produce over 260,000 cloned descendants in six hours. Each spore lives for about 48 hours and as older fungi die their bodies accumulate, forming a slime that ultimately floats upwards into the fuel, a bit like soft candy floss- so it doesn't take long for the bugs to dominate the entire fuel system.

Fungal infestation can 'spoil' the fuel and the sludge and residue is drawn into the engine, quickly clogging filters, causing loss of power, narrowing fuel lines and eventually leading to engine breakdown. The damage does not stop there. A portion of sludge adheres to the inner walls of the tank and fuel lines producing corrosive hydrogen sulphide that causes metal defects and pitting of the injectors and fuel related components.

Condensation can and will occur at many points of discharge and delivery including the refinery, fuel depots and fuel jetties, in holding tanks and in all storage tanks. At the fuel/water interface there is both hydrocarbons and dissolved oxygen providing the idea environment for the fuel bug.
Cladisporium resinae can have many guises ranging from mousse, treacle, candyfloss, cotton wool etc and forms tangled threads a few microns in diameter, forming thick, tough mycelium mats at fuel/water interface. These micro-organisms will consume rubber gaskets, O-rings, hoses, tank linings and coatings in an effort to obtain their mineral content.

Diesel bug is not a single species of microbe. It can comprise a collection of bacteria, yeasts and moulds. It can exist even in fuel that is quite clean, but at low levels. If it does not enjoy suitable conditions to enable it to flourish, there is little to worry about, as minor contamination will be filtered out as the fuel is drawn through to the engine.

'Suitable conditions' essentially means the presence of water, because the microbes live and multiply on a fuel/water interface. They live and reproduce in the water, but feed on the nutrients in the fuel. Given the presence of water, warm or humid conditions will also help them to propagate. The number of bugs required to pose a problem is many millions, so the level of contamination is measured as a logarithmic power in colony-forming units (CFUs). 'Clean' fuel will have a rating of up to a few thousand (2x103cfu/lt), light contamination which is enough to cause a problem is up to a couple of million (2x106cfu/lt), while heavy contamination will be up in the tens of millions (1x107cfu/lt).

Identifying diesel bug is easy through oil analysis and there are several ways of eliminating the contamination through additives and filtration.