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The Safe Use of Ozone in Water Treatment – Layers of Protection

I’ve long thought that ozone is arguably the pool industry’s most underused technology, primarily because of the perception that it’s difficult to control and potentially dangerous. One of the biggest hurdles of using ozone in a commercial pool is that, in most situations, you can’t run it 24 hours a day. The reason is concern over un-dissolved ozone in the water causing off gassing.

I certainly understand that concern in the sense that no one should ever be exposed to breathing ozone gas because it is highly toxic. If, however, treatment systems are set up correctly, ozone levels can be controlled using layers of protection against exposing bathers, while at the same time making the most of ozone’s remarkable oxidizing powers.

Often, the only safeguard using ozone is to simply set an oxidation-reduction potential (ORP) controller to shut off the ozone generator at a reading of 750 millivolts. In my view, that’s a sloppy way to do it because when the ozone is off, the water becomes more vulnerable, like an open wound exposed to infection. If that was the only way to prevent ozone exposure, then I could understand the resistance to using it, but that’s just not the case.

In fact, when we developed our SRK HydroZone 3® system, setting it up so the ozone can run all the time, to maximize the benefits of ozone’s presence, was one of our key design objectives. Here’s a thumbnail sketch of how it works and why there’s no remote chance that ozone will off gas and expose bathers to harm. 

HydroZone 3: Layers of Protection

Layer 1

After the water’s been filtered and heated, we route 25 percent of the flow to a side stream where it passes through the ozone generator. The size and output of the unit is based on bather load and other environmental factors. The water leaves the ozone unit and immediately enters the contact tank, where we can manipulate the contact time and flow rate. This is where the majority of ozone is dissolved in the water and consumed, which serves as the first layer of protection against off gassing.

Layer 2

After the water leaves the contact chamber, it flows through a static mixer where any remaining ozone bubbles are broken up into ultra-tiny nanobubbles. The main purpose of the static mixer is to be sure we’re not sending any large bubbles through the UV unit, which can distort the light absorption process.

After the static mixer, the water re-enters the other 75 percent of the flow. At that point, we have an ORP sensor that enables us to adjust the ozone’s system output when the oxidation demand rises.

Layer 3

The UV system is the third layer of protection because UV light destroys ozone and turns it into oxygen. The reaction between ozone and UV also generates hydroxyl radicles by way of advanced oxidation processes (AOP), which supplements the oxidation of organic compounds still in solution.

Layer 4

We measure the ORP again after it leaves the UV chamber. Invariably, when the UV system is on, the ORP will drop to somewhere between 350 and 400 mV. When it’s off, we get the same reading as the sensor before the UV unit. When the ORP drops, that is a direct indicator that the ozone has been destroyed. If for some reason, the ORP remains above a set level (500 mV, for example), then you can reduce the ozone generator’s output or shut it down. That almost never happens.

The Result

There’s a lot more to it than that, but we have multiple redundancies that, together, reduce the risk of ozone exposure to virtual zero. It simply cannot, does not, and will not happen.

This is all part of the beauty of finding synergies using different technologies. Eliminating the risk of exposure to ozone is one of those important synergistic benefits.

the Water Geek


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A blog about all things water, written by SRK's founder Steve Kenny.