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Effects of Contamination

As fuel ages, it degrades. Contaminants will accelerate fuel degradation. Arguably, water is the most damaging contaminant. It is attributed to a host of chain reactions. There are generally three forms of water contamination in fuel:

  1. Free Water – forms in the tank bottom usually once the fuel has reached saturation which can be as high as 1500 ppm water. This form of water represents a very high risk and is associated with microbial growth.

  2. Emulsified Water – found as tiny droplets of water suspended in the fuel. Fuel will appear cloudy. This form represents high risk.

  3. Dissolved Water –the fuel holding water from the environment. Surfactants or biofuels help to suspend the water in the fuel by reducing the surface tension that naturally occurs between fuel and water.

When water is present, microbes can grow. They commonly find their home in emulsified or free water. Microbes do not colonize easily in dissolved water. However, dissolved water does effect the stability of fuel causing accelerated aging. The picture to the right shows free water in dyed diesel fuel. The water contained a high level of microbial growth, a direct result of water 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 live off of 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.

The picture to the left is of a diesel fuel sample that was taken from a retail fuel system less than six months old. When the underground storage tanks were installed, water was used to ballast the tanks. After a thorough investigation, it appeared that residual ballast water remained in the tank prior to filling them with fuel the first time. The water mixed with the diesel fuel (containing 5% biofuel – B5) and decomposed at a very rapid rate. Within one month, dispenser parts were showing signs of accelerated corrosion and required premature replacement. This lead to the investigation that revealed the contamination problem. During this short time acid levels and microbial contamination reached a very high level. Ethanol cross-contamination was detected.

This example shows how rapidly fuel contamination can occur. By the time the contamination was found and addressed, the retailer spent in excess of $15,000 on repairs and decontamination.

Water also presents a problem with ethanol enriched fuels. Ethanol is both hydrophilic – easily dissolves in water and hygroscopic – water absorbing. Ever-present water is often suspended in ethanol blended fuel until it becomes heavy enough to drop out. Ethanol and water are miscible. 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 it reaches saturation.

Tank monitoring systems may not be able to detect small amounts and water finding paste may fail to recognize water in fuel. The only sure way of determining water in fuel is to take a good sample of the fuel. Bottom sampling is the first defense against phase separation, discussed later.

How does water enter a tank system? To name a few through fuel delivery, condensation, leaky caps or seals and holes in tanks and lines. The speed at which water enters fuel can determine how quickly water becomes dissolved or emulsified. The most common form of water – dissolved – is usually present. Small amounts of dissolved water will not cause fuel to be cloudy and normally do not present a problem until enough accumulates.

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 fuel. 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. The water in fully phase separated fuel will pull 90% of the ethanol out of the fuel to the bottom. This phase layer of water and ethanol must be disposed of and the fuel left will need to be tested and blended with fresh fuel to meet proper specification. Since the ethanol (an octane booster) is absent, the fuel left is substandard and will not meet the octane requirement. Water in fuel is very costly. It will damage the fuel, fuel system and equipment. The presence of water increases liabilities and risks.

Particulate contamination comes in many forms. Dirt, organic compounds and microbial solids are common as fuel and fuel systems age. Airborne particulates enter fuel systems through vents and openings. Fuel system deficiencies and human error also allow particulates to contaminate the fuel. No matter how they get in, they all cause damage and result in the premature aging of the fuel.

The fuel aging process is normal, but there are variables that accelerate the process. The amount of particulates entering the fuel and atmospheric conditions play a part. Without filtration, every 8,000 gallon delivery of fuel will contain almost 11 ounces of particulate contamination – much of it microscopic. This is not enough to visually see, but it is enough to seriously affect fuel quality. It is measureable and will accumulate with every delivery. In 2007, BP did a fuel cleanliness study on diesel fuel at retail. There findings confirm that the fuel being sold did not meet the specification recommended by the WWFC for clean diesel. Since then, product cleanliness has not improved. Peer review research continues to confirm the need for additional improved filtration.

Accumulated particulates, water and acids from microbial activity accelerate the aging process adding to the particulate problem. Due to HDS, diesel fuel and biodiesel both have reduced stability in storage. As they degrade, they form gums, sediments, acids and peroxides. These separate from the fuel and collect along the bottom of the tank, on the sides and suspend within the fuel itself. Increased heat and the presence of moisture and acids serve as an accelerator. This is all part of the oxidative instability of diesel products, resulting in fuel system damage (corrosion) and engine performance issues that lead to engine damage or failure.

Gasoline exhibits some of the same problems as diesel. Oxidative degradation results in gum and resin deposits forming. Ethanol enriched fuel presents additional challenges. When stored improperly, atmospheric moisture enters the fuel and speeds up the formation of gums and solids as well as increases the probability for phase separation. This all leads to corrosion damage and engine failure.