R/O Brine Discharge Content ?

[Pelagic]

Does anyone know approximately what the chemical and specific gravity makeup of the Brine Discharge from a typical R/O water maker would be?

I have a client who wants to have a therapeutic salt water tub on his large yacht, so I am looking at a simple way to increase the salt and mineral content by plumbing the brine discharge into the tub.

Have not found any data on what is in this R/O byproduct?

[GordMay]

I think this is a very bad idea.
Just smell a typical R/O reject brine.
R/O membrane reject brine is roughly twice as saline (& more dense) as the feed water supply.
Virtually all of the “impurities” in the feedstock will have been concentrated in the reject.
Why not use a conventional pool/spa salt water chlorinator?

[Pelagic]

Good point Gord but they just finished a trip to the Dead Sea (which inspired this request) and I remember the smell inside the enclosed swimming pools as being pretty bad.

Will do a test but also study a salt water chlorinator… thanks

[Jim Cate]

Originally Posted by GordMay

I think this is a very bad idea.
Just smell a typical R/O reject brine.
R/O membrane reject brine is roughly twice as saline (& more dense) as the feed water supply.
Virtually all of the “impurities” in the feedstock will have been concentrated in the reject.
Why not use a conventional pool/spa salt water chlorinator?

G'Day Gord,

Are you sure about the doubling of the salinity? From a vague memory, I thought that a typical RO unit recovered about one tenth of the fresh water from the volume pumped through it. That is, one had to pump 10 gallons of sea water through the unit to get one gallon of fresh. If that memory is correct (and I know I could be wrong), then the salinity would not be anywhere near doubled. And I suspect that the increase in the concentration of the "impurities" may be just what these folks want... except that one would be concentrating the bacterial content as well as the inorganic stuff.
Seems a strange thing to do, but what do I know?


So in general I think that I agree that it isn't a great idea!

Cheers,

Jim

[Pelagic]

Thanks Jim

In many 3rd world countries the locals believe that bathing in sea water is therapeutic.

The Dead Sea has a whole industry based on that, so the idea of an increased sea water tub is not that farfetched.

Therapeutic Uses of Sea Salt | eHow.com

[Minggat]

Originally Posted by Jim Cate

G'Day Gord,

Are you sure about the doubling of the salinity? From a vague memory, I thought that a typical RO unit recovered about one tenth of the fresh water from the volume pumped through it. That is, one had to pump 10 gallons of sea water through the unit to get one gallon of fresh.

35 years of water treatment here. But i'm going to shoot from the hip just the same. Gord is right. Typical recovery is 40-50 %.

Saw a great idea out of Orange County when I was there last. Welcome to TugTub a portable, inflatable and lightweight hot tub that floats in water!

I'm thinking I might just like to try swamping the dink with the hot water for a cheaper version of this.

I've been to the Dead Sea. Eeeewwwww. Better to just make a return visit than drag one around with you.

[Jim Cate]

Originally Posted by Minggat

35 years of water treatment here. But i'm going to shoot from the hip just the same. Gord is right. Typical recovery is 40-50 %.

Saw a great idea out of Orange County when I was there last. Welcome to TugTub a portable, inflatable and lightweight hot tub that floats in water!

I'm thinking I might just like to try swamping the dink with the hot water for a cheaper version of this.

I've been to the Dead Sea. Eeeewwwww. Better to just make a return visit than drag one around with you.

OK Mingat, I bow to knowledge over deceptive memories. Thanks for setting me straght.

Cheers,

Jim

[Tellie]

Originally Posted by Jim Cate

OK Mingat, I bow to knowledge over deceptive memories. Thanks for setting me straght.

Cheers,

Jim

Actually Jim, unless I'm missing the math approach Minggat is using, typical boat type watermakers are roughly a ten to one ratio. Usual brine discharge will be nine gallons to one gallon of product water made. Commercial RO systems use multiple membranes thus gaining multiple passes of the same concentrate over many membranes before being discharged.
One could reverse a boat watermaker system and dump the product water overboard. Then retain and re-cycle the brine discharge in the tub passing it again through the watermaker several times to achieve higher concentrations of salinity.
A simple solution might be to carry a five gallon bucket of sea salt on board and throw a few scoops in the tub when needed.

[VirtualVagabond]

Originally Posted by GordMay

Why not use a conventional pool/spa salt water chlorinator?

Chemistry was my weakest subject, but I have had a few saltwater chlorinator swimming pools over the years. Is there some way to reverse the process I don't know about?
OP is looking for more salt, not chlorine.
I used to throw bags of salt in, so the chlorinator could make chlorine... not the other way around.... Don't tell me I'm flunking chemistry again, 45 years later

[Minggat]

[QUOTE=Tellie;480060]Actually Jim, unless I'm missing the math approach Minggat is using, typical boat type watermakers are roughly a ten to one ratio. Usual brine discharge will be nine gallons to one gallon of product water made. Commercial RO systems use multiple membranes thus gaining multiple passes of the same concentrate over many membranes before being discharged.
One could reverse a boat watermaker system and dump the product water overboard. Then retain and re-cycle the brine discharge in the tub passing it again through the watermaker several times to achieve higher concentrations of salinity.
QUOTE]

OK, I gave a sloppy response.
99% reject pertains to the salts. So what is rejected by the membrane (concentrate) then is going to leave the pressure vessel in the brine flow. While the recovery in small pleasure craft units may be less than 40%, 10% sounds way low. But, for purposes of this conversation, using the brine to make a seawater spa is not so wonderful.

I don't think Tellie was trying to say reverse the RO, but rather where the different streams are going. Thus capturing the brine. I would NOT recycle the brine though.

As far as multipal membranes to get multipal passes goes,.. well, sort of. Multipal membranes in a single pressure vessel (typically 40 ft long with 6 membranes inside). I think it would be more accurate to say that the feed becomes more saline after passing thru each membrane, but it would not be ready to be called concentrate just yet because it is diluted with the feedwater. But I don't want to debate word choices.

SWRO designs just don't not bother with multipal passes systems anymore. Seawater is too plentiful for that. There are lots of non seawater applications where the actual recovery rate is 98 + % of the feedwater flow. They will take the reject of a first stage and feed it directly to the second stage.

Bottom line. Don't bother using RO brine stream to fill the spa.