Ion/Molecule sizes and nanofiltration or ultrafiltration

[LobsterOfJustice]

When running ultrafiltration you basically have two options... save what the filter retains, or save what passes through the filter.

Saving what the filter retains is useful in protein purification because it lets you hang on to large molecules and remove the fluid around them. This way you can either increase the concentration of a particular molecule, or you can exchange what fluid a molecule is suspended in by pushing the fluid out and pumping in new "background" fluid. However, this isn't useful in our application, since we are trying to remove the large molecules, not retain them.

So the other option, saving what passes through the filter, is basically how an RODI works. In order to keep the filter from very quickly clogging and becoming unusable, the retained fluid is typically passed over the membrane to sweep away whatever the membrane retains. This is why your RODI produces waste water. The problem with this scenario however is that you will generate much more retained fluid (waste in this scenario) than the amount that passes through the membrane. Again, this isn't very useful in our application, as you would need to remove a large amount of water from the system along with whatever molecules you are filtering out - and the amount of water passed through the filter would be comparatively small.

I could think of a potential application where you accept the fact that you are removing water from the system - say as part of a water change - but use ultrafiltration to slightly concentrate the amount of organics in the water that is removed. However, I think the complexity and cost of a system that did this would be significant, and you would likely see very slim effects.

The other issue is that, as a whole, I don't think the idea of removing all molecules above a certain size is a desired goal. The process is going to be very nonspecific and I would imagine you would end up removing just as many good things as bad.

 

[LemoL]

@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.

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.

I think I get what you're trying to do/ask and I don't think anyone is understanding your question. Yoh basically want a list of the molecules/ions that get filtered out and a list of stuff that could come through so you can make your decision on whether or not to use this over reverse osmosis because UF is cheaper.

I am researching now and I may be installing a UF system on my water supply for my fresh water fish room. So far it looks good. It looks like it keeps good DISSOLVED minerals like calcium etc and it will remove any free floating particulate like virus, bacteria, algae, lead, arsenic, chlorine, chloramine etc. I'm honestly wondering why no one is raving más about these uf systems because they can produce clean water for fish better and faster THAN Rodi units because it won't strip dissolved minerals which a lot of fish need salt and freshwater a like. Anyway I'll let you know how it goes. Follow my YouTube channel called ADHD Aquatics for an update soon

https://youtube.com/c/Lemolish

 

[Randy Holmes-Farley]

I think I get what you're trying to do/ask and I don't think anyone is understanding your question. Yoh basically want a list of the molecules/ions that get filtered out and a list of stuff that could come through so you can make your decision on whether or not to use this over reverse osmosis because UF is cheaper.

I am researching now and I may be installing a UF system on my water supply for my fresh water fish room. So far it looks good. It looks like it keeps good DISSOLVED minerals like calcium etc and it will remove any free floating particulate like virus, bacteria, algae, lead, arsenic, chlorine, chloramine etc. I'm honestly wondering why no one is raving más about these uf systems because they can produce clean water for fish better and faster THAN Rodi units because it won't strip dissolved minerals which a lot of fish need salt and freshwater a like. Anyway I'll let you know how it goes. Follow my YouTube channel called ADHD Aquatics for an update soon

https://youtube.com/c/Lemolish

Edit: I see this is a very old thread, but for some reason it popped up and I thought I'd address this last post. I also know the person I am responding to has not been on in years, but don't want to leave this hanging for others to read.

I don't think the author has a good handle on what an ultrafilter will do, and we did not misunderstand what the OP was asking years ago. He specifically was asking about filtering reef tank water, and we gave the correct answer: no matter what it does, it will clog almost instantly.

The author is considering a different application, in fresh water purification, and contradict him or herself by claiming it removes minerals (ones you don't want, lead, arsenic) and it leaves minerals (ones you want such as calcium). It cannot do both.

lead and arsenic are dissolved minerals, as is copper.