CYA reduction with Sodium Hypochlorite

[Pb2Au]

Here is a patent from 1978 showing how to reduce CYA in water using sodium hypochlorite.

US Patent 4,075,094 - Sodium Hypochlorite Treatment fro Removal of Cyanurate Compounds from Aqueouss Waste Streams, Ronald H. Carlson, FMC Corp., Feb 21, 1978.

On a weight basis, this reaction requires a ratio of 259.5 parts by weight of sodium hypochlorite to 100 parts by weight of cyanuric acid. At least 90 percent of the cyanuric acid nitrogen is oxidized to nitrogen gas, the balance being oxidized mostly to nitrates. The reaction of sodium hypochlorite with cyanuric acid proceeds most rapidly at pH 9.0 to 10 and increases in rate 2-3 times for every 10.degree. increase in temperature. The effect of the initial concentration of cyanuric acid and sodium hypochlorite on the reaction rate will be discussed below. The residence time for destruction of 95 percent of the cyanuric acid present in the waste stream can range from more than 200 hours to less than 5 minutes depending upon the reaction conditions.

 

[Melt In The Sun]

Interesting, but I'm not sure how applicable it is to pools. So, if you had 100 ppm CYA, you'd have to bring the FC to 259.5 (!) and your pH up to 9-10 (!) and crank up the heat. Sounds to me like a recipe for massive limescale formation!

 

[duraleigh]

Yeah, unless I am missing something, it appears entirely inapplicable to pool conditions.

If I owned that patent and had ten bucks, I would be worth ten bucks, I think!

 

[chem geek]

This topic was already discussed in the Degradation of Cyanuric Acid thread under the sub-topic "CYA Degradation by Oxidation from Chlorine" and in a later post in that same thread. As Dave notes, it's simply not practical given the very high FC and pH levels that are required to make the reaction go reasonably quickly.

Since there are calcium hardness reducers such as HotSpring® Vanishing Act™ in a bag, I don't know why no one does something similar using melamine. Perhaps it's harder to keep melamine attached to some surface to keep it in the bag. The calcium remover may be essentially ion exchange resin or might be something that precipitates calcium such as phosphate or oxalate (though I'm not sure how they keep those from coming out of the bag).

 

[Pb2Au]

Yes, I thought chlorine level and pH and perhaps temp were too high to make it practical. However, the residence time of 5 minutes under certain conditions intrigued me. If you could optimize the process, super-scale conditions would only exist for 5 minutes and CYA would be gone.

Melamine (the reagent used in the CYA turbidity test) was sold as a CYA reducer in the 1980s by Applied Bio Chem. It was called Melatrine. You added the powder to the pool and it created a whole pool of precipitate just like when you make the CYA reagent test. As I understand it, the precipitate was so small that most sand filters would not remove it. Then you waited for settling and vacuumed to waste and used a clarifier for the remainder. Water loss further reduced the CYA level. If the pool had a DE or cartridge filter it would work. But it required cleaning the cartridges multiple times due to the large amount of precipitate. It didn't sell much and was such a pain no one bought it.

You could use melamine in a bag but you might have the same problem with small size precipitate. I think however that 1 lb of CYA requires about 1 lb of melamine. I think the molecular weights are similar. So each 12 ppm of CYA in 10,000 gallons needs 1 lb of melamine and produces 2 lbs of precipitate.

I have heard of specific wave length UV light reducing CYA.I don't know what nm wavelength destroys CYA. And I have also heard that ultrasound might work. No other info.

 

[brg88tx]

this would be a good experiment for someone to try who had high cya problem. take an initial cya test, then (at the hottest time of the year) pour in many, many bottles of bleach and super duper shock the pool and then take additional cya tests every 24 hours to see if it had any effect. it might not completely eliminate it, but if it took cya down from 150 to 50 then it might be worth it as opposed to water replacement.

 

[chem geek]

I received the following PM from a new user RShurie and am posting it and my response here so that everyone can share in the info:

I was wondering, not being a chemist, is there a way one could reduce the CYA using the method described here by incorporating some sort of Hydrogen Peroxide generator before the filtration system? The quotation below was taken from the "Scientific Paper" you mention there. . .

"Yet another method for removing dissolved chlorinated cyanurate compounds from aqueous waste streams is described in U.S. Pat. No. 3,878,208. That patent discloses a method of dechlorinating the waste stream by treatment with hydrogen peroxide. It is an advantage of this process that the cyanuric acid (or its sodium salt) precipitates from the waste stream and may be recycled back to the chlorination zone. Approximately 65 to 98% of the cyanurate compounds dissolved in the waste streams are recovered in this manner. However the waste stream, after the solid cyanurate values have been precipitated, retains in solution a low level of organic matter -- of the order of 200 to 3,000 ppm."

BTW, your posts are extremely insightful and valuable to the community; thank you for taking time to participate.

Ron

Welcome to TFP!

Patent 3,878,208 refers to mainly adjusting pH so that at low pH cyanuric acid is precipitated while at high pH sodium cyanurate is precipitated. The problem is 1) that extreme pH must be used and 2) the degree of precipitation is limited and while fine for removing bulk quantities when starting at high concentrations, it doesn't work well when we are dealing with trying to reduce 200 ppm to 50 ppm.

The patent uses hydrogen peroxide to dechlorinate so that only CYA is left. As you know, you can do that in a pool (i.e. have zero FC) and still have a lot of CYA left in the pool. The solubility of CYA at pool pH is quite high. In distilled water it has solubility to 2700 ppm and would be even higher at pool pH, probably closer to 10,000 ppm. One has to substantially lower the pH to precipitate the CYA or to substantially raise it to precipitate sodium cyanurate. This is impractical for pools.

 

[JohnN]

That melamine theory is interesting. I would be willing to try it before this winter (I will be replacing the liner next year, so I am not worried about ruining anything.) The problem is, I don't know where to find any melamine.

 

[chem geek]

There used to be CYA reducing products on the market that used melamine, but they generally produced a precipitated cloudy mess in the pool. The problem is that the pool is then saturated with CYA and melamine so if the CYA level goes up, it becomes cloudy again unless you have outstanding circulation and filtration.

 

[JohnN]

Ok, so melamine isn't a great idea. I guess if it worked without causing more problems, it would still be on the market.

 

[JohnT]

Ok, so melamine isn't a great idea. I guess if it worked without causing more problems, it would still be on the market.

IIRC, it was fairly expensive, so it was only an option when water replacement was difficult or expensive.

If one could confine such conditions to a small tank where pool water was slowly pumped through and precipitates could settle out (such as the Liquidator tank) a useful system might be feasible.

 

[RShurie]

Thanks guys!