Yeasts, fungi and bacteria are with us every day. There are good ones and bad ones, or intentional and unintentional ones. Mushrooms are often welcome in salads or on pizza, yeast is used for baking, among other things, and bacteria convert milk into yoghurt.
and bacteria turn milk into yoghurt. But there are also moulds and yeast cultures that nobody wants to have. The same applies to strains of bacteria that live in diesel fuel and can multiply there.
Diesel bacteria require sufficient water to survive in the fuel, as they only multiply and grow in the separating layer between the two liquids. Accordingly, it can be said that the higher the water content in the diesel, the greater the likelihood of a bacterial outbreak. However, it is not the microorganisms but their excretions in the form of white, grey or brown slime that lead to problems and machine failures.
The water content in diesel is favoured by condensation in half-filled tanks or by defective seals through which rainwater or seawater can penetrate. However, the increased proportion of bio-diesel in normal fuel since 2007 also favours the survival of bacteria through increased water retention.
Prevent, recognise and treat
To avoid infestation by diesel bacteria, fuel should only be taken in at well-frequented bunker stations and petrol stations. - Condensation is minimised by filling up the tank and insulating it well. In addition, fuel additives are available on the open market to prevent an outbreak of bacteria. However, some diesel heaters do not tolerate fuel treated in this way and fail.
If you do get the "disease" on board, it is important to recognise this as quickly as possible. For example, by the colour and cloudiness of the fuel. Diesel with a high water content is cloudy and becomes darker in colour. The fuel can then be treated by shock dosing with the diesel additives.
In order to contain the spread of germs and their legacies, a suitable filter system should also be installed on board. Especially because the "chemical clubs" attack the bacteria and render them harmless, but do not remove the suspended matter. To achieve greater operational safety, you should invest in a switchable double filter system with water separator and sight glass. This means that in the event of an engine failure due to a blocked fuel filter, you can quickly switch over and restart the engine to get out of the fairway or reach the next harbour.
The flow rate is important when dimensioning filters. Only in this way can the proper functioning of equipment such as water separators be guaranteed. A filter that is too small will not work due to the high flow velocity. If it is too large, on the other hand, the speed of the diesel is not sufficient to utilise the entire filter surface.
Disinfection systems from QL (Volvo Penta) or WMMT are selected according to the same principle. These work without electricity on the basis of magnetic fields, which change the balance of the microbes electronically so that they no longer multiply and therefore do not produce acids and viscous substances. The magnetic sterilisers are installed directly in the fuel supply line before the filter. This allows the latter to collect the treated residues from the fuel. The disadvantage is that this type of sterilisation system only works when the engine is running.
Professional help
If the diesel is so heavily infested that the fuel filters become clogged again and again within a short period of time, the only thing that usually helps is professional cleaning of the fuel system, including the tank. Mikrofiltertechnik from Geesthacht has specialised in this area and has been combating diesel bacteria and their legacies since 1993. With the expertise acquired over the years, work processes have been optimised and special tools, such as a mobile filter trolley, have been developed.
All skippers who want to clean their tank system on their own must bear in mind that diesel bacteria and their residues are hazardous waste that can only be disposed of at the pollutant collection centres. Information on where to find these can be obtained from the municipal waste disposal company.
