Introduction
In 1958, a USAF B-52 jet crashed. A study of the wreckage concluded that the jet fuel was contaminated by water, which led to five out of its eight engines flaming out on approach. This reason was, in the 1950s and 60s, quite commonplace.
Research to investigate the problem was in its infancy then. However, scientists had already made some surprising conclusions. Many of these crashes were not caused solely by water, but also by microbes. It would become clear, only decades later, that bacteria and fungi were the primary perpetrators.
Explained
The matter is more complicated than it seems. Fuel is produced in refineries, where temperatures invariably exceed the denaturation point of most proteins, meaning microbes are killed. However, during transport, fuel is exposed to the air, which is far from sterile. The longer is the duration of transport, the greater the extent of contamination. If fuel contains even trace amounts of water ( a microbe- magnet), it makes for a breeding ground for microbes, where the creatures multiply and thrive.
Microbial colonies
The picture below is a depiction of how colonies form at the water-fuel interface.
The presence of water is unavoidable. When fuel is transported in underground pipes, the low temperatures cause water vapour to condense and form droplets which contaminate it. Additionally, water may be present in the pipe as residue from any previously transported substance.
Deeper dive
Bacteria of the genii Bacillus, Micrococcus, Pseudomonas and Arthrobacter, Fungi such as Aspergillus and Fusarium and Yeast such as Candida are some troublemakers. Each organism causes a slew of issues, four of which I have covered:
Fuel Degradation
Bacteria can degrade fuel over a long period of time. They release the enzyme mono-oxygenase (a type of oxygenase) which breaks down hydrocarbons to release energy which they use. Essentially, alkanes like tetradecane are ‘microbe food’. The metabolic pathway is rather interesting.
alkanes —----> fatty acids —----> metabolism as usualThe result is a less efficient fuel and the risk of clogged fixtures by waste metabolites.
Sulphate reducing bacteria
The next nuisance is sulphate reducing bacteria (SRB). Sulphate ions (induced into the fuel by the presence of water or the use of additives) are reduced and hydrogen sulphide (H₂S is formed. The H₂S can reduce fuel quality and vary its composition. Additionally, it is a corrosive substance.
sulphate ----> hydrogen sulphide (impurity)Corrosion
Corrosion, our third enemy, is no joke. The presence of acids alongside metals is a recipe for disaster. Structures weaken, and dangerous cracks form in the most important components of the plane. Large colonies of certain microbes contribute to corrosion by producing acetic and citric acid among many other organic ones.
Biofilm
Perhaps the most common issue, incidentally the one that claimed the B 52 jet, is the formation of biofilm. The fungus Khuskia oryzae is notorious for producing this sticky layer, a mixture of microbes and their metabolites. Over time biofilm thickens, forming a slime which can clog pipes, pumps and filters, impairing fuel supply and therefore engine activity.
Remedying the problem
The most effective solution to microbial contamination was to use ethylene glycol monomethyl ether (EGME), which inhibits growth. Furthermore, the composition of fuel has changed since the 50s and 60s, and is not as conducive for colony formation. The number of such accidents has consequently decreased since then.
It is quite intriguing how such minuscule cells can wreak so much havoc upon gargantuan giants
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