Water passing through SWG reaches breakpoint chlorination?

[Olga]

I read an article that mentioned that as water passes through the SWG it reaches breakpoint chlorination and gets rid of chloramines. Then someone commented saying that was a ridiculous statement. Intuitively the notion that breakpoint is reached in the SWG makes sense to me, since at the point of chlorine generation (in the SWG) the chlorine concentration would be incredibly high, thus at breakpoint. I've also noticed that my pool has never needed shock; combined chlorine has not been a problem.

Google searches have produced no scientific articles that prove or disprove or even discuss this idea. I've found no sales pitches touting it as a benefit either, aside from the one mentioned above.

Anyone have a link or thoughts?

 

[domct203]

I really can't comment on the chemistry happening inside a SWG cell, but I will add that I have a manually chlorinated (12.5% bleach) pool, and following TFP guidelines my CC's have been pretty much 0.0ppm for three seasons.

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Do you have a link to the article you read discussing this?

 

[Jezza]

I would also add that stuff gets into the pool that is oxidized to create CC's long after the SWG has created the chlorine.

 

[JoyfulNoise]

First off, let's stay away from the concept of breakpoint chlorination as it is a term used (or should I say, abused) by the industry and it has lots of misunderstanding associated with it. See these posts to understand the fallacies surrounding breakpoint chlorination -

Certified Pool Operator (CPO) training -- What is not taught

Is the formula for too high?

To the idea that an SWG "superchlorinates" the water passing through it, you don't need much science, you just need to look at the numbers. Assume that an SWG is running at the slowest speed possible to generate chlorine which, for most models, is about 15GPM. AT that speed, one would expect the highest level of chlorination possible. For our purposes, let's use an IntelliChlor IC-40 cell -

1.4lbs/day * (16 oz /lb) / (24 hr/day) = 0.933 oz/hr

15 gal/min * 60 min/hr = 900 gal/hr

(0.9333 oz/hr) / (900 gal/hr) = 0.00103 oz/gal of chlorine gas

In terms of FC, the water inside the cell is seeing roughly 7.8ppm FC. If one has 70ppm CYA in the water (which is the lowest recommended level for an SWG), then the FC/CYA ratio is about 10%. That's hardly "superchlorination". Increasing the flow rate of the water through the cell (most pools operate at 40GPM or more) only dilutes the chlorine further.

As others have stated, a manually dosed pool that is clean and clear will also have very low CCs. CCs are the by-product of chlorine reacting with bather waste (although not all forms of bather waste produce chemicals that register as CCs) and they usually only high in outdoor pools that are improperly cared for.

 

[Jimrahbe]

Olga,

One of the benefits to using the TFP method, whether using a SWCG, or dosing with Liquid Chlorine, is that you never have to add "Shock" to your pool on a weekly basis.

Thanks for posting,

Jim R.

 

[Olga]

Thank you for the comments and explanations. The calculation about expected levels in the cell was very helpful.