Disinfection of swimming pool water

There are many ways to disinfect water swimming pool.

The main ones, their advantages and disadvantages, as well as the position of our company, are summarized below. Its effectiveness water disinfection depends on water hardness and pH.

That's why the first thing we need to check and adjust is the pH. (And of course, in the event that we are going to use water from an artesian well, it is recommended that a recent sample be given for analysis in order to ensure its suitability and the disinfection of the water).

pH adjustment

The desired pH of pool water is between 7.2 and 7.6, with an ideal level of 7.4. There are two reasons that define 7.4 as ideal:

A) The pH of human blood is 7.4.

B) The vast majority of water disinfectants are inactive when the pH of the water is higher than 7.8 (eg chlorine is only 20% active above pH 7.8).

To adjust the pH of the water to the desired level, we use pH minus (pH^–) to lower the pH and pH plus (pH⁺) respectively to increase it.

With regard to throwing the chemicals into the pool, it is recommended (for the pools of our technology) that they not be thrown undiluted into the pool, because they cause stains on the membrane. The correct method is to throw them into the basket of the machine or, after dissolving them in a bucket full of hot water, to throw them around the perimeter of the pool.

Another important factor is the hardness of the water, which affects the dosage of the chemicals in a pool.

Water hardness 

High hardness of the water combined with a high pH, leads to the creation of salt deposits on the surfaces of the pool. The only way to minimize these deposits is to keep the pH of the water close to the 7.2 range. If we want water free of deposits, the use of a softener is recommended.

Disinfection of swimming pool water

The presence of pathogenic microorganisms in water is favored by certain factors, such as neutral pH, the presence of organic matter which is their food, as well as the existence of nutrients, such as nitrogen and phosphorus, which are essential in their biosynthesis.

Because of their very small size, microorganisms are very difficult to completely remove from water only by physicochemical processes, such as sedimentation and filtration, so to ensure their absence in water, disinfection is required.

DISINFECTION is the treatment of water that aims to destroy or inactivate any pathogenic microorganisms it may contain, in order to protect the health of bathers.

A very important factor is the ability of the disinfectant to maintain a residual concentration in the recirculation system and ensure a final result that protects public health.

The usual disinfectants used to treat water in swimming pools are the following:

• Chlorine
• Bromine
• Electrolysis
• Ozonation
• Ultraviolet (UV) radiation
• Active oxygen
• Ionization

1) CHLORINE

The most common and most effective disinfectant is chlorine. Chlorine has the ability to neutralize all pathogenic organisms, such as bacteria, coliforms, viruses, etc. (active or inactive), which may contain the pool water. We can find it in solid, gaseous or liquid form:

• Solid chlorine.It is used in the form of a tablet (200 gr) and in the form of a granule, which maintains the characteristic of slow dissolution in water. Solid chlorine also includes immediate dissolution chlorine, known as shock chlorine. The latter is used when some time has passed since the last use of the pool, as a precaution after every 15-20 days of use of the pool and definitely at the first start of the pool.
• Gas or Liquid chlorine.There is also chlorine in gaseous or liquid form, but it is not used. Especially the gas which is also dangerous.

Some of the problems with chlorine are:

1. Its combination with amines (organic compounds produced by saliva, urine and sweat) creates chloramines. Chloramines, in addition to the stench they create, are essentially the "death" of chlorine. They are produced even if we have a lot of free chlorine in the water and the only way to break their bond is by superchlorination (shock chlorination).
2. In indoor pools where there is no proper ventilation and dehumidification system, chlorine can cause respiratory distress to swimmers.
3. In direct contact with the membrane it creates discoloration, i.e. (indelible) stains.

It should be mentioned here that if we properly maintain the amount of chlorine in the water and pay attention to its pH, the amount of chlorine in the pool water is perhaps even less than the amount of chlorine contained in the tap water (EFDAP).

2) BROMINE

It is administered in the form of a slow-dissolving tablet. Its advantages are that:

1. As a disinfectant it remains active even when the pH is greater than 7.8.
2. The reaction of bromine with the organic compounds of the water binds a small amount of bromine in contrast to chlorine where a larger amount is bound (bound chlorine). In other words, more free bromine (disinfectant) remains in the water.
3. The amines produced in the water remain active, without binding the chlorine of the water and this increases the disinfecting capacity.
4. The use of bromine as a disinfectant does not exempt us from the use of chlorine. In fact, the chemical combination used for disinfection is 1/3 chlorine and 2/3 bromine. Also, shock chlorination remains as a process.

Its main disadvantage is its price, which is higher than that of chlorine.

Bromine has the effectiveness of chlorine but the greater cost. Due to the limited amount of chlorine it contains, it does not leave the smell of chlorine in the room. Recommended for indoor use, small pools and spas.

3) ELECTROLYSIS

Electrolysis is based on the production of chlorine from salt, which is used as a raw material. The two advantages of using this method are that:

1. The form of chlorine produced leaves no unwanted residue.
2. We achieve lower costs in our consumables.

Installation is easy by placing the electrolysis chamber in the piping system of the recirculation machine and an operating panel, which is placed near the pool panel. First, we add the necessary amount of salt (preferably already dissolved) to the pool water.

Afterwards, the salted water, through recirculation, passes through the electrolysis chamber. This is where the salt (sodium chloride) is broken down and the chlorine produced acts as a disinfectant as it diffuses into the pool water.

Electrolysis cannot be used at temperatures below 15^TheC. In addition, the same observations as for chlorine apply.

The chlorine produced from salt is a friendlier form than industrial chlorine, so it feels better on the skin than chlorine tablets.

Chlorine in the correct dosage does not cause sensitivities or skin irritations. Electrolysis systems have grown by leaps and bounds in recent years mainly due to the reduction in electrode manufacturing costs and simplified overall construction. In addition, swimmers report better water quality, less irritation and generally more enjoyable swimming. In Australia, 90% swimming pools use salt electrolysis systems to disinfect the water. 

It is a way of disinfection that is gaining ground every day. Chlorine produced from salt is a friendlier form than industrial chlorine.

4) OZONISM (O₃)

The ozone it is considered as caustic as chlorine to bacteria and pathogens found in water. The gas is released into the pool water by an injection that is accompanied by a noise. The degassing chamber (a special chamber for isolating ozone from the air) keeps a certain level of water inside it.

The mixture produced is passed through activated carbon and released into the pool water. It has no residual effect and for this reason it needs the presence of chlorine as a complementary disinfectant, simply reducing the required amount of it.

Its advantage lies in the absence of consumables, as special high-voltage lamps are used, producing it from atmospheric air. water disinfection

Its disadvantages are significant: 

1. The equipment we mention above for adding it to the pool water is extremely expensive.
2. It does not ensure residual action and controllability of the network.
3. Always needs power supply and maintained maintenance.

5) UV CHAMBER

The use of UV radiation can help neutralize pathogenic organisms such as bacteria, viruses and protozoa. The ultraviolet radiation is produced in a special chamber, through which the pool water passes, which is disinfected as it is irradiated.

Exposure of microorganisms, bacteria, viruses, etc., to UV radiation causes irreparable damage to their genetic material, which renders them inactive.

It cannot be used alone as a disinfectant, but only as a supplement to another agent (e.g. chlorine or bromine), because it does not leave a disinfectant residue in the pool water (sanitizing residual). Because it reduces the content of chloramines, free chlorine is enhanced and disinfection is more effective. 

Very good recirculation of the water and at an appropriate flow rate in the piping is required to ensure that all of the water passes through the electrode. Also, when there are suspended particles in the water, the efficiency of the system is reduced.

It does not ensure the hygiene of the pool. It can only be used as a supplementary means, to reduce the amount of the main disinfectant, which can be chlorine or bromine.

6) ACTIVE OXYGEN

Active oxygen is the well-known oxygen (hydrogen peroxide, H₂THE₂). It is perhaps the only water disinfection method that completely eliminates chlorine. It is supplied in liquid form, but also in powder form.

Disinfection of water is done with liquid oxygen in a dosage of 250ml/50m³ pool water. The liquid oxygen released into the water ensures that there is always disinfectant in the pool.

Oxygen in powder form is more reactive and is used as an oxygen shock, similar to chlorine shock. Shock oxygen is used at a dosage of 1kg/100m³ when some time has passed since the last use of the pool, preventively after every 30 days of pool use and definitely at the first start of the pool.

Its application can be done by hand, but also by installing a dosing system. Caution is needed because it is very active in direct contact with human skin (whitens it for 2-3 days).

The disadvantages of this disinfection method are the following:

1. It does not work across the entire range of bacteria (leaving the range 10% unaffected).
2. When the pool water temperature rises above 28 degrees Celsius, the active oxygen is completely deactivated.
3. It is not suitable for use in pools that are already burdened with an organic load (e.g. commercial pools), as the ammonia produced reduces its effectiveness.

As a means of disinfection it is acceptable, but its effectiveness is directly affected by the pH value, which must be maintained in a certain range (7.0 – 7.4), by the water temperature and by the load of the pool. I mean in addition to the increased installation costs, very meticulous maintenance is required on which the pool's water quality also depends. 

7) IONIZATION

By ionization we mean the method of water disinfection with silver and copper ions, which neutralize the organic and inorganic pathogenic elements of the water respectively. The electrodes used to produce the ions consist of 97% copper and 3% silver. This method of disinfection, like the previous one, acts in addition to water chlorination. It only achieves the reduction of consumption of other chemicals. 

Copper is photosensitive and can create black or green deposits on the walls of the pool, as long as it is lined with a membrane. Therefore, its use in a pool with a membrane is not recommended.

It is a complementary method, to reduce chlorine in the pool. It should not be used in a pool with a membrane because there is the possibility of creating indelible spots on the film. Greening of the skin and hair of swimmers has been observed in overdose.

Water disinfection