Pseudomonas bacteria has the ability to cause corrosion to any open or closed water system. Once the bacteria is established it forms a jelly like film which clogs valves and reduces heat transfer. The anaerobic conditions created between this film and pipe work provide a breeding environment for other bacteria including SRB’s and NRB’s. It also creates a barrier to debris preventing a successful chemical clean if not treated properly.
As it is a living organism it will reappear if not completely destroyed. The results of pseudomonas within the system are often shown by changing commissioning results, greasy films on strainers and often as muddy reddy brown colouring to the water. In simple terms these have been linked to corrosion.
Sulphate Reducing Bacteria (SRB’s)
This is one of the most destructive groups of biological foulants because they cause corrosion resulting in severe localised pitting of pipework surfaces. They have been implicated in severe corrosion problems for copper, iron, steel and aluminium pipe work. As a result of their metabolism, they produce hydrogen sulphide which attacks iron and steel and forms the end of produce ferrous sulphide. Steel thus becomes pitted, and cast iron becomes ‘graphitised’.
Nitrite Reducing Bacteria (NRB’s)
This bacteria gasses to produce ammonia. This poses a risk of stress corrosion cracking to brass/copper components such as valves and fittings. As with SRBs above these are anaerobic bacteria which tend to produce acid (corrosive) by-products. These as with SRBs dwell beneath deposits or in systems with limited oxygen. In the event that NRB’s are detected in the absence of a
N.B. Low/Medium NRB levels detected in isolation of any other Heterotrophic plate count is unlikely to be of concern and system(s) will be deemed under microbiological control.