Preserving RO Membrane with Silver Oxide

[dennisail]

Hello guys.

Since I have finished my pacific crossing and will mostly be doing weekend sailing, I can take my watermaker offline. I have some silver oxide which another cruiser gave me.

How exactly do I use this to preserve the membrane. I believe I just have to mix it up with RO water then flush it through the pressure side of the membrane at low pressure?

How long will it stay preserved for?

The packet of silver oxide says I need to mix 1 gram for 100L of water. I think this treatment just for adding to water tanks for purification. How much do I need to mix up to preserve a membrane and will an overdose hurt the membrane?

Thanks, Dennis.

[colemj]

If you plan to have the membrane preserved for more than 6-12 months and your membrane has had much use already, then just throw it out and buy a new one when you are ready to go off longer term again.

Mark

[daddle]

Originally Posted by colemj

If you plan to have the membrane preserved for more than 6-12 months and your membrane has had much use already, then just throw it out and buy a new one when you are ready to go off longer term again.

True. Membranes are just not that expensive anymore. I've read that even the constant flushing and cleaning might be a waste of time and running costs. I have certainly abused mine at times. Still works as poorly as it did new (it's not a great model).

[Minggat]

What you may have learned by the responses so far is that there are plenty of opinions to be had. If you don't have an answer, throw out an opinion which contains no answer.

Having been in the water treatment industry of 40 years now, and seeing RO in it's infancy, and now being out of touch apparently, I have never heard of silver oxide preservation. Obviously it is out there because you got some. I Googled it and got nothing. So I am very interested in the answer to your question.

Let's not let this die.

[dennisail]

As I said a cruiser gave it to me. Maybe the best part of this solution was the good will. I googled it and also got nothing. Hence asking here.

How would someone that has been in the industry for 40 years do it? What other chemical can I use? I would still buy a new membrane if I went off on a long term cruise. But I'm not going to throw it away without even trying to preserve it that seems like a huge waste.

My whole unit was off ebay new for $2300 and does 4gph and is 12V. It has had its share of issues (especially the HP pump) but due to pressure control issues the membrane has seen off the dial pressures (1400psi plus!) often and still does 300ppm.

[Jacko]

Hi Dennisail
the standard method is to use ( Metabisulfite ) This is available in and Woolies store in the home brew section they use it to clean the bottles.

I have an Echotech 50 ltr unit so I am going by their method. It sounds like you have the standard size membrane as I do so i will run through what I do at the end of the season.

Remove filters and purge out system with R/O water ( or you can use back flush if you have a carbon filter )
You should have a 3 way valve to let you then feed water via hose into you pressure pump to the membrane.
Attach a lengh of hose to this valve so that you can draw water from a 2ltr bucket.
Fill bucket with 2ltrs of unchlorinated water ( R/O water or carbon filtered)and add 100grams of metabisulfite powder and mix
Place hose end in the bucket and lift bucket above pressure pump and turn pump on make sure your pressure valve is totally free and your test valve is open
When all the water is drawn from the bucket shut down the pump and close the valves Your done

Hope this helps Cheers Jacko

[Minggat]

All good info. Metabisulfite, also known as sodium bisulfite can be found in Home Depot I am told. Used as tree root killer.

But I hate to give up on the silver oxide idea. Worthy of investigation. Don't pitch it just yet.

Just a note. The words "back flush" are like fingernails on a chalkboard when you are talking about RO. And usually people don't really mean back flush. That is a word that can only apply to filters. I cannot imagine it applying to a cartridge filter such as mentioned here.

An RO membrane is not a filter. Any reverse of flow would inflate the envelopes and cause irreparable damage.

Just trying to split a few hairs here.

[nhschneider]

The instructions that came with our Spectra Cape Horn watermaker say to either pickle it (of course, using their secret chemical which is expensive and no doubt toxic - not necessarily what you'd want associated with your drinking water) or to 'winterize' it using propylene glycol, which isn't toxic and can be purchased from RV supply stores as its often used to winterize the water storage systems (both fresh and waste) in motor homes, trailers, etc.

Recently, I had a medical procedure done (the embarrassing one) and had to drink a huge quantity of polyethylene glycol. I did a little research and found there is very little difference between polyethylene glycol and propylene glycol except that propylene glycol does have a much lower freezing temperature than polyethylene glycol. A friend of mind (PhD in chemistry) confirmed my assumption that for watermaker storage, either could be used.

All that said, it might be more economical to just forget preserving the membranes and buy new ones when you want to go cruising again

Fair winds and calm seas.

[noelex 77]

Like others I have never heard of silver oxide.
I don't see any need to use anything but the standard chemicals.

A word of warning. The standard chemical (metabisulfide ?)is used in the food industry and I thought it was pretty harmless, but I spilt some on my skin many years ago when pickling an previous watermaker and it produced quite a bad skin reaction, particularly where there was a few cuts on my hands.

I now have a Spectra watermaker and their compound is different. I have only pickled it once otherwise its been running every second day for the last 3 years.
I didn't get any skin reaction, but took more precautions.

[dennisail]

Thanks guys! I used to make home brew beer. I remember using a white powder that seemed pretty potent with fumes. I guess this is the metabisulphide?

[phorvati]

I started using PG-100 polypropylene glycol (RV Antifreeze), instead of sodium metabisulfide. Back when I used metabisulfide, it would take awhile(few batches) for water production to go up to what it was before storage period. But with PG-100 the last two winters, I am back to 100% production on the first batch after storage. Also with PG-100, there is no mixing necessary, just run few gallons through, and you're done.

[BuckeyeFieldSup]

Membrane manufacturer's typically recommend sodium metabisulphide. And yes it gives off some potent fumes when mixed with water.

Russ

[BuckeyeFieldSup]

Originally Posted by Minggat

Just a note. The words "back flush" are like fingernails on a chalkboard when you are talking about RO. And usually people don't really mean back flush. That is a word that can only apply to filters. I cannot imagine it applying to a cartridge filter such as mentioned here.

An RO membrane is not a filter. Any reverse of flow would inflate the envelopes and cause irreparable damage.

Amen brother. There's no "back" about it. Flushing an RO membrane typically just requires high rates of flow trhough the element w/ the restriction on the concentrate line removed/opened.

Russ

[Tellie]

Just a note. Be careful with using anything other than the factory recommended pickling solution. If you use standard sodium MB on your Spectra system please, please, call me. I'd love to sell you a new Clark pump at $3,600. But seriously, the best advice is phorvati's. PG-100 is the way to go. It will not only store your membranes longer than any of the powdered mixes, it will help lubricate vital internal components and help seals, O-rings, valves etc. to remain in good state. Remember the large percentage of powdered storage solution is either product water or distilled water. This water can be corrosive over a period of time. SodiumMB will pickle your membrane but does have slight degrading effects on the membrane each time it's used. In an Oxygen deprived environment like is found inside a pickled watermaker that sits for months on end nasty things can happen. Like your pre-filters, the pickling solution is not an area to all of a sudden go cheap on for a few supposed dollars savings. Every season I get the same calls two days before they want to go to the Bahamas from people that bought a 10K watermaker that they figured they'd save a $10-$30 on by buying cheap pre-filters and using some other storage solution other than what the manufacturer recommends. Save the cheap SodiumMB for making the beer and wine and when it's finished and ready for consumption Call Tellie up, invite him over for a six pack or two and chances are good he'll bring you the right storage solution for your watermaker, even trade.

[Matt Johnson]

Originally Posted by Tellie

Just a note. Be careful with using anything other than the factory recommended pickling solution. If you use standard sodium MB on your Spectra system please, please, call me. I'd love to sell you a new Clark pump at $3,600. But seriously, the best advice is phorvati's. PG-100 is the way to go. It will not only store your membranes longer than any of the powdered mixes, it will help lubricate vital internal components and help seals, O-rings, valves etc. to remain in good state. Remember the large percentage of powdered storage solution is either product water or distilled water. This water can be corrosive over a period of time. SodiumMB will pickle your membrane but does have slight degrading effects on the membrane each time it's used. In an Oxygen deprived environment like is found inside a pickled watermaker that sits for months on end nasty things can happen. Like your pre-filters, the pickling solution is not an area to all of a sudden go cheap on for a few supposed dollars savings. Every season I get the same calls two days before they want to go to the Bahamas from people that bought a 10K watermaker that they figured they'd save a $10-$30 on by buying cheap pre-filters and using some other storage solution other than what the manufacturer recommends. Save the cheap SodiumMB for making the beer and wine and when it's finished and ready for consumption Call Tellie up, invite him over for a six pack or two and chances are good he'll bring you the right storage solution for your watermaker, even trade.

I don't see it written often enough... Tellie, your help is much appreciated on this website. If it wasn't for your postings, I don't know how much I would have spent on watermaker mistakes.

Thanks for your time,

Matt