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Subject: Re: TWL: RE: reverse osmosis and salt
From: Wesley Eldred (weldred@XXX.XXX)
Date: Wed May 01 2002 - 15:10:24 EDT
Mel:
There is another issue involved. From an army manual:
9-2. Remineralization and aeration. Pure water is
a relatively reactive chemical. When air is dissolved in
extremely pure water, the resulting solution is extremely
corrosive. Water without dissolved air tastes flat and
objectionable. Water that contains very little hardness
appears to be unhealthy for drinking purposes.
Therefore, the designer of a desalination system must
consider some posttreatment options, such as
remineralization and aeration, in order to produce a
healthful, noncorrosive, pleasant-tasting water.
Wesley
Wesley Eldred wrote:
>
> Mel:
>
> The following, from the description of a household reverse osmosis
> system, may clarify the issue:
>
> "Water molecules penetrate the thin layer of the reverse osmosis
> membrane and diffuse through it
> molecule by molecule. Dissolved salt ions would also diffuse through
> this layer, except that the
> solubility of the salt ions in the membrane is much less than that of
> the water. Thus, the water
> moves through more rapidly with the result that a separation occurs. The
> driving force is furnished
> by both the pressure and the concentration differentials across the thin
> layer.For water, the
> pressure effect is the most important. Therefore, increases in pressure
> increase the water flux
> without a corresponding increase in salt flux."
>
> It would appear that some salt does pass and how much depends on system
> pressure.
>
> Wesley
> weldred@XXX.XXX
>
> "hknott4@XXX.XXX" wrote:
>
> >
> > ..REVERSE OSMOSIS watermakers (not evaporative ones, which aren't so bad)
> > remove enough salt for the water to be palatable, but it's not all the
> > salt. The resulting water is much more conductive at the voltages found
> > in the water heater...
> >
> > Very interesting, Keith. Although I don't have a watermaker, I was under the impression that they produced water that was close in chemistry to deionized water... that in a properly functioning one, the membrane allowed the passage of the water molecules, but not the salt molecules, period. That there was no "in between" or "only removes some of the salt."
> >
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