Homemade RO watermaker

Discussion in 'Boat Design' started by Bod, May 23, 2019.

  1. Bod
    Joined: Aug 2012
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    Location: Leicester

    Bod Junior Member

    Hi
    I have recently blundered into trying trying to desalinate seawater with an RO unit. Didn't realise domestic RO is different to marine so it got blocked very quickly!

    Is is feasible to make a DIY watermaker as they cost so much to buy. I like the idea of making my own so I'm better placed to repair it underway. Even the posh new ones seem unreliable anyway.

    There is a link on a thred in this forum but it's dead so a new thread seems a good idea. It stated 800psi was needed and the pump needed non corrosive parts.

    Anyone here made their own or know of anyone?
    Ta
     
  2. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

  3. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    The parts are all made in China, anyone can assemble them but these guys do a good job of putting the kit together.
     
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  4. Sean Duval
    Joined: Mar 2019
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    Location: yuma az

    Sean Duval Junior Member

    This is one area where I can confidently be of help.

    RO is part of my work experience in that I am a water and waste water operator...fully graded out and able to operate any potable treatment or distribution system, and any waste treatment or collection system in the state.

    Ro...
    The biggest issue in desalination is that the dissolved solids (we will call them salts from here on) can only be concentrated so much before they start to create crystals in the RO membrane. Temperature affects this as solubility is often temperature sensitive. Sometimes proportionally and sometimes inversely proportionally (carbonates for example)
    The way to deal with this is to figure out which salts will begin to precipitate 1st....you do that by calculating out a langalier saturation index....this will allow you to determine the optimum recovery of desalinated water by percentage. As long as you stay below this recovery number your good to go. For freshwater RO systems that is usually between 70 and 85 percent as product the remainder as waste stream... salt water is if I recall correctly 3% salt to begin with.....
    Or 30000ppm salt...fresh water is usually 500 to 2000ppm salt. Big difference. But also different chemistry to some degree.

    If you recover too much water and crystals form in the waste stream of the membrane they will get caught up and accumulate eventually blocking, perforating, or otherwise damaging it.

    Other issues, you need to calculate your osmotic pressure and then make sure your pump can reach that pressure plus what's needed to reverse the osmosis process. You will also need to provide clear water to the pump and membrane so that it doesn't get plugged up with sediments and detritus.

    You can clean the membranes as well....
    Dawn unscented dish soap is an industry standard for detergent when it comes to cleaning...
    Citric acid is used to dissolve mineral type deposits...as that is a low ph job.
    Caustic is used to dissolve organics....believe me you would be shocked at what grows in water filters.

    Do not use bleach or chlorine it generally destroys the membranes.

    Feel free to ask questions that are more specific and I'll try to answer them as I can...my lunch break is over so back to work.
     
  5. Angélique
    Joined: Feb 2009
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    From the YouTube channel: Sailing Emerald Steel

    Apr. 5, 2014


    Apr. 29, 2016


    Aug. 6, 2018
     
    Last edited: May 23, 2019
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  6. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Household units used for anything from hydroponics to aquariums to watering batteries are rather different devices to a seawater desalinator. They aren't designed to operate with as much solids, aren't designed to run at the pressures needed for seawater desalination, and often are of inferior quality with respect to the membranes used. But they are good enough to treat tap water for washing windows or watering orchids. Many are primarily used for removing the treatment plant chemicals, which are undesireable or harmful for many things.
     
  7. Bod
    Joined: Aug 2012
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    Bod Junior Member

    Excellent thanks chaps loads to go at there.
    Is it possible to unblock my domestic RO membrane? It stopped outputting water after a few minutes of desalination. Is it possible to save it or will it need to be replaced?
     
  8. Sean Duval
    Joined: Mar 2019
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    Location: yuma az

    Sean Duval Junior Member

    Maybe.
    Likely not.
    If this was a little under sink type unit...most likely expense not worth repair. Additionally repair likely not possible on the membrane, or impractical at best...I would toss the membrane.
    The rest of the equipment associated with it should be salvageable. By that I mean the membrane housing and all the prefilled housings and such.

    If you choose to you likely would be successful removing the membrane from its housing...the prefilters from theirs and flushing it all out with drinking water.

    Put in new membrane here in USA approximately 50 to 75 dollars and new prefilters both sediment and carbon and can most likely be able to use the unit again for domestic water filtration...aka cleaning up city water. Not sure where you are but it may be less expensive to just buy a new unit via Amazon than to repair it.

    Why....my guesses are that you packed it with salt...it is remotely possible depending on pressure used that you just hit osmotic equilibrium and it stopped...
    If so than it is very possible that running it with drinking water being fed to it could allow it to work again. To desalinate seawater take about 27 bar or better I believe...so if your pump wasn't capable of that, then it may recover or partially recover with potable water run through it at domestic type pressures. You could try using your present system and simply feeding it good clear salt free water and see what it does.

    What was/is your feed pressure with saltwater?

    The real question is as usual in the boating world...is time or money more valuable.

    Your welcome to PM me and we can discuss RO over phone at length as I would be willing to PM you my number.

    My advice would be expect a total loss and everything above that will be a good thing.
     
  9. Bod
    Joined: Aug 2012
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    Location: Leicester

    Bod Junior Member

    the pump was only a puny 60psi as that is the maximum for the unit. yeah i will try and flush with fresh water to revive it failing that new membrane. water is still passing through the 3 prefilters so they should be ok. dont know much about the resin filter not sure what that actually does!
     
  10. Sean Duval
    Joined: Mar 2019
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    Location: yuma az

    Sean Duval Junior Member

    Resin filter is usually ion exchange....aka softening.
    Interestingly usually these can be recharged via super saturated sodium chloride solution. But if sealed cartridge usually 1 time use for polishing.
    At 60psi I doubt that you made much if any water....I also doubt that you concentrated much salt.

    Good chance for rinse and use for home
     
  11. JosephT
    Joined: Jun 2009
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    JosephT Senior Member

    This sailing couple has been very resourceful with their vessel...and no question saved thousands of dollars in the process.
     
  12. Keith777
    Joined: Aug 2018
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    Location: bc

    Keith777 Junior Member

    Uae a electric karcher pressure washer..has to be above 800 psi
     
  13. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Sean mentioned 85% of water going through an RO unit turns into freshwater. It seems to me that with seawater, the ratio is about 10%
    turns into freshwater. Not only is salt the issue but a high amount of critters, plankton etc
    The high bypass allows continual washing of the RO membrane surface while taking a small amount through it.
    You can certainly build it but with saltwater, everything has to be stainless, plastic due to corrosion.
    There are companies that sell the important components to make your own. One had an adapter made to mount to the front of D6 Volvo diesels
    with an electric clutch, so when running, you used in existence power for the main pump.

    We had a 12 volt Little Wonder at one time and it would take about 8 hours to produce 80 gallons prox
     
  14. Angélique
    Joined: Feb 2009
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    Thanks Barry, when I looked for it the below 12 volt Little Wonder 250 showed up, seems to be not so noisy as the post #3 Karcher high-pressure pump, but still nosy.



    ‘‘ This is a short operational evaluation of our watermaker aboard Guenevere. We use it at least once every 3 or 4 days when out. If we do not use it in 3 days, we fresh water flush it. If we are not going to use it for over a month, we preserve (pickle) it. It has worked very well for us. The sound you here in the video is with the mic in the aft cabin withing 12 inches of the unit (during the close-up) and in the view of the water going into the jug you here what it sounds like in our cockpit. During the video it is running off of our solar panels and battery power. ’’

    On the same shot also the below 110 volt Village Marine Modular Watermaker showed up, he didn't let it hear while working . . .



    ‘‘ A step by step guide to installing a Village Marine modular watermaker. ’’
     
    Last edited: Jun 2, 2019

  15. Angélique
    Joined: Feb 2009
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    Does ‘‘ . . . we preserve (pickle) it . . . ’’ means running a fresh water vinegar solution through it ?

    If so, is this a good idea, and what percentage of vinegar would the long time preservation flush need ?
     
    Last edited: Jun 2, 2019
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