Microbial induced corrosion, also known as biocorrosion, is when colonies of microorganisms form a layer of film over metal surfaces. This layer acts as an incubator for bacteria and fungi that inevitably cause the metal to decay. Without eliminating the microbial film that prevents corrosive chemicals from escaping, the corrosion can permeate metal and create holes within them. One common example of this comes steel plates collected from the hull of the Titanic.
To understand how bacteria can deteriorate metal so efficiently, you have to begin with what promotes the deterioration: biofilms. Biofilms are collections of microorganisms banded together inside a typically aqueous solution. The plaque that collects on our teeth is one case of biofilms forming in our bodies, where they form cavities.
Biofilms are only a mild problem when they’re corroding the teeth in our mouth, but they can easily be fatal. A primary reason hospitals maintain sanitary environment is to reduce the likelihood of biofilms forming on equipment or in patients’ wounds. Once biofilms are introduced into a person’s body, they’re difficult to remove. They kill thousands of people in the U.S. every year and cost the healthcare industry billions of dollars in replacing contaminated implants and medical equipment.
Individual bacteria roaming a surface or wound are easy to get rid of — just keep the surrounding area clean and use antibiotics until the infected area has healed. Biofilms are considerably more difficult to remove because bacteria use chemicals to work together as a single superorganism. Some focus on growing the biofilm; others create more slime for the bacteria to reside in. They can even take in nutrients as a single unit, expel waste, and grow dormant when antibiotics attempt to take them out.
When these biofilms attach to metal the chemicals they create cause a series of electrochemical changes happening that lead to corrosion. Biofilms form a microscopic ecosystem underneath the surface they cling to. Similar to how the ozone can prevent certain gases from escaping Earth, the biofilm stops oxygen from passing into the metal. This, combined with some natural corrosive chemicals that microorganisms create within the biofilm, such as sulfuric or citric acid, causes the metal to break down.
Combating biofilms requires biocides. Biocides are substances capable of destroying stubborn biofilms even when antibiotics can’t. Tetrakis hydroxymethyl phosphonium sulfate, otherwise called THPS, is one of the most popular biocides used in the oil and gas industry. Unfortunately, bacteria are capable of adapting even to biocides. Some studies suggest ways of improving commonly-used biocides by mixing them with certain amino acids.
It’s unknown if biofilms will ever cease being a problem for health, gas and oil industries. What’s certain is that they’re one of the many underlying reasons why proper sanitation procedures are important to maintaining society. From the bathroom to hospitals to industrial pipes, staying clean is essential to preventing individual microorganisms from banding together into a corrosive tool greater than the sum of its parts.