[charles_west]

Hello,

I'm part of a group that is working on a process to mineralize organic wastes to create a sterile hydroponic fluid for use in small closed ecosystems.

One oxidation option we are looking into is using NaClO.  All the the chemicals used need to be recycled and bleach is attractive because it can be remade from a salt brine.

Unfortunately, it creates a by-product of NaCl which is mixed with all of the salts that we need in our hydroponic fluid. 

I was wondering: Is there was any simple way to separate NaCl from other salts such as potassium dihydrogen phosphate, potassium nitrate and magnesium sulphate?

If there isn't, we should probably mark NaClO off from our list of wet oxidation candidates.

Thanks!

[Arkcon]

Briefly, its not trivial to remove NaCl from a solution of other strongly soluble salts.  NaCl can't be easily precipitated, and those others are too soluble as well.  Also, you're likely working at the 100's of ppm level, and that's too dilute to effectively remove anything.  You might want to look at just how much NaCl  ends up in your media.  Plants can survive higher levels of NaCl in hydroponic media, than they can in just plain water on soil.  The canonical author on these sorts of topics is H. M. Rech.

[vmelkon]

If it is low concentration of salts, probably osmosis would remove all the salts. Then you can add the salts you want to the pure water.

[Arkcon]

If you can't use hypochlorite to remove organics, you can use hydrogen peroxide, but that is a little expensive.  Another answer is ozone.  You can try it out with a small tank, and if its suitable, you can buy an ozone generator, they're pricy, but that's initial capital outlay, you won't have to buy tanks and tanks of chlorine, and have the empty tanks returned, so it save money, in that way.

[charles_west]

We need to separate out the salts so that we can use the fertilizers.  We have had positive results with bleach oxidizing organics so far, but if the salts cannot be separated then we definitely need to change tactics.

In space, energy is plentiful but mass (for equipment and chemicals) is not.  All chemicals we are working with have to be regenerated.  Other candidates we are looking at are hydroxyl radical reactions (such as Fenton's reagent and dissolved ozone).  We are also looking into normal thermal decomposition followed by treatment of the resulting gases.

Thank you both for excellent replies.