Microbial Infestation of Marine Fuel Oil

Is Purification and Filtration of Oil Sufficient?

Ships store huge quantities of fuel/diesel for use during long voyages and it is certainly a grave matter if the oil gets spoiled halfway through the ocean. Normally the oil is cleaned before using, but is purification of oil sufficient to ensure a stable quality of the oil?

Filtrating fuel, diesel and lubricating oil by means of filter and strainer is not enough. Though filter and strainer do most part of the job, the filtration process requires a bit more. Fuel and diesel oils are often found infected with minute microorganisms. These infesting bacteria are present in the oils and are not filtered out using strainers or filters. Moreover, if the temperature and condition of the oil are favorable the microbes often grow and multiply at astounding rates, causing detrimental effects on the oil. This effect of micro organisms on the oil is known as microbial infestation.


Microbial infestation degrades the oil and leads to formation of acids and sludge, metal staining, deposits and serious corrosion. When the microbes reproduce they tend to generate slime and eggs, which when rot gives out foul smell in the form of hydrogen suphide. This smell is an indication that oil is contaminated by microbial infestation.

Causes and Ways to Fight

One thing that is extremely harmful and which leads to increase in microbial infestation is water in oil. It is extremely important to remove oil from the system in order to avoid contamination. If water is there in the oil, in presence of oxygen and appropriate temperature condition, the bacteria multiplies ,infesting the system. Thus removal of water or reducing its presence to minimum is the best method to prevent microbial infestation. Moreover, it is also required to keep the temperature at the extremes to prevent bacteria growth. The higher the temperature at settling, service and drain tank of fuel oils, the better.

One more method to prevent contamination is by adding chemicals to the oil. Standardized test kits are available to detect the presence of bacteria in the oil. Biocides can also be used to kill the bacteria present in the system. In case the system is treated with chemicals, it is imperative that it is completely flushed out at the end to prevent contamination of fresh oil.


Though chemicals do a pretty good job in preventing microbial growth there are a few drawbacks. It has often been seen that the microbial growth returns after some time and the chemicals added cause the organic matter to form solid particles that get stuck on the inside of the fuel tank. One more aspect that the chemicals or the filters doesn’t seem to resolve is agglomeration of asphaltines, the process by which high carbon content, heavy crude oil molecules are formed. These molecules join with each other to form large clusters, which causes difficulty in combustion. This phenomenon increases the presence of black smoke in the exhaust and reduces the engine performance and efficiency.


Chater, K.W.A. & Somerville, H.J. (1978) The Oil Industry and Microbial Ecosystems. New Jersey: John Wiley & Sons Publications