Is RO Water oxygen free??

[PaulHilgeman]

????? Thanks in advance.

 

[Diver165]

????? Thanks in advance.

I assume you're talking about reverse osmosis water. I had a friend who used to install high end aquariums and she used it. It's also used in wine making quite a bit.

So i wouldnt think it's oxygen free.

 

[JimTheHick]

No. RO only removes salts/impurities, not dissolved gas.

 

[PaulHilgeman]

Thanks guys.

 

[GilaMinumBeer]

????? Thanks in advance.

If RO were Oxygen free you'd have Hydrogen.

I don't think WalMart has the license for that.

Yet.

 

[PaulHilgeman]

I meant dissolved oxygen.

 

[TyTanium]

Haha, good one.

 

[Special Hops]

No

 

[ajdelange]

Yes, but not completely and it's going to depend on a few things. RO membranes apparently have some rejection capabilities against oxygen but the rejection is not that great e.g. about 75% in the case of my system. Thus if the water arriving from my well is at about 4 mg/L DO (which it is) the water out of my RO system is at about 1 mg/L. If your source water has more DO than mine so will your RO water and conversely if your source has less.

 

[samc]

When it is poured or shoots out of the faucet I assume it is getting additional aeration, therefore more Oxygen is added at that point. Un-scientific but probably accurate.

 

[bstacy1974]

Yes, but not completely and it's going to depend on a few things. RO membranes apparently have some rejection capabilities against oxygen but the rejection is not that great e.g. about 75% in the case of my system. Thus if the water arriving from my well is at about 4 mg/L DO (which it is) the water out of my RO system is at about 1 mg/L. If your source water has more DO than mine so will your RO water and conversely if your source has less.

There's a pressure drop across the membrane, which makes some dissolved gases volatilize to atmosphere. I've found that if you let RO water sit in an open container, it will reabsorb some O2 and CO2 from atmosphere.

 

[ajdelange]

Yes, I forgot to enlarge on some of the other "few things" it would depend on. One is definitely oxygen pickup after the RO processing. When I measured the DO out of the system the permeate tubing was placed in the bottom of a glass which was allowed to overflow as the RO unit ran with the meter probe shoved down into the bottom of the glass close to the end of the permeate tube. IOW, no opportunity for O2 takeup. Similarly, when I measured the well the aerator was removed from the faucet and water was flowing into a glass with the tip of the faucet beneath the water.

In normal operation the water from the RO unit flows into an atmospheric tank where it sits plenty long enough to come to equilibrium with the atmosphere and thus would contain about 8 mg/L. Before use it is pumped into a pressure tank where it can also sit for a long time at a pressure of 3 - 5 atmospheres (absolute) and thus could, if there is air in the pressure tank (outside the bladder) contain 24 - 40 mg/L O2.

Thus one has to be a little thoughtful in deciding that the water is low enough in DO for any particular purpose. Don't know what OP's intent is but if it is to use RO water to dilute beer I'd say even the straight-from-the-membrane was water not sufficiently free of DO.

 

[BeerBrent]

Yes, but not completely and it's going to depend on a few things. RO membranes apparently have some rejection capabilities against oxygen but the rejection is not that great e.g. about 75% in the case of my system. Thus if the water arriving from my well is at about 4 mg/L DO (which it is) the water out of my RO system is at about 1 mg/L. If your source water has more DO than mine so will your RO water and conversely if your source has less.

this.

 

[ajdelange]

There's a pressure drop across the membrane, which makes some dissolved gases volatilize to atmosphere. I've found that if you let RO water sit in an open container, it will reabsorb some O2 and CO2 from atmosphere.

Don't think I follow this. Although there are an infinite number of combinations of the way things can be let's stick with my particular situation as an example. The water comes from a well in which, apparently, it sits for a short enough period of time or there is enough of a CO2 blanket such that its O2 content is half what would be expected if it were in contact with the atomosphere. It is pumped to a pressure tank where it sits at about 4 atm. pressure until a faucet is opened. The pressure tank has a bladder and has been in service long enough that any oxygen in the water space (i.e. not in the bladder) has long since been dissolved so it is not picking up any more oxygen in that tank even though at 4 atm. If going to a typical Home Depot type RO unit it will be presented to 1 side of a membrane and the outlet of that chanell will be opened to the atmosphere through an orifice such that there is a pressure drop relative to the inlet but not so much as to cause the concentrate to flow out at gallons per minute. Until the concentrate flows out through that orifice it is protected from the atmosphere. The permeate side is, in this kind of system, usually connected to a pressure tank and while at initial start up the pressure in that tank may be atmospheric, water will continue to flow until the pressure in the tank plus the osmotic pressure (which for most water supplies is going to be 1 or 2 psi). Only when that water is drawn will it be exposed to atmospheric pressure. And you cannot be thinking that the O2 comes through the membrane and then escapes to the air when the water is drawn because in that case the water would be at atmospheric saturation when it is, in fact, much lower. It's pretty clear from my simple experiment that O2 removed from the feed goes out in the concentrate stream just as does any other contaminant.

 

[bstacy1974]

Don't think I follow this. Although there are an infinite number of combinations of the way things can be let's stick with my particular situation as an example. The water comes from a well in which, apparently, it sits for a short enough period of time or there is enough of a CO2 blanket such that its O2 content is half what would be expected if it were in contact with the atomosphere. It is pumped to a pressure tank where it sits at about 4 atm. pressure until a faucet is opened. The pressure tank has a bladder and has been in service long enough that any oxygen in the water space (i.e. not in the bladder) has long since been dissolved so it is not picking up any more oxygen in that tank even though at 4 atm. If going to a typical Home Depot type RO unit it will be presented to 1 side of a membrane and the outlet of that chanell will be opened to the atmosphere through an orifice such that there is a pressure drop relative to the inlet but not so much as to cause the concentrate to flow out at gallons per minute. Until the concentrate flows out through that orifice it is protected from the atmosphere. The permeate side is, in this kind of system, usually connected to a pressure tank and while at initial start up the pressure in that tank may be atmospheric, water will continue to flow until the pressure in the tank plus the osmotic pressure (which for most water supplies is going to be 1 or 2 psi). Only when that water is drawn will it be exposed to atmospheric pressure. And you cannot be thinking that the O2 comes through the membrane and then escapes to the air when the water is drawn because in that case the water would be at atmospheric saturation when it is, in fact, much lower. It's pretty clear from my simple experiment that O2 removed from the feed goes out in the concentrate stream just as does any other contaminant.

Man? You must be an engineer? The pressure drop is when the water moves across the membrane, leaving the gases on the reject side, venting, eventually, to atmosphere. As far as my second statement, if I take a glass of RO water and leaving on the counter, it will reabsorb stuff. I was simply backing up what you were saying about your well water being 4mg/L, etc., etc.

 

[ajdelange]

You must be an engineer?

I was going to respond affirmatively in the past tense but I guess it's a congenital disease that one never recovers from.

The pressure drop is when the water moves across the membrane, leaving the gases on the reject side, venting, eventually, to atmosphere.

OK. But looking at my system which again is not representative of all systems but certainly not unusual either: I have recovery set up so that 2 liters of concentrate go down the drain for each liter of permeate. So 3 liters in feed, containing 3*4 = 12 mg O2 enter the system. One mg goes out in the liter of permeate and 11 go out in the 2 liters of concentrate for 5.5 mg/L. So while the concentrate is concentrated in O2 the level is still below saturation and it would actually take up O2 from the air.

Now if I adjusted the recovery to 50% (1 liter of concentrate per liter of permeate) the concentrate would contain 7 mg/L O2 which is still below saturation but I think it's pretty clear that a higher level of O2 in the feed and a higher recovery rate could establish conditions at which the concentrate exceeded 8 mg/L and there would be venting.

As far as my second statement, if I take a glass of RO water and leaving on the counter, it will reabsorb stuff.

No doubt about it and pretty quickly too.