Towards a better tinyhouse

Inventing to freedom?

Capacitive deionization

with 2 comments

I was just thinking of various ways to remove salt from water, and decided to look into this technology again. I had heard about this before now, but it goes by several different names, and I previously searched “electrosorption”, but turns out the more common term is “capacitive deionization” (ever notice that, how finding the right search terms for what you want is often half the battle?). It’s not a new idea by a long shot, by apparently good electrodes for it have only been developed in the last 5 years or so.

Anyway, it’s a cool idea, and it turns out you can buy small under counter units that do it, one company that offers one is Aqua Ewp LLC. I emailed them asking for the price, these companies never post the dang price for things. I mean, it’s kind of a critical parameter. Another company selling the technology, but the units are probably too big, which is focused on high purity water, so might be pretty expensive, is a subsidary of Siemens, Ionpure. (Turns out that is a different technology, but I though I saw an article that said they were offering at least 1 CDI unit) Maybe they use electrodes, though which could be obtained separately at a reasonable price. Same deal with AEWP. There might be more companies out there.

The electrode module (“cell”?) is the hard part, all you have to do is apply a volt or two to the electrodes, and reverse the flow every once in a while and stuff. You should pretreat the water with carbon to remove stuff that would be adsorbed to the electrodes (again there is the problem of checking if the carbon filter has been used up, but there is always the possibility of using a flow meter and knowing the filter’s water treatment capacity by previously measuring it). If you could just buy the electrodes, the rest would be easy to do yourself. A switch mode power supply for a computer could make a good power supply. If it is a battery powered unit, it’s even easier, just a big NiMH battery would be fine. Maybe charge the battery pack’s cells in series and discharge them in parallel.

At the end of the day it has to be cheaper than RO, though, which I would think it certainly should be, given the simplicity and the materials involved, but, like any newish technology…

It doesn’t give you all your water back, but it’s pretty good.

This technology is not the same as Electrodeionization, which is something I still have to read up on.


Written by gregor

September 6, 2010 at 07:26

Posted in Uncategorized

2 Responses

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  1. I have purchased a unit from AQUA EWP cost about $3000 I belive the price would reduce if you bought 20 or greater.
    The electrode are the critical part but you could use Activated Carbon Fiber sandwiched between bi-polar membrane sheets and the power supply should be able to drive 2 to 3 amps at 1.2 volts.


    September 7, 2010 at 06:12

    • Sorry it took so long to let your comment through, I’m still new to this blogging stuff. Thanks for the good info, the company has not reponded to me, and I wouldn’t be surprised if they never do – you email them saying you are interested in buyng it, and they don’t even answer you, how on earth do companies like this stay in business?? Easy way to lose a $3000 order.
      I assume you are talking about the under sink 400 lpd unit? A price like that is depressing, that’s for sure…. given the concentration ratio of 5 to 10, do it yourself reverse osmosis might be a lot cheaper. Not only for the same number of liters per day, but on a per liter per day basis, but looking into the price of the membrane cells themselves is still an option. Well, what do you expect with a new technology; they will charge whatever they can get until someone else starts to offer competition.

      I have read a bit about the electrodes serendipitously while I was searching for info about this, and I haven’t heard of activated carbon fiber, but worth looking into. I think a piece of glass mat might work well for the separator, but there is still the problem of connecting the actual electricity to the carbon electrode, which I have read is a real challenge. Pain in the bum to try to make your own, though.


      September 7, 2010 at 06:39

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