Biocide: A term misunderstood by hygiene professionals according to Microbial corrosion experts

There are seven ways by which microbiologically influenced corrosion (MIC), or microbial corrosion, can be treated:

1.Chemical treatment (application of biocides),

2. Physical treatment (Coating),

3. Electrical treatment (CP),

4. Mechanical treatment (PIGing),

5. Design modification (to prevent conditions that can be leading into MIC, for instance, fluid stagnation, that is, having a linear velocity less than 1.5 m/s),

6. Material upgrade (replacing materials less resistant to MIC with more resistant ones),

7. Training

While 1 to 6 are active treatments (meaning that they are applied only when the damage is already done. This is the approach used by almost all industries globally), training is a proactive approach because by refreshing/updating one's knowledge about MIC, many of failure instances can be prevented or managed much more effectively (Corrosion prevention is NOT the same as corrosion control: corrosion prevent is applicable to Greenfield projects whereas corrosion control is applicable to Brownfield projects. There are other distinguishing features between the two that I have explained in full in:

Rif i, “Corrosion Policy Decision Making: Science, Engineering, Management, and Economy”, Wiley, December 2021.

Chemical treatment which revolves mainly around formulation and application of biocides is a matter that can be interpreted differently if you are an engineer or a microbiologist: for one thing, the ideal status of a system for hygienist microbiologist is sterilizsation whereas for an engineer the ultimate goal will be disinfection. The difference, with simple words, is that sterilization means no microorganisms whereas with disinfection you know you can't get rid of all microbes in the system. This makes sense: you may have a sterlised operation room in a hospital however it is a too farfetched dream to have the same conditions in an oil&gas pipeline or in topside assets of an off-shore platform such as a strainer.

Another issue is that, our microbiologist friends (or at least a majority of them) believe bacteria can get used to biocides so that from time to time changing the biocide you use is advised. Perhaps by proposing such a prescription, what microbiologists have on their mind is superbugs and antibiotics.

Neither bacteria get used to biocide nor is biocide the same as antibiotic. I have explained these two very important matters in three of my books in detail:

1. Reza Javaherdashti, Farzaneh Akvan “Failure Modes, Effects and Causes of Microbiologically Influenced Corrosion: Advanced Perspectives and Analysis”, Elsevier, 2020.
2. Reza Javaherdashti, Kiana Alasvand, Biological Treatment of Microbial Corrosion, Elsevier, 2019.
3. Reza Javaherdashti, Microbiologically influenced corrosion-an engineering insight”, Springer-Verlag, UK, 2nd Edition 2017.

Hygienist aim at "management" of a biofilm (by the way, as I have stated several times, biofilm is a wrong term!). It means that even if the biofilm is present but it does not contain pathogenic bacteria, they believe they have done their job perfectly. Such an approach is a catastrophe for an engineer: we do not want biofilms at all: in a heat exchanger they decrease heat transfer efficiency, in a pipeline they constitute electrochemical cells (e.g. differential aeration cells and thus are leading into pitting) and so on.

Last but not least, for microbiologists as long as planktonic bacteria is null or below a certain level, the job is done. It is the force by the engineer that it is the sessile bacteria count that matters to enable us accept or reject a biocide.

For us engineers, hydrogen peroxide is classified as a biocide. Biocidal effect of hydrogen peroxide may be due to it providing other alternative cathodic reduction in addition to oxygen reduction, thus enhancing the possibility of ennoblement which is of critical importance when the materials of interest are stainless steels.

When you work with professionals with a microbiology background, be alert all the time: their assistance is invaluable however you must be very careful about their recommendations especially if they are coming from a background that only taking care about hygiene matters!