BoatBanter.com - View Single Post

Mark Borgerson

In article s.com,
llid says...
"Mark Borgerson" wrote in message
g...
RO filters DO NOT pass dissolved metals. If they did they would be of
little use in generating fresh water from sea water.

Unless you use a laboratory-quality still, RO water will be as pure
as distilled water if the filter is operated properly.

Mark Borgerson

WRONG! Even the best membranes may pass up to 5% of heavy metal ions.

I agree. I overstated the efficiency of RO filters. The efficiency
of RO filters depends a lot on the type of filter, the ionization state
of the metals and the feed pressure.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFX-46WM6V7-1R&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&vie w=c&_acct=C000050221&_version=1&_urlVersion=0&_use rid=10&md5=aabc45cb84f81de69db133da6e5cf12c

To quote from this abstract:

"An experimental investigation was conducted to study the performance
of an aromatic polyamide (ES 20) ultra-low-pressure reverse osmosis
membrane (ULPROM) for separating divalent (Cu2+, Ni2+) and hexavalent
(Cr6+) heavy metals from bulk solution. The influence of operating
pressure, feed concentration, pH, and effect of other ions (Ca2+ and Mg2
+) on the ULPROM performance was studied. The investigation was
conducted for synthetic wastewater and wastewater from the heavy metal
industry. Experimental results show that the rejection increases with
increasing feed pressure, it is dependent on feed pH and is higher at
higher pH. Increasing concentration of other ions slightly decreased the
rejection of heavy metals. Generally, rejection of heavy metal is found
to be greater than 95% for the ULPROM tested, which suggests the
suitability of such membranes for industrial application for recovery of
heavy metal and reclaiming wastewater."

These ultra-low pressure filters are not the same as those used to
purify drinking water and the reference isn't talking about
making drinking water.

If you are purifying seawater for drinking, heavy metals are not
generally a problem, since they are generally in the parts per
million range or less in seawater.

This is far more than proper distilled water using heat and condensation.

Neither RO filters nor distillation are particularly effective in
removing metal ions if you then use metal pipes or containers for the
reulting water.

To get lab quality water generally requires double distillation
and deionization.

For drinking water made from seawater, RO filters may result in
a few parts per thousand of sodium and chlorine and a few hundred
parts per billion of heavier metals. This is probably comparable
to still that you will find on a boat---but the RO filter will
be a lot more energy efficient.

Mark Borgerson