Reverse Osmosis to remove CYA?

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T

TreeFiter

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In The Industry
Jul 2, 2012
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Saugerties, NY
I was browsing around on the internet, and I came across a thread where someone recommended using reverse osmosis to filter out calcium from pool water, and they warned that it would also remove CYA in the process. My knowledge on reverse osmosis is somewhat limited, so I'm hoping someone here might be able to confirm this.

I'm thinking that if this could work, it might be an option for treating some of the pools I run into that have accumulated CYA and still rely on tablets for chlorination.

Most of the RO systems I've seen are 5 stages. Do each of these stages remove different types of impurities? Would I be able to take one or two stages to remove Calcium and CYA?
 
It removes pretty much everything from the water. I don't know too much about the process specifics, but I do know it is not a selective thing. There is no "CYA removal stage". It runs around $500 to treat a single pool, which is why it is only available in the Southwest where water is at a premium. I doubt it would be a financially viable option in the Northeast.
 
Pool RO systems are fairly complex. They require pre-treatment stages to remove things which can damage the membrane, and they use extremely high pressure pumps. There are several groups nationwide who have figured it out, but they don't document exactly what they have done. As a result, setting up your own system is still quite complex.
 
Thank you all for your replies. I was thinking it might not be a bad idea if I could use a system similar to what they install in a house. You can pick up a low end system for about $150. I was hoping to be able to set it up on an auxiliary system and leave it for a week or so, but it sounds like it wouldn't be that easy.
 
I have seen waste numbers on RO as high as 5 to 1. Three, four, and five stage units all contain just one membrane. Additional stages just increase time between servicing. If my memory serves me correctly a three stage is particulate, carbon, membrane. Four stage is large micron particulate, small micron particulate, carbon, membrane. I think the five stage adds another absorption filter of some type. RO membranes can not handle chlorine so breakthrough of the aborbtion portion of the unit is also the end of membrane life.
 
An ro would remove CYA and if you went with CA membranes (cellulose acetate), they can handle the chlorine. The unit would be very cost prohibitive though. A small 50 GPM system (3 membrane first stage, 2 second, one third) would run in the $100-$150k range. The household units that are much cheaper only recover about 30% of the water you put in.

Also, a CA system will only return 50-60% of the water removed back into the pool (the rest would have to go to waste) and that is for a 3 stage system making a simple drain and refill MUCH more cost effective anyway. Even a PA membrane 3 stage system rejects about 25% and it will quickly be destroyed by chlorine.

Usually the more stages to a system, the better your recovery is. In a 3 stage system, the reject from the first stage of membranes passes into the next stage and you recover more clean water then the reject from that stage passes through the third stage.

That's also not taking into account the cost of the pre-filters needed ahead of the RO. RO membranes are designed to remove salt not debris. Any debris in the water (even down to dissolved flocculant or tannins) will destroy the membranes in a VERY short time.
 

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