Controlling Bacteria in Closed Systems

With the increasing complexity of building services in today’s complex work space environments, the need to manage and control bacteria in closed systems is becoming ever more important. Bio-fouling from bacteria including pseudomonas, sulphate reducing bacteria, nitrite reducing bacteria, other slime formers and biofilm can lead to major performance, reliability and life-cycle issues for closed heating and chilled water systems.

Here we consider how bacterial contamination can be introduced in to such heating and chilled water systems and what we can do to control it.

Closed system water sources

Care needs to be taken when filling any new or existing closed system with water as this can be a primary route for bacterial contamination entering the system.

The water source used to fill the closed system, which may be from an incoming mains water supply or water served from a central source must be tested to identify any bacterial contamination present, and treated using a suitable biocide to kill the bacteria before the water is added to the system.

Ideally, the water should be tested for the presence of common bacterial contaminants including pseudomonas, sulphate reducing bacteria, nitrite reducing bacteria, nitrite oxidising bacteria and TVC (22°C) and TVC (37°C) before it is introduced in to the system.

This testing will help to determine the most suitable water treatment programme to be used.

Once the water tests are complete a suitable closed system water treatment programme should be developed to control any contaminating bacteria identified in the mains water or stored supply to be used.

Filling closed systems with water

Ideally, the water that is to be used to fill the closed system should be stored in water tank of suitable capacity. The water can then be accurately treated with a suitable biocide before it is used. If it is not possible to use a water tank then the biocide selected can be added directly in to the water stream before it enters the closed system.

Additionally, a suitable corrosion inhibitor should also be added at a carefully controlled rate in to the water supply used. This will help to protect the system from unwanted corrosion until pre-commission cleaning is undertaken.

Bacteria in closed systems, flushing and pre-commission cleaning

Any closed system flushing, pre-commission cleaning etc. should be carried out in accordance with the following standards and codes of practice.

BSRIA Guide BG 50/2013
BSRIA Guide BG 50/2013 – Water Treatment for Closed Heating and Cooling Systems.
British Standards
British Standards BG 29/2012 – Pre-Commission Cleaning of Pipework Systems.
CIBSE AM14
CIBSE AM14 – Non-Domestic Hot Water Heating Systems.
BS 8552:2012
BS 8552:2012 – Sampling and monitoring of water from building services closed systems. Code of practice.

Flushing and chemical cleaning of closed systems

System flushing is an important process, essential to the success of any effective chemical cleaning programme.

If a new or existing closed system is contaminated with engineering debris, corrosion by-products, bacteria or even biofilm, and flushing is not completed prior to the chemical cleaning procedure the clean may fail to be effective.

Once the closed system has been flushed, chemical cleaning should be carried out immediately, certainly within 24 hours.

A typical closed system chemical cleaning programme might include the following activities:

Static flushing
Dynamic flushing
Degreasing
Biocide treatment (where closed systems are at risk from bacterial contamination)
Removal of surface oxides (typically for systems with mild steel components)
Effluent disposal / final system flushing
Neutralisation (for inhibited acid cleans only)
Passivation
Corrosion inhibitor and biocide dosing

Essential record keeping

Maintaining detailed records at all stages of the testing, flushing, cleaning and filling process is essential to ensure a successful outcome. Test results, flushing velocity records etc. are all vital and should be carefully recorded.

Monitoring and testing of quality parameters across the complete closed system are also important to obtain a complete understanding of system conditions throughout the system, not just in the plant room.

World-class water treatment engineering solutions

Water Treatment Services are a leading independent UK water management company offering expert water management solutions including the management of closed heating and chilled water systems, water disinfection, cleaning and chlorination, pre-commission cleaning and engineering support services..

With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers, site service specialists and technical experts we can offer water management treatment services including across the whole of the UK.

Contact us today to learn how our water management solutions can ensure your building services installations are maintained to achieve optimum performance.