Microbiological Analysis of Fuel (Diesel Bug)
Sample of diesel drawn from a visiting Super Yacht's day tank. Note the heavy microbial contamination at the interface between the water phase on the bottom and the cloudy diesel on top.
Diesel Bug infections are a problem in today's fuel, especially if it is stored for any length of time. Your engine or engines can suffer from any number of problems. These can include
- loss of power due to blocked or plugged filters
- damage to your fuel reticulation system, particularly the injector nozzles
- excessive exhaust fumes and smoke, and
- costly operational expenses such as extra filters and fuel.
Marine Diagnostics can provide sampling, laboratory analysis and reports on diesel fuel for its microbiological make-up i.e. bacteria, yeast and fungal infections (Diesel Bug). Along with the reports we can offer long-term recommendations for dealing with these types of damaging infections.
Where possible we draw the samples from your fuel reticulation system ourselves, or you can provide us with the sample or samples for analysis. Samples need to be in very clean, preferably sterile bottles, and where possible be delivered to the laboratory on the same day it is taken. If there is a delay in getting the sample to us it should be stored in a refrigerator so that any microbiological growth in the fuel cannot advance. Samples can be either drawn from the bottom of the tank or from the drain valve on your fuel water separator/filter. Samples need to be larger than 120ml for best results.
Results for this type of testing take around seven days because the laboratory has to grow the cultures. Once the reports are received from the lab we interpret the results into an easily understood, personalised report which includes information on Diesel Bug infections and recommendations which will provide you with a clear way forward. From there our sister company, Oil Conditioning Systems NZ Ltd, can provide you with solutions and equipment to deal with the problem.
Information on Microbiological Contamination of Fuel (Diesel Bug)
In the presence of water, fuel storage systems provide an ideal environment for microbial growth resulting in a loss of fuel quality and problems of blocked fuel lines and filters. In addition fuel emulsion and corrosion of fuel tank linings, hoses and metals including stainless steel can occur. Microorganisms can selectively degrade various hydrocarbon components of the fuel and fuel additives. Several different microorganisms can grow in fuels depending on the conditions present and fuels are particularly vulnerable to contamination during transportation and prolonged storage. Many of the additives in fuels act as nutrients for the growth of these various organisms with most of the spoilage occurring at the fuel-water interface.
Fungus
The presence of filamentous fungi always indicates that the fuel is contaminated with water as these organisms grow at the interface. Their spores may remain viable in the fuel in the absence of water for many weeks or even months. They form slimes and mats and increase emulsion in the fuel. They also excrete polysaccharide materials, which appear as a greasy clogging material. Hormoconis resinae is the more usual fungus found but other species do occur and result in similar problems. Hormoconis resinae has the ability to grow in relatively anaerobic conditions, which makes it a problem in fuel storage systems.
Hormoconis resinae (Fungi - Diesel Bug). Represented by the dark growth on the plate. Unfortunately this is almost completely covered by the yeast cultures.
Bacteria
Bacteria also require water to grow but are largely confined to the fuel phase. Aerobic bacteria (requiring oxygen) can cause a haze in the fuel and filter blockage due to secretion of an extra cellular material. The sulphate-reducing bacteria (SRB) grow in the water under a layer of fuel and can utilise sulphate in the place of oxygen and are hence anaerobic. Sulphates are reduced to sulphides, which accelerate tank corrosion, increase the sulphur content of the fuel, and contribute to sludge formation and give off a sulphide smell. Their presences always indicate a long-standing infection as they feed on the by-products of other organisms. Also they thrive when the other organisms have used up all the oxygen. Their presence suggests a potentially high corrosion hazard.
Slide showing Aerobic Bacteria
Yeast
Yeasts (mainly Candida sp.) do not require a water phase but may grow throughout the fuel. They are copious acid-producers and also produce surfactants contributing to a haze and fuel emulsion. They grow at slightly more basic pH than fungi and often are present as a result of contamination with seawater. The succession is fungi: yeast: bacteria: SRB.
Housekeeping
Control of microbial contamination always comes down to good housekeeping to eliminate dirt from the fuel and minimise water at the bottom of the storage tanks by regular draining, preventing ingress of water and minimising condensation by keeping the tanks as full as possible. Complete exclusion of water is impossible in most storage tanks. In the case of very severely contaminated tanks it might be necessary to resort to manual cleaning, as the surface slimes are very difficult to remove. After cleaning, a biocide treatment may ensure a 100% kill.
The Biocide needs to be effective in controlling a wide range of bacterial and fungal growths in the fuels, they also need to be safe to use at low concentrations in protecting both the fuel and water phases, be fast acting and have easy application. They must also be compatible with fuel additives and be non-corrosive. In most cases of contamination, an initial shock treatment is advisable with further maintenance dosing.Suitable biocides are:
Diesel FuelBiocide BC-250 Manufactured by Fueltreat Australia Pty Ltd.
Fuel Biocide, Tergo Industries Ltd
Biocide Additives
Please be advised that while the use of a biocide product will kill most of the Diesel Bug it will not remove it from the tank. Dead Bugs are as bad if not worst than live ones. They are still able to block the filters. If the decision is to use this type of product, then I would recommend that a spare set of fuel filters is kept at the ready as well as the knowledge on how to change them in an emergency. Biocide products are also toxic and need to be handled with care.
Fuel Mag
A second and more permanent solution to dealing with the Diesel Bug problem is to fit the fuel lines between the tank and fuel filters with a product called Fuel Mag. Fuel Mag's provide a far safer and healthier way of dealing to the bug. The Fuel Mag's provide a magnetic force which breaks the bond between the individual spores, thus breaking down the microbiological growth into single molecules, small enough to pass though the filters. The injectors then eject the spores. The remaining spores in the fuel, which is returned to the tank, are dormant and unable to reproduce, thus the contamination is slowly eliminated. Fuel Mag is also a one off cost that is simple to install and requires no ongoing maintenance. It is also non toxic to both the marine environment and human health.
