Sanipro: Cooling towers

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Cooling towers are used in the industries and in the tertiary fields for the cooling of industrial processes or for air conditioning.

Legionella bacteria are naturally present in cold water. They are also present in hot water networks at temperatures between 25 and 45°C in conditions that are favourable to their development (nutrients, biofilms). They can cause a serious illness: Legionnaire's Disease; one which has become a major challenge in terms of public health issues.

The treatments traditionally used against Legionella bacteria are of the chemical biocide variety. There are several disadvantages to these treatments:

The different parameters for optimal efficiency (dosage, pH, resistance phenomena…) are complex
The use of continuous injection, which requires high levels of input, may be required, thus raising operating costs
They generate by products that are rejected into the environment during de-concentration phases
Chemical biocide injection alone does not always enable full control of the level of Legionella bacteria

Shutting down a system for curative or preventive action against Legionella bacteria is expensive.

Biocide injection is no longer the ultimate weapon for destroying Legionella bacteria in water distribution circuits.

BIO-UV offers a concept that provides a true bacteriological barrier every time a risk factor is identified:


	UV TREATMENT OF COLD WATER FROM THE WATER METER INLET UV TREATMENT OF HOT WATER CLOSED CIRCUITS UV TREATMENT COMBINED WITH PREVENTIVE TREATMENT OF BIOFILMS

TREATMENT OF COLD WATER AT THE INLET

The source of contamination of Legionella bacteria is the cold water inlet (bore holes or other local resources…) or by the "crossing" of different cooling towers.

Legionella is a bacteria that is naturally present in water. It is also present in drinking water. Culture analyses (NFT 90-431) highlight some of the germs present, the bacteria that are 'cultivatable'. PCR analyses show all bacteria, notably the non-cultivatable and cultivatable viable bacteria.

Example of analyses carried out on a water network:

Water source	NFT 90-431 analysis	PCR analysis
Drinking water	unidentifiable	13 000 UG/liter

It is clear that the risk of contamination via cold water is very high and more important than the risk of contamination through "crossing".

Erect an initial bacteriological barrier to avoid contamination by new bacteria.

A BIO-UV sterilizer enables continuous treatment of cold water thus avoiding contamination of water networks:
Example of results obtained:

Water source	PCR result before UV	PCR result after UV
Drinking water	13 000 UG/liter	unidentifiable, < 250 UG/litre

This solution is very easy to apply and has a low investment and maintenance cost.

Analyses carried out by Laboratoire Bouisson Bertrand in Montpellier, an accredited independent laboratory.

TREATMENT OF THE WATER CIRCUITS

Water in cooling towers networks is contaminated by Legionella bacteria because:

The water network design is not always ideal in terms of germ prevention,
The water network design is not always ideal in terms of germ prevention,
The biofilm that always forms in the circuit releases Legionella by detachment or abrasion.

Contamination by release from the biofilm must be treated.

Erect a second bacteriological barrier to treat, on a constant basis, the Legionella released by the biofilm.

The sterilizer enables continuous treatment of water in a circuit.
Example of results obtained:

Water source	PCR result before UV	PCR result after UV
Circulating water	1 500 000 UG/liter	400 000 UG/liter
Circulating water	5 100 000 UG/liter	400 000 UG/liter

It is possible to notice a significant reduction that is accumulated at each cycle.
A significant level of efficiency that enables, during circulation through a closed network, continuous destruction of the legionella released by the biofilms.

Different strategy for the installation of the sterilizer are proposed in function of the volume of water circulating, of the flow rate of the cooling tower and in function of the conditions of the pipes and of the existing biofilm:

Treatment of 100 % of the flow circulating,
Treatment of 100 % of the flow circulating,
Treatment in the tank.

The target is to have the whole volume circulating passing through into our sterilizer, at the level of 1 volume every 2 hours up to 3 volumes per hour, in function of our personalized diagnosis.

Our sterilizers in the IBP/AM series have been designed specifically for the treatment of hot water at between 35 and 75°C. Unlike standard UV lamps, which are not as efficient beyond temperatures of 40°C, the BIO-UV sterilizers are equipped with dedicated high performance lamps which guarantee performance up to 75°C.

Analyses carried out by Laboratoire Bouisson Bertrand in Montpellier, an accredited independent laboratory.

TREATMENT OF BIOFILMS

Biofilms are the favourable place for the development of legionella bacteria.
It is necessary to limit as much as possible their development, in order to limit as well the risks of « spreading » or release, and so:

to facilitate the treatment of the bacteria circulating into the sterilizer installed on the cycle or in derivation,
to limit the use of chemical biocide products.
to limit the risk of contaminating per release.

To limit the risk of contamination of the circulating water per release.

To eliminate the existing biofilms, it is necessary to proceed with 2 operations:

elimination of muds and cleaning of the installations and of the networks,
disinfecting.

The complementary water treatments (softening, anti-tartar, anti-corrosion) bring their contribution to avoid the development of the biofilms = that means prevention.

We advise to use a solution based on H202 in shock for the preventive biocide treatment against the development of the biofilm. This H202 solution will be efficient:

for the disinfection,
for the biofilms treatment.

This H202 solution will be also catalyzed by the UV rays, when passing through the sterilizer, making stronger its oxidant power and eliminating the residues of H2O2.

This H202 solution can be injected through a dosing pumps (optional) and used in complements of the UV sterilizer ONLY for the "shock" treatment at the start-up.