A biocide is chemical treatment formulated to effectively stop the growth of microbial. It is crucial to ensure the correct biocidal treatment regimen is in place and regularly checked to avoid the dangers related to microbial growth like health risks as well as heat transfer losses under deposit corrosion.

In our previous blogpost, we covered the most important aspects to consider when selecting a biocide. This blog post focuses on choosing the most efficient closed-circuit biocides.

There are many elements that can adversely impact the microbial concentrations in closed-circuit systems, and they must be considered

1. Cleaning prior to commissioning

When a new system is installed it is crucial to make sure that the system is clean and that the pre-commission cleaning procedure (as described in BSRIA BGR29/2020) includes an appropriate biocide to use in a biocidal flushing process when it is necessary.

2. Concentration

It is essential to ensure that a suitable closed-circuit biocide and closed-circuit inhibitor is present in the system in the correct concentration from first pressure test and filling, as well as on an ongoing basis.

3. Formulation based on Nitrite

An economical neutral nitrite-based formula that quickly passesivates and is suitable for multi-metal systems containing aluminum, such as Polyhib LC could be an appropriate choice. However, alternatives are also available, so contact our technical department to get assistance on the best product for this purpose. The right biocide should be used if Polyhib-LC is used to hold the system once it has been filled.

4. Testing of closed system chemistry, and monitoring of microbiological activity

Closed system chemistry testing is a crucial element of any maintenance program. Monitoring of microbiological activity in the system also plays an important role. In response to high levels of bacteria, shock dosage with an appropriate Biocide chemicals, should be done in order to manage them.

5. Testing for biocide sensitivity

Over time, it is possible that resistance will develop to a specific biocide and a change in the biocide dosage regimen could be required. It could be necessary for some systems to undergo a biocide-sensitivity test in order to find the most effective biocide. Our on-site laboratory is able to accept samples for analysis of the biocide's sensitivity. We will then conduct the analysis on behalf of customers. Contact us for more information and prices for this test service.

6. Biodispersants

Where high levels of bacteria and a build-up of biofilm is observed, the administration of an effective biocide in conjunction with a biodispersant compatible like BV167 or BV1455 may be needed. When biofilm is removed off metal surfaces, it is crucial to determine the source of this biofilm. If the system is equipped with strainers or filters that are scattered throughout the system they will have to be inspected and cleaned frequently after dosing to remove biofilm that has been dislodged. Blockages can be experienced if the system is equipped with tiny bore pipework that's not lined with filters or strainers. Biodispersants are therefore not suitable for all systems.

7. Temperature

A biocide is typically not needed if the temperature of the fully circulated LPHW (Low Pressure hot water) systems remains constant at or above 60°C. If such a system is in seasonal use it is recommended that a biocide is added and circulated throughout the system before the system is shut off. BSRIA BG 50 recommends a minimum circulation time for cooling and heating circuits of an hour each day, even for seasonally employed systems.

8. Glycol

To stop the growth of bacteria in the chiller system which contains glycol, it is necessary to ensure that the glycol concentration is at least 25 percent. The glycol concentration is biostatic i.e. it inhibits the development and growth of bacteria. Glycol can be used as an ingredient in the diet of bacteria at this threshold.

Important to note that biocidal products should be handled with care and all employees are required to wear appropriate Personal Protective Equipment (PPE). Before using any biocide, it is crucial to review the Safety Data Sheet (SDS).