Why do RO units waste so much water?

Discussion in 'Test Kits, Controllers, Reactors and Dosers' started by RocketRooster, 8 Jan 2013.

  1. RocketRooster

    RocketRooster

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    I was told earlier today that RO units "waste" a lot of water by 'bypassing' a lot of it. I was under the (obviously mistaken) impression that you just plug it in, it needs some pressure and voila.

    Why do they do this? Is it to flush the stuff that stays behind on the "dirty" side of the membrane or what?

    What can be done to reduce this wastage (It'll go into my garden but still...) ?

    Thanks!
    Riaan
     
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  3. RiaanP

    RiaanP Moderator

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    yes.

    Else, all the dirt that they flush will be in the membrane, seriously shortening the lifespan of the membrane.
     
  4. RocketRooster

    RocketRooster Thread Starter

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    I was told it's only got like a 30% efficiency or somesuch... surely that's excessive? :eek:
     
  5. Ridwaan

    Ridwaan

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    Maybe someone can put the ratios here if they know it...

    Something like 3 litres of Waste water to 1 litre RO water...Not sure...LOL!
     
  6. RocketRooster

    RocketRooster Thread Starter

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    Apparently the latest and greatest units have a 1:1 (50%) efficiency.

    When my pond outside is finally up and running this won't bother me too much - it also needs water changes, so I'll simply run my RO overflow straight into the pond and use the pond's water for the garden.

    But it does mean I'm going to have to think carefully about how and where I do my RO setup.
     
  7. RiaanP

    RiaanP Moderator

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    Due to location, my RO waste runs directly into my drain. Previous property it did run into the garden.
     
  8. Ridwaan

    Ridwaan

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    This is the boss in R.O machines IMHO
    http://www.vertexaquaristik.com/Pro...100RODI/tabid/202/language/en-US/Default.aspx

    Contact @Submariner
     
    Last edited by a moderator: 26 Nov 2015
  9. RocketRooster

    RocketRooster Thread Starter

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    Measuring the efficiency of your RO unit should be a simple excercise. Take two identical containers, one for receiving RO water and one for waste water. Wait for the waste container to fill up, then measure the relative amounts. Will give you your ratio.
     
  10. Dave F

    Dave F

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    Can you add an additional membrane to an existing ro unit to make it more effective?
     
  11. Mewik

    Mewik

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    apparently you can run another membrane and DI on the waste pipe, I guess the output will be slightly less than the 1st membrane though and it might need a pump to boost the pressure. Also you can store the waste water and then you basically pump it back through the RO unit again and again. @The Waterboy - Marco is the man to ask. I remember reading about the above in a thread he was commenting in a while back.
     
    Last edited by a moderator: 26 Nov 2015
  12. RocketRooster

    RocketRooster Thread Starter

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    I hope Marco weighs in on this thread. :thumbup:

    Correct me if I'm wrong here - if the waste overflow's function is to flush the muck from the membrane - then logically the waste water's TDS is more concentrated going out than coming in from the tap.

    So that would mean that recycling it is a false economy, since you are increasing the load on the membrane by a greater amount each time you cycle the same waste water.
     
    Last edited by a moderator: 26 Nov 2015
  13. Nemeziz_za

    Nemeziz_za

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    The outflow has a flow valve, so you can force more through the membrane by closing the exit waste tap more.

    Or am I wrong?

    If I am right, what is the correct amount that this tap should be closed? Or do you have to test the RO water thats produced repeatedly to find the right amount of restrictive waste flow setting?
     
  14. Dave F

    Dave F

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    @RocketRooster I think you make a good point. @Mewik, I was asking because of the thread I had read, and you right i am sure it was @waterboy who mentioned it.
     
    Last edited by a moderator: 26 Nov 2015
  15. Mewik

    Mewik

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    The waste tap must always be 100% shut when making RO. You are only supposed to open it once a week or so to flush the membrane out. Opening the waste valve flushes the outside of the membrane and removes the build up of waste....:whistling: I think

    Think we need an expert here to clear this lot up :)
     
  16. Mewik

    Mewik

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    Yeah Expert needed.

    From what I understand when you reuse the water the useable RO water that you get out will become less and less each time, so yeah the TDS in the waste must get higher and higher until a standard single membrane can no longer filter the water to a useable level and you will get TDS in the RO water. Suppose you could run the waste through another 2 or more membranes if its really manky, but the costs of the membranes compared to water come into it then. Water is pretty cheap and I don't really feel like I am destroying the planet when I run a tap.....so single membrane and waste pipe down the drain for me :blush:
     
  17. Lord_Blackadder

    Lord_Blackadder

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    It's completely fine to drink or use the waste water on your garden, just FYI.
     
  18. vatso

    vatso

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    @ Mewik - you always need waste water coming out of your RO unit!! I run 2 membranes so I get more RO water out and I have a ration of 1:1 RO to Waste water my TDS out the RO water no RI resin is 3.

    I also don't need a booster pump as I have enough pressure some people on the forum have seen my RO unit.

    There is very little to an RO unit just to add they are simple they just filter more and more and more that's it
     
  19. mariusmeyer

    mariusmeyer

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    The quality of the feed water will also affect the waste ratio. The higher the tds of the inlet water the more water out the waste.
     
  20. craig redfern

    craig redfern

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    Just installed my RO unit today, still flushing the system out but going by what i see you do waste alot of water to make RO. And to fill my 25l containers with RO will take ages
     
  21. RocketRooster

    RocketRooster Thread Starter

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    What happens when you block off the waste outlet on the RO unit with a valve (while it gets pressure from the water mains)? Do the membranes get damaged from the pressure or does the RO unit itself run the danger of popping?

    See, I was wondering if one could plumb these things just before a basin tap or cistern or whatever, so whenever the water flows, you get RO produced.


    Hmmmm..... just had an idea.
     
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