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Water disinfection

Nowadays, water is used in many different ways – it is indispensable for many processes: from proper functioning of various systems and devices, through industrial and agricultural production, to direct use.

Therefore, in order to effectively optimize the use of limited water resources, it is necessary to apply the most effective methods of water treatment – including, above all, disinfection.

Depending on the purpose for which the water is to be used, as well as its parameters and other factors (e.g. ecological and economic), various methods of disinfection are applied – both in the case of water for household use and that for public and commercial use. This includes process water, water in cooling and air conditioning circuits, water in swimming pools, etc.

Choosing one disinfection method is not always the right idea – sometimes it is advisable to use various techniques and their combinations. Granimex – with its many years’ experience and the extensive knowledge of its team of specialists – is able to offer its customers optimal disinfection methods (taking into account all necessary factors – according to individual needs and expectations of each customer).

Disinfection can be carried out in many ways – the basic division distinguishes between physical and chemical disinfection.

Physical methods include ultraviolet radiation, ultrasound, and thermal methods.

There are more chemical disinfection methods and they are used in a much wider “field” of applications. These include: chlorine, chlorine dioxide, sodium hypochlorite, chloramines; ozone.

The above-mentioned methods are the most commonly used, which does not mean that they are the only ones – disinfection can also be carried out using silver or copper ions, or ultrafiltration.

Chemical methods

Definitely the most commonly used. There are several of them, each has its pros and cons. Let’s pay attention, for example, on the division according to the bactericidal effect of each of them. The strongest in this respect will be ozone, the weakest – chloramines.

Chemical disinfection methods are divided according to their effect time. Chloramines have the longest disinfecting effect, while ozone has the shortest.

This example shows that the choice of disinfection method is not always obvious and that the use of a particular method(s) should always be determined by the individual characteristics of each project.

Brief overview of chemical disinfection methods

  • chlorination

Still the most commonly used method, although chlorine is increasingly losing the competition to chlorine dioxide.

Chlorination is also the oldest method of water disinfection. It consists in adding chlorine (in the form of gas) to water. However, sodium hypochlorite, which takes the form of a solid at room temperature, is increasingly used for this purpose.

Hypochlorite is quite unstable and poor storage conditions (e.g. exposure to sunlight) cause rapid volatilization of chlorine. Keep in mind the rules for storing hypochlorite – among others, it cannot be stored in aluminum or stainless steel tanks.

To carry out effective chlorination, it is necessary to take into account the pH value of water (the higher it is, the more agent we need). Do not overdo the amount of disinfectant – contrary to appearances, this does not contribute to the resistance of the water to the presence of harmful substances.

Regardless of whether you use chlorine gas or hypochlorite – the product of their decomposition will be hypochlorous acid (i.e. the substance that has the right disinfectant effect).

To increase the effectiveness of chlorination, it is necessary to take care of prior removal of various organic and mineral compounds from the water, in turbid water chlorine is less effective. The reduction of organic compounds is also extremely important, because chlorine reacting with them, can form potentially carcinogenic by-products.

  • chlorine dioxide

Increasingly used gas (definitely less “burdensome,” also in terms of the above-mentioned by-products, as it does not react with organic agents), very well soluble in water. It is a strong disinfectant. It has a longer effect than chlorine and its effectiveness does not depend on the pH of water.

Another advantage of using chlorine dioxide is its ability to eliminate the potentially very dangerous biofilm that forms on the walls of various devices that come into contact with water. Biofilm encourages the growth of colonies of Legionella bacteria, which may cause the dangerous disease – Legionnaires’ disease. Another advantage of using chlorine dioxide is that it is odor-neutral.

Disinfection with chlorine dioxide is most commonly used in the food industry.

  • ozone treatment

At the same time, it is the strongest disinfectant, but on the other hand, it is poorly soluble in water and has a very fast decomposition time, thus it is usually necessary to also use additional disinfection methods after ozone treatment. The main advantage of this agent is that it decomposes to the level of oxygen.

Ozone treatment is particularly popular in the food industry. This method is also often used for water treatment in cooling circuits and swimming pools.

Physical methods

  • disinfection with ultraviolet light (UV)

This is a modern method of disinfection, based on ultraviolet radiation. It is completely “non-invasive” – its use does not cause changes in water parameters.

The UV radiation effectively eliminates various types of dangerous microorganisms present in water.

This would certainly be a method that is used more frequently (due to its high efficacy and rapidity) but its drawback is the scope of effect – it disinfects effectively but only directly at the point of use. Therefore, it is necessary to support this method with chemical disinfection.

Ultraviolet radiation is suitable for process water, among others.

  • thermal method

This method needs high temperatures in order to be effective, hence it is not cheap. It is used, among others, in the pharmaceutical industry.