The Science Of Supplemental Disinfection Systems

The expensive, cumbersome ozone systems of the past have given way to smaller, modern systems that provide public pools a viable water-quality solution at an affordable cost. Many are skid-mounted with flange-to-flange hook-ups for easy installation as a partial wall-mount or floor-mount.

An ozone disinfection system consists of two basic components:

• The ozone-generation system, which manufactures ozone gas

• The ozone-management system, which dissolves the gas into the water while preventing off-gas of undissolved ozone.

The ozone-management system maintains appropriate ozone levels in the water regulated with an oxidation reduction potential (ORP) controller/monitor. These components operate in unison, and are installed in an existing public pool as a side-stream to the pool’s main filtration system. Ozone is introduced to the water after filtration (and heating), 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 system output is increased as the water quantity or organic loading increases.

When sized and applied in compliance with the MAHC, the broad spectrum oxidation of an ozone system offers significant benefits:

• It controls the chloramine levels in the water to 0.2 PPM or less.

• It potentially eliminates “shocking” for chloramine reduction.

• It offers significantly more oxidation than free available chlorine (FAC) alone.

• It produces a minimum 3 log (99.9 percent) kill of Cryptosporidium parvum and other RWI pathogens in a side-stream applied single-pass.

• It provides micro-flocculation to aid filtration and water clarity.

• It reduces the amount of chlorine usage to maintain an FAC residual.

• It is not intended to be used with bromine because ozone oxidizes “spent” bromine (bromide) back to useful bromine, which depletes the ozone before it can oxidize the organic contaminants in the water.

Comparing Ozone To UV

There remains some confusion about the difference between an ozone system and a UV system. Some of this confusion stems from UV-generated ozone that was commonly used in residential pools and spas before compact CD ozone generators took over in the 1990s. Still, UV-generated ozone has never been used in public pools because the systems cannot make enough ozone to benefit the pool water.

Ozone is a natural oxidizer. Ozone gas dissolves in water to kill microorganisms, destroy organics that create chloramines, and break down existing chloramines by oxidation. This oxidation happens 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 then enters the pool, providing further oxidation of contaminants. There are no consumables in an ozone system.

UV light inactivates microorganisms and breaks down chloramines with light energy. This happens only while the water is in the UV chamber, and as long as the water has no turbidity. Once the flow leaves the chamber, no further process occurs. UV provides no oxidation except in trace amounts as a result of the formation of a limited number of hydroxyl free radicals.

Comparable Costs

Ozone and UV technologies are comparatively priced at approximately $30,000 for a 100,000-gallon pool. Ozone systems have a larger footprint than UV. Operational costs of each system vary with the local price of electricity. However, the minimal maintenance and reduced chemical requirements of an ozone system can create cost savings, resulting in a system payback of three to six years on a 100,000-gallon pool, varying by bather load. UV lamps must be replaced every three to 12 months, and must be figured into the maintenance costs for these systems.

The safety and health of our public recreational waters is of great concern to aquatic-facility operators and officials. When deciding the appropriate supplemental disinfection system for your commercial or public-pool operations, it will be worth the effort to compare ozone and UV.

Beth Hamil is vice president of corporate compliance for Del Ozone, an ozone-sanitation technology company based in San Luis Obispo, Calif. She has been active in aquatics since 1978 and in the ozone industry since 1982. During this time, Beth has been deeply involved in formulating standards and guidelines for supplemental disinfection and ozone aquatics, and educating industry and public audiences about ozone sanitation through her writing and speaking engagements. She can be reached via e-mail at beth@delozone.comThis e-mail address is being protected from spambots. You need JavaScript enabled to view it.

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