Methods to fight against Legionella – ionization or chlorination?

The problem of the occurrence of the Legionella bacteria affects various centres in Poland like hotels, schools, nursing homes or hospitals. The appearance of Legionella in a hot water installation poses a real threat to people’s health and even life. Then, it is necessary to take concrete actions. Many directors and managers of the centres where such a problem has arisen are looking for an effective solution. What method should be chosen among the several ones available on the market? Ionization or chlorination? Or maybe overheating?  In this article we will try to make a short analysis of the methods based on electrolysis and the use of chlorine.

ionization or chlorination

Ionization or chlorination

It is worth mentioning that on the market there are several methods applied to control Legionella. The quickest way is thermal disinfection. Unfortunately, this method often does not give long-lasting effects and may cause corrosion. Among the other methods, the customers most often look for the answer to what will be better: ionization or chlorination? These are two (or basically 3) methods that we will try to briefly discuss.  

 

Using chlorine while the fight against Legionella

The removal of Legionella bacteria using chlorine is very well-known in Poland. This method often allows to get rid of the unwanted bacteria. Dosing this element into the installation enables to disinfect a water system because chlorine is a strong oxidant. When discussing the use of chlorine in the fight against Legionella, it is necessary to divide the options into two possibilities present on the market: hyperchlorination and the use of chlorine dioxide.

 

Hyperchlorination in the fight against Legionella

In this case, disinfection of the system is based on the use of a chlorine compound, primarily an aqueous solution of sodium hypochlorite or calcium hypochlorite. Chlorine is a good oxidant. However, it should be applied under appropriate conditions, as it can then function effectively. It works well in waters with very low turbidity. Another factor influencing the effectiveness of this method is the pH level. When pH = 8.0 the effect of chlorine is limited and > 8.5 it practically stops. A temperature is also an important element. At 15-20˚C, the proportion of active chlorine decreases by circa 1 g/l per hour. It should be noted that we need to flush the entire system after disinfection. The disadvantage of this method is a high tolerance of Legionella to free chlorine, so its effectiveness is not always satisfactory. The bacteria can reappear after approx. 2 months because chlorine has less effect on the biofilm which is the place of multiplication and life of the bacteria. A side-effect of this method is also the formation of halogen compounds (endangering people) and the increase of corrosivity of the installation.

 

Removal of Legionella with chlorine dioxide

The advantage of chlorine dioxide is that it is more stable than free chlorine especially at higher temperatures. It is able to better penetrate deeper layers of the biofilm and is less corrosive than the hyperchlorination method. ClO2 is better soluble in water (pH 4-10) but its usage may cause the formation of the by-products. These are chlorines and chlorates. In warm water we dose about 3-5 mg/l of chlorine dioxide. In order to increase the effectiveness of the method it is possible to rinse the system. This allows the disinfectant to be distributed throughout the whole installation. Please note that this method should not be used in installations and equipment made of copper. The Polish Association of Manufacturers of Plastic Pipes and Fittings has also issued a statement in which it discourages the use of chlorine dioxide for disinfection of the installation made of PE.  

 

Elimination of Legionella by ionization

In many cases, the elimination of Legionella using chemical disinfection has proved to be insufficient. However, an alternative method was developed which releases the silver and copper ions into water through electrolysis. These ions are toxic to various microorganisms and disturb their proper functioning. Electrolysis effectively destroys the biofilm which is the main habitat of the bacteria. This method works effectively up to pH = 8. The WHO indicates this method to eliminate and reduce the occurrence of Legionella. The use of the silver and copper ions does not cause corrosion of the installation. The process of fighting against Legionella with the usage of the ionization method is successfully carried out in Polish hospitals and other centers.

Ionisation or chlorination

Ionization with the Bifipro system

The Bifipro technology uses the electrolysis process to destroy the biofilm and to eliminate the Legionella bacteria. A continuous monitoring is an important element of this system. It allows you to better control the amount of the bacteria in water and to react in an emergency. Bifipro doses a proper amount of copper and silver to the installation and effectively removes the bacteria contained in it. Thanks to Bifipro, the Institute of Tuberculosis and Lung Diseases in Warsaw – after more than a 10-year fight against Legionella and after using various methods – has got rid of a burdensome problem. See the PDF attachment below for the history of the fight against Legionella.

 


The text is based on the article:
Matuszewska, A. Stankiewicz, Metody dezynfekcji stosowane do usuwania zanieczyszczenia pałeczkami Legionella z instalacji wodociągowych w zakładach opieki zdrowotne. Narodowy Instytut Zdrowia Publicznego – Państwowy Zakład Higieny w Warszawie, Hygeia Public Health 2017, 52(3): 226-233