05/2003

"Diesel-Oil Pest"

What is important to know about micro-organisms in diesel fuel and lubrication oil?

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Uncountable kinds of bacteriums and cyanobacteriums as well as fungi and alga are forming the biological group of micro-organisms. Micro-organism can just be recognised and identified by micro-biological laboratory surveys and tests.

The contamination of the diesel fuel or lubrication oil can perform with every fuel filling as well as through tank ventilation and other pollutions. Micro-organisms can only survive, grow and multiply themselves in the water phase of any medium.

Survival, growth and multiplication of the bacteriums, fungi and various other micro-organisms in fuel and lubrication oil is just possible because of their very good adaptability to the attacked mediums.

Fig. 1 and Fig. 2:
Microbiological identification tests of insufficient dewatered diesel fuel

Micro-organisms have a low nutriment consumption; they just need carbonhydroxides, nitrogen, phosphate, sulphur and different trace elements for their growth and multiplication. Depending on the kind of organism water, temperature, protein, sugar, fat, vitamins and different trace elements (nutrition) as well as light, the pH-value and the oxygen-contents can be growth causing parameter for the micro-organisms.

Fig. 3:
Germ-concentration in a storage tank

The consequence of the micro-biological attack are manifold; the micro-biological destruction causes quality loss of the oil and fuel and the by products of the micro-organisms´ metabolism destroy the material of the tanks, pipes, filter elements etc. Sulphuretted hydrogen, which is also a by-product of microbiological metabolism, supports corrosion while the micro-biological slime, which arises, blocks the filterelements, fuel and oil pipes, water separators and injection pumps.

The phenomenon of blocked fuel-filter, fuel pipes and slimy tanks is widely known. Quite recently this symptom for this microbiological attack has been noticed more often aboard ships as well as at land-based plants.NFV, Norddeutsche Filter Vertriebs GmbH knows the reasons: With each filling of the tank micro-organisms such as bacteriums, yeasts and mould fungus, which can occur in the fuel oil, reaches and therewith infect the fuel system of the plant with the "Diesel-oil pest".

Whether these micro-organism are responsible for the biological surface film, the Diesel-oil pest, depends on the special environment and the surrounding. Essential for the multiplication of this micro-organisms are water and substrate. Because fuel or oil as an organic substance impersonates a substrate for the micro-organisms, the water content of the fuel is the limiting factor of the micro-organism-growth.

Just because of the condensation of humidity, water is to be found in each tank. Does the water-concentration inside the tank increas up to 60 – 100 ppm, this can result in a fast micro-organism multiplication. The consequence is the development of a biological film, which blocks the filter-elements, pipes and other parts; – in short "Diesel-oil pest" attacks the plant.

Fig. 4 and 5:
Surface destruction inside a ship´s fuel oil tank

How can the "Diesel-oil pest" be prevented?

Conclusion to the above mentioned aspects is, that the water content in the diesel-fuel is the decisive factor, which has to be reduced. This can be performed by continuous fuel and oil treatment, which prevents the fuel and oil of the water-concentration increase to a limit of up to 60 ppm. Mechanical separators which performs the centrifugal separation, as well as some other dewater-plants (e.g. filter separators), which manufacturers assure its plants ability of 100 % separation result according to DIN, does not work.

The still valid DIN 51601 prescribes a rest water content of up to 500 ppm in the diesel fuel. Neither the diesel-fuel specification of the oil-industry nor the NATO ones are sufficient and adapted to the storage possibilities, because those allow rest-water concentrations up to 100 ppm, which itself is a very good biotope for the micro-organisms. A real effective and durable way to prevent the fuel of the water-concentration increase, and therefore the multiplication of the micro-organisms, is the usage of the shown Fuel-Treatment System FTS of Norddeutsche Filter Vertriebs GmbH.

As the same problem is known for oil, NFV developed the Oil-Treatment System OTS, which uses the same principle. OTS and FTS type systems are two-staged plants, performing in the first stage a deep finest filtration and in the second stage the phase separation/ coalescense with the restraining of the remaining very fine water-droplets in an additional fitted separator membrane. Both systems are proved and approved by Germanischer Lloyd.

NFV assures the plant´s high water separation results.Supplementary to the a.m. OTS and FTS plants NFV developed a more reasonable and less space requiring plant system for the same purpose, the Filter Water Separator for Oil type OFWA and the Filter Water Separator for Fuel type KFWA. OFWA and KFWA are one staged plants, which are equipped with a combination element, consisting of a filtration layer and the phase separator/coalescer element. Both system can be tailored to customers demand and be additionally equipped with a separator membrane.

Fig. 6:
Schematic sketch of a NFV fuel treatment plant

When the tanks have been conquered by the microorganisms it is to late for succesfull oil or water treatment, now just the usage of the special biocide (further informations by NFV) can help to get the micro-organisms killed.