Re: [Amel Yacht Owners] Re: Watermaker and transmission fluid

Craig Briggs

Thanks for the explanation - makes sense. Given the membrane is fouled, I would guess the danger may be that, even though you might be able to run the system and produce fresh water, that will be contaminated no matter how long you run it.  Sound right? Wonder if fresh pickling would destroy the old fouling. (Or maybe just bite the bullet and buy new membranes to stay on the safe side.)
Craig SN68

---In amelyachtowners@..., <greatketch@...> wrote :

If the membrane is pickled with sodium metabisufite (also called sodium pyrosufite) the issue with long term storage (beyond about 1 year) is not damage to the membranes from the pickling solution, but rather that the pickling solution losses its biostatic properties and the membranes foul from biological growth.  

When dissolved in water sodium metabisufite gradually hydrolyses to release sulfur dioxide leaving a solution of sodium sulfite. Sulfur dioxide is a strong reducing agent, and a very effective microbiocide.  Once all of the sodium metabisulfite hydrolyses, and the resulting sulfur dioxide reacts and dissipates, there is nothing left to protect the membranes from biological growth.  The usual recommendation is that the membranes should be re-pickled after a year to keep them safe.  I would guess that timeframe is actually highly variable depending on initial water quality, pH, bioburden, temperature, and other variables.

This is the same reason that membranes sold "wet" have a relatively short shelf life.  It is not the membranes that "go bad" rather it is the pickling solution.

Bill Kinney
SM160, Harmonie
Annapolis, MD, USA

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