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.

What’s in My Fuel? (Part 2)

Where Does Contamination Come From?

fuel supply chain

Fuel contamination comes from many sources including product aging, the environment, microbial infection, transportation and fuel system deficiencies. The image above showing the fuel supply chain from refining to end user demonstrates many places where contamination is likely to occur.

At every point in the transportation of fuel contamination is a concern, compounded by the growing demand for cleaner fuels. Once fuel is refined, it often goes into temporary storage prior to being conveyed to a terminal. Delivery might include pipeline, ship, barge, tanker or rail car before arriving at terminal storage. Fuels may be allowed to settle prior to being shipped to its next destination. Settling is important as it permits contaminants to fall out and be pumped off. However, if settling time is not provided contaminants are likely to be transferred to the next location. Tankers transfer fuels from terminals to intermediate storage or end users. This might include additional storage or directly into equipment.

Many of the components of a fuel distribution center are made up of low to mild carbon steel. Tanks, pipes and pumps are very susceptible to corrosion. Rust and metal particulates are often carried downstream to the end user. Water always presents a problem. Throughout the distribution system water can be transferred along with fuel. Even pipeline cleaning, called pigging can attribute to higher contamination levels. Even when filtration is a part of the distribution chain, it may not be adequate.

Of the contamination studies, most agree that particulate and water contamination serve to be ongoing challenges. Biofuels tend to test dirtier than non-biofuel samples. On average, a tank that receives 8,000 gallons of fuel a week can gain as much as 35 pounds of particulate contamination per year. This does not include the potential for water contamination. Much of the filtering done through dispensers – especially retail – proves to be inadequate for providing fuel that meets today’s engine cleanliness requirements.

For more information check out Dixon’s CleanFuel website or call us at 1-800-874-8976.


What’s in My Fuel (Part 1)


This is the first of a three part series on fuel contamination dealing with the forms of contamination commonly found in fuel. There are three broad forms: gas, liquid and particulate. Each of these offer varying degrees of potential damage to fuel and fuel systems.

Most do not see air as a contaminant, but it is. As a fuel system breaths, air brings with it a host of contaminants including bacteria, moisture, dust and particulates. Liquid contamination consists primarily of three types: water, fuel cross-contamination and acidic byproducts from microbes. The third form of contamination, particulates, include foreign particles like rust, scale and sand. Contaminates can also include components of the fuel itself that separate and drop out due to the aging and decomposition process.

The most problematic liquid contaminant is water. Unfortunately, all fuel contains water. The allowable limit is 0.05%. This is equivalent to 2.5 gallons water in 5,000 gallons of fuel. Because most fuels contain biofuel additives or blends, water creates additional challenges. Cross contamination is also an issue. There are few dedicated delivery systems meaning different fuels are carried back-to-back. The practice of switch-loading is common. Switch-loading takes place when one product is carried in the same container preceding another without cleaning the prior product. A common cross-contamination problem is ethanol enriched fuel (E-10) in diesel fuel. Acidic byproducts from microbial contamination and fuel aging are also a major concern.

There are numerous types of particulate contamination. Everything from rust to microbes. The types are too many to list. A majority include rust, sand, microorganisms and hydrocarbon components that have separated during the aging process. As a hydrocarbon ages, it breaks down. There are several forms of contaminants that separate as a result a few of which are:

  • Asphaltines are asphalt like particles found in crude oil. When fuel ages it oxidizes creating these byproducts. They are generally thought to be harmless because of their tiny size – 0.5 to 2.0 microns in size. During the fuel aging process the substance can stick together and on equipment or filter surfaces causing damage to both the fuel system and engine. Water is known to accelerate the formation of Asphaltines.
  • Wax crystals form in diesel fuel as a result of low temperature. During the winter months, additives are often added to fuel to change its low temperature characteristic. Without the additive, waxes will often form and separate, clouding the fuel and clogging filters. Engine and fuel system damage can occur.
  • Acid formation in aging fuel.

Each type of contaminant has the capacity to damage a fuel system or engine. Depending on the type and amount, damage can range from minor to severe. As fuel ages and is left unchecked equipment damage is almost certain. The shelf life of fuel is 3-6 months without some level of maintenance. If water is present, fuel will degrade faster. Both water and heat speed the process allowing for accelerated biological growth.

Contact Dixon Pumps for help with contamination control at 1-800-874-8976 or check out our CleanFuel website.

Fuel Contamination

free water in offf road diesel

Fuels are quite different from those a decade ago. There are numerous problems associated with the quality of fuel. Diesel and gasoline are not problems in and of themselves. However, a combination of factors have contributed to a whole host of serious and potentially dangerous concerns. Between 2004 and 2006, the EPA mandated the reduction of sulfur in fuel and the addition of biofuels (ethanol and biodiesel). These along with the removal of lead produced more than a few unintended consequences. Many in the petroleum industry are trying to determine the proper response to these unforeseen problems.

Before 2004 it was not uncommon for fuel to have a 5 or 6 year shelf-life. According to the most recent research, fuel begins deteriorating before it ever reaches the end user. In fact, if water is present, it can degrade by as much as 95% within 30 days of refining.

Current fuel studies show that the fuel coming out of terminals have minimal biocide, leaving them vulnerable to microbial contamination. Additionally, if fuel is exposed to other contaminants it will exacerbate an already serious problem. Water exposure, cross-contamination and the addition of biofuel contribute to the problem.

Water contamination can happen at any time during the transportation and storage of fuel. During barging and shipping, water exposure is a constant problem. Even when pumped off, some amount of water remains in the fuel. Transport truck delivery also provides a potential for water to enter the fuel. Driver error or incompetency can lead to water entering the fuel. It is not uncommon for drivers to leave tanker access ports open, allowing water and contaminants to enter the fuel. Another common mistake made by drivers occurs when dropping fuel. Standing water often enters the fuel tank when the driver makes the delivery. Many of the most egregious errors take place during seasonal weather events.

Once delivered, water intrusion can occur both naturally and systemically. Naturally, water enters fuel through the process of condensation. Temperature differences or variances change the humidity levels in the fuel system producing condensation. Over time, condensation will settle and become measureable. However, while it is suspended in the fuel it is virtually undetectable. Systemically, water can enter into the fuel through leaks and weaknesses within the fuel system itself. Often leaks are small and water creeps in virtually undetected until the damage is done.

When water enters conventional fuel, it settles, generally dropping out of the fuel at a rate of one foot of fuel per hour. That means a tank with 10 feet of fuel will require 10 hours for the water to settle. Unfortunately, most fuels contain a bio-mix of either ethanol or biodiesel. Both are considerably more water soluble than conventional fuel and contain more suspended water in the fuel.

Ethanol is hydrophilic – it loves water. In ethanol enriched gasoline up to .5% water can be suspended in the fuel before the water begins to drop out. This process is called phase separation. When the water drops it takes with it the ethanol. The ethanol and water mixture is the perfect breeding ground for microbes, the most common of which is “acetobacter.” This bacteria is associated with the creation of acetic acid. When ethanol and water bond chemically, they create a perfect environment for the acetobacter to reproduce at an alarming rate.

Regulations allow up to 5% biodiesel to be mixed with conventional diesel without any labeling or notification. As with ethanol, biodiesel is very soluble. According to the EPA in its most recent study, “Diesel blended with biodiesel can hold in solution more water than diesel without a biodiesel component. This means more water is likely arriving in USTs entrained in fuel today since biodiesel is more common in diesel than prior to 2007.”

Both ethanol and biodiesel are microbial food sources. Most of the microbes affecting fuel require a water interface to multiply. The combination of a readily available food source and interface make today’s fuels difficult to maintain. Microbial growth has become common and the corrosion problems associated with them are very serious.

Additionally, most carriers practice switch loading – transporting gasoline and diesel in the same trailer or truck compartment – contributing to the problem through cross-contamination. The EPA discovered 90% of diesel tanks tested contained ethanol contamination suggesting that cross-contamination is the norm. Recent research confirms that the ethanol contamination in diesel is likely the main cause of corrosion in fuel systems and engines. Research asserts, fuel system corrosion was not a major problem until ethanol was in common use. Ethanol cross-contamination in diesel and the serious corrosion in fuel systems lends to this assertion.

All of this adds up to the need for a fuel quality management program. If you own a fuel system, fuel management is a reality.

Killer Contamination


Imagine having almost ten gallons of contaminants in your fuel tank like the picture shown above.  The site owner had been replacing filters more frequently and noticed higher than usual maintenance costs on his fuel equipment. Imagine the surprise at what was found in the bottom of the tank.

Sample your fuel to determine visual clarity.  If the fuel looks bad something must be done.  In the case of the contaminated fuel, the fuel sampled had become contaminated over a short period of time. Microbes were eating the fuel and leaving behind an acidic byproduct in the tank.   The contaminants removed from the tank were part of a larger problem.  The acids found in the bottom and mid-tank samples, a by-product of the microbial infection, were eating away at the fuel system components.

It was estimated that the contaminated fuel had cost the owner more than 35% higher maintenance costs on his fuel system. It likely cost him customers as well. Do you know what is in your tank? Dixon Pumps sells fuel samplers and equipment to clean your tank and fuel. Call us and we will help you find the answer.