Swimming Pool Disinfection Methodologies & What’s Best for You!
One of the important aspects of maintaining a healthy pool is to keep the number of microorganisms that cause waterborne diseases down.
Metcalf and Eddy define disinfection as “the selective destruction of disease-causing organisms. All the organisms are not destroyed during the process. This differentiates disinfection from sterilization, which is the destruction of all organisms.”
To demonstrate, disinfection is carried out for pool water while sterilization is done for milk, say, by ultra heat treatment.
Overall, water, and I mean city water, process water, cooling water, wastewater, recreational water can be disinfected by many means, and the choice of process to be used will be determined by several factors. As already stated, end use, water source, available processes and ultimately economics play a big part as to which procedures are to be used.
Disinfection can be carried out by several means. These can be through:
1. Chemical Agents
This type of disinfection method involves the application of a liquid chemical agent to eliminate most pathogenic microorganisms, except for bacterial spores on inanimate objects or surfaces.
2. Physical Agents
Swimming Pool disinfection with the use of physical agents involves the process where all the living microorganisms, including bacterial spores are killed .
3. Mechanical Means
Swimming Pool disinfection by mechanical means do not destroy the source but removes it instead to reduce the possibility of infecting others.
This is a type of swimming pool disinfection methodology that exposes an object to radiation.
Chemical Agents for Swimming Pool Disinfection
There is a range of chemical agents that have been widely used for disinfection. Here’s a brief overview the most commonly used chemical agents for swimming pool disinfection.
A popular choice for swimming pool disinfection, Chlorine handles the three main jobs in keeping a swimming pool clean as it sanitizes by destroying bacteria and germs, oxidizes by controlling organic debris from perspiration and body oils, and deters algae.
Bromine is an option for swimming pool disinfection that is commonly used in spas but also works well for swimming pools. Bromine doesn’t break down easily in hot water, so it’s favored over chlorine. But because it’s more stable in water than chlorine, it’s also not as easy to wash off.
It was during the WW1 when Iodine was first discovered suitable for water treatment during World War I. According to the CDC, iodine water treatment is still acceptable where treatment by boiling the water is unavailable.
Ozone is one of the most effective disinfection agents. It works well for swimming pool disinfection as it can be used ls to replace disinfectants that contain chlorine and bromine containing disinfectants.
Phenol and its compounds
Phenolics are derivatives of phenol that have been modified to improve antimicrobial activity when used along with detergents. They are able to exert action by causing injury among plasma membranes.
Swimming pool disinfection with the use of alcohol allows penetration of most materials, destroys all microorganisms and endospores through cross linking of proteins and nucleic acids especially when used at low room temperatures. However, it requires long exposure times and is explosive and toxic when used in pure form.
Heavy metals and related compounds
Heavy metals allow antimicrobial action through oligodynamic action. Combination of heavy metal ions with sulfhydryl (—SH) groups, proteins are denatured.
Physical agents are ones that employ heat and light. Boiling water is one of the most primitive methods to purify drinking water and is known to kill a myriad of pathogens when used.
Some methods use ultraviolet light to kill microbes in the water. Problems that arise in the use of ultraviolet light is how UV can actually penetrate the water to actually disinfect a significant volume of water, some industries that use this method of purifying water is the manufacturing industry. Where the presence of microbes pose small surface defects on surface finishes, like painting.
Mechanical means to disinfect water includes the use of filters and screens. Ultrafiltration and reverse osmosis are both used to disinfect drinking water.
The use of radiation to treat water is pretty much limited to the use of gamma rays to disinfect water and wastewater.
Which one to use?
So, with the many ways to disinfect water, just what are the means that are normally used to disinfect pool water. Of the many methodologies stated above, chemical means by chlorination and bromination are widely used to treat pool water. Because of the relative ease to use these two methods, the abundance of treatment chemicals also makes the use of chemical agents a preferred choice.
In fact, Melbourne has come up with clear guidelines how to treat pools with the use of chlorine and bromine-based chemicals.
The most common chlorine-based chemicals used in the pool water treatment are calcium hypochlorite and sodium hypochlorite. Another chlorine-based chemical, Sodium Dichloro-S-Triazinetrione is also available in the market in granular form. Bromine would be in the form of commercially available bromine chloride, usually in stick form
The twice a year visit of the City of Melbourne officials to a pool owner’s facility will involve a check on the microbiological quality of the water in the pool. The checks are as follows:
- There should not be over 100 colony forming units per mL (cfu/mL) when a Total Bacterial count is conducted. This means that the standard allows some microorganisms to be found in the pool water, consistent with the definition of disinfection. This, with reference to the two items that follow regarding coliform and Pseudomonas aeruginosa.
- There should be no coliform bacteria found in 100 mL of pool water sample.
- There should be no Pseudomonas aeruginosa found in 100 of pool water sample.
The City of Melbourne recommends that pool operators and owners take a proactive approach in adhering to the standards. To maintain and monitor microbiological growth in the pool, the pool operator or owner must establish their own testing procedures. Although the operators can set up a facility within their premises to test for these microorganisms, only lab results coming from a third party lab is honored by the City of Melbourne when it comes to lab test results.
Should a sample fail the test results conducted by a third party laboratory, the following procedures are recommended by the City of Melbourne as a remedial course of action:
- With chlorination or bromination as a widely accepted methodology and the preferred method adapted by the city, a slug or shock dosing of the choice chlorine or bromine chemical agent must be added to the pool to kill off the excess unwanted microorganisms.
- The pool water treatment and the pool water maintenance program is automatically reviewed for weak spots or inefficiencies.
- Faults or weaknesses in the program or chemicals used should be rectified.
- A sample should be taken again and sent to the lab for testing.
- Should the submitted sample the pass the microbiological screening, the pool is allowed to be used and the problem is deemed rectified.
Pool owners and operators should take note that until the problem is rectified, bathers are not allowed to use the pool. Steps 1 to 4 is repeated until the problem is rectified. It is essential that you work closely with your chosen third party laboratory to ensure a timely turnaround time for your lab results.
Chlorine or Bromine? Helping You Determine the Best Swimming Pool Disinfection Options
Swimming pool disinfection often leaves pool owners with the choice between chlorine or bromine. To make the choice easier, here’s a comparison that states their main differences, including their pros and cons.
- Chlorine can be added in the form of tablets, sticks and in granular form. Bromine, on the other hand, is in the form of tablets.
- There is an additional cost involved for pool owners and operators opting for the bromine alternative as bromine cannot be added directly into the pool, as the bromine does not readily dissolve in water, bromine is dissolved prior to use and fed into the swimming pool.
- There are advantages and disadvantages using either chlorine or bromine. Bromine is more stable in hot applications making them the product of choice for heated spas or any installation greater than 40°C.
- Bromine, just like chlorine has a particular smell that is harder to rinse off compared with its chlorine counterpart.
- Bromine also carries out its disinfection differently compared with chlorine, as bromine kills the microorganisms in the pool, some of the active ingredients remain active and continue its disinfecting properties. Chlorine, when it kills the microorganisms form residuals that eat up the active ingredients. In effect, you will use much less bromine to treat a pool compared with its chlorine counterpart.
- Outdoor pool installations that use chlorine also need a stabilizer, cyanuric acid, to keep the chlorine chemicals in the pool as UV light from the sun dissipates the chlorine into the air. Indoor pools do not need to use the stabilizer.
Chlorine chemicals that are used in swimming pool water treatment categorized into two: inorganic chlorine, and inorganic chlorine.
Calcium hypochlorite, lithium hypochlorite and sodium hypochlorite are the commercially available forms of inorganic chlorine that is used to treat swimming pools. They have similar modes of action, choice will mostly depend on availability and cost.
Trichloroisocyanuric acid, potassium dichlorocyanurate and sodium dichlorocyanurate (anhydrous or dihydrate) on the other hand are the most common forms of organic chlorine-based chemicals used by swimming pool owners.
Bromo-chloro-dimethyl hydantoin (BCDMH) is the most popular bromine-based chemical of choice.
So whether you use chlorine or bromine to disinfect your pool water, the decision remains still with the pool operator or owner.
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