Which bugs are involved?
The organisms currently found growing in fuel include bacteria and fungi (yeasts and moulds), withHormoconis resinae (H.res) being the main fungi that causes the most problems. Commonly referred to as‘the diesel bug’ or ‘the jet fuel fungus’, H.res can produce vast quantities of biomass, while the most common yeasts are Yarrowia Lipolytica & Candida Kerosenii.
The main bacterium that thrives in fuel is Pseudomonas Aeriginosa. These organisms are believed to work as a consortium, living in the moisture or water generated by condensation and/or leak ingress while feeding off the Alkanes and additives in the fuel.
As may be expected with fast growing organisms, new variants are always potentially evolving, particularly as fuel spec’s change to meet modern environmental requirements.
Algae in Diesel Myth:
While some believe the sludge they see in diesel is Algae, they are misinformed. Algae require sunlight for regeneration. Of the 125 microbes known to have been found in light to middle distillate fuels, the 30 that grow and have the potential to cause damage only require water to give them life as there is obviously no sunlight available in a fuel tank.
The Science – a basic overview
There are 3 groups of micro-organisms known to grow in fuel – bacteria and fungi (moulds and yeasts).
The main organisms involved are:
- Hormoconisresinae (H.res); formerly Cladosporium resinae
- Yarrowia Lipolytica
- Pseudomonas Aeruginosa
- There is also anaerobic Sulphate Reducing Bacteria (SRB’s), known to live in the depths of tanks, that produce vast quantities of acid, which attacks tank structures.
The organisms work as a consortium, using the environment around the fuel water interface as their main habitat. They generally live in the water phase and feed on the fuel. Their respective activity waxes and wanes as they compete to digest the various Alkanes and additives present in fuel.
Environmental conditions are known to affect organism growth rates – moisture and warmth are key growth boosters. Tropical conditions are therefore ideal for accelerated bug growth.
Hormoconis resinae (H.res) is a fungus which behaves in the same way as most of its class. It produces black/brown filamentous growth, which produce fruiting bodies, which in turn produce spores, so spawning the next generation. This process takes at least 2 days to begin with first spores found in around 21 days.
The volume, and therefore filter blocking potential, of this organism’s filaments & fruiting bodies is not adequately represented by the normal method of detecting bacterial contamination ie counting colonies grown on agar plates.
Yarrowia Lipolytica in common with all yeast, is a simple single cell microscopic organism. Yeast is able to ferment sugars for the production of ethanol and is common in soil and salt water. Yeast is also found on the skin surfaces and in the intestinal tracts of warm-blooded animals, where they may live symbiotically or as parasites. Yeast multiply as single cells that divide by budding or direct division, or they may grow as simple irregular filaments (mycelium). Yeast colonies tend to be cream/brown in colour and contribute mass to the mix of organisms which block filters.
Pseudomonas Aeruginosa is a simple bacterium . Pseudomonas is a gram-negative rod type organism which often has a characteristic sweet odour. It is widespread in nature, inhabiting soil, water, plants, and animals (including humans). Although individually microscopic, en masse pseudomonas aeruginata creates the “plastic bagging” effect, which also contributes to clogging filters and fuel lines with ‘slime’.