Fouling by slimes produced by bacteria, yeasts and/or moulds can cause severe filter plugging, blocking of fuel lines and injectors and consequently then cause excessive wear and failure of engines and system components. Fuel fouled by microbial slimes can fail particulate specifications.
Microbial slimes in filters and pipework
Microbial growth in fuel tanks and fuel systems can result in rapid and severe corrosion. For example occasional problems occur in aircraft wing tanks due to the growth of moulds and also yeasts and bacteria which produce organic acids and also stimulate corrosion by creating oxygen gradients which enhance electrochemical corrosion cells. In steel tanks, growth of Sulphate Reducing Bacteria (SRB) in water and sludge in the bottoms of tanks can cause pitting corrosion. For more information see Microbially Influenced Corrosion.
Corrosion pits in three different tank surfaces
Growth of Sulphate Reducing Bacteria (SRB) in fuel tanks can also cause sulphide spoilage of fuels. The fuel becomes corrosive and will fail sulphide limit specifications.
Black sulphide development in water phase under jet fuel sample
Increased water content
Microbial surfactants can stimulate the suspension of water in fuel causing it to become hazy and causing failure of fuel water separators.
Although the microbes need water to grow they need very little. In practice there is often sufficient water in the bottom of large storage tanks and even in the fuel tanks of road vehicles such as trucks and buses for some microbial growth to occur. The microbes tend to be most active at the interface between the water and fuel and also on internal tank and system surfaces. When the tank contents are disturbed, for example when the tank is refilled, the microbes become suspended in the bulk fuel where they cause fouling and may be passed on down the distribution chain to contaminate facilities downstream. Costs for decontaminating facilities are high. Prevention of problems by good housekeeping and regular monitoring is most definitely more cost effective than the “fire brigade treatment” of problems and the consequential losses due to system and equipment failures.
Hazy fuel sample with suspended and settles microbiological material