Microbial Problems in Fuels

Microbes can contaminate a wide range of petroleum fuels from heavy residual fuel oils to gasolines and cause very costly operational problems for suppliers, distributors and also end-users such as airlines, ship and small boat operators, haulage companies, bus and train operators and power generators. The problems include:

Fouling

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.

Aviation Fuel showing microbial fouling at the fuel water interface

Corrosion

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.

Corrosive brown fungal growth on the internal surfaces of an aircraft fuel tank

Sulphide Spoilage

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.

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.