COOLING TOWER WATER

Monitoring of Legionella risk in cooling towers – Quantification of intracellular ATP, a fast biological indicator for surveillance and securisation of water installations

Legionella – the microbial risk common to all cooling towers

Cooling towers are efficient heat removal devices.  The inconvenient of these installations is the emission of aerosols, potentially contaminated with Legionella. A strict regulation exists in many European countries concerning contamination of cooling tower water by Legionella bacteria.
Legionella, an aquatic bacteria present in all water installations, is the responsible agent of Legionella disease, a severe pneumonia with 10% mortality rate. The disease is contracted through the inhalation of aerosols containing Legionella bacteria. Legionella in circulating water of cooling towers come from a massive proliferation in the biofilm formed on the surface of water circuits. Surveillance of biofilm is essential in cooling towers. 99% of microorganisms are present in the biofilm and only 1% are planktonic (present in circulating water). Installations under microbiological drift can be characterized by the presence of a biofilm releasing flocs of microorganisms in the water circuit, often containing Legionella bacteria.
Controlling Legionella proliferation in cooling towers requires control of biofilm  forming and control of proliferation of microbial flora including amoeba – natural hosts of Legionella bacteria.

Surveillance of cooling tower installations using QGA™ and QG21I™ kits

Control of Legionella risk in cooling towers requires implementation of a surveillance plan based on different physical, chemical and microbial indicators.
2^nd generation of ATP-metry allows measurement in only minutes of the total living flora in water samples. Zones presenting high contamination with total living flora are the zones where releasing biofilm is present, containing often amoeba – factors of risk for the proliferation of Legionella. Control of these factors leads to control of the proliferation of Legionella and securing the installation.
Quench-Gone™ Aqueous (QGA) and QG21I  kits allow the quantification of microorganisms through the measurement of only intracellular ATP in samples from cooling towers and industrial process water. Intracellular ATP is an indicator of living biomass. All living cells contain ATP- aerobic or anaerobic bacteria, protozoa, amoeba, and algae.  
The principal interest of this technology for operators is the reactivity for anticipating microbiological drifts even before Legionella isolation from water samples by classical culture –based techniques. Efficiency of chemical or non chemical water treatments can be immediately verified on all microorganisms, viable and cultivable but also on viable non cultivable microorganisms. 

Surveillance plans based on QGA and QG21I kits include microbial mapping of the water installation and the selection of critical points (critical zones include presence of biofilm, stagnant water, corrosion) to be controlled on regular basis as preventive actions.

QGA and QG21I – fast biological tools for surveillance of cooling tower installations

The 2^nd generation of ATP-metry, called Quench-Gone, allows performing a diagnosis of the active biomass present in the cooling tower installation. A biological mapping is first performed, allowing implementing a Methodical Analysis of Biological Risks using cATP (Intracellular ATP) indicator.
The aim of the use of QGA in cooling towers is to:

1. Localize critical zones, presenting high level of microbial concentration and uncontrolled biofilm
2. Determine parts of the installation requiring chemical cleaning for decreasing biofilm
3. Optimize cleaning and disinfection actions and validate the impact on the biofilm
4. Validate efficiency of treatment strategies
5. Prevent associated sanitary risks
6. Limit environmental impact

Results are immediately available (3 minutes per sample) and new decisions for treatment- disinfection can be undertaken during the same day for securing the installation.
After validation of all the corrective actions, critical points are controlled on regular basis using QGA kit for early detection of new degradation or drift in microbial quality of water.