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.