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Subject: Water purification systems

Water purification systems

From: Phil Geis <geis.pa<-at->
Date: Friday, February 27, 2009
Melissa Potter <melissa_potter [at] ago__net> writes

>...
>A reverse osmosis system with 5 micron pre sediment and carbon
>filters plus a storage tank of 120 gallons has been recommended.  I
>am concerned about the possibility for bacterial growth in the
>storage tank, even with flushing the system once a week.

There is no "possibility" in the system you describe--it is reality
(but I do hope the carbon filter is upstream from RO).  With carbon
filter, a static system and the (plastic?) storage tank--flushing
once a week is a hand wave at the bugs--biofilm will develop.

I guess the question is--how bad does it need to get before it
compromises your application.  Some industries, like the
semiconductor folks, can't stand even the slightest level of bugs in
their water. Well-maintained Millipore systems Robert mentioned are
pretty good (e.g. Milli-Q) is they can give you the volume you need.

For perspective, all tap water include low levels of bacteria
(especially pseudomonads)--the low level part being the product of
the little bit of hypochlorite left from municipal treatment. Carbon
filters typically are used to remove chlorine and end up as bug
reservoirs--providing both a physical and nutritive (via absorbed
organics) structure for microbial growth--that sloughs off as chunks
of biofilm that, in your case, will limit the life of RO membranes.

Bacteria grow in purified water to millions of cfu/ml so your
storage tank is really an incubation vessel--flushing once a week is
more gesture than substance.  Industries that must have bug free
water use constant control measures such as heat and ozone.  Some
use UV and filtration with high turbulence circulation.  Stainless
is the material of choice--and PVC is anathema to purified water
microbiologists.


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                  Conservation DistList Instance 22:49
                   Distributed: Sunday, March 1, 2009
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Received on Friday, 27 February, 2009

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