The Effects of Microbial Contamination   The physical effects of microbiological contamination (diesel bug) are the formation of sludges, biofilms (slimes) and surface or interfacial scums. These occur in the fuel tank and also manifest themselves as material which block filters.
	This is "live diesel bug" that can be found in tanks and filters

Fuel that is infected with bacteria is not reliable and there are many and varied consequences of using contaminated fuel.These include:

1. Encouraging growth of further contamination

2. Reduced filter life (fuel filter clogging and blockage)

3. Coalescer malfunctions

4. Engine wear due to variations in fuel flow

5. Corrosion of the fuel system

6. Corrosion of engine fuel injectors

7. Damage to in-line instruments

8. Corrosion of the fuel/storage tanks and lines

9. High fuel consumption

10. Blockage of pipes & valves

11. Increased water content (damage to components from water)

12. Breakdown of diesel (poor lubricity)

13. Health problems (Endotoxin producing bacteria)

14.Total engine failure (starvation of fuel) 

Ultimately, performance suffers and fuel consumption and maintenance costs increase, but perhaps the most critical concern is the real potential for blockages in the fuel system which cause engine failure while underway - with potentially devastating consequences 

Microbial Contamination

Microbial Contamination has been referred to as fuel bug, diesel bug, fuel contamination, dirty diesel, fungus diesel, stagnant diesel, diesel jelly, murky diesel, slimy diesel, smelly diesel. However the most common name is Diesel Bug.

The most common response from a diesel engine owner or a fleet manager is "I do not have a diesel bug problem.'
What clogs fuel filters? What causes Fuel pumps to prematurely malfunction? What is the residue left on injectors? A problem to some has to be major repairs or a total engine starvation leading to a shutdown. Given time this may well happen. But by then it is far too late! Preventative maintenance is the key.

Others in the know are aware that once diesel has left the refinery it becomes contaminated by water, condensation, the fuel tanks themselves, or even the air. Almost all diesel has some microbial contamination; by addressing the ongoing issues pre-emptively, the DE-BUG owner can also receive positive side effects 

Growth in Fuels and Oils   Microbial contamination (Diesel Bug) of petroleum products is a well documented and serious problem facing the petroleum industry.  Where ever diesel is used or stored, bacteria, moulds and yeasts are able to degrade the hydrocarbons in the diesel and yet more are able to feed on the intermediate by-products of the degradation.  The problem is larger than one might think. US military aviation bases showed that 90% of bases tested had evidence of microbial contamination

Evidence of the "bugs"

Virtually all fuel has some bacteria life however it may not be that apparent to the naked eye. These microbes start off as small microscopic single, separate living cells. At this point, they can pass though any size filter medium, and injector nozzles. However, their growth can be very rapid. Given the right conditions, a single cell weighing one millionth of a gram can grow into a bio-mass of slimy algae mats weighing 10 kilograms within twenty four hours. By the time you can visually see evidence of growth, the infestation problem is quite severe. Not all growth happens so suddenly. In some situations, growth occurs slowly, creating problems during development.

There are many different types of organisms that make up what we refer to as diesel "bugs". Generally, there are aerobic types; requiring oxygen for metabolism, and anaerobic types that don't. The aerobic types are responsible for the algae and slimy mats, while the anaerobic bacteria, known as SRB's (sulfur reducing bacteria) produce hydrogen sulfide as a by-product of their metabolism. Combined with moisture, strong sulfurous acids are formed, which are corrosive to metals. Evidence of this type of bacteria is usually seen a black grit resembling coffee grinds. The following are some telltale symptoms of microbial contamination:

Black grit - in filters, and water separator bowls

Corrosion - to fuel system components due to acids produced

The diesel fuel itself, since it is degraded, also shows symptoms:

Color - fuel is darker, and can be more opaque

Odor - a rotten egg smell due to hydrogen sulfides

This is live diesel bug adherring to the fuel tank.
 

Using Biocides

Biocides are frequently used to treat severe contamination, however many of them are hazardous chemicals and require careful handling. Although some are marketed as being "environmentally friendly", many are harmful to the environment and waste disposal contractors may need to be called in if waste containing dead microbes and biocide are to be removed.

Adding biocides to the fuel system can actually cause more problems. The fallout of dead cells collecting on the bottom of the tank forms a sludge material that can still find its way into the fuel system, clogging fuel lines and filters, potentially leading to performance problems and possibly engine damage. This can be especially true in rough weather when the contents of the tank are effectively shaken into suspension.

Furthermore, over time biocides lose their effectiveness as microbes build up immunity to the chemicals. Occasional dosing can actually accelerate this action and some owners have reported bio-mass growth in systems despite regular treatments with biocides.

Thus biocides can actually contribute to the problems of microbial contamination; not only by causing a large amount of sludge to build up but by also giving a crew a false sense of security. 

Fuel For Food?

Diesel fuel is an organic compound made up of hydrogen and carbon, and is actually a good food source for these microscopic organisms. Within a fuel tank, there is water for germination, carbon for food, dissolved oxygen and sulfur for respiration, and trace elements for growth. May not sound good to you, but to the diesel bugs, its filet mignon!