Biofilms and scales

Microbiological control

Biofilms and scales

Bacteria cannot be considered as stupid creatures. Like all living species they prefer to built their houses/cities in the best living environment in conditions and resources.

So, inside a cooling water system they prefer to build their colonies inside heat exchangers, worm pipes or at the critical process equipment.

When biofilm is developed onto heat exchange surfaces it is a disaster also in scale inhibition.

Biofilm is restricting cooling water to cool the heat exchange surfaces, and is making an isolation barrier. So the temperature of the metal surface increases and in addition to process cooling problems, the scale tendency increases.

Scale formation is supported by the biofilm community, because:

	it creates roughness at the surface, so improves the attachment of the biofilm
	Creates more surface and pores for the more sensitive population to live in
	Creates heat accumulator, which is “uniformizing” the temperature variations

Scale forming ions like Calcium and Magnesium are easily diffused into the biofilm and can reach the metal surface and react to make the scale.

It is not the same for the scale inhibitors we are normally using for antiscale protection.

	Polymers we are normally using are anionic and are deactivated at the extracellular slime which is cationic.
	Phosphonates, polyphosphates and nitrogen containing compounds are nutrients for bacteria. So our “scale preventing” threshold inhibitors “are eaten” from the bacteria, and never reach the heating surfaces.
	If we are using acid for pH control, the acid is deactivated at the cationic extracellular slime, so pH control over the heating surface cannot be achieved.
	Especially, if we use sulfuric or sulfamic acid for pH control, we accelerate the activity of SRB (Sulfate Reducing Bacteria).

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