“Viruses are the smallest of all the microbes. They are said to be so small that 500 million rhinoviruses (which cause the common cold) could fit on to the head of a pin. They are unique because they are only alive and able to multiply inside the cells of other living things. The cell they multiply in is called the host cell.
A virus is made up of a core of genetic material, either DNA or RNA, surrounded by a protective coat called a capsid which is made up of protein. Sometimes the capsid is surrounded by an additional spikey coat called the envelope.”
When it comes into contact with a host cell, a virus can insert its genetic material into its host, literally taking over the host’s functions.
An infected cell produces more viral protein and genetic material instead of its usual products. Some viruses may remain dormant inside host cells for long periods, causing no obvious change in their host cells (a stage known as the lysogenic phase). But when a dormant virus is stimulated, it enters the lytic phase: new viruses are formed, self-assemble, and burst out of the host cell, killing the cell and going on to infect other cells. Viruses attack bacteria, known as the lambda bacteriophage, which measures roughly 200 nanometers.
So, with all that being said, how are viruses treated in our local swimming pools?
If the local pool water is treated with only chlorine (1ppm Free chlorine, pH 7.5 and Temp 26 degrees Celsius), according to the CDC, it takes approximately 16 minutes for viruses to be killed. Viruses are chlorine resistant, meaning they are not easily destroyed by chlorine alone.
Whilst most Australian commercial pools operate at levels higher than 1ppm of chlorine, they also often have water at temperatures higher than 26 degrees Celsius and have the most important variable, pH, to consistently maintain to ensure there is more active chlorine (Hypochlorous Acid) than there is inactive chlorine (Hypochlorite Ion) in the water.
However, if your local pool has a form of ‘secondary sanitation’ equipment fitted to its plant room, which is not reliant on maintaining constant pH levels to be effective, then the risk of a swimmer contracting a virus is significantly decreased.
What is secondary sanitation?
Secondary sanitation is the second line of defense for chlorine (primary sanitiser) and is highly recommended for use on every public pool by the health departments in every state and territory of Australia as it provides the most effective treatment when it comes to the smallest pathogens such as viruses.
What types are there?
There are three main types of secondary sanitisers used, which are listed below from least oxidation potential through to the greatest oxidation potential;
1) Ultraviolet Light (UV)
2) Ozone gas (O3)
3) Advanced Oxidation Process (AOP), which combines UV and Ozone technology to produce Hydroxyl Radicals.
How does Ultraviolet Light (UV) work?
Anne Rammelsberg, a chemistry professor at Millikin University, offers this explanation:
Ultraviolet (UV) light kills cells by damaging their DNA. The light initiates a reaction between two molecules of thymine, one of the bases that make up DNA. The resulting thymine dimer is very stable, but repair of this kind of DNA damage – usually by excising or removing the two bases and filling in the gaps with new nucleotides is fairly efficient. Even so, it breaks down when the damage is extensive.
The longer the exposure to UV light, the more thymine dimers are formed in the DNA and the greater the risk of an incorrect repair or a “missed” dimer. If cellular processes are disrupted because of an incorrect repair or remaining damage, the cell cannot carry out its normal functions. At this point, there are two possibilities, depending on the extent and location of the damage. If the damage is not too extensive, cancerous or precancerous cells are created from healthy cells. If it is widespread, the cell will die.
How does Ozone gas (O3) work?
Ozone (O3) is formed when a high-voltage arc passes through the air between two electrodes. It is also formed photochemically in the atmosphere, and it is one of the constituents of smog. Ozone is a bluish and toxic gas with a pungent odor. Ozone is unstable because it breaks down to give molecular oxygen. Its low solubility and instability require that it is to be generated on site and introduced into the water as fine bubbles.
How does Advanced Oxidation Process (AOP) work?
Conventional oxidation processes are used in water treatment to disinfect water, to reduce toxins, odour and colour or to reduce manganese and iron levels in potable water. These processes may not destroy all toxins and have the potential to create dangerous disinfection by-products (DBPs). Advanced oxidation process (AOP) utilises the strong oxidising power of hydroxyl radicals that can reduce organic compounds to harmless end products such as oxygen.
Oxidation is defined as the transfer of one or more electrons from an electron donor(reductant) to an electron acceptor (oxidant) which has a higher affinity for electrons. These electron transfers result in the chemical transformation of both the oxidant and the reductant.
In advanced oxidation processes AOPs the hydroxide radical, OH not the OH¯ hydroxyl ion as in bases, is produced in a first step. This molecule has a very strong oxidizing and disrupting ability that may, depending on conditions, turn a complex (recalcitrant or refractory), organic molecule into CO2 and H2O.
The first reaction of OH with many volatile organic compounds (VOCs) is the removal of a hydrogen atom, forming water and an alkyl radical (R). OH + RH H2O + R Oxidation reactions that produce radicals tend to be followed by additional oxidation reactions between the radical oxidants and other reactants, (both organic and inorganic), until stable oxidation products are formed.
AOPs are reactions where first, hydroxyl radicals are produced, secondly, these radicals react with and destroy degradable organic and inorganic compounds. Typically, methods such as Ultraviolet light (UV), Ozone gas (O3), Hydrogen peroxide H2O2, Fenton’s and titanium dioxide TiO2 are combined (synergistic effect) to increase OH formation. Combining methods increases reaction rates 100 – 1000 times compared to using either ozone, H2O2 or UV alone.
Written by: John Morrison BSc