Swimming pool Disinfection methods

There are many ways of disinfecting the swimming pool water. The main methods are summarized and presented below, including their advantages and disadvantages as well as our company's stance on them. The efficiency of the water disinfection depends on the water hardness and the pH. In fact, pH is the first factor that we should control and adjust (in case we want to use artesian well water, it is highly recommended that a recent sample of this water to be subject to analysis in order to ensure its suitability).

 

pH adjustment

The desired pH of the swimming pool water is between the limits of 7.2 and 7.6, with the ideal level being 7.4. There are two reasons according to which 7.4 has been specified as the ideal level:

A) The pH of human blood is 7.4.

B) The vast majority of the water disinfectants is inactive when the water pH is higher than 7.8 (e.g., chlorine is only 20% active when water pH is higher than 7.8).

We use pH minus (pH-) in order to lower the pH while we use pH plus (pH+) in order to increase it.

Chemicals are recommended to be thrown in the swimming pools in soluble form, since insoluble chemicals are likely to cause membrane stains.

Water hardness constitutes another major factor which affects the swimming pool chemicals dosage.

 

Water hardness

Water with high hardness combined with high pH results in salts deposits on the swimming pool surfaces. The only way to minimize these deposits is to maintain the pH of the water at the level of 7.2. In case we want the water to be deposit-free, the use of water softeners is highly recommended.

 

Water disinfection

The presence of pathogenic microorganisms in the water is favored by a number of factors, such as neutral pH, the presence of organic matter which constitutes their food, and the presence of nutrients such as nitrogen and phosphorus, which are necessary for their biosynthesis. Due to their very small size, the microorganisms are very difficult to be completely removed from the water only by employing physicochemical processes, such as precipitation and filtration. Therefore, in order to ensure their removal, water disinfection is required. 

Disinfection is the water processing which aims to destroy or inactivate the pathogenic microorganisms which it may contain, in order for the swimmers health to be protected.  

The most crucial factor is the ability of the disinfectants to maintain a residual concentration in the recirculation system and ensure a final result, which will protect public health.

 The most usual means of disinfection used for the water processes in the swimming pools are the following:

• Chlorine

• Bromine

• Electrolysis

• Ozonation

• Ultraviolet (UV) radiation

• Active oxygen

• Ionization 

 

1. CHLORINE


Chlorine is the most widespread and effective disinfectant. It has the ability to neutralize all pathogenic microorganisms such as bacteria, coli form bacteria, viruses, etc. (active or not), which pool water may contain. It can be found in solid, gaseous or liquid form:
  

  • Solid chlorine: It is used in tablet form (200 gr) and in granules which retain the characteristic of the slow dissolution in the water. Shock-chlorination, the chlorine of rapid dissolution, also belongs to the category of “solid chlorine”.  Shock chlorination is preventively used when much time has passed since the last use of the pool, also after 15-20 days of the swimming pool use and necessarily when the swimming pool starts to be used. 

  • Gas or liquid chlorine:  Chlorine can be also found in gaseous or liquid form, but it is not used. Especially, gas chlorine is considered as extremely dangerous. 

Some of the problems deriving from the chlorine use are the following:

A.   When chlorine is combined with amines (organic compounds derived from saliva, urine and sweat) chloramines are created. Chloramines apart from generating smell they practically constitute chlorine’s “death” given that they are produced even if there is a lot of free chlorine in the water. Shock-chlorination is the only way to break the bond between chlorine and amines.

B.   In indoor pools where there is no adequate ventilation and dehumidification system, chlorine can cause respiratory distress to swimmers.

C.   When chlorine comes in direct contact with the pool membrane, it creates discoloration, (indelible stains).

 

It is worth noting that when the amount of chlorine in the pool water is properly maintained and when the latter’s pH is regularly checked, the amount of chlorine in the pool water is probably even less compared to the amount of chlorine contained in tap water.

 

2. BROMINE 

It is used in tablet form undergoing slow dissolution. The advantages of this method are the following:

A.   As a disinfectant it remains active even when the pH is higher than 7.8

B.   The reaction of bromine with the organic compounds of the water binds a small amount of bromine contrary to chlorine which binds a larger amount (bound chlorine). In that case there is more free bromine (sanitizer) in the pool water.

C.   Amines produced in the water remain active, without binding the water chlorine, thus, the disinfecting capacity is increased.

D.   The use of bromine as a disinfectant does not prevent us from using chlorine. In fact, the chemical combination used for decontamination is 1/3 chlorine and 2/3 bromine. Moreover, the shock-chlorination still needs to be used.

 

The main drawback of this method is its higher price compared to chlorine’s.

Bromine is as effective as chlorine, but its cost is higher. Due to the limited amount of chlorine that bromine contains it does not generate the chlorine odor. It is recommended to be used in indoors, small pools and spa.

 

3. ELECTROLYSIS


Electrolysis is based on the production of chlorine by salt, which is used as a starting material. There are two advantages of this method:
  

  1. A.   The form of the chlorine produced does not create any undesirable residues

  2. B.   Low-cost consumable is achieved 

The installation is easily completed by placing the electrolysis chamber into the piping system of the recirculation machine, also by placing the operation panel, which is installed near the pool table. The required quantity of salt (preferably already dissolved) is first added in the pool water. Then, the salted water, through the recirculation process, passes through the electrolysis chamber. At this point, the decomposition of salt (sodium chloride) takes place, and the chlorine produced acts as a disinfectant as it gets diffused in the pool water. 

Electrolysis cannot be used at temperatures falling below 15οC. Moreover, the same remarks made for chlorine also apply to electrolysis. 

Chlorine produced by salt is more environmentally friendly compared to industrial chlorine, thus leaving skin feeling better than the chlorine tablets. 

When chlorine is used in the right dosage, it does not cause skin sensitivities and irritations. Electrolysis systems have experienced rapid growth in the last years mainly due to the reduction of the electrodes manufacturing costs and the overall simplified process. In addition, swimmers report better water quality, less skin irritations and generally they seem to find swimming more pleasant. In Australia in the 90% of the swimming pools, salt electrolysis systems for water disinfection are used.

It is one method of disinfection which constantly gains ground. The chlorine produced by salt is more environmentally friendly compared to industrial chlorine.

 

4. OZONATION 

Ozone is considered to be equally effective as chlorine to bacteria and pathogenic microorganisms found in the water. The gas is released in the pool water through injection accompanied by a noise. The degassing chamber (special chamber for isolating the ozone from the air) holds a certain water level. The mixture produced is passed through activated carbon and gets released into the pool water. It has no residual activity and therefore chlorine needs to be used as a complementary disinfectant, reducing the quantity of the disinfectant agent. 

This method’s main advantage lies in the absence of consumables, since special high-voltage lamps are used in order to produce ozone in the air. 

This method’s disadvantages are important: 

A.   The process of placing the equipment mentioned above in the pool water is extremely expensive

B.   Its residual activity and the ability to control the network are not guaranteed

C.   Power and meticulous maintenance are always required.

 

5. ULTRAVIOLET IRRADIATION CHAMBERS

The use of ultraviolet radiation is likely to contribute to the neutralization of the pathogenic microorganisms such as bacteria, viruses and protozoa. The ultraviolet radiation is generated in a special chamber, through which the pool water passes and gets disinfected, as it is being irradiated. The exposure of microorganisms, bacteria, viruses, etc., in the UV irradiation results in the irreversible damage of their genetic material, making them inactive. 

This method cannot be used as a standalone disinfectant, but only complementarily to other methods (e.g. chlorine or bromine), since it does not leave any disinfecting residues in the pool water (sanitizing residual). By reducing chloramines content and free chlorine is strengthened and the disinfection becomes more effective. 

In this case, proper water recirculation and specific flow rate in the pipes are required, in order to ensure that the entire water quantity passes through the electrode. Moreover, when there are suspended particles in the water, the efficiency of the system decreases.

This method does not ensure the hygiene of the pool. It can only be used as an additional/complementary means to reduce the amount of the main disinfectant, which can be either chlorine or bromine.

 

6. ACTIVE OXYGEN PEROXIDE

Active oxygen is also known as peroxide (hydrogen peroxide, Η2Ο2). It is probably the only method of water disinfection which can completely remove chlorine. It can be found in liquid but also in powder form.

Water disinfection is implemented by using liquid oxygen in the right dosage (250ml/50m3 of pool water). The liquid oxygen which gets released into the water ensures that the pool constantly contains a disinfectant.

Oxygen in powder form is more active and it is used as oxygen shock, similar to shock-chlorination. The oxygen shock is used (in the dosage 1kg/100m3) when much time since the last use of the swimming pool has passed, after 30 days of continuous use and when the swimming pool starts to be used.

Its application may be done manually, but also by installing a metering system. Caution needed when it comes in direct contact with human skin. 

The disadvantages of this disinfection method are the following: 

A.   It is not effective for eliminating the whole range of bacteria (it leaves 10% of the bacteria range unaffected)

B.    When the temperature of the pool water rises above the 28°C, the active oxygen gets completely off

C.   It is not recommended for swimming pools where there is already an increased organic load (eg professional pools), given that the ammonia produced reduces its effectiveness

Active oxygen is acceptable as a disinfectant, but its effectiveness is directly influenced by the pH level, which should be maintained in a specific range (7.0 - 7.4) and from the water temperature. In other words, a very meticulous maintenance is required which also influences the pool water quality. 

  

7. IONIZATION 

This term is used to describe the method of disinfecting water with copper and silver ions. The former eliminate the organic pathogenic microorganisms while the latter remove the inorganic pathogens from the pool water. The electrodes used for the production of ions, consist of 97% copper and 3% silver. This disinfection method, like the previous one, acts complementarily to the chlorination of water. What is mainly achieved is the chemicals consumption reduction. 

Copper is photosensitive and it is likely to create black or green deposits on the pool walls, as long as the pool is lined with membrane. Therefore, this method cannot be employed when the pool membranes have been placed.

It is a complementary method used to reduce chlorine in the pool. It should not be used in pool lined with membrane because it is likely to cause indelible stains on the membrane. When the dose is excessive, greening of the swimmers skin and hair has been observed.

 

TABLE OF SWIMMING POOL DISINFECTANTS 

 

 

 

Chlorine 

 

It is a very effective disinfectant, highly recommended for all types of swimming pools, but not recommended in cases of clinically proven respiratory distress.

     

Bromine

 

Bromine is equally effective as chlorine but way more expensive. Due to the limited amount of chlorine that bromine contains it does not generate the chlorine odor. It is recommended for indoors, small pools and spa.

     

Electrolysis

 

It is effective and the chlorine produced by salt is more environmentally friendly compared to industrial chlorine.

     

Ozonation

 

It is reliable but extremely expensive. Special equipment and particularly meticulous maintenance is required and therefore chlorine use.

     

Ultraviolet (UV) radiation

 

The hygiene of the pool is not ensured. It can only be used as an additional/complementary means to reduce the amount of the main disinfectant, which can be either chlorine or bromine.

     

Active oxygen

 

It involves increased installation and consumable cost and a very meticulous maintenance which also influences the pool water quality. It is recommended in cases of swimmers whose body has been clinically proven to react negatively when it comes in contact with chlorine. Its effectiveness is reduced at temperatures above 28οC.

     

Ionization

 

It is a complementary method used to reduce chlorine in the pool. It should not be used in pool lined with membrane because it is likely to cause indelible stains on the membrane.