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05 Nov 2013
Posted By: Martin Moss
Comments: 0

Non oxidising biocides are used alongside oxidising biocides to ensure a low population of microbes such as legionella. Two non-oxidising biocides can also be used in an alternating programme as in certain circumstances a reduced efficiency can develop . Using them, one should monitor the microbiological activity in the cooling water on a regular basis by dip slide analysis and specific Legionella analysis on a quarterly basis.

What Are They?

Non oxidising biocides are chemicals that attack certain organs of the micro-organism. This may be the cell wall or reproductive system. Non oxidising biocides include Ammonium salts, Glutaraldehyde, DBNPH and Isothiazolinones.

All are very toxic so should be used usually in low doses to prevent damage to the environment when the cooling system is bled. They all have differing half lives and persistence so it is essential that the system volume and bleed rate of a cooling system are known so that a killing dose level is held in the system for the requisite time.


Relatively small doses are usually used. Between 50 and 300 ppm depending on the type of biocide and the cleanliness of the system water. It is usual to add them to the water using a suitable pump and timer system.

Addition to the cooling system should be based on the known half life. Essentially you should top up as soon as the dose concentration falls to below the killing concentration. Your Water Treatment contractor would be able to help with this.


In order to maintain an effective toxicity the cooling water should be monitored regularly for chemical and microbiological composition. This will ensure that microbial levels are kept at safe levels at all times.

Find out More

To find out more about this subject please call our specialist team on 01925 713273, or email us info@advanced-water.co.uk

Categories: General


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