Editor's Note: This is the first of two columns on supplemental sanitization systems. Next month we'll look at UV systems.
Since 1961, when the U.S. Public Health Service published a model ordinance governing the sanitation of public pools with chlorine, that has been the standard water treatment chemical. While chlorine is effective in reaching certain water quality standards, scientists are learning more about its limitations and hazards. These findings, in part, have inspired the Centers for Disease Control and Prevention to form a Model Aquatic Health Code.
The soon-to-be-published MAHC will include a section on the importance of supplemental disinfections systems (SDSs). In the present draft, two recommended SDS technologies are listed in the MAHC: ozone and ultraviolet light (UV).
UV achieved earlier adoption among pool designers for its simplicity. Ozone, on the other hand, has been used to sanitize municipal water for the past 100 years, is widely used as life support for aquatic mammals and fish in commercial aquariums, and is the primary supplemental sanitation technology for the hot tub industry. But it still has yet to earn its place in supplemental disinfection for commercial pools.
A big reason for that are the complexities and confusion within the aquatics industry as to what ozone is, how it works and how it compares with UV. To clear those up, it’s necessary to first look more closely at the role of chloramines and RWIs as the impetus for supplemental disinfection.
In the 1930s, chemists discovered that chlorine could react with organic material in water and create chloramines. In pools, these are documented to be unhealthy for people and can cause damage to indoor facilities. Ever since the discovery of chloramines, the challenge has been to balance antimicrobial efficacy (keep the water sanitized) and swimmer safety (eliminate chloramines).
In the past two decades we have added to this an increasing concern and awareness of recreational water illnesses, or RWIs. “RWI” is a term coined by the CDC to describe illnesses caused by microorganisms, as well as those from chloramines. Some microorganisms, including Pseudomonas aeruginosa, E. coli, Staphylococcus aureus, Giardia and cryptosporidium parvum (crypto), can cause serious illness in swimmers.
In a perfect world, chlorine would handle all of these except crypto, which is resistant to chlorine. However, the repeated outbreaks of the chlorine-sensitive microorganisms have shown that conventional chlorine treatments are not adequate and some type of supplemental system should be considered.
Fortunately, new and improved technologies provide affordable solutions that are readily available for the reduction of chloramine compounds as well as increased protection from microorganisms in the pool: the aforementioned supplemental disinfection systems. By supplementing chlorine, SDSs provide increased kill of microorganisms as well as reduction of chloramines. This leads to significantly reduced chlorine off-gassing and its harmful effects to swimmers and facilities.
Ozone, an SDS option, has been widely used for municipal water and commercial pools in countries outside the United States for more than 100 years. In recent years, the expensive, cumbersome ozone systems of the past have given way to smaller, affordable, modern systems that provide public pools with a viable water quality solution at a low cost. The complexity rumors about ozone systems are widely overstated and outdated. Today’s commercial ozone systems are simple, compact and efficient. Many are skid-mounted with flange-to-flange hook-ups, which enable easy installation as a partial wall-mount or floor-mount.
An ozone system consists of two basic components that ensure optimum performance at the lowest operating cost: an ozone generation system and an ozone management system.
The ozone generation system manufactures ozone gas. The ozone management system efficiently dissolves the gas into the water, simultaneously ensuring no undissolved ozone is available to off-gas in the pool equipment room or at the pool water surface.
The ozone management system utilizes an oxidation reduction potential (ORP) controller/monitor to maintain proper ozone levels in the water. These components operate in unison and are easily installed to an existing public pool as a side-stream to the pool’s main filtration system. The ozone is introduced after the filtration (and heater), and before the chlorine feeder. The side-stream flow is normally 15- to 25 percent of the main flow, depending on the size and type of pool. The ozone system output is increased as the water quantity or organic loading increases.
Ozone is a safe and efficacious antimicrobial oxidizer. In public recreational water, it is used in conjunction with chlorine. Pool water clarity and quality is improved because of ozone’s potent and rapid oxidation of organic and inorganic compounds. Ozone is cost-effective, uses little energy, is safe for pool patrons and will not cause structural degradation to the facility or HVAC system.
An ozone system’s broad spectrum oxidation, when properly sized and applied to any aquatic venue, will:
• Control the chloramine levels in the water to 0.2 ppm or less
• Offer significantly more oxidation than free available chlorine (FAC) alone
• Produce a minimum 3 log (99.9 percent) kill of cryptosporidium parvum and other RWI pathogens in a side-stream applied single-pass
• Provide microflocculation to aid filtration and water clarity
• Reduce the amount of chlorine usage to maintain an FAC residual
It is not recommended that ozone be used in conjunction with bromine. When used with bromine, ozone oxidizes “spent” bromine (bromide) back to useful bromine. This depletes the ozone before it can oxidize the organic contaminants in the water.
Though ozone and UV systems are completely different technologies, some people are confused about the distinction between the two. Perhaps part of the confusion stems from UV-generated ozone that was readily utilized for residential pools and spas until the late 1990s, when breakthrough compact CD ozone generators took over that market. UV-generated ozone is never used on a public pool because the systems cannot make enough ozone to benefit the pool water.
Ozone is a gas that is dissolved in water to kill microorganisms, destroy organics and break down chloramines by oxidation. This occurs immediately at the ozone gas injection point, and continues as the side-stream remixes with the main return. A small residual (~0.1 ppm) of dissolved ozone will enter the pool, providing further oxidation of contaminants. There are no consumables in an ozone system.
In comparison, UV light inactivates microorganisms and breaks down chloramines with light energy. This only happens while the water is in the UV chamber, and as long as the water has no turbidity. No further process occurs once the flow leaves the chamber. UV provides no oxidation except as trace amounts as a result of the formation of a limited number of hydroxyl radicals. UV lamps are replaced every three to 12 months, so replacement costs must be considered when determining ownership expenses.
As a rule, ozone and UV technologies are comparatively priced. Each costs approximately $30,000 for a 100,000-gallon pool, with the ozone system having the larger footprint. Operational cost will vary with the local price of electricity for either technology. However, ozone does not entail the same maintenance costs as UV. With savings from labor and reduced chlorine usage, a system can pay for itself in three to six years on a 100,000-gallon pool, depending on bather load.
Ozone and UV can be used together to create a synergistic approach to water sanitation. This process has been in use for drinking water, food processing and waste water for many years. It is one of several advanced oxidation processes that are in commercial use today in selected industrial processing. The technology has rarely been used in public pools to date, but with the advent of improved technology and cost reduction, perhaps it will be the wave of the future for RWIs and chloramine elimination.
As aquatics facility operators and officials look to increase the safety and health of our public recreational waters, it is clear that supplemental disinfection systems will offer strong protection. Several states have already mandated the use of SDSs for their high-risk swimming venues such as interactive sprayparks, and it is likely more states will rapidly adopt the MAHC for these as well as all public aquatics facilities. With this in mind, operators and officials are wise to learn about the power of ozone sanitation