Disinfection & Biocide Control in Closed Water Systems
It is much easier and more cost effective to maintain microbiological control within a closed heating and cooling system than to clean up a badly fouled system containing heavy build-up of biofilm. – BSRIA BG29/ 2012
Biocides are highly recommended for closed circuit heating & chiller systems operating below 60C or if there are areas within the system which do not consistently reach this temperature, seasonal systems which normally exceeds this temperature would also benefit from the introduction of a biocide just prior to shut down so control is maintained throughout months operational dormancy.
How often should I dose a closed system biocide? In a system with effective treatment you should expect to dose a biocide every 3 months and should measure biocidal effectiveness via dipslide once a month. If your dipslide shows increased growth and a loss of bacterial control then it is time to bring your next chemical dose forward to bring the system back under control.
Key point to maintain a clean system:
- Keep the system free of debris & settled solids
- Use a biocide in the pre-commissioning stage & system flushing
- Use an effective biocide to maintain control through the life of the system
- Monitor microbiological levels on an on-going basis
- Use a shock dose tactic should bacteria levels & biofilm reach unacceptable levels
Where control with a biocide has been difficult to attain it may be appropriate to perform laboratory evaluation on the water as a different biocide may be recommended.
Which biocide should I use in my Closed System? In most cases, Accepta recommend the use of a Non-Oxidising Biocide such as Isothiazolinone, a broad-spectrum biocide which is also especially effective against Pseudomonas – see BC-ITA above. Other effective biocides include Bronopol & DBNPA, these biocides may be recommended where a break from the use of Isothiazolinone is needed due to increase in bacterial resistance or if they are already used as the primary biocide and work well for that system.
Control of bacteria in a closed system is not just recommended to remove biofilm, many bacteria are happy to feast on your inhibitors and will actively breakdown corrosion inhibitors used in your heating systems degrading protection and wasting money. Biocidal control should be an ongoing regime as a shock dose of biocide will never normally be enough to kill all bacteria and prevent regrowth as they cannot be 100% effective. Continual monitoring is recommended as bacteria may become resistant to a certain biocide overtime and a there may be a requirement to cycle biocides to prevent this.
