Diesel and Biocides

       Dirty Fuel. Every fuel has an Achilles heel: propane requires leak monitors and careful operation; gasoline requires ventilation and careful installation, and now with e-10 and e-15 gasoline, it has a tendency to separate when the temperature swings. When diesel is mentioned on any internet forum, advice springs forth regarding best type of filter or polishing system, the best stabilizing additive for long-term storage, the best additive for cleaning the tank, and sometimes, biocides for killing the bacteria and fungus that too often infect diesel tanks. Advice is given against each of these alternatives, by some poor sailor who misapplied the products or equipment he chose and got poor results. To maintain reliable operation of a diesel engine you must have clean fuel - fortunately, others have gone before us and there are no great mysteries.

Lubricity Additives
Though no the focus of this page and outside my area of expertise, this test report seems responsible and interesting: The Diesel Place. Remember, though, that general purpose additives and biocides serve completely different purposes and neither can replace the other. Because biocide formulations cannot easily be modified after registration as pesticides, there are no products blended to do both.
Dirty Fuel
       Dirty fuel itself is quite uncommon in the United States, at least as it leaves the refinery. While occasional problems are not unheard of, heavy-duty trucks ply our highways reliably, day-in and day-out. Diesel has some inherent chemical instability and can polymerize and form sludge in the presence of oxygen; this will also happen in dark, airtight storage at a much lower rate. To reduce sludge formation the conventional wisdom and common practice is to maintain storage tanks completely full and to treat with a storage additive that inhibits polymerization.  These additives are quite effective and can extend a storage life of diesel fuel to several years. Some sludge will form, but the buildup will be easily managed by filtration, fuel polishing, and sometimes cleaning every 15 years or so.
       Biological contamination is different matter. Recreational boats don't run every day like trucks; they spend their time snugged up to a dock for months at a time, rocking gently in a warm, humid environment. Standby and emergency generators and fuel storage depots face similar extended non-use periods, and metal working fluids in factories (oil/water mixtures) circulate in a warm, open environment; both are subject to infection and both have long research histories. Diesel fuel is quite biodegradable, and given a small amount of water and exposure to bacteria and fungal spores from purchased fuel or even from the atmosphere, troublesome volumes of biomass can grow in no time. It doesn't take much water - any trace, free or emulsified - and though true condensation inside a fuel tank is very limited under most circumstances, fuel can absorb minor amounts of water and then drop them when the temperature swings in the fall.  Add warm weather and gentle agitation as the boat rocks at dockside, and you have an effective incubator.
    Biodiesel may be a bit less stable. I don't have person experience, so I won't say.  Also note that if you are burning biodiesel your oil change intervals need to be shortened; one of the characteristics of biodiesel is that it is less volatile than ULS diesel and thus it accumulates in the crankcase, eventually replacing much of the lube oil. John Deere Test.
       At the on-set of an infection, filtration seems to help; the filters will catch the larger clumps of bacteria, but individual organisms are much smaller than the finest filtration. Bacteria and spores measure only 0.1 microns and so even the finest filters, even those rated at 1-micron, pass enough organisms to continue the infection.  Eventually enough biomass accumulates inside the tank and fuel train that either a change in fuel chemistry or vigorous mixing on a rough day knocks some loose, and the boater finds his filters plugging faster than he can change them.
    Biological growth is instantly recognizable as brown, gray, or black snot-like substance that coats the inside of the tank, pipes, and fuel filter elements. Not a polite description, but that's what it looks like and it's easy to recognize and remember;  it's a sinus infection in your tank. If the sludge collecting on your fuel filter consists of fine particulates, rust, or tarry material that leaves a black, sticky residue on your fingers, you're not looking at biological contamination and you can skip to another web page. You may need to clean your tank - please read the tank cleaning notes at the bottom of the page - and you're good candidate for fuel filtration and stabilizing additives. If the material is slimy - in severe cases slimy stalactites of goo will hang from the filter - you have a biological infection. Read on.

Oil and water phase controls;
Both are infected, the water more so.
    The only cure for a serious microbial infection is to kill it with biocides.  Unlike a sinus infection that will pass in time as your body rallies to its defense, your fuel infection is unlikely to resolve itself.  Forum comments and articles sometimes suggest that treating a fuel tank with biocides can be dangerous and damaging to an engine; it is not the biocides that are damaging, but rather the dead bodies that suddenly release from the surfaces. This surge of slime clogs filters and can cause fuel starvation and other damage.  Like a badly infected limb, it is optimistic to hope that antibiotics alone will cure the infection without surgery; the dead tissue must be removed. In your body you have brigades of cleanup mechanisms; white blood cells and the lymphatic system clean up after battle.  In a fuel tank you have only filters, and this goo plugs them fast.  Please read the tank cleaning notes at the bottom of the page; it's not as bad as it sounds. Try to burn the fuel down as low as possible when you suspect a tank cleaning is in your future.
    Magnetic bug killers are also marketed and receive considerable anecdotal press. Practical Sailor tested two widely available units - De-bug and Algae-X - in the April 15, 1997 issue and concluded they had no observed effect on microbial growth; as such and absent any new 3rd party information on their effectiveness, I'll assume they're marketed as a joke. Don't embarrass yourself by being caught with one on your boat. It's like installing a sign that says "A gump lives here."
    Any manufacturer claiming their product is a biocide and is capable of killing biological growth must register that formulation with the USEPA as a pesticide or anti-microbial. As you easily can imagine, this is an involved and strictly regulated process; as a result, there are far fewer formulations than there are products on the market. Most piggy-back on existing registrations and I found that all of the products readily available to boaters belong to one of four formulations:

Active Ingredient Category    Water or Fuel     Products (Tested)

Dioxaborinanes                         Fuel                 (T) Bio-Bor JF

Di-thiocarbamates                     Water               Ako-Nobel/ALCO Aquatreat DM-30
                                                                      (T) Valve Tech Bioguard WS
                                                                      (T) Star Brite Bio-Diesel
                                                                       FPPF Kill-em

Morpholine and compounds    Water/Fuel        Power Service Bio-Kleen

Azole / Thiocyanates               Water              (T) Raycor Bioguard

Fuel "A" cultures after 48 hours

Toxicity information for each product is available online: MSDS information, EPA pesticide registration listing, and manufacture use restrictions.  Although none of these are good for you, none are carcinogenic and all have been reviewed by the US EPA. OSHA regulates their use in metal working fluids where exposure to vapors and mists is probable and continuous in machining operations. For the recreational user, the use of gloves is suggested when handling concentrate; this precaution is not required when handling the diesel fuel mixture.
       The conventional wisdom is that water soluble products give a better quick-kill; they enter the phase where the microorganisms live. Fuel soluble products may be better for maintenance dosing, as they blend more easily with the fuel and better reach all portions of the fuel system.  While these subtleties are important when treating 100,000-10,000,000 gallon storage tanks, I think they have no firm application for the recreational boater.  All of these products have some solubility in both phases and recreational boats don't typically have tanks 300 feet across that are not subject to movement. I found no important difference in kill speed in my tests; what can a few hours matter?
       There's nothing like a good basement science project. My workroom is part laboratory and is suited for this. My wife finds it a little frightening.

Testing Materials
       I collected infected fuel from two contaminated tanks and conditioned the samples to ultra-low sulfur (ULS) fuel oil for three weeks. Under the microscope it was clear that both were seriously infected with bacterial and fungus. Contrary to colloquial speech, these infections don't contain algae, which require light for photosynthesis.
       The ULS diesel fuel used in these tests was all from one refiner; variation from one refiner to the other can be toxic to bacteria, and you will hear the occasional story of a fuel change solving a problem. Possible, but not common. You will hear that adding a small (2%) amount of gasoline will kill the bugs. Probably true, since diesel bugs can't tolerate gasoline and I did observe kills do to solvents in some cases. In cold climates adding some gasoline in the winter to reduce wax formation is common. On the other hand, just 2% gasoline in diesel will reduce the flash point of diesel from 140 F to less than 100 F, and diesel engine installation aren't designed to handle flammable fuels. There are better solutions. Read on.
    Bio-diesel fuel used in these tests is an ASTM compliant fatty acid methyl ester (FAME)derived  from a mixture of soybean oil and chicken fat, and is typical of the Virginia market. Independent research from multiple sources suggests that bio-degradability of bio-diesel should be comparable to ULS diesel but different, and that is what I found also; the bugs grew nearly 10 times as fast in the bio-diesel mixture initially, even though they were not bugs conditioned to or specifically chosen for that ability. Growth then suddenly stopped, for no apparent reason. This behavior has been observed by other researchers and is not well understood. Biodeisel is more prone to absorbing water, and I did not test that. A link to the biodeisel association: http://www.nrel.gov/vehiclesandfuels/pdfs/43672.pdf

Testing Procedure.  
    After the conditioning period test tubes were prepared with 10 mL of contaminated water, 140 mL of diesel fuel or B-20 mixture, and the manufacturer recommended dose of biocide. The tubes were inverted three times to simulate the minor amount of mixing present as a tank is filled or the boat is moved, but they were not vigorously shaken. Control tubes containing each infected diesel and B-20 sample without biocide were also prepared and tested for the presence of bacteria to establish a baseline. Relative microbial counts of control and test cultures were determined through the use of dip-slides prepared to be reactive to both bacteria and fungus. All slides were incubated at 80F. The dip slides were incubated at 80 F for 48 hours, with observations obtained 12 hour intervals. Reading is simple - compare the slides a picture in the kit.

 (Click to enlarge image)
  (Dip-slide test kits available through Fisher Scientific and others supply houses)

     Controlled testing is always surprises me. Like any antibiotic, it seems the cure depends on the sickness. In fuel "A" we found that carbamate-based biocide performed very well and repeatably. Oddly, Star Brite Diesel and Staydyne Performance Formula did too, better than other registered biocides. How can this be? Like many home-remedies, they simply had the right stuff for this infection. I suspect the solvent was enough to shock the bacteria. In fuel "B" the borinane and thiocyanate formulations shone, but not the other biocides or general performance additives.  So, is the cure for your infection Amoxicillin or Bacitracine? It depends on the infection.
       Should you vary the biocide from time to time to prevent the development of a resistant culture? The most consistent users - airports - typically pick one biocide (generally Bio-bor JF) and stay with that one product. I might switch twice each year.
       The combination I like best is Biobor JF combined with Startron Diesel. Both are effective biocides, but they kill complementary groups. Startron has also tested very well as a performance and anti-coorsion additive, making this a reliable and economical one-two punch.
    Because bacteria depend on water, fuel polishing and the use of water separating additives will help with prevention. Filtration removes fine particles and makes fuel/water emulsions less stable, and separation additives destabilize emulsions making water removal easier. Emulsions generate enormous surface area and allow bugs to be more mobile within the fuel system. Without water and fuel/water emulsions the tank becomes a poor environment for microbial growth. Some boaters swear by fuel polishing as means to eliminate bacteria?it is simply effective housekeeping.

Tank Cleaning

    There's no getting around it; once filters start clogging no additive or treatment make it stop; it's time to roll up your sleaves. Commonly assumed this is a job for professionals, or at least a job that is extremely messy, it's no so bad with some planning. Every tank is different and every do-it-yourselfer is different, but the following thoughts should see you through.
  • Burn the fuel down. Rather like putting off going to the doctor, don't wait until the problem is fatal.  Take your medicine early, burn the fuel out, and clean the tank.
  • Access. Hopefully the tank is fitted with a sufficient access opening.  Sure, it's possible to add a larger opening to a tank; however the safety precautions involved are beyond the scope of this blog. Hire a professional. Do not simply cut into an empty tank with a saber saw - the heat from cutting can generate enough fumes cause a fire or explosion.  Additionally, the access hole must be sealed in a manner compliant with the appropriate code.  Still... it may be possible to clean the tank through the existing openings with some ingenuity. Read on.
  • Pumping. Although diesel fuel is not a flammable liquid, flammable mist can be generated by excessive agitation.  The use of a shop vacuum is dangerous and has caused several fires; I've seen them.  The safest pump is a manual bilge diaphragm pump, and most common brands are equipped with nitrile and neoprene elastomers that are compatible with diesel fuel; logical, since fuel and oil in the bilge is not unheard of. Head pumps are also so equipped. No electric pump should not be located in a confined space where vapors can accumulate.
  • Overflows. Be certain a person is stationed at each end of the pumping operation, and that one of these people can stop the pumping.  It's surprisingly easy to lose track of time and overflow the receiving container. If siphon is possible, have a ready means to stop it.
  • Solvents.  Some have suggested wiping down the inside of the tank with solvents in order to remove the last bit of residue. Clearly, this can be an extremely dangerous practice because of the flammable and toxic breathing atmosphere that can be generated, even with low- or non-hazardous solvents. If you want to wipe down the inside of the tank, use a rag moistened with diesel fuel. An aqueous degreaser such a Simple Green works to, but you'll have to remove the entire residue. I use diesel fuel.
  • Power washing. In many tanks baffles or limited access openings will make it impossible to reach all portions of the tank.  The professional tank cleaner's solution is to use a power washer. The accessible portions of the tank will be washed down using an ordinary fan tip, though the end of the lance may be bent somewhat to improve access to the tank roof. To reach more remote portions of baffled tanks a tank cleaning nozzle capable of spraying in all directions is used. (example; McMastter/Carr, part number 322225k31. Though only rated at 100 psi, a typical power washer does not have the flow to produce over 40 psi pressure. Manufacturer; http://www.lechlerusa.com/products/tank_washing_9.asp) The nozzle is attached to the end of a short piece of pipe (1-foot x 1/4" schedule 40 steel is typical; this is critically important to provide stiffness and to prevent the hose from turning back on itself and coming back out of the tank access hole, much like a snake crawling back up the arm of the handler. This stinger is attached to the length of flexible hose (3-10 feet of the same hose that the power washer lance is fed with), which is then attached to the tip of the power washing lance in place of the usual nozzle. This extension is fed through the baffles in the diesel tank and will reach all areas. The tank cleaning nozzle/stinger is fed by hand and water flow must not be triggered until the nozzle is well inside the tank; a second operator is needed to control the water flow through the lance.  Ideally, the lance should only be triggered when the nozzle is in position and separated from the operator by at least one baffle. The water, sludge, and fuel that is rinsed off will typically drain back to a low area under the access hatch and can be continually pumped out while the power washing is in process.    Protective equipment during this sort of power washing includes heavy rubber gloves (not examination or dish washing), a sturdy (but cheap!) raincoat, and face shield.  Although caution will keep the power washing nozzle in the tank while the water is on, high-pressure water can cause extremely nasty injuries. The following link describes possible hazards using more powerful equipment, but the illustration is valuable (http://www2.worksafebc.com/i/posters/2005/WS%2005_07.htm).
  • Disposal. The marina's used oil collection tank should be able to accept the contaminated fuel heel; contamination with polymerization sludge or biological fouling will not present any problems for the used oil recycler. Contamination with gasoline or solvents is not acceptable.  For additional information contact www.NORANEWS.org, the National Oil Recyclers Association. Oily water is a problem for recyclers, so try to minimize the volume.

Please notice that these suggestions focus on safety.  Cleaning out a fuel tank is no complicated trick with the proper tools.  Doing so safely and efficiently requires thought and preparation.

Reference Information:
General descriptions of differences between conventional diesel fuel and ULS diesel fuel.
professional mariner

Description of biodegradability of Bio-diesel. This laboratory is affiliated with bio-diesel producers.

Typical bilge pump materials and compatibility specification.
Whale Pumps