Microbiologically Influenced Corrosion
Microbiologically Influenced Corrosion (MIC) refers to corrosion brought about by the presence and activities of microorganisms in biofilms, on the surface of pure metals or metal containing materials. Since the organisms involved, bacteria (aerobic and anaerobic), algae, fungi, and others, are generally ubiquitous, MIC can occur in almost every environment. Each of these groups can cause different problems, not just corrosion. For example, slime forming bacteria can cause plugging, loss in efficiency of heat exchangers, clouding, taste and odor problems. Iron related bacteria, including iron oxidizing and reducing, can cause plugging, corrosion, cloudiness and color change.
If these nuisance microorganisms are present, MIC can occur on these surfaces if a nutrient source and water are also present. Their impact can make the water unsafe, unacceptable or unavailable due to losses in flow through plugging or equipment failure due to corrosion. Generally, testing for more than one group of bacteria with a combination of tests should be used to determine which ones are present and causing problems.
Acid Producing Bacteria
Negative (left) Positive (right)
Significance
Acid producing bacteria are capable of producing organic and inorganic acids which can significantly drop the pH beneath the biofilm into the acid range. Under these conditions, an acid-driven form of corrosion can occur causing metals to dissolve and concrete structures to lose integrity. These acidic metabolic by-products are produced under very reductive (oxygen free) environments. The sulfate reducing bacteria are often found within this nutrient rich, oxygen free environment.
Telltale signs of acid producing bacteria corrosion include, but are not limited to, pitting corrosion and pinhole leaks.
Types of water/sources that may be tested include: hot and cold water distribution systems, open and closed recirculating heating and cooling systems, water-based fire protection sprinkler systems, and water-based fracturing fluids in gas and oil industry.
Test Method
APB-BART™ Biological Activity Reaction Test for Acid Producing Bacteria. Manufacturer: Droycon Bioconcepts Inc. Saskatchewan, Canada
Turn Around Time
10–12 days
Test Code
113
Iron Related Bacteria
Negative (left) Positive (right)
Significance
Iron related bacteria include both iron oxidizing and iron reducing bacteria. These bacteria function under different reduction-oxidation (redox) conditions and utilize a variety of substrates for growth. This consortium is complex and includes stalked and sheathed bacteria as well as heterotrophic and slime forming bacteria. Examples of this group include: Gallionella, Crenothrix, Sphaerotilus, Siderocapsa, Thiobacillus and Pseudomonas.
The iron utilizing bacteria can be problematic in that they can cause corrosion of iron and steel. This process can cause pitting of the metal surface, resulting in pin hole leaks. These bacteria can also accumulate iron to the point where the growth becomes a hard encrustation or tubercle. Over time these deposits can reduce water flow and affect system performance.
Types of water that can be tested include: potable water plumbing systems, cooling towers, heat exchangers, water heaters, and water based fire protection sprinkler systems.
Test Method
IRB-BART™ Biological Activity Reaction Test for Iron Related Bacteria. Manufacturer: Droycon Bioconcepts Inc. Saskatchewan, Canada
Turn Around Time
10–12 days
Test Code
109
Slime Forming Bacteria
Negative (left) Positive (right)
Significance
The slime forming bacteria is the name given to a group of bacteria that are capable of producing a variety of extracellular polysaccharide polymers. It is these long chain molecules which act as the foundation and cement for the formation of biofilm. The slime-like growth coating the inside of pipes and fixtures is called the biofilm. The purpose of this slime layer appears to be protective. Under harsh environments (e.g., temperature changes, chemicals, shortage of nutrients) slime layers can get thicker. As the biofilm matures, aerobic bacteria creating the biomass produce metabolic by-products all the while consuming oxygen. This facilitates micro-environments underneath the biofilm which can then support the growth of anaerobic bacteria. The slime forming bacteria are an important part of the microbial influenced corrosion process in that they can function under different reduction-oxidation conditions. This transition of aerobic to anaerobic environments within the biofilm supports the growth of iron related, sulfate reducing and acid producing bacteria.
The slime producing bacteria can cause engineering problems related to the reduction of hydraulic or thermal conductivity as well as clogging, taste, odor and color changes.
Types of water sources that may be tested include open-evaporative cooling systems, water-based fire protection sprinkler systems, condensers, and well water.
Test Method
SLYM-BART™ Biological Activity Reaction Test for Slime Producing Bacteria. Manufacturer: Droycon Bioconcepts Inc. Saskatchewan, Canada
Turn Around Time
10–12 days
Test Code
111
Sulfate Reducing Bacteria
Negative (left) Positive (right)
Significance
This test is specific for sulfate reducing bacteria such as Desulfovibrio, Desulfomonas and Desulfotomaculum. These bacteria require metal ions as a source of energy and produce hydrogen sulfide as an end result. They are probably the most destructive group of bacteria causing microbial influenced corrosion. Detection of these bacteria can be problematic. They are strict anaerobes and grow deep within biofilms. In fact, sulfate reducing bacteria may not be present in the free-flowing water over the site of the fouling. Their presence relates to corrosion problems, taste and odor problems (“rotten egg” odors), and blackened waters. Slimes rich in sulfate reducing bacteria tend to also be black in color.
Types of water sources that may be tested include: oxygen-deficient environments such as deep wells, plumbing systems, water softeners and water heaters; condensers.
Test Method
SRB-BART™ Biological Activity Reaction Test for Sulfate Reducing Bacteria. Manufacturer: Droycon Bioconcepts Inc. Saskatchewan, Canada.
Turn Around Time
10–12 days
Test Code
110
Sample Transport
See Sampling and Shipping page for instructions.
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