Microbially induced corrosion

Microbial-induced corrosion (MIC) is a common phenomenon caused by the metabolic processes of biofilm-forming microorganisms. It can damage materials such as metal, concrete, rubber, plastic, and other materials. MIC is a major problem in water distribution systems because it can reduce the service life and quality of pipe materials. This can lead to pipe leaks and, in some cases, even to blockages or contamination of the water distribution pipes.

What is MIC corrosion?

Microbiologically induced corrosion (MIC) is a form of material degradation caused or accelerated by microorganisms that can influence the corrosion process. As a result, metals such as steel (stainless steel), copper, and aluminum can often be corroded very rapidly in humid environments.

How does MIC occur?

MIC occurs when microorganisms attach themselves to surfaces and form a biofilm there: a slimy layer in which bacteria can hide and multiply. Among other things, acids and gases are produced within this biofilm that chemically attack the metal and accelerate the electrochemical corrosion process:

• Hydrogen sulfide: a highly reactive gas that can accelerate the MIC process. It can be recognized by a rotten-egg smell coming from pipes.
• Sulfuric acid: this highly corrosive substance can cause accelerated MIC corrosion and a drop in pH.
• Acetic and lactic acids: Acids produced by the bacteria in the biofilm. They constantly erode specific areas in the pipes and fittings, which can accelerate MIC.
• Ammonia (NH₃): particularly harmful to copper or copper-containing alloys in the piping system.

Indicators and consequences of MIC

There are several factors that can help you identify MIC:

• An unpleasant smell of rotten eggs coming from your pipes.

• Localized pitting (pitting corrosion).

• One of the following biofilms

• • Black/dark gray biofilm: Often indicates sulfate-reducing bacteria (SRB) that produce iron sulfide (1).

• • Red/brown/orange biofilm: Indicates iron-oxidizing bacteria (IOB) that form bulky rust nodules (2).

• Rapid material loss, leaks, or pipe blockages.
• Presence of the following bacteria in water samples
  • Sulfate-reducing (SRB) bacteria: such as Desulfovibrio, Desulfotomaculum, and Desulfobacter (3).
  • Acid-producing bacteria (APB): such as Clostridium.
  • Sulfur-oxidizing bacteria: such as Acidithiobacillus (or Thiobacillus), Thiothrix and Beggiatoa (4).
  • Iron bacteria: such as Gallionella ferruginea and Leptothrix (5).
    
    

MIC can result in high costs and may even necessitate the replacement of part of the system; it is therefore important to prevent this before it occurs.

Furthermore, the problem is often addressed only at the site of the leak, but biofilm spreads throughout the entire system. It is therefore better to choose a solution that addresses the root cause of the problem rather than merely resolving the symptoms.

Where is MIC most commonly found?

Common industries where MIC can be a problem include:

• Cooling water & cooling towers
• Food and beverage industry
• Wastewater treatment and process water recycling
• Oil, gas, and chemical industries

In all of these environments, MIC bacteria can form biofilm, resulting in accelerated corrosion, clogging, and an increased risk of leaks and process contamination.

How can HOCl help combat MIC?

HOCl as a disinfectant offers an effective solution for MIC. HOCl (or hypochlorous acid) is a powerful disinfectant that can combat a broad spectrum of microorganisms and their byproducts. It can be used to disinfect process water systems where MIC is a problem. In low concentrations, HOCl is particularly effective at combating biofilm and a wide range of bacteria, fungi, algae, and other microorganisms that can cause Microbial-Induced Corrosion.

HOCl has many advantages over other disinfectants:

• The disinfectant produced by the Watter system is not a CMR substance, and no personal protective equipment is required to use it.
• It is a cost-effective and easy-to-use solution for addressing MIC. It is dosed in low concentrations, so less product is needed to achieve the same effect.
• It is effective against a broad spectrum of microorganisms and against biofilm.

On-site production of HOCl using the Watter system

For companies that want to prevent MIC without having to purchase and store large quantities of hazardous chemicals, the Watter system offers a proven, effective solution with the following benefits:

1. Always having an effective, ready-to-use disinfectant on hand when needed.
2. By producing the disinfectant on-site, companies become independent of suppliers and thereby save on transportation costs;
3. It is a method with low operating costs (water, salt, and electricity), allowing companies to save money on the purchase and storage of flammable and hazardous chemicals;
4. The Watter system is an automated, self-correcting solution. This ensures that the quality of the disinfectant remains consistent.
5. Low operating costs: The Watter system runs on water, salt, and electricity, keeping the costs of using the system low.

Preventing MIC

By switching from traditional chemical disinfectants to in situ-produced HOCl using the Watter system, companies can:

• Effectively combat biofilm and MIC-related microorganisms with low dosages.
• Extend the service life of piping systems, tanks, and equipment by reducing the risk of pitting and corrosion damage.
• Reduce the costs and complexity associated with the procurement, storage, and handling of hazardous chemicals.

References

1. Enning, D., & Garrelfs, J. (2013). Corrosion of Iron by Sulfate-Reducing Bacteria: New Views of an Old Problem. Applied and Environmental Microbiology, 80(4), 1226–1236. https://doi.org/10.1128/aem.02848-13
2. Judit Knisz, Eckert, R. B., Gieg, L. M., Koerdt, A., Lee, J. S., Silva, E. R., Torben Lund Skovhus, Stepec, A., & Wade, S. A. (2023). Microbiologically Influenced Corrosion - More than just Microorganisms. Fems Microbiology Reviews, 47(5). https://doi.org/10.1093/femsre/fuad041
3. Qi, Bei Meng, et al. “The Disinfection Efficacy of Chlorine on Sulfate-Reducing Bacteria and Iron Bacteria in Water Supply Systems.” Applied Mechanics and Materials, vol. 316-317, Apr. 2013, pp. 657–660, https://doi.org/10.4028/www.scientific.net/amm.316-317.657. Accessed 13 Jan. 2020.
4. Shi, Xun, et al. “Comprehensive Review on the Use of Biocides in Microbiologically Influenced Corrosion.” Microorganisms, vol. 11, no. 9, 30 Aug. 2023, pp. 2194–2194, https://doi.org/10.3390/microorganisms11092194.
5. Zinati, Gladis, and Xuifu Shuai. “FS516: Management of Iron in Irrigation Water (Rutgers NJAES).” Njaes.rutgers.edu, Dec. 2005, njaes.rutgers.edu/fs516/.