1-Good fuel ---> >>>>
Clean, dry, usable fuel with no emulsified water.
2-Emulsified Fuel and Water- Some types of microbes excrete emulsifiers as part of their waste.>>>>
The result is a layer on top of the growth that looks like strawberry milk
3-Fuel/Water Interface --->(*see below please) >>>>
4-Water Bottom --->Sludge >>>>
(microbe waste and debris ---> from fuel degradation)
Microbiological growth*, algae, bugs, biomass, sludge --- Whatever you call it, it doesn't sound good, does it? And it shouldn't!
The fact is, short of a major structural failure, an infestation of microbiological growth is about the worst thing that can happen to your fuel tank.
The microbes are mostly bacteria and fungi, and there is never just one type. They live in cooperative groups with the byproducts from one type helping another type to survive and thrive. There can be many different types in the same fuel tank.
These "consortiums" need two things to survive: fuel for food and a tiny amount of water.
The *Fuel/Water interface* in an infested tank is more of a zone than a line. This is because some of the bugs give off emulsifiers, like soap and mix water into the fuel next to them.
A fuel system with bugs is attacked at every point. Acidic waste eating the tank, the sludge build-up from accelerated degradation of the fuel, and the microbes actually changing the physical and chemical properties of the fuel are all a recipe for a major problem.
One of the waste products created by biological growth, and normal fuel aging in a diesel tank is sulfuric acid. Acid is heavier than water and fuel; hence it settles to the bottom of the pits and stays there until it is removed or neutralized by the chemical reaction of corroding the metal.
As the pitting from corrosion gets deeper, the less likely it is to stop without sterilizing and possibly lining areas of the tank. You can't kill all the bugs by cleaning, but you can take away their hiding spots (sludge and water) and then treat the tank with biocide to keep them from coming back.
Many tanks have access plates to clean and inspect the interior. Sometimes there is good enough access to clean, inspect, and maybe even repair a tank. Most of the time, there isn't.
There is no set layout for valves in a fuel system. For various reasons, a valve might be almost anywhere in the system.
On-shore tanks almost always have a shell around them known as the secondary containment. If the inner shell leaks, the outer shell will keep the fuel contained. On a boat, the hull is actually the secondary containment. If fuel leaks from the tank or plumbing, the bilge becomes an active part of the fuel system.
What nobody ever wants is the discharge to become an active part of the fuel system in the bilge pump and overboard.
Sometimes it does happen, though...........
Biocide is something that should be added to every diesel tank nowadays. Once in a long while, when I was a commercial fisherman, I heard something about someone or another that got "algae" in their fuel tank and clogged up their fuel system. I never heard of biocide; nobody seemed to need it! Considering that most of the people I was around all had fishing boats, heavy equipment, or farm equipment that ran on diesel, it was very uncommon. Today, with fuel that is ultra-low sulfur (sulfur kills bacteria) and more unstable (easier to digest), and the probability of genetically enhanced bacteria not stopping at cleaning up oil spills, it is almost a certainty.
Today there are three types of diesel tanks: tanks that have always used biocide consistently, tanks that have just started using biocide recently, and tanks that have never used biocide.
The last two types will probably be a mess inside. Whether there is active biological growth or not anymore, the mess created before biocide will still be there. Biocide just kills it, and it doesn't help clean up the sludge already in the tank. If the growth in the tank is the variety that grows up, the side of tank biocide will make it lose its grip, adding to the sludge!
The first step to a fuel supply you can count on is to find out what’s in your tank. The best time to do this is before you notice a problem.
If biocide is a new word to you, or you’re just not sure about the history of the tank, it might be time to find out. Examining fuel samples from the lowest points in the tank will usually tell the story.