BCA, INC.
BIODETERIORATION CONTROL ASSOCIATES, INC.
MICROBIAL CONTAMINATION CONTROL SERVICES
Fiberglass
Tank Biodeterioration Risks
A
Short Annotated Bibliography
The
July, 1997 issue of National Petroleum
News contained the following report:
"UST
linings failing in Iowa”
A
preliminary report issued by the Iowa Underground Storage Tank (UST) Financial
Responsibility Program reveals a significant percentage of tank linings are
failing well before their estimated life expectancy.
"This
is something petroleum marketers should be aware of, say the Texas Petroleum
Marketers and Convenience Store Assn., because the 10-year warranties most
liners offer are beginning to expire. Under
federal regulations, lined tanks must be inspected 10 years subsequent to
installation and then every three years afterwards."
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Although
many factors may contribute to tank corrosion and premature tank lining
failures, one controllable cause is frequently overlooked.
FQS has compiled the following annotated bibliography to help promote
general awareness of the documented role of microbes in polymer deterioration.
We hope you find this bibliography informative.
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Glossary:
The
articles listed in this bibliography are all technical.
They discuss analytical methods and biological processes that are
unfamiliar to non-scientists. The
following glossary should help the reader understand some of the more technical
terms used below.
Bacteria
- Bacteria are single-cell organisms that lack a clearly visible internal cell
organization. This means that when
you look at a bacterium under a microscope, you don't see any internal
structures. There are millions of
different kinds of bacteria. Each
has unique requirements for air (some can't tolerate any oxygen), food types
(most "eat" small molecules with less than six carbon atoms), and
environmental conditions. Bacteria
are so small that you can't see a group of them (a colony) until there are over a billion individual cells.
Approximately ten million cells will make a fluid slightly cloudy.
Bacteria are one of the two groups of microbes
that degrade fuels and fuel systems.
Biocide
- Also called antimicrobial or preservative
- a chemical used to kill microbes. Industrial
biocides are used in virtually every imaginable manufacturing practice from
paper production to metalworking. Biocides
are used to disinfect water supplies and protect materials from biodeterioration. Biocides
must be approved for each end-use by the U.S. EPA under regulations coming from
the Federal Insecticide, Rodenticide and Fungicide Act (FIFRA).
Biocides used in systems that contain on-highway fuels must also be
approved as fuel additives. These
regulations come under the Clean Air Act, and are also EPA's responsibility.
Biodeterioration
- This is the special name given to biological processes that cause economic
damage. Microbes causing fuel
degradation or fiberglass tank failure are two good examples of biodeterioration.
Biofilm
- If you are in the fuel business, you need to understand what a biofilm is.
Many microbes produce a sticky, slimy material.
This material serves several critical roles.
It helps microbes attach to surfaces.
Once enough of this material is produced, it forms a film.
This film may eventually grow to be more than ¼-inch thick.
Whole microbe communities, made up of many different types of bacteria
and fungi, live within the biofilm. As
communities, they can change their environment (much like a space ship or
submarine makes its own environment), and carry out chemical reactions that no
single microbe could. This is why
biofilms are so important in biodeterioration.
Biofilms also protect the microbes that live within them from biocides
and other agents that might kill bacteria and fungi.
Debonding
- This is the process by which the chemical links between a coating and the
surface to which it has been applied are broken.
Blistering is often the first
sign of debonding. As blisters, or
bubbles, grow, the coating may flake away from the coated surface.
Debonding may start when water and/or microbes seep through small pores (holidays)
in a coating.
Electrochemical Impedance Spectroscopy (EIS)
- This is an instrument used by structural engineers to test for changes in the
structural integrity of polymeric or plastic materials.
Enzyme
- A large molecule that functions like a machine.
Made up of long chains of amino acids, enzymes do all the cell's
conversion processes; converting food into new cells, biofilm, energy and waste
products. All organisms from
bacteria to mammals depend on enzymes to carry out the chemical reactions of
life.
Fiber reinforced polymeric composite (FRPC)
- Fiberglass (fiberglass is a
registered trademark for Owens Corning's line of FRPC products) and related
materials are manufactured from either spun glass or carbon and any of a variety
of polymers. Polymers
are long chains of molecules. Latex
and polyurethane are polymers. Embedding
fibers into a polymer makes it a composite
material. Thus the term FRPC, fiber
reinforced polymeric composite. These
materials are also known as fiber reinforced plastics, or FRP.
Fungi
- The earliest single or multi-cellular organisms that have true internal
organization. Yeasts are single
cell fungi. Mushrooms are large,
multi-cellular fungi. There are
many microscopic fungi (like bread mold) that grow in long chains, or filaments. These are
called Molds. Yeasts and molds join the bacteria and are the major microbes
involved in biodeterioration.
Microbe
- A general term used for any organism that can't be seen without looking
through a microscope. As used in
our discussions of fuel and FRPC biodeterioration, microbes
are bacteria and fungi, combined.
Mineral acid
- This term refers to simple acids like hydrochloric acid and sulfuric acid.
Typically mineral acids are very corrosive.
Organic acid
- This is acid form of an organic molecule.
Most organic acids are relatively weak, as compared with mineral acids. However, they can corrode (etch holes) metal and polymer
surfaces during prolonged exposure. Low
molecular weight organic acids (small molecules, with one to six carbon atoms
for example: formic acid, acetic acid and citric acid) are more aggressive than
those of higher molecular weight (larger molecules; with more than six carbon
atoms).
Scanning electron microscope
- A special type of microscope that uses a beam of electrons instead of visible
light to enable researchers to see very small objects in great detail.
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Gu,
J. D. Microbiological Deterioration and Degradation of Synthetic Polimeric
Materials: Recent Research Advances. Internat.
Biodet. Biodeg. 52(2): 69-91.
Dr.
Gu reviews biotransformation of a wide range of polymeric materials including
coatings and composite material (fiber reinforced plastics).
His excellent descriptions of the various processes by which polymeric
materials are degraded are augmented with illuminating photographs and electron
micrographs.
Tascioglu,
C., Goodell, B., Lopez-Anido, R., Peterson, M., Halteman, W. and Jellison, J.
2003. Monitoring Fungal degradation of
E-glass/phenolic fiber reinforced polymer (FRP) composites used in Wood
Reinforcement. Internat. Biodet.
Biodeg.51(3): 157-165.
The
authors used microscopy, interlaminar sheer strength by short beam testing and
ultrasonic non-destructive testing to determine whether common wood decay fungi
penetrate and degrade FRP. The investigators demonstrated reductions in interlaminar
strength and extensive fungal filament penetration of the fiber-resin matrix.
Scanning electron microscopy provided strong evidence of fugal growth
causing fiber-resin debonding.
Gu,
J. D., Roman, M., Esselman, T., & Mitchell, R. 1998. The
Role of Microbial Biofilms in Deterioration of Space Station Candidate Materials.
Internat. Biodet. Biodeg. 41(1): 25-33.
The
scientists on this research team demonstrated that biofilm microbes degraded
fiber reinforced polymeric composites (FRPC defined above).
The investigators compared FRPC that contained biocide with unprotected
FRPC. Biocides that have been used
to protect latex and other polymers did not prevent either biofilm development
or FRPC degradation.
Ray,
R., Little, B., Wagner, P. Hart, K. 1997. Environmental
Scanning Electron Microscopy Investigations of Biodeterioration. Scanning
19: 98-103.
The
authors demonstrate the utility of environmental scanning electron microscopy (ESEM)
for examining microbially influenced corrosion and biodeterioration.
Visualization of dense microbial populations growing in FRP within the
space between disbonded resin and fibers serve as one example of ESEM’s
utility. The authors hypothesize
that microbial gas production contributes to the mechanical damage that
microbial growth causes to FRP.
Gu,
J. D., Lu, C., Mitchell, R., Thorp, K., & Crasto, A.
1997. Fungal Degradation of
Fiber-Reinforced Composite Materials. Material.
Perform. 36:37-41.
The
researchers measured FRPC biodeterioration in terms of increased water content
and loss of structural integrity. They
report that the first degradation step is often water seeping into the composite
between the polymer and the fibers. After
this, the water causes mechanical damage by expanding and contracting within the
FRPC; causing the fibers to separate from the polymer.
At the same time, microbes attack the polymer with special enzymes.
These enzymes are believed to break the polymer down into smaller
molecules that can be used as food.
In
their study, the team looked at five different types of FRPC, and found the same
biodeterioration processes to occur in all of the composites.
Gu,
J. D., Ford, T., Thorp, K., & Mitchell, R. 1996. Microbial
Growth on Fiber Reinforced Composite Materials.
Internat. Biodet. Biodeg.
37(3-4): 197-204.
Investigators
studied biodegradation of five different polymers used in composite material
production. They also compared growth on glass and carbon fibers, the two
types of fiber used in FRPC.
Through
scanning electron microscope photographs and microbial growth data, the authors
demonstrate that: a) fungi can form colonies on both glass and carbon fibers
used in FRPC; and b) fungi can use each of the polymers tested as their only
food source.
These
findings are particularly important because they demonstrate that, as long as
water is present, microbes can degrade FRPC.
Sand,
W. 1994. Microbial Deterioration of
Materials -- Fundamentals: Microbial Destruction Mechanisms. Korros.
45(1): 10:16.
This
review article discusses the various mechanisms by which microbes are able to
degrade polymers; including resins used in fiberglass.
The author lists seven categories of biodeterioration processes that may
cause changes ranging from minor discoloration to total destruction:
1)
Attack by mineral acids (sulfuric, nitric; carbonic) causing resin
breakdown;
2)
Attack by organic acids (acetic, citric, oxalic, gluconic, etc.) causing
both resin breakdown and cation chelation (chelation
occurs when an atom with a multiple positive-charge - like iron: Fe4+-
binds with several negatively charged, organic molecules).
Both chelation and acid attach weaken polymer structure.
3)
Salt stress caused by water retention by products generated by processes
(1) and (2), and leading to freeze-thaw attack and crystallization swelling
attack. Water and crystals expand, forcing polymer away from fiber.
This process is similar to the one that causes rocks to crack and
mountains to erode. When water
seeps between narrow rock fissures and freezes, something has to give.
Generally it's the rock. During
each freeze, more space is created. Since
the crack is now larger, during the next thaw, more water is trapped.
The cycle repeats itself until the rock splits apart.
In FRPC, the composite becomes increasingly brittle.
4)
Production of hydrogen sulfide, nitrogen oxides and metal sulfides.
These chemicals are both noxious and can
degrade FRPC.
5)
Production of biofilms that cause localized corrosion, water retainment
in porous materials, and effects to hydrophobic surfaces.
(Hydrophobic surfaces repel water.)
It changes surfaces so it becomes hydrophilic (water loving).
Since biofilms don’t coat surfaces uniformly, they create conditions
favorable to the formation of physical and chemical gradients
(conditions change across short distances).
An example of a gradient is the temperature difference you feel between
the surface and the bottom of a pond. The
water is warmest at the surface, where it has been warmed by the sun. Below the surface, and down to about 20 feet, the temperature
decreases, as depth increases. Below
that depth, the temperature remains nearly constant. The zone of temperature change is a gradient.
Across a biofilm, the distance between the "high" and
"low" ends of a gradient may be less than 0.0001 inches.
These physical and chemical gradients stress the structure of composites.
Moreover, they create special environments in which problem microbes can
thrive.
6)
Enzyme cleavage of insoluble resin organics to small, water soluble
molecules. In other words; enzymes
attack the polymers and break them down into smaller pieces (depolymerize) that
will dissolve in water.
7)
Wetting agent production, increasing solubility of hydrophobic
substances. (note explanation of hydrophobic
under category 5). Microbiological
produced wetting agents are chemicals that disperse non-water soluble chemicals
in water. They also help water to
form a flat film on the surface that normally repels water like a FRPC.
The author notes that it is difficult to recognize the direct or contributing role of microbes in FRPC degradation. Since microbes live as complex communities within biofilms, it is difficult to reproduce "real-world" conditions in the laboratory. Non-biological forces may also cause some of the problems that are caused or accelerated by microbes. Consequently, FRPC biodeterioration may often be misdiagnosed.
Kopteva,
P., Zanina, V.V., Kopteva, A. E. 1988.
Bacterial Degradation of Polymer
Coatings on Gas Pipelines. R.
Zh. Korr. Zashch. Korr. 2K614.
The authors compare biodegradability of several coating materials. Although bitumen coatings were more readily degraded than polyethylene or polyvinyl chloride, all coatings studied were degraded. The authors reported that microbial communities changed the structural properties of the coatings. These changes caused decreases in the strength and adhesion properties of each of the polymers studied. Consequently, corrosion between coating and steel piping was accelerated.
Stranger-Johannessen,
M. 1987.
Microbial Deterioration of Corrosion Protective Coatings.
In E. C. Hill, J. L. Shennan and R. J. Watkinson, Eds. Microbial
Problems in the Offshore Oil Industry.
John Wiley & Sons, New York. Pg.: 57-71.
The
author uses literature citations and case studies to build a compelling argument
for including biodeterioration resistivity testing to coatings performance
evaluations. In earlier
publications, the author has demonstrated that microbes cause corrosion
protective coating debonding (see definition in the glossary) and blistering. Routinely,
"unexplainable" coating failures can be attributed to microbial
activities.
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BCA
is dedicated to helping you control microbial contamination problems before they
hurt your operations. Our
consulting services, line of test kits and supplies, fuel biocides, additives,
and tank cleaning services are all designed to help you to improve your
profitability by reducing your corrective maintenance costs as well of your risk
of fuel system failures caused or accelerated by microbes.
For
more Product and/or Technical assistance please contact: Dr.
Frederick J. Passman