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  • Recovery vs Rejection

    A $10 gift certificate to the first person who can clearly explain the difference between rejection and recovery, as it relates to RO's. This question comes up all the time with customers and many (most?) don't have a clear understanding of the terms.

    Russ
    RODI Systems & Supplies www.BuckeyeHydro.com Info@BuckeyeHydro.com
    Dosing & Booster Pumps, 2-part additives, Salifert products, Solenoids, Phosphate Remover, Bulkheads, filter socks...

  • #2
    Isn't it recovery is the water or the amount of water produced by the membrane Clean water permeated through the membrane (water recovered from the filtering process) Rejection is the solids that are not passed through called waste water.

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    • #3
      Originally posted by szwab View Post
      Isn't it recovery is the water or the amount of water produced by the membrane Clean water permeated through the membrane (water recovered from the filtering process) Rejection is the solids that are not passed through called waste water.
      Did you google that?

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      • #4
        nope. Bits of info I remembered from Russ's meetings with CORA

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        • #5
          Szwab - let's call it "close enough!"

          Recovery: Percentage of the feed water that becomes permeate (RO water). So if you have a 4:1 ratio of waste water to permeate, you'd have a (1/5=) 20% recovery. In a perfect world you'd have a membrane with 100% recovery without ruining (scaling or fouling) the membrane.

          Rejection: Percentage of the TDS in the feed water that is sent to the drain via the concentrate ("waste water"). So if you had feed water with 280 ppm TDS, and RO water with 9 ppm TDS, you'd have a [100% -(9/280)=] 97% rejection rate. In a perfect world you'd have a membrane with a 100% rejection rate so you wouldn't need a DI stage. You can see why it's important the know the TDS of both your feed water and RO water - both are needed for this calculation. One sign of a membrane gone bad is decreased rejection - but because the TDS of most feed water streams is not constant, you really can't judge the functioning of the RO membrane purely based on the TDS of the RO water - you have to calculate the rejection rate.

          Does this make sense?

          Russ
          RODI Systems & Supplies www.BuckeyeHydro.com Info@BuckeyeHydro.com
          Dosing & Booster Pumps, 2-part additives, Salifert products, Solenoids, Phosphate Remover, Bulkheads, filter socks...

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          • #6
            Follow up question - Contrary to what certain vendors claim, you don't need to add a second piggybacked membrane to increase the recovery.

            What part of an RODI system controls the recovery rate?
            RODI Systems & Supplies www.BuckeyeHydro.com Info@BuckeyeHydro.com
            Dosing & Booster Pumps, 2-part additives, Salifert products, Solenoids, Phosphate Remover, Bulkheads, filter socks...

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            • #7
              Originally posted by Buckeye Hydro View Post
              Follow up question - Contrary to what certain vendors claim, you don't need to add a second piggybacked membrane to increase the recovery.

              What part of an RODI system controls the recovery rate?
              Flow restrictor!

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              • #8
                membrane matched with the flow restrictor.
                Bill
                Creativity is intelligence having fun.

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                • #9
                  Yes - the lowly $4 flow restrictor controls the waste water ratio. By changing the capacity (flow) of the flow restrictor you can change the waste water to purified water ratio. An additional piggybacked membrane IS NOT required. In fact, a piggybacked membrane (membrane plumbed in series) should NOT be used to reduce the waste water ratio below about 4 to 1 (20% recovery) unless you're OK with shortening the life of the membranes.

                  Russ
                  RODI Systems & Supplies www.BuckeyeHydro.com Info@BuckeyeHydro.com
                  Dosing & Booster Pumps, 2-part additives, Salifert products, Solenoids, Phosphate Remover, Bulkheads, filter socks...

                  Comment

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