Diesel plague

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When diesel oil pest occurrence is of microorganisms (bacteria, yeasts, molds) in the diesel fuel designated visible formation of a biosludge. This can lead to malfunctions in diesel engines because the bio-sludge causes clogging of filters and fuel lines and thus hinders the flow of diesel fuel to the engine. The presence of high levels of microorganisms in the fuel can damage the tank and fuel system through biocorrosion . This is particularly noticeable in vehicles that are used seasonally (boats, mobile homes, agricultural equipment) with long idle times and diesel-powered emergency power generators. Microorganisms feed on hydrocarbons and also need water, which is always contained in diesel to a small extent.

Spread and infection

Microorganisms that are able to multiply in hydrocarbons have been known since 1895 . The first problems with contaminated fuels were observed in kerosene in 1956 . The hose fungus Cladosporium resinae was isolated and described in English as "Kerosene Fungus". The contamination can occur within the entire supply chain from the refinery through the intermediate storage to the vehicle tank. The lubrication and diesel oil tanks can be infested with organisms every time the tank is filled, through tank ventilation and any contamination. The refinery process can be viewed as a sterilization process, but the fuels can be infected after a short time after distillation during transport and storage. By adding biodiesel , the microorganisms are offered components that are readily biodegradable and lead to increased bio-sludge formation. Diesel plague occurs predominantly in vehicles or tanks or canisters that are rarely used and the fuel is stored in their tanks for a correspondingly long time. Oil heating systems in seldom heated houses are also occasionally affected. The most common finding is in the tanks of ships.

species

Bacteria (e.g. cyanobacteria ) as well as molds and yeasts can grow in diesel fuel .

According to ASTM E159.10, Pseudomonas aeruginosa , Amorphotheca resinae and Yarrowia tropicalis (formerly Candida tropicalis ) are used as representative microorganisms .

Sulphate-reducing bacteria, which lead to microbiologically induced corrosion, also grow under anaerobic conditions (see: Anaerobic biocorrosion ).

Multiplication

Basic conditions for germ growth

Microorganisms can only survive, grow and multiply in the water phase of a medium. In order for the microorganisms to multiply, they need water and nutrients. Since the fuels represent food for microorganisms as organic substances, the water concentration in the fuels is the limiting factor for the growth of microorganisms.

Microorganisms can colonize almost all naturally occurring substances and are often able to attack or even break them down. For the microorganisms to multiply, they need water and nutrients and a suitable temperature. Microorganisms are very adaptable - germ growth is only suppressed at −18 ° C and there are so-called thermophilic germs that multiply above 100 ° C. A favorable temperature in the tank is usually given and z. B. cannot always be influenced in the case of storage tanks outdoors. According to the specification, diesel fuel according to the current DIN EN 590 may contain up to 200 mg of water per kg of fuel. Since the water is not dissolved in the fuel, but mostly in the form of an emulsion , it settles down over time and is then available for the microorganisms to grow. Fuels are organic substances that represent food for microorganisms; By adding up to 7% by volume of biodiesel, easily biodegradable components are also available. The exponential multiplication of the microorganisms results in bio-sludge formation, which can lead to filter blockages and microbial corrosion.

consequences

The consequences of a microbiological attack are manifold: the microbial destruction leads to a loss of quality of the diesel and lubricating oil and the metabolic products of the organisms destroy the material of tank walls, pipes and filter elements. The hydrogen sulfide supports the corrosion and the resulting microbiological slime clogs filter elements, diesel and oil lines as well as water separators and injection pumps. This is accompanied by damage from bacterial anaerobic corrosion .

Testing for microbial contamination, control, prevention

There are different methods for testing fuels.

Regular dewatering of the diesel fuel filter as part of maintenance at least reduces the contamination. In order to reduce the formation of condensation due to the cooling, moist compensating air, the tank should always be full. However, a safety room because of the thermal expansion of the fuel must remain. The tank suction line should be designed at the deepest point in the tank in order to primarily suck off the specifically heavier water, which then collects in the diesel filter and can be drained off. If this is not possible, the tank must be drained regularly at the bottom drain. Total emptying and cleaning may also be necessary.

Another possibility is the addition of special additives. Since a fixed percentage of biodiesel has been added in accordance with legal requirements, an increased growth of bacteria and fungi has been observed. Biocides can be added to the fuel in the case of minor infestation that does not yet lead to functional impairment. These kill the germs so that their remains are destroyed via normal combustion. However, since the end of 2018 there has been a ban on the sale of biocidal diesel additives against diesel plague to private consumers, as these are classified as carcinogenic.

Filter elements, which avoid bacterial growth in the diesel filter, offer a harmless possibility of remedy. The specifically treated filter mat has a similar effect to an antibiotic for the diesel filter, which has a positive effect on the entire system. With the help of such filter media, the system is maintained and a prevention against diesel plague is created.

See also

Web links

Individual evidence

  1. ^ Studies on the 'Kerosene Fungus' Cladosporium Resinae (Lindau) De Vries
  2. ↑ Technical notes of interest to Marine Engineers ( Memento of December 13, 2013 in the Internet Archive )
  3. ↑ Microbial growth in diesels and other fuels containing fatty acid methyl esters (FAME) (PDF; 364 kB)
  4. ↑ Microbial Contamination in Diesel Fuel - Are New Problems Arising from Biodiesel Blends? ( Memento of November 29, 2014 in the Internet Archive ) (PDF; 1.1 MB)
  5. ↑ Dutch report on diesel plague html, Dutch, accessed on 25 May 2009
  6. ↑ astm.nufu.eu: Standard Practice for Evaluation of Antimicrobials in Liquid Fuels Boiling Below 390 ° C
  7. ↑ J. Kleikemper, MH Schroth, WV Sigler, M. Schmucki, SM Bernasconi, J. Zeyer: Activity and diversity of sulfate-reducing bacteria in a petroleum hydrocarbon-contaminated aquifer. In: Applied and environmental microbiology. Volume 68, Number 4, April 2002, pp. 1516-1523, PMID 11916663 , PMC 123867 (free full text).
  8. ↑ IP 385: Determination of the viable aerobic microbial content of fuels and fuel components boiling below 390 ° C - Filtration and culture method
  9. ↑ ASTM D6974-09 Standard Practice for Enumeration of Viable Bacteria and Fungi in Liquid Fuels — Filtration and Culture Procedures