Fuel System Microbiology Basics (Part 1)


It is no secret the damage unchecked fuel systems incur due to microbial contamination. Product loss, liability increases and Microbial Influenced Corrosion (MIC). MIC is responsible for significant financial cost. According to NACE International, corrosion within the fuel industry accounts for over $7 Billion in annual losses.

We will be discussing the adverse roll microorganisms play in damaging fuel systems. The following summary is meant to be an overview. Please note that this is not an attempt to cover every aspect, but only highlight major problems found today in fuel systems. Let’s start with the basics.

There are three microorganisms commonly found in fuel systems: algae, bacteria and fungi. Algae when found in fuel does not appear to be a major contributor to fuel system damage when compared to bacteria and fungi. Yeast and molds are the most common fungi found. Fungi often observed in the water-fuel interfaces on the bottom of tanks form a thick membrane or film evident in bottom samples. Bacteria are single-cell microorganisms found everywhere. Three broad types are relevant to the fuel industry: aerobes, anaerobes and facultative anaerobes.

Aerobic bacteria require oxygen to survive. Oxygen found commonly in water-fuel interfaces and condensation provide a ready source. Anaerobic bacteria cannot tolerate oxygen and will likely die; others can remain dormant. The most common and damaging anaerobe found in fuel systems is Sulphate Reducing Bacteria (SRB). We will talk about this specifically in later posts. Facultative anaerobes can survive in both oxygen and anoxic (without oxygen) environments.

The most important thing to realize is that no one single microbe is causing the problems associated with fuel contamination and fuel system damage. Microbes work in consortia (communities working together). Biodeterioration (the detrimental change to materials due to bioorganic activity) results from microbes working together. Over the next few months, our posts will describe in more detail how microbes interact, contaminate fuel and damage fuel systems.

Fuel and Tank Cleaning Fact vs. Fiction

Reality Check

Fuel contamination and dirty tanks are a reality for tank owners today. Poor fuel quality is responsible for rising costs for tank and fuel system owners.

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Liability issues caused by microbial influenced corrosion abound. The tank owner is faced with skyrocketing maintenance costs and liabilities that were not a problem a decade ago. Contaminated fuel attributes to the corrosion issue, part of the larger global corrosion problem costing over $2.5 trillion dollars each year. Corrosion represents the single largest expense in the US economy, 6.2% GDP. Today’s tank owners are having trouble coming to grips with the cost of bad fuel. Separating fact from fiction will help identify an acceptable solution to dirty tanks and contaminated fuel.

Fiction often begins with the idea that tank and fuel cleaning is too expensive. Fact exposes the truth – you cannot afford to have dirty tanks and fuel. The rising cost of equipment, maintenance and liability issues are all attributed to contaminated fuel. The cost benefit of clean tanks and fuel far outweigh the cost to clean.

Fiction includes believing your tanks and fuel are clean. Fact – almost 75% of fuel sampled contain moderate to serious contamination. Exposing the dangers of blind belief that your tanks are clean is a necessary step to taking appropriate action. A fuel sampler is an investment worth making. Monitoring devices and water finding paste can fail. The most effective way to determine what is in your tank is to take a bottom sample.

Helping tank owners peel away fact from fiction is key to reducing the costs associated with contaminated tanks and fuel. Identifying cost effective options to clean and maintain tanks will help owners to take the necessary steps to fuel quality management and tank maintenance. Call Dixon Pumps at 1-800-874-8976 or check out our Online Store where you can order a fuel sampler and much more.


What’s in My Fuel? (Part 3)

The Effects of Dirty Fuel

As fuel ages, it degrades. Contaminants accelerate fuel degradation. Water is the most damaging contaminant and is attributed to a host of chain reactions. When water is present, microbes can grow. They commonly find their home in emulsified and free water. Microbes do not colonize easily in dissolved water. However, dissolved water does effect the stability of fuel causing accelerated aging. The pictures above show serious contamination in diesel fuel. The water found at the bottom of the tank contained a high level of microbial growth, a direct result of the contamination. Bacteria and fungi (including yeast and mold) will grow wherever water is found. Most of these microorganisms are aerobic – meaning they require oxygen to live and grow. Water supplies the need.

While there are other types of microbes – anaerobic and facultative anaerobes – aerobics are the primary ones found in fuels. Anaerobic microbes do not require oxygen to survive and facultative anaerobes can live in both oxygen and non-oxygen environments. While rarer, they are sometimes found. Aerobic microbes require very little water to multiply. Small areas of condensation on a tank wall can sustain a colony of aerobes. This microbial contamination causes biodeterioration of fuel. As fuel deteriorates, a layer of biofilm forms at the fuel/water interface in the bottom of the tank. Biomass colonies can also form and suspend within the fuel layer, especially when biofuel is present.

Microbes feed off hydrocarbons. They are often referred to as hydrocarbon utilizing microorganisms or Humbugs. As they eat the fuel, they produce an acidic byproduct. The acid settles to the bottom of the tank, remains suspended in the fuel and forms an acidic vapor in the fuel system raising the acidic content of the fuel system and causing microbial influenced corrosion (MIC). One of the most prevalent acids found is acetic acid caused by Acetobacter bacteria. They generate acetic acid from ethanol. Due to cross-contamination of fuels, ethanol is found in most fuel types including diesel allowing for the reproduction of Acetobacter and the production of acetic acid.

Acid formation accelerates the decomposition of fuel especially biodiesel. The molecules of biodiesel are predominantly fatty acid methyl esters (FAME). Its breakdown usually happens slowly unless water is present. The chemical breakdown of FAME by water (hydrolysis) is accelerated in an acidic environment. As a result biodiesel has a very short shelf life.

Most problems can be minimized with a fuel quality management program. Regular fuel sampling and immediate water removal when found. A Fuel Quality Management Program helps to identify contamination problems long before they reach the level seen in the photos above.  Contact Dixon Pumps for help with contamination control at 1-800-874-8976 or find additional information at our CleanFuel website.

Bad Fuel = Corrosion

corrosion on parts

One of the constants in the petroleum equipment industry is corrosion. THe problem continues to cost the industry billions of dollars each year. When I talk with tank owners, they think that corrosion is a result of moisture.  Although that is a contributing factor, the real culprit is microbial contamination.

All fuel has some level of contamination.  If left uncheck and unmanaged, the fuel will continue to degrade at an alarming rate.  Microbial influenced corrosion or MIC results in damage of varying degrees.  As microbes reproduce in the fuel, their waste by-products continue to disperse throughout the fuel system.  The waste is likely acidic.  Acidic sludge and slime will accumulate at the bottom of the tank.  This acidic layer, its dispersants and off-gassing vapor cause damage.

Fact – acid on metal equals corrosion.  Over time, if left unattended, the microbial growth within the fuel system will result in accelerated corrosion.  The corrosion will be evident inside the tank and outside the tank on the fuel system components.  STP components in the sumps, tank risers and dispenser parts are all affected.  Eventually a catastrophic event could occur resulting in a release of fuel into the ground.  At the very least, higher maintenance costs to equipment will result both for the fuel system owner and the equipment the fuel is being pumped into.

What can be done?  First, take regular bottom samples. Be proactive rather than reactive.  This will save you both time and potential liability. Start managing your fuel and saving money.

Ethanol Blended Fuels

phase separation samples

Problems and Solutions


In 2006 the EPA Renewable Fuel Standard (RFS) mandated the use of ethanol blended fuels. Since that time, conventional gasoline has been blended with 10% ethanol (E10). This is known as the “blend wall” – the capped limit of ethanol content for gasoline. (Renewable Fuel Standard (United States), 2018) It is expected the EPA will increase the blend wall to 15% (E15) to meet the ever-increasing requirements created by the RFS. (IER, 2016) This is considered the maximum blend without major upgrades to petroleum industry infrastructure. Industry experts agree the majority of petroleum equipment is not manufactured to withstand ethanol above 15%.

Today over 90% of gasoline sold contains ethanol, producing unintended consequences and challenges to the industry. (Franklin Fueling Systems, 2012) The introduction of ethanol blended fuels brought increased concerns with water. Water has always been a concern, but ethanol exacerbates the potential problems. The two most pressing issues are phase separation and accelerated fuel system corrosion.

Phase Separation

Ethanol is both hydrophilic – easily dissolves in water and hygroscopic – water absorbing. (Jain) (F. John Hay) Water is always present in fuel at some level, often suspended in the ethanol blended fuel until it becomes heavy enough to drop out. Ethanol and water are miscible. (Helmenstine, 2017) That is, they dissolve in each other.  Ethanol is also lighter than conventional gasoline so it remains suspended in the fuel unless enough water bonds to it. Because water is heavier than fuel, with enough volume, it will drag the ethanol to the bottom once enough is present. Research shows it only takes .398% water in fuel for phase separation to occur. (F. John Hay) At saturation the water and much of the ethanol separate from the fuel and drop to the bottom of the tank. This is phase separation. Because ethanol is used to raise octane, the fuel above the phase layer at the bottom of the tank is now substandard. Fuel can also remain partially phase separated. This happens when enough water enters the fuel but has not reached saturation. During this stage, fuel can become hazy often clogging filters and shutting down engines.

It does not take much water to cause fuel to phase separate. Less than 20 gallons of water in 5,000 gallons of fuel will result in phase separation. Tank monitoring systems may not be able to detect that small amount and water finding paste can be difficult to read if this is the method used for identifying water in fuel. The only sure way of determining water in fuel is to take a good bottom sample of the fuel. Bottom sampling is the first defense against phase separation and will be discussed in detail later.

How does water enter a tank system? To name a few through fuel delivery, condensation, leaky caps or seals and holes in tanks or lines. The speed at which water enters the fuel can determine how quickly water becomes dissolved or emulsified. There are three common forms of water found in fuel. The most common is dissolved water. Because fuel is never 100% dry, it usually contains small amounts of dissolved water. Small amounts of dissolved water will not cause fuel to be cloudy and normally do not present a problem. Rapid flowing water enter a storage tank or rapid agitation will result in instant absorption resulting in emulsified water in fuel. A slow leak may take weeks to show up in the fuel. (Jain) Depending on the amount of water, the fuel may range from dissolved to emulsified. Free water is the form found on the bottom of tanks and is commonly found during phase separation. When dissolved water by volume becomes heavy enough it drops out of the fuel, settling to the tank bottom. System inspections are important to minimizing water issues and can often catch a problem before it becomes unmanageable.

Phase Separation Remediation

Can phase separated fuel be remediated? The simple answer is yes. Most phase separation can be corrected, although if there is a catastrophic event that causes large volumes of water to enter the fuel, the alternative may be disposal. There are a few simple steps to correcting phase separation.

  1. Determine the volume of phase at the bottom of the tank. This can be accomplished by using a fuel sampler. First take a sample on the very bottom of the tank, then at 1 inch increments until you determine where the phase ends and the fuel begins. There is a definite difference in the phase layer and the fuel layer on top (see photo). After determining how many inches of phase you have in your tank, you will know how much needs to be pumped out. Once the ethanol drops out of the fuel and forms a layer on the bottom of the tank, it cannot be reintroduced into the fuel. It must be properly disposed of with the water and contaminants.Ethanol phase pic
  2. Pump off water/ethanol phase and properly dispose of waste. Take bottom samples from the lowest accessible point in the tank to verify you have removed all of the phase before moving on to the next step. Keep in mind that it may be necessary to remove the STP pump for proper access to the lowest point in the tank. It is important at this stage to verify. It is also important to refrain from stirring the fuel too much. Stirring can cause emulsification.
  3. If available, use a filtration system that has coalescing and water separation capability to remove any remaining dissolved water. It is likely that some water remains and needs to be removed. Remember not to stir the fuel during filtration. The suction hose should be placed on the bottom of the slowest access point in the tank and the return should be above the fuel level in order to minimize any unnecessary agitation. Speed is not your friend when removing water from ethanol enriched fuel. Moving the fuel across the filters at a slower velocity will allow for improved water removal. Once the water has been adequately removed, the fuel octane level will need to be tested.phase tank diagram
  4. If phase separated fuel was 87 octane E10, it is possible to blend 93 octane E10 fuel at a ratio of 1:1 to correct the octane level in the fuel. For example, if you have 3,000 gallons of regular remaining in the tank, blending 3,000 gallons of 93 octane premium fuel should correct the octane deficiency. Always verify octane through testing once blending is complete. If the phase separated fuel was 93 octane E10, then the fuel should be usable as 87 octane fuel. Again, octane testing should be completed to verify results.


A second problem attributed to ethanol is corrosion – specifically microbial influenced corrosion or MIC. (Charles H.D. WIlliamson, 2015) Fuel deterioration has been documented since 1895 and accelerated deterioration since 1994. (Passman, 2013) So what has changed and why is corrosion such an issue today? Since the mandated use of ethanol, MIC has increased and become a serious problem. MIC costs the United States an estimated $50 billion per year in damage. Oil production, transportation and storage are all affected. (Institute for Corrosion and Multiphase Technology, 2018) In the most recent research, accelerated corrosion has been associated with the presence of ethanol in fuel. (U.S. EPA, 2016)

Tank Corrosion

corrosion inside tank

Water must be present for there to be microbial growth. Because ethanol is both hydrophilic and hygroscopic, ethanol blended fuels are more water soluble. In other words, water is more easily dispersed in fuel. Condensation is more easily absorbed. It is also thought that ethanol serves as a food source for microbial growth. (Charles H.D. WIlliamson, 2015)

The combination of water and ethanol serve as the perfect breeding ground for microbes. These hydrocarbon utilizing microbes produce acids. The most prevalent, Acetobacter produces acetic acid. Once the colony gains control of a fuel system, corrosive growth accelerates. Unlike typical corrosion that can take years to seriously damage a fuel system, MIC can form overnight and severely damage a system within months. Costly damage has been seen in fuel systems less than six months old.

Sump Corrosion

sump corrosion

How does the damage occur? A microbial colony begins to grow when water is present and feeds on the hydrocarbon producing an acidic byproduct. This acid will lay on the bottom of the tank and remain suspended in the fuel with any water that may be present. The combination of water, microbes, acids and deteriorating fuel form a biomass. “At the fuel-water-tank interface, all of the necessities of life are present: a carbon source, water, an electron donor (the hydrocarbon/ethanol blend and/or metals in the tank), and an electron acceptor such as O2 or previously oxidized metal (e.g., rusted steel).” (Charles H.D. WIlliamson, 2015) Even cathodically protected stainless is susceptible to corrosion. Carbon steel definitely proves no match.

As the biomass grows and accumulates on the tank bottom, an acidic off-gassing is common. The vapor fills the tank and enters the dry spaces within the fuel system. Corrosion in submerged turbine pump (STP) sumps is often a result of MIC.


While ethanol is the catalyst to an abundance of problems, there are some simple answers. No doubt phase separation and corrosion present challenges to the industry but neither are insurmountable. For both of these problems the common denominator is water. Neither phase separation nor MIC are an issue without water. If you can keep your fuel dry, then neither are an issue. All it takes is a little management.

Fuel Quality Management (FQM) is the buzz phrase that seems to be taking front stage in the battle against ethanol issues. Most realize that fuel will not manage itself. Today’s fuels need to be managed for quality. FQM is about reducing risk and limiting problems associated with water. A few simple steps are all it takes.

  1. Regularly bottom sample the fuel. Because of the potential for human error and the possibility of weather related water issues, fuel should be sampled monthly at a minimum. Ideally, bottom sampling should be done with every new load of fuel or weekly. If you do not have a bottom sampler, purchase one. They are easy to use and become the first line of defense. The diagrams below show how easy a sampler is to use. Once a sample is retrieved, it can easily be emptied into a clear sample jar for viewing.tank sampling diagram
  2. Test fuel on a quarterly basis for water and bacteria or more frequently if water is present. If bacteria is detected, administer a quality biocide to kill microbial growth associated with MIC.
  3. If water is present, immediately remove and properly dispose of it. It is imperative to keep the fuel as clean and dry as possible. If the fuel has degraded or phase separated, hire a fuel specialist to clean your tank and fuel or purchase a cleaning unit to maintain your own fuel.
  4. Clean your fuel and tanks when needed. All of the problems associate with phase separation and MIC are due to water and contaminants getting into the fuel.
  5. Do a monthly inspection of your fuel system to determine any deficiencies. If found, have them repaired as soon as possible.


Ethanol blended fuels present challenges but are not impossible to deal with. Maintaining clean, dry fuel is the most important aspect of avoiding problems like phase separation and corrosion. Professionals like the ones at Dixon Pumps can help provide answers to problems you already have or programs and equipment to limit the challenges you are presently faced with.


Charles H.D. WIlliamson, L. A. (2015, June 20). Applied Microbiology and Biotechnology. Microbially Influenced Corrosion Communities Associated with Fuel-Grade Ethanol Environments, pp. 6945-6957.

  1. John Hay, I. M. (n.d.). Ethanol and Water Contamination: Results and Observations. Lincoln: University of Nebraska.

Franklin Fueling Systems. (2012). Why Phase Separation Occurs and What You Can Do About It. Madison: Franklin Fueling.

Helmenstine, A. M. (2017, March 8). Miscibility of Fluids. Retrieved from ThoughtCo.: https://www.thoughtco.com/miscibility-of-fluids-608180

IER. (2016, May 24). Latest Analysis. Retrieved from Institute for Energy Research: https://instituteforenergyresearch.org/analysis/epa-mandates-renewable-fuel-levels-10-percent-blend-wall/

Jain, S. (n.d.). Ethanol-Water Phase Separation White Paper. Veeder-Root.

Passman, F. (2013, February 26). Microbial Contamination and Its Control in Fuels and Fuel Systems Since 1980 – A Review. International Biodeterioration & Biodegradation, pp. 88-104.

Renewable Fuel Standard (United States). (2018, February 21). Retrieved from Wikipedia: https://en.wikipedia.org/wiki/Renewable_Fuel_Standard_(United_States)

Renewable Fuels Association. (2011). Fuel Ethanol Industry Guidelines, Specifications and Procedures. Washington: Renewable Fuels Association.

Russ College or Engineering and Technology. (2018, February 22). Institute for Corrosion and Multiphase Technology. Retrieved from Ohio University: https://www.ohio.edu/engineering/corrosion/research/projects/mic.cfm

U.S. EPA. (2016). Investigation of Corrosion-Influencing Factors in Underground Storage Tanks with Diesel Service. Washington: U.S. Environmental Protection Agency.