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Most people don't think twice before jumping into a swimming pool. During the summer and on weekends, a community swimming pool can be full of people of all ages and genders. While the pools are intended to provide relaxation and entertainment, they also expose users to aquatic facility-associated sickness, particularly infectious disease outbreaks and pool chemical-related health events (e.g., respiratory distress or burns). As a result, pool hygiene becomes critical in order to avoid aquatic facility-related sickness. If you swim often at a public pool, you will definitely run into problems like darkening skin, burning eyes, itching, a strong smell, etc. This is mostly because chlorine is used as a disinfectant in the pool(1). Chlorine, in the form of hypochlorite, chlorinated isocyanurate, chlorine tablet etc., is the most common disinfectant used in pools. It kills microbes/germs and keeps organisms like algae from growing at a large scale. But more and more evidence shows that this chlorine-based method of disinfection and the effects of using it too much has various health hazards(2). Chlorine operates on the substitution principle where it reacts with organic matter like body fluids, skin and algae waste. This non-specific reaction of chlorine is the main concern as many of these reactions lead to generation of toxic Disinfection By-Products (DBPs) like Trihalomethanes (THMs). Unfortunately, THMs are classified as class II carcinogens. It means, frequent use of swimming pools disinfected by chlorine increases the exposure to these carcinogenic compounds(3). In addition, chlorine has certain limitations on its applicability to kill germs or microbes. For example, its effectiveness decreases a lot when it is exposed to sunlight or when the pH of the water changes (the best pH range is between 5.5 and 7.5). This means that the pool operator often has to adjust chlorine levels to keep the desired level of disinfection, which subsequently leads to increased formation of THMs. This also increases the pool-chemical related sickness like eye irritation and burning the skin. This is a typical example of how you can solve one problem by making another one.
But the question is: Is there something we can use instead of chlorine that has all the good traits about chlorine but not the bad ones? The answer is yes, which is why we're going to detail here about chlorine dioxide, a molecule that does amazing things. Even though the name sounds a lot like chlorine, chlorine dioxide has a different chemical structure and chemical reactivity than chlorine(4). In chlorine dioxide, the chlorine atom is connected to the two oxygen atoms by an electron that jumps between the two oxygen and chlorine atoms. These jumping electrons are responsible for providing oxidative power or disinfection power to chlorine dioxide. Here unlike chlorine, only electrons get transferred and not the chlorine molecule. In simpler terms, chlorine dioxide kills microorganisms through a process called oxidation (whereas chlorine kills microorganisms through a process called chlorination). This unique way of killing with chlorine dioxide doesn't produce any THM like by-products(5). It is estimated that chlorine dioxide is 2.5 times more effective as a disinfectant than chlorine due to its oxidative chemistry, selective reactivity (unlike chlorine, it does not react with all organics), independence from pH effects, and the fact that it remains as a gas when dissolved(6). Additionally, chlorine dioxide is an effective deodorizer and disinfectant, and it can even eradicate water-borne infections like Cryptosporidium, which is resistant to chlorine.
Someone may wonder why, with so many positive attributes, chlorine dioxide isn't used more in pools. The main reason is that it must be generated on-site and cannot be stored or moved like chlorine(7). To address this, MicroGO® has been working for a couple of years and devised an in-situ chlorine dioxide generator called Tubelet™. Tubelet™ delivery system produces 100% chlorine dioxide on-site at a substantially lower cost while assuring that the treated water is devoid of unreacted reactants or any DBPs. The Tubelet™ in-line treatment system is also IoT enabled, wherein it guarantees that the disinfection levels can be maintained and can be tracked remotely, ensuring that the pool is safe any day and anytime. It is what we call the perfect amalgamation of science + engineering and technology to solve human problems. Let us work together to make the swimming pool a place to jump and relax rather than a potential source of infection or aquatic facility-related hazard.
References:
Mood, E. W. (1953). American Journal of Public Health and the Nations Health, 43(10), 1258-1264.
Angione, S., McClenaghan, H., & LaPlante, A. (2011). A review of chlorine in indoor swimming pools and its increased risk of adverse health effects.
Manasfi, T., Coulomb, B., & Boudenne, J. L. (2017). International journal of hygiene and environmental health, 220(3), 591-603.
Gordon, G., & Rosenblatt, A. A. (2005).Ozone: science & engineering, 27(3), 203-207.
Lykins Jr, B. W., & Griese, M. H. (1986).. Journal of American Water Works Association, 78(6), 88-93.
Encyclopaedia of Physical Science and Technology (Third Edition), Academic Press, 2003, Water Conditioning, Industrial, John M. Donohue,Editor(s): Robert A. Meyers, Pages 671-697
Simpson, G. D., Miller, R. F., Laxton, G. D., & Clements, W. R. (1993, March). In Corission- National association of corrosion engineers annual conference.