From sources to end-users, the potable water industry can experience microbiologically-related problems. Most of these problems are related to disease-causing microbes, which most water companies do a good job of controlling with disinfectants. However, those microbes which cause biofouling (slimes), deposition, and microbiologically influenced corrosion (MIC) are poorly controlled in many aspects of the industry. These problems often compromise the function and integrity of system components by reducing water production rates and/or producing bad waters, interfering with fluid flow, causing component failures due to blockage or leaks, and contaminating other systems with corrosive or odiferous materials.
Why Potable Water Facilities Experience Microbiologically-Related Problems MIC occurs throughout water distribution systems, especially in areas where residual disinfectant levels drop—even temporarily—below levels required to control microbes. In addition, MIC-related microbes—including aerobes, slime formers, iron-related bacteria, anaerobes, organic acid-producing bacteria, and sulfate-reducing bacteria (which produce corrosive sulfides and consume hydrogen)—are, in general, more resistant to disinfectants, such as chlorine, than many pathogens (e.g., coliforms) which are used as indicators of disinfection efficacy. Therefore, water deemed as properly disinfected may be adequate to control pathogens but often will not control MIC-related microbes.
Also, microbes in biofilms and deposits are much more resistant to disinfection than microbes in the bulk water. Therefore, water distribution systems with “adequate disinfection” can suffer from biofouling, deposition, and MIC and serve as sources of MIC-related microbes to potable water, fire protection systems, and other water-using processes in homes, commercial facilities, schools, and the like.
Microbiologically-Related Problems Experienced in Potable Water Systems Potable water systems may experience a variety of microbially-related problems. Many times, these problems occur simultaneously in an affected system and may not affect all systems uniformly, due to differences in environmental, operational, chemical, and biological factors. These microbial problems include:
1. Biofouling and plugging of geological formations from which the water is produced and water well components (especially stainless steel screens) due to biofilms. This can lead to greatly reduced water production rates and production of “bad” waters (waters with taste, odor, and staining problems).
Biofilms (also called slimes), which are formed by microbial communities—in most cases composed of many different types of microbes (e.g., aerobic, slime-forming, anaerobic, acid-producing, iron- and manganese-depositing bacteria, molds and sulfate-reducing bacteria)—attach to surfaces in contact with non-treated or inadequately treated waters. Biofilms are an early indicator of microbial activity.
2. Reduced flow rates due to deposition.
Over time, biofilms grow in thickness and areal extent due to microbes depositing iron and manganese and accumulating corrosive materials such as chlorides. Biofilms mature by collecting more types of microbes (and, therefore, more biochemical reactions) and non-biological materials (e.g., sand, debris, organic and inorganic materials) and form deposits. Discrete deposits are a clear indication of microbial activity.
3. Loss of integrity in system components due to under-deposit pitting-type corrosion.
Once deposits are established, and given the right environmental conditions, microbial metabolic by-products—such as organic and inorganic acids, hydrogen, carbon dioxide, sulfides, and ammonia—accumulate within the deposits due to the activities of microbes and other chemical reactions. These metabolic by-products corrode the underlying metal and often lead to rapid under-deposit pitting-type corrosion beneath the deposits. This type of corrosion is a telltale sign of MIC. Microbes can both initiate corrosion and accelerate existing corrosion.
4. Component failures due to under-deposit leaks.
Once corrosion and MIC advance to the stage of under-deposit pitting corrosion, the metabolic by-products in deposits corrode the underlying metal until leaks develop under the deposits. Pinhole leaks are another telltale sign of MIC.
5. Contamination of waters and other systems using potable waters with corrosive and odiferous materials due to microbial metabolic by-products.
The accumulation of metabolic by-products (listed in #3) can lead to water with serious taste, odor, and color problems (due to rust and sulfides) and water which has corrosive properties. If this water is then used in other systems, those systems can become contaminated and will likely be affected by similar problems.
6. Damage to coatings and destruction of underlying metal due to microbial activities.
Microbes enter holidays in protective coatings in pipes and storage facilities. Once established, microbial production and accumulation of corrosive materials under the coating (and next to the metal surface) causes further disbonding of the coating, allowing damage to the coating and underlying metal to spread and proceed at very rapid rates. The disbondment acts to trap and concentrate microbes and corrosive materials next to the metal surface, causing even faster corrosion to occur. Since this occursunderthe coating, the site is not protected by cathodic protection and cannot be treated using corrosion inhibitors and biocides. These problems can occur on the inside or outside of equipment.
Materials Affected Most metals and alloys, except titanium, are rapidly attacked by MIC under some conditions in potable water facilities. Thousands of cases of MIC in facilities across North America using potable water have been reported and investigated—many by BTI Products and its sister company, BTI. These cases have involved steel, galvanized steel, stainless steels, aluminum, copper, and their alloys.
Many cases of MIC in potable water and fire protection systems in homes, office buildings, and commercial facilities have resulted in pinhole leaks within months of construction. Most of the severe pitting in stainless steels is seen in welds and heat-affected zones, although we have seen a few cases where whole pieces of stainless steel were affected.
Although still susceptible to MIC, fewer cases of MIC have been seen in cast iron and ductile iron.
Systems Affected The following potable water facility systems are all potentially susceptible to biofouling, deposition, and MIC:
Heat exchange devices
Storage tanks (including water and fuel tanks)
Nuclear waste storage facilities
Ultrapure water-utilizing devices
Fire protection systems
Whether this “MIC potential” progresses to rapid and severe MIC-type corrosion depends on local conditions—even in the same “system”—over time.
Diagnostic Products for Potable Water Industry Systems BTI Products offers test kits designed specifically for diagnosis of microbial problems in potable water industry systems. Our test kits provide microbiological, chemical, and site-specific information important in diagnosis of microbial and other problems and in the design of treatment and prevention strategies. BTI Products and its many water industry clients use BTI Products test kits to investigate MIC and design effective treatment programs.
BTI Products kits can be used foralltypes of samples—including those containing water, particulates, corrosion products, hydrocarbons, and/or other materials. BTI Products test kits are designed to test for MIC-related microbes in samples from freezing to boiling temperatures and from a wide variety of salinities (from fresh water to sea water or production brines). They can be used to test for MIC-related microbes in almost all real-world samples and, most importantly, can be used by untrained industry personnel, on-site, to obtain accurate and pertinent data quickly and inexpensively.1
Recommended Diagnostic Test Kits
MICkit® 4to test locations using cathodic protection or coatings for chemistries important in corrosion diagnosis and treatment
MICkit® 5to test potable water facilities for microbes involved in biofouling, deposition, and MIC
MICkit® Comprehensiveto test potable water facilities for microbes and chemical parameters involved in biofouling, deposition, MIC, and other forms of corrosion
MICkit® Pipe Inspection Kitto physically inspect pipes in systems that have tested positive for MIC-related bacteria and/or systems with a history of leaks/failures
MICkit® FPSto specifically test fire protection systems for microbes and chemical parameters involved in MIC
MIPkit™ FPSto specifically test fire protection systems for the most common microbes and chemical parameters involved in MIC
Diagnostic & Mitigation Services for Potable Water Industry Systems BTI Products can also assist in evaluation of samples, test data, field-site investigations, and design and implementation of mitigation measures. BTI Products performs and supports research and testing programs related to causes, prevention, and treatment of microbial problems for individual clients.