Ion/Molecule sizes and nanofiltration or ultrafiltration

Discussion in 'Reef Chemistry by Randy Holmes-Farley' started by Wrasse-cal, Jan 3, 2018.

  1. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    @Randy Holmes-Farley

    I'm curious about the relative sizes of the various ions/molecules we try to keep in/filter out of our tanks in the context of nanofiltration or ultrafiltration as a means of aquarium filtration.

    Size+of+Materials+That+Are+Removed+By+Various+Separation+Processes.jpg Substances+Removed+From+Water+By+Membrane+Filtration+Processes.jpg

    To your knowledge, has this been considered? My suspicion is that using either method would cause indiscriminate stripping of desirable and undesirable compounds alike, but perhaps I am wrong.
     
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  2. Cory

    Cory Valuable Member R2R Supporter Article Contributor

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    Are you talking about cetrifuging the aquarium water? I would love a filter based on this principle.
     
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  3. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    I’ve seen reference to pressurized systems that would function like a RO System, just with a larger membrane.
     
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  4. Cory

    Cory Valuable Member R2R Supporter Article Contributor

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    Have you heard of dialyseas?
     
  5. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    No, I hadn't. Thanks.

    Looking though at the website part list for the "dialyseas," I only see reference to RO filters and carbon in the system, so it's not really using the larger nano/ultra membranes, which is what I was curious about.

    My question though on the larger nano/ultra membranes really though depends on whether there is a significant enough difference in size between desirable and undesirable molecules such that membranes could be used. I see, for example the possibility that the effluent from one membrane filtration might be fed through another, finer membrane to isolate out what is desired. That however all depends on the relative size of undesirable compounds being larger or smaller than desirable ones--hence my original question.
     
  6. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    I'm not sure what exactly we'd try to filter out of reef aquarium water, but whatever you intended, it would clog very fast and become unusable. :)
     
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  7. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    Theoretically, everything that's not in natural sea water. :p
     
  8. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    To use a really crude analogy for what I'm curious about:

    Assume a box for the tank. The box containing marbles (assume nitrate molecules or some other undesirable), tennis balls (assume calcium in usable form for corals) and sand (assume NaCl). Tennis balls and sand are desirable and we want to keep them. Marbles are not.

    Filter one would separate tennis balls from everything else. In this case, the contents that don't pass through the filter i.e., the tennis ball "effluent" would go back in the box.

    Filter two would separate the marbles from the sand. In this case, the sand would pass through the filter back into the box and the marble "effluent" would be rejected.

    Obviously this all depends on the sizes of "marbles," "tennis balls" and "sand" and if the desirables are all different sizes than the undesirables.
     
  9. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    Such filters work based on size. Nearly all organic molecules are bigger than any inorganic ion.

    So if it didn't clog (it will), what you remove would be organic matter and particulates like detritus, bacteria, etc..

    You would not be able to distinguish the many different inorganic ions. :)
     
  10. Cory

    Cory Valuable Member R2R Supporter Article Contributor

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    Sounds like you want a membrane thats selective enough to remove just nitrate and let the rest through. That would be pretty sweet. I dont know of anything that would work.

    What i want is a continous centrifuge polishing my water all day. Imagine the chunks it would collect.
     
  11. LobsterOfJustice

    LobsterOfJustice Well-Known Member

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  12. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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  13. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    But keep in mind this isn't anywhere close to ultra filtration. It is just assisted sedimentation of large particulates.
     
  14. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    The literature about these centrifugal filters claims that they are capable of filtering out particles 20-100 µm in size. Google tells me the industry adopted term "micro-filtration" describes membrane filters capable of filtering particles 10- 0.1 µm. Though the terms are qualitative, my limited understanding is that nano and ultra-filtration filters particles 0.1 μm down to 0.005 μm.

    The upshot perhaps being that the clogging concern you identified might not be an issue provided filtration was done using centrifugal filtration first, then with progressively finer membrane filters.
     
  15. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    I'm just not seeing what you are trying to accomplish that is useful for a reef tank.

    The centrifugal filters linked above replace a filter sock. Nothing appreciably smaller will spin out.

    To get proteins to come down out of solution by spinning requires very expensive ultra centrifuges. No way that can be practical. More than ten thousand dollars to spend an hour spinning down a few mL of tank water to remove proteins. GAC and other binders do this pretty well for a tiny fraction of the cost and time.

    I've used 0.45 micron syringe filters lots of times, including to test aquarium samples, to remove particulates, bacteria, etc. But they clog too fast to usefully treat an aquarium, and the flow rate is like drip, drip drip.

    Beyond that, there's no way you are going to separate inorganic ions from reef aquarium water by size, so separating out nitrate, phosphate, aluminum, etc. by size can't work.

    Sorry to be a negative nanny, but this just isn't a useful path forward, IMO.
     
  16. Wrasse-cal

    Wrasse-cal Active Member R2R Supporter Build Thread Contributor

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    No need to apologize. :)
     
  17. Cnidoblast

    Cnidoblast Active Member

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    I'm curious if anybody's ever tried making a filter based off of column chromatography
     
  18. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Article Contributor Expert Contributor

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    To some extent, that's what polymer media like Purigen does, just not in column form. :)
     
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  19. LobsterOfJustice

    LobsterOfJustice Well-Known Member

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    And if you run it in a media reactor, there's your column.
     
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  20. Cnidoblast

    Cnidoblast Active Member

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    Woops! I totally forgot purgien is repackaged chromatography resin!!!!
     
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