Aquaponic Gardening

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This one is kind of 'out there' but I could really use some help...

Does anyone know, in practical terms, how one would go about using magnesium, to precipitate struvite out of the humonia, and reclaim your phosphates while lowering N content? I think struvite should have an NPK value of 6-29-0 (Mg-10).

The urinary stones people sometimes get is called Struvite -  NH4MgPO4·6H2O) is formed when urine hydrolyzes to ammonia (usually because of an infection) and raises the pH to alkaline values, then forms a precipitate with magnesium and phosphates. 

The first part (urea converting to ammonia) has already happened just by storing the humonia in a bottle, so we are all part way there already...


Now how, and in what quantity to add the magnesium (in what form), and is it necessary to add as much as their is phosphate in the humonia, and how do you know how much that would be (approx) ?

Any help or pointers would really be appreciated, before I start doing this.

Storing the 100's of litres of humonia is getting to be a pain, space wise, and Struvite (which apparently will just dissolve in water later when you need it) seems like a pretty keen thing to have on the farm...

I don't think you'd get any of the potassium to precipitate out, so the effluent that is left over might be a decent fertilizer in it's own right for plants in middle of the fruiting cycle. Plus it shouldn't now plug up your irrigation equipment with precipitates...Again this is the effluent left once you've removed the struvite...

The struvite itself however should be good (like any other high P fertilizer) for seedlings, then flowering stages, and maybe a good way to give cucurbits the Mg boost that they seem to need. ***Edit***(And will, like all phosphate based fertilizers eventually form a precipitate with the CaHCO3 in your 'hard' high pH well water. So small misters/sprinklers/emmiters are at risk, but this seasons cheap irrigation tape did alright. No real clogging.)

That's the idea anyways...

Thanks guys.


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A "box of rocks" would be cheap. Since you wouldn't have solids to deal with you could go with smaller sized rocks than would be typical for AP (they still need to be pH neutral, so no CaCO3 (limestone) containing rocks.

Joni Solis said:

So Vlad, can you point me in the right direction as to what is the best kind of bio-filter to use for pee water. A bio-filter that would be cheap to make would be the best for me right now. Thank you for your help.

Vlad Jovanovic said:

Yes, you would filter the water through a bio-filter in much the same way that you would 'fish water'...nothing special 

Joni Solis said:

Thank you Vlad for this information. So is there any info here about how to pretreat this water?

Vlad Jovanovic said:

Yes, the non-recirculating B.A Kratky set up can use humonia as an input source, but you would still need to 'pre-treat' the water through a biofilter.

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