A swimming pool or spa is a complex ecosystem, where water is exposed to many things that can affect both aesthetics and safety.

A smart cleaning and sanitation protocol is crucial for ensuring a safe and enjoyable experience while minimizing cost and liability. Pool and spa water quality management systems will usually include the following components:

• Macrofiltration
• Microfiltration
• pH control
• Disinfection
• Nutrient control

While other aspects of effective pool and spa management are important to understand, this article will focus only on disinfection and especially, the use of ozone as an effective adjunct to traditional chlorination protocols. The de facto standard for pool disinfection in the US is chlorine, delivered as a stabilized solid or liquid. Chlorine is easy to add, relatively safe to store and quite cost effective for the average residential or institutional operator to use within an intelligent water quality management protocol. Remember to maintain compliance with local laws; some US localities mandate a minimum chlorine residual level, regardless of the efficacy of other methods used. Chlorine is not always the best solution for all applications and is not entirely effective against all waterborne contaminants, leaving the door open for adding ozonation and advanced oxidation processes (AOP).

Most contaminants that we deal with in pools and spas are introduced by the swimmers themselves, meaning that contamination types and levels will fluctuate dynamically and often dramatically, depending on the number of users, as well as their standard of personal hygiene.

Contaminants in pools and spas can be broadly categorized as follows:
• Macroparticulates (hair, bandages, lice, clothing fibers)
• Microparticulates (skin flakes, mites, soap scum, precipitated minerals, fecal matter)
• Dissolved pollutants (urine, sweat, tears, mucous, bodily fluids, saliva, beverages, etc.)
• Microorganisms (bacteria, mold, fungi, and viruses)
• Nutrients (phosphates, nitrates and other building-blocks for living organisms)

A properly designed filtration system will remove macro and microparticulates, leaving only dissolved pollutants and microorganisms to be addressed. Dissolved pollutants come from both dissolved solids as well the organic constituents of mammalian body fluids, and contain ammonia, fats, carbohydrates, proteins and amino acid complexes that can be a food base for bacteria. Naturally, these are usually found at very low levels and aren’t in themselves harmful or aesthetically unappealing to swimmers. When these compounds react with chlorine-based disinfectants, incomplete oxidation can allow chloramines to develop in the water, which of will contribute significantly to unpleasant odors andas well as irritate the eyes and possibly the respiratory system.

According to the Journal of Sports Medicine:
“… that there are health-related problems associated with swimming in chemically-treated pool water. Swimming pool water is disinfected in the interests of public health, although it would appear that chemical disinfection of the pool water may be the cause of many of the health-related problems that have been reported. There is medical evidence suggesting that exposure to chemicals such as chlorine and its derivatives, chloramines or chloroform may damage the respiratory epithelium and cause increased vascular permeability and oedema of the mucous membranes lining the airways and lung, both of which may result in severe inflammatory reactions.”

Innovative owners and operators want the aquatic environment to be clean, safe, and aesthetically appealing to those who use it while keeping operating costs reasonable and allowing for easy operator training. Ozonation is one of the alternatives to chlorination that fits the bill to make pools cleaner, clear, safer, and easier to maintain. You may already know about ozone, how it is produced and the general benefits/disadvantages relating to potable water treatment, so we’ll simply explore how adding ozone to a pool can have significant benefits.

Since ozone is such a powerful oxidant, its benefit is immediately apparent in that it will rapidly destroy many organic compounds while also inactivating bacteria, fungus, mold and viruses without risk of resistance build-up or immunity. Ozone concentrations as low as 0.5 mg/L have been shown to be quite effective in inactivating waterborne pathogens like Pseudomonas and Legionella in a significantly shorter time than with aqueous chlorine or bromine. Ozone is also very beneficial in reducing the overall organic load of the water while having a slight coagulating effect of certain colloids, thereby making the microfiltration process more effective and efficient. An additional benefit of ozone is that it decomposes into stable oxygen (O2), which is beneficial to the overall health of the recreational aquatic environment.

When adding ozone to an existing chlorine pool, it is helpful to understand the chemistry of the pool. Testing to ascertain the following will be very helpful when discussing the project with your vendor or consultant:
• Water hardness
• Total alkalinity
• pH
• TDS/Conductivity
• Phosphate
• Nitrate
• Ammonia

Ozone can be injected intermittently or continuously, depending on how much residual chlorine you intend to maintain in the pool. Typically, ozonation can reduce chlorine demand by up to 90 percent%, and very small amounts of residual chlorine need to be used. Continuous injection of ozone can perform the “heavy-lifting”, and a low dosage of chlorine will then act as the “backup” for maintaining bacterial control. I have employed continuous ozonation in pool and spa projects to significantly reduce the total oxidative demand of the water allowing for extremely low chlorine dosing while maintaining compliant residuals.

Once you have decided on the amount of ozone required, application method and type of equipment to deploy, it’s a matter of selecting vendors and manufacturers. You’d be wise to select vendors and manufacturers who have an established service and technical support program, along with training on installation and service and a local supply ofr maintenance/replacement parts. You should also consider using equipment and components certified to NSF/ANSI 50, especially when working with commercial pools and spas so that you can have the additional verification of material safety, operator protection measures, disinfection efficacy, and quantified level of Cryptosporidium inactivation. Also be mindful of requirements for adjusting pool chemistries, installation complications, and operator training of operators to maintain the equipment configuration. Maintenance on ozone equipment is certainly more complex than just throwing chemicals into the water. A well-motivated maintenance technician with some careful training, will easily adapt to working with an air dryer, ozone generator, ozone compressor and other related devices.

Naturally, ozonation will not cure all ills, since it is only effective for a few seconds as the water passes through the piping and filtration train, not the entire pool itself. We want the ozone to be consumed or destroyed before it reaches the main body of the pool, so that bathers aren’t exposed to irritating free-ozone. Consequently, unless the residual pool sanitation protocol is properly developed and followed, algae accumulation in the pool is possible and almost inevitable. Be sure to periodically shock the pool or spa as well as testing free chlorine levels in the main pool or spa water and following proper maintenance and dosage protocols.

Ozone disinfection technology leverages the power of natural oxidation to make pool and spa water cleaner, clearer, and safer. Taking the time to learn how to harness this powerful technology will improve your ability to serve your clients.

1. Journal of Sports Medicine [SPORTS MED.], vol. 21, no. 4, pp. 256-261, 1996