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