Effect of AOP/Ozone/UV to Chlorine

Bob Jakob

In The Industry
Jun 21, 2018
14
North Kingstown, RI
So, if you were going to put a AOP/Ozone/UV unit in as secondary treatment it should be before the chlorinator? Would the Ozone have an effect on the catalyst on blades of chlorinator?
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,503
NW Ohio
Yes. It will also destroy chlorine if placed before it. That's what UV does. If placed before the SWG I'm not sure how the cell will handle the ozone either.

These units are rather pointless when you boil it down. Just another in the long line of "chlorine's old, what's new?" sales pitches. Chlorine is boring, but it works just fine by itself and in a residential pool is only hampered by secondary oxidation or sanitation attempts.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,503
NW Ohio
No, AOP does not provide additional additional sanitizing of the pool water and thus the FC/CYA Chart must still be followed.

What chlorine resistant bacteria do you believe will be introduced in to your pool? How many people do you have swimming in your pool that you are not in regular contact with? Are we talking about dozens of people in the pool several hours a day every day?
 

Bob Jakob

In The Industry
Jun 21, 2018
14
North Kingstown, RI
Not talking about my particular pool. Just trying to get a grip on the AOP concept. There seem to be some benefits that you are overlooking. Any water that goes through the AOP unit will be sanitized / oxidized and that should reduce the chlorine demand in the pool? I realize that the residual needs to be provided by chlorine.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,062
Tucson, AZ
It's not overlooking the benefits, quite the opposite - when you consider the supposed benefits of any kind of AOP system, they do not justify the costs or complexities involved.

Tell me, exactly how many cases were reported to the CDC last year of people swimming in a single family residential pool contracting cryptosporidium parvii ? Here's a link -


So that's 444 cases over 12 years, or about 37 cases per year and and 35% were traced to contaminated recreational water facilities. That's about 13 cases per year. But let's assume it's triple that value since this reporting likely only covers commercial facilities that are required to report such data. So what, maybe about 40 cases of crypto per year....

Now there are approximately 10.4 million residential pools in the USA, and so my chances of contracting crypto by some crude math is - 40/10,400,000 or about 3.8 in a million....

So, given how small that risk is, do you believe that the benefit of AOP in eliminating chlorine resistant microbes is worth the installation costs (hundreds to thousands of dollars) as well as the on-going maintenance expenses and time spent troubleshooting the systems when they go down as well as the detailed chemical balancing required to run a low chlorine pool?

Remember to that these units only treat water that flows through them and will only kill planktonic (free-floating) pathogens. Algae and bacteria that has become sessile forming mats and biofilms will be completely unaffected by an AOP system.

Another thing to consider is this - exactly how much chlorine is saved by pairing an AOP system with a low level of chlorine. Chlorine is one of the cheapest sanitizers available and so it would take decades in any realistic scenario for the offset expense of using low chlorine to pay for a AOP system.

If you think about this logically, then there really is no benefit to installing an AOP system except to the installer that makes the money off of it. A pool owner can easily run a residential swimming pool using nothing but chlorine chemistry and be perfectly safe.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,062
Tucson, AZ
Going back to your original question - yes, any secondary oxidizer will likely interact with chlorine and reduce it.

Ozone, UV-A/B & UV-C, peroxide, MPS, etc, all react with chlorine to varying degrees as well as with organic contamination in the pool water. Rates and efficiencies vary depending on the chemical species involved so there's no easy rule of thumb. If a clean swimming pool with little bather waste has chlorine in it and you bubble ozone into the return lines, you will undoubtedly reduce a lot of the chlorine as the ozone will not have anything else to react with. A UV lamp placed in the plumbing stream will also contribute to chlorine loss as much as it will do for oxidizing organic waste or inactivating pathogens.

There are very few situations where an additional AOP system would be recommended. In a residential setting, the only time I could see a pool benefiting from an AOP system would be in an indoor pool where there is no UV light from the sun. In that case, running a UV sterilizer could help to keep the buildup of permanent CC's low. Ozone would only help in a pool if it were designed with a contact tank setup and an air purge to remove the build up of ozone.

Again, the benefits of all these process are minimal at best and so, for the residential pool owner, they make little economic sense.
 

TheDeuce

Gold Supporter
Jul 9, 2019
118
Winnipeg, Manitoba
Going back to your original question - yes, any secondary oxidizer will likely interact with chlorine and reduce it.

{snip}
So if one is doing a SLAM and has a "UV Assistance" unit in their system (because they built the pool before learning about TFP) would that contribute to a failed OCLT? Not trying to hijack the thread but I'm SLAMming my pool for the first time (kinda blogging my progress in the Newbie section) and I'm oh-so-close to passing (1.5 ppm loss, near 0 cc). Do these UV units have that kind of nighttime effect?


m.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,062
Tucson, AZ
So if one is doing a SLAM and has a "UV Assistance" unit in their system (because they built the pool before learning about TFP) would that contribute to a failed OCLT? Not trying to hijack the thread but I'm SLAMming my pool for the first time (kinda blogging my progress in the Newbie section) and I'm oh-so-close to passing (1.5 ppm loss, near 0 cc). Do these UV units have that kind of nighttime effect?


m.
You should always being running your SLAM with any kind of automated chlorine dosing system (eg, SWG) and other chemical equipment turned off. If you are near the end of a SLAM (or think you are), you should simply dose your pool water up to shock level when the sun has gone down and then leave the pool alone until morning and recheck. Nothing else should be adding or taking away the chlorine.
 

WaterTech1968

In The Industry
Sep 4, 2007
38
AOP systems are known to be most effective for in-door pools for dramatically reducing combined chlorine levels. This is main reason they are used by commercial installation, to assist with water to comply with regulations.
Installation normally looks like ->pump->filter->AOP-SWCG->outlet. Heaters are in parallel to AOP and SWCG to avoid affect on heater warranty :)
A powerful AOP system will improve clarity of the water and reduce possibility of chlorine resistant bacterial contamination. It's just a shame that many AOP systems sold to the market are poorly designed with low ozone output and low UV density, sometime creating bad name as they under deliver.
AOP in nutshell: Ozone injected in to the water, UV cause ozone to decompose to free radicals that is even less stable and oxidise organics rapidly. At the same time, UV decompose combined chlorine with help of ozone and free radicals at the same time.
 
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