By Misha Shifrin
After over a decade of building and supplying many ozone generators for water treatment all over the world, I had noticed that we hardly sell anything locally.
It seemed strange to me, so I decided to call several different local water treatment professionals to find out what was the reason behind this
I asked them if they had ever used an ozone generator for water treatment. To my surprise, all of them answered yes. I then asked them if they are now using ozone in their applications. To my astonishment, all of them answered no. I asked them why.
“Because ozone doesn’t work,” was the answer from all.
This was the equivalent of someone telling me that the world is flat. Ozone for water treatment had always been an excellent choice for all our clients — effective, reliable, relatively inexpensive and ecologically clean.
I decided to ask one of the people I had approached — let’s call him “Joe” — to explain to me why an ozone generator didn’t work for him and why he is so dead-set against using ozone.
One customer’s nightmare
Joe told me that a few years ago he had installed an ozone generator for his customer’s 100-cubic meter (26,400-gallon) residential swimming pool. It was an air-fed, air-cooled ozone generator, purchased from one of the largest ozone generator manufacturers in North America. He was told it would produce enough ozone to completely disinfect the pool.
To his disappointment, the ozone generator did not do the job. The pool water turned cloudy and after a few days it started to smell.
In the end he had to install a supplementary chlorine injection system, which rectified the problem for about eight months.
Then he got another call from the customer, telling him the water was not as good as it used to be. When he checked, the ozone generator was not working. He had to take it apart and scrape the buildup off the electrodes. One of the electrodes cracked, and he had to order a new one from the manufacturer.
In summary, it was a nightmare scenario, which no one really needs. It was why he was not touching another ozone generator again, and Joe also told me some of his friends in the business had had similar experiences.
Looking at the numbers
I took out my calculator and started to check what might have gone wrong at Joe’s customer’s pool. Follow my steps:
1) 1 cubic meter (m³) = 1 million grams (g) of water
2) 1 g ozone dissolved in 1 m³ creates an ozone concentration of 1 part per million (ppm).
3) 100 g of ozone dissolved in 100 m3 pool will create a concentration of 1 ppm.
4) A residual ozone concentration of 0.03-0.05 ppm is typically recommended for chemical-free swimming pools. Let’s say that 0.04 ppm residual would have done a good job for Joe’s customer.
5) 100 g x 0.04 ppm = 4 g of ozone dissolved.
6) At a pool water temperature of 25 degrees C (77 F), half of the ozone is destroyed every 15 minutes (half-life of ozone at that temperature = 0.25 hour [h]). Therefore we need to inject 4 times more ozone in order to maintain the concentration every hour. As a result, at least 16 grams per hour (g/h) of ozone should have been dissolved to maintain the required concentration in the pool.
Checking the equipment
Joe told me that his ozone generator was rated at 16 g/h.
I visited the ozone manufacturer’s Web site, where I learned that the ozone was produced from that generator at 1 percent concentration by weight.
In our lab experiments, we have never managed to dissolve more than 6-10 percent of ozone at 1 percent concentration.
To dissolve 60-70 percent we usually need a concentration of 6 percent or higher.
Joe’s generator was only dissolving 1.6 g of ozone (16 g x 10%=1.6 g), creating a concentration of only 0.004 ppm, which was one-tenth of what was required.
Such a low ozone concentration is approaching levels where, according to a University of Maine study*, even distilled water disinfects better than ozone.
No wonder Joe’s generator didn’t work.
If he had found for his customer a 25 g/h oxygen-fed ozone generator, which produces ozone at 6 percent concentration, he would have had an ecstatically happy customer with crystal-clear, chemical-free swimming pool water — and a lot of referrals.
The first service call for such a higher-production ozone generator might not have occurred until many years after the installation, and probably would have been accompanied by many compliments for a job well done.
It is a sad fact that — especially with outdated, poorly performing generators — correct information sometimes is not getting to the water treatment professional in the field. After a few bad experiences with ozone applications, they may come to the conclusion that “ozone does not work.”
In retrospect, better information about generator performance and capabilities would help the whole industry, consumers and our earth.
* Study by Kristi Crowe, Ph.D., Department of Food Science & Human Nutrition, and Alfred Bushway, extension food science specialist, University of Maine, 2006.
This article was published in August 2009 in Water Tech. Magazine
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