Closed System Biocides

The accumulation of microbiological slimes, biofilm and general bio-fouling in closed circuit water systems can be problematic. The build-up of such unwanted foulants can reduce system efficiency, and increase operating and maintenance costs.

Closed System Biocides

Closed heating & cooling systems can become a breeding ground for a range of troublesome microbes if they are untreated.

These include such micro-organisms as pseudomonas, nitrifying and sulphate reducing bacteria. These microbiobiological issues can cause fouling, destroy closed system inhibitors such as Nitrite and cause MIC (microbially induced corrosion).

If you are a water treatment specialist, FM or maintenance company who regularly resells water treatment products to your customers why not apply to become an Accepta Registered Reseller.

A biocide is essential to prevent slime growth in chilled water loops and we would always recommend a closed circuit biocide is incorporated in any system operating below 60°C.

Accepta’s range of tried and tested disinfectants and biocides are designed to be particularly suited to closed system treatment and are in use around the world.

We have rated our biocides for their effectiveness against the three main bacterial issues found in closed systems. Pseudomonas, Sulphite Reducing Bacteria (SRBs) and Nitrite Reducing Bacteria (NRBs)

Closed System Biocides and their effectiveness against common biological issues.

Stability
Effectiveness against
Codes
Description
pH
Temp
Pseud
SRBs
NRBs

1.5% Isothiazolinone, broad spectrum general purpose. Cost effective primary biocide.

pH Stability:

4 - 8

Temperature Stability:

<50oC

Good effectiveness against Pseud

Medium

Moderate effectiveness against SRBs

Low

Good effectiveness against NRBs

Medium

20% DBNPA. Rapid biocidal action & excellent environmental profile.

pH Stability:

6 - 8.5

Temperature Stability:

<50oC

Excellent effectiveness against Pseud

High

Excellent effectiveness against SRBs

High

Excellent effectiveness against NRBs

High

Bronopol liquid biocide

pH Stability:

4 - 8

Temperature Stability:

<60oC

Good effectiveness against Pseud

Medium

Excellent effectiveness against SRBs

High

Good effectiveness against NRBs

Medium

THPS based biocide. Rapid biocidal action & excellent environmental profile.

pH Stability:

3 - 10

Temperature Stability:

<60oC

Excellent effectiveness against Pseud

High

Excellent effectiveness against SRBs

High

Excellent effectiveness against NRBs

High

24% Glutaraldehyde based Biocide.

pH Stability:

7- 10

Temperature Stability:

<50oC

Excellent effectiveness against Pseud

High

Excellent effectiveness against SRBs

High

Excellent effectiveness against NRBs

High

Bronopol & Isothoazolinone blended liquid biocide

pH Stability:

4 - 8

Temperature Stability:

<50oC

Good effectiveness against Pseud

Medium

Excellent effectiveness against SRBs

High

Good effectiveness against NRBs

Medium

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.

Closed System Water Testing

A suite of microbial analysis for closed water systems can be found on the BSRIA water analysis including the following:

  • Aerobic Colony Count 30C (Also expressed as TVC)
  • Nitrite Reducing Bacteria
  • Sulphite Reducing Bacteria
  • Pseudomonas

This micro analysis sits alongside a complete chemistry analysis in compliance with BSRIA Closed Heating and Cooling System BG 50/2015 as highlighted in chapter 6.4: Management of the Water Treatment Program.

If you require advice about choosing your Biocide and suspect your system may have issues with bacterial resistivity please contact us.

Dipslides

Dipslides are an important measure of micro-bacteriological control in closed loop water systems and should be used at least once a month to measure biocidal effectiveness within the system. As soon as significant growth is measured on the dipslides it is time to bring forward the next biocide dose.

Accepta supply a range of dipslide incubators to fit from 2 up to 25 dipslides available to order online, as well as this Accepta supply the standard TTC dipslides recommended for closed systems.

View our range of Dipslide Incubators here.

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