By Greg Reyneke, CWS-VI

Ozone concentrations as low as 0.5mg/L have been shown to be quite effective in killing waterborne pathogens, like Pseudomonas and Legionella, in a significantly shorter time than with chlorine or bromine.

Most water treatment professionals who read this magazine should be quite familiar with the benefits of ozonation for drinking and process water applications. In the new economy, smart operators are now broadening their portfolio of treatment applications to include pools and spas to ensure that they can help their valued clients with all of their water quality management needs. Pools and spas are uniquely profitable applications for the water quality management practitioner, if you understand the fundamentals and are willing to take the plunge. Like any body of water, a swimming pool or spa is an ecosystem, where water will be exposed to many things that can compromise both aesthetics and safety, necessitating an appropriate cleaning, clarification and disinfection protocol. Pool and spa water quality management systems will usually include the following components:

  • Macrofiltration
  • Microfiltration
  • pH control
  • Disinfection

While other aspects of effective pool and spa management are important to understand, this column will focus only on disinfection and especially the use of ozone as an effective alternative or adjunct to traditional chlorination protocols. Remember to maintain compliance with local laws; some US localities mandate a minimum chlorine residual level, regardless of the efficacy of other methods used. The defacto 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. As scientists, legislators and operators have learned, however, chlorine is not the best solution for all applications and is not entirely effective against all waterborne contaminants. The vast majority of contaminants that we deal with in pools and spas are actually introduced by the swimmers themselves, meaning that contamination types and levels can fluctuate dynamically and often dramatically, depending on the number of occupants, as well as their level 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 other minerals, fecal matter)
  • Dissolved pollutants (urine, sweat, tears, mucous, semen,vaginal discharge, saliva, beverages, etc.)
  • Microorganisms (bacteria, mold, fungi and viruses, bothpathogenic and benign)

A properly designed filtration system will remove macro and microparticulates, leaving only dissolved pollutants and micro-organisms 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 will contribute significantly to unpleasant odors and irritate the eyes and possibly the respiratory system.

In the Journal of Sports Medicine we read:

“While swim training may improve fitness and reduce morbidity
associated with asthma, there is both anecdotal and scientific information to suggest 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, clear, safe and aesthetically appealing to those who use it while still 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.

Benefits of ozone
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 killing waterborne pathogens, like Pseudomonas and Legionella, in a significantly shorter time than with 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 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 OEM or consultant:

  • Water hardness
  • Total alkalinity
  • pH
  • TDS/conductivity
  • ORP

Ozone can be injected intermittently or continuously, depending on whether you are planning (or forced) to retain a minimum residual chlorine level in the pool. It is outside the scope of this column to discuss the philosophical merit of one versus the other, but suffice it to say that each has its unique advantages. The deployment of such methods will depend on what you determine is best for the overall operation of the specific pool or spa. Once you and your vendor have decided on the amount of ozone required, application method and what specific equipment to deploy, it’s a matter of adjusting pool chemistries and then training to maintain the pool. Maintenance on ozone equipment is certainly more complex than just throwing chemicals into the water. The average monkey is definitely not up to the task, but 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 designed to condition the water passing through the piping and filtration train, not the pool itself. We want the ozone to be consumed or destroyed before it reaches the pool itself, so that bathers aren’t exposed to free ozone. Consequently, unless the pool sanitation protocol is properly developed and followed, algae accumulation in the pool is possible and almost inevitable. A simple solution is to periodically shock the pool with 35-percent hydrogen peroxide or to maintain a slight chlorine residual in the water.

Ozonation technology leverages the power of natural oxidation to make pool and spa water cleaner, clearer and safer. Yes, there is a slight learning curve to begin mastering the art, but if you take the time to learn more about this valuable addition to your skill set, you won’t be disappointed!


  1. Journal of Sports Medicine [SPORTS MED.], vol. 21, no. 4, pp. 256-261, 1996
  2. Reyneke, Greg. “Dealer Dynamics: O3– Good for You, Good for Me.” WC&P International, August 2012

About the author
Greg Reyneke is Managing Partner at Red Fox Advisors, a multidisciplinary research, development and consulting company with a strong emphasis on water, air, microbiology and energy projects. He also serves as an advisor to the ProFlow Dealer Network, a Pentair Platinum Partner and is a member of the WC&P Technical Review Committee.


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