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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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how about a coffee filter paper? I guess not enough surface area. would a brown paper bag work? might be slow to drain but should get everything.

oooh...I'll probably avoid the brown paper filter paper might work (very un-common material here) but is too small...I'm gonna go with synthetic fiber because it dries super fast and doesn't seem to retain the moisture well...doesn't get soggy like some of the other stuff I tried (cotton/natural fiber). Moisture in this case, smells like rancid piss, so I'd like to avoid working with a 'wet' absorbent filter...

I wish i could contribute, but I don't know about chemistry. 

I did read that calcium carbonate will precipitate out if the solution is heated.  I wonder if this might help

Hehe...Yeah, I get that in my hot water tank a lot...not sure how to apply that here though. So far Bob, obtaining the desired precipitates has been a breeze.

The struvite on the synthetic mesh has been dry for some time and has been collected. Its sitting pretty in a jar.

The struvite on the cotton  fibre mesh, is much harder to reclaim...and smells bad.

I also, (per Bob's first post) left some struvite in 20-30ml of effluent in an open glass jar in the looks like very, very little of the effluent has evaporated. So just leaving it out to dry seems out of the question.

I have to go into town today and will buy the cheapest, worst quality all synthetic nylon T-shirt at the Chinese boutique. This should have a smaller weave than my 'saw dust catcher' and 'should' make a greatfilter. (the dust catcher did OK, but it'd be nice to lower the amount of particles that made it through,). Hopefully that should take care of the filter material issue. (Unfortunately, the reactors design and operation relies heavily on a decent filter...which right now in my head, is looking like a t-shirt with the arm and head holes sewn shut)...

Chris it appears thus far that I need less than the (we'll just round up) 10 grams of MgSO4-7H2O to precipitate the phosphates out of the humonia. I'm thinking that this is because (unlike the study you posted) I'm not using KOH to raise pH to 9 for the 'fresh slurry', or in this case humonia. It has had time to age and raise it's pH by itself. During this time a certain amount of phosphates have 'naturally' precipitated out due to the magnesium already present in the urine. I can see their presence in the bottom of all the bottles. I eat a borderline almost all plant based diet which probably helps to raise the Mg content of my urine even more...Which has already reacted in the stored bottles...Leaving a bit less for this "manual" process.

So the 1:1.6 ratio is probably a bit high. Even using the 1:1.1 ratio I suggested seems a bit high because of the above...

I haven't settled on an "optimal" weight of Mg yet, because I've been busy with other stuff and honestly, doing the same thing over and over again (processing 1 litre, then trying to re-process to check for 'leftover' phosphates) is pretty boring...

And once I have a good filter (I know have the material I wanted), I can do more meaningful comparisons.

I'd like to thank you again for you taking an interest and helping out in this matter. I appreciate it much. 

Thanks for the update. I agree on your comments regarding the humonia aging, pH level and content of Mg already present which is reducing the required needed to fully react. I think the other big unknown is really the P level in your specific samples vs the "common case" which i believe is where the numbers came from, yes?

I apologize that I haven't been able to be more involved practically. I used the last of it recently on the garden from the first experiment in "Let me pee in bottles and see if i get any kickback from the Ms." Experiment success so I can start saving more :)

Vlad you have devoted a lot of time helping me, so as long as it takes less time to show me what to do than it would take you to do it, I'd like to help.   I have not saved any pee, but I make it fresh everyday

OK, so I'm down to adding 5 grams Epsom to 1 liter humonia and even that amount of Mg looks like its doing the trick just fine. I will confirm this in a couple hours, then try again with an even smaller amount...

I'm not going to wait 24 hours or even overnight anymore, as it seems pointless. (Not sure why those guys in the study were doing that...maybe it was a Union job or something...?)...The reaction seems to be complete within minutes of stirring, then just a matter of the precipitates settling out...which really doesn't take more than an hour or two...

Leave it to the Chinese to make a proper struvite filter material...!

The $2.50 all synthetic button down shirt works like a charm..! (so far).

Late (new member) to this struvite thread:

About extracting struvite (ammonium magnesium phosphate):

* let urine stand  warm to hydrolyse several days for available NH3 and NH4+ (struvite only incorporates <4% of urine's  ammonia)

* add "bittern" from a salt pan works' (leftover after extracted NaCl) or from a source selling this bittern as the tofu coagulant "nigari"

* struvite extraction solution ratio =  1.3 magnesium to 1 phosphorus per urine liter is ideal (estimate urine ~0.8 gr. phosphorus/Lt. and estimate commercial "nigari" bittern at ~2.3 - 2.6 % magnesium by weight)

* control urine/bittern solution's pH  (at excess pH ammonia is not going to interact fully with phosphorus); adjusting solution to  7.4 - 7.8 pH gives good ammonium phosphorus struvite bonding

* control methodology of how process urine/bittern solution: stir up to 1.5 hours (longer stirring does not create more struvite) and perform speed of stirring at 100 RPM  to get most phosphorus by weight in struvite crystals

OK, I'm a noob here, and I think this is my first post, and it is nearly a year after this conversation began, but I just stumbled across it and had a process technique which will speed this process dramatically... ie. less than a day for complete dry crystals.

First Vlad, thanks for all of the amazing posts. I have drooled over their quality info.

This subject is however my opportunity to help with something I know.

Think 5 gal bucket or gallon milk jug or similar, though I lean toward the wide mouth and volume convenience of the bucket for SEVERAL reasons, speed and efficiency being at the top of the list. Cause this stuff STINKS!

OK, beginning AFTER chemical reactions have taken place, and BEFORE filtration, which I would not do at all due to difficulty of recovering sediments which are stuck in and clogging the filter. My process below should eliminate ALL of these losses as well thus increasing output from the system.

Separation can be sped up dramatically without filtering everything by allowing the solution to stand and the precipitates to settle to the bottom of the container, with the container tilted at an angle so that the solids collect into the lowest point. then dipping or pumping or siphoning off the liquid down to near that level.

My technique is based upon a siphon. A four foot long 3/8" clear hose for the siphon will allow you to SEE the liquid level and thus not ingest any in the process of starting the siphon. Most would consider this as rather critical.

Once the liquid has over flown the bucket's side, and collected into the bottom of the tube, remove the tube end from your mouth and lower the opening into a second container which is below the level of the bucket to begin full flow and to collect the effluent.

Continue lowering the source end of the tube with the liquid level until you have removed as much of the effluent as possible without vacuuming up your sediment. Then lift the tube from the surface of the liquid and thus break the siphon. Set tubing aside for rinsing and storage for reuse on the next batch.

Now, pour remaining solution into a different / third container, and rinse bucket with small volume of distilled water or effluent to obtain ALL sediment... or simply set aside as any remaining sediments will just be added to future batches using this same bucket.

Finally, use or build a "Solar oven" which you can make with scraps easily. Basically a box with 2" foam walls, ALL painted flat black inside, and closed with a glass front facing the sun. A small opening in the bottom and a small opening in the top of opposite walls will allow a cross ventilation and allow the heated air to carry away the evaporated water.

Now pour your left over sediment rich solution onto a black cookie sheet or into a cast iron pan or similar black or dark colored flat wide pan and set inside and close up the oven.

Common temps in these ovens on a sunny day are 2-300*F and this should evaporate all liquid in the solution within hours leaving behind your desired sediment minus the unwanted liquids.

Obviously you then remove transfer the powder to a seal-able container and store for later use.

I hope this helps Vlad.

Hi John...thanks for the all the ideas and your kind words...

I've pretty much got the process down to just a few minutes, plus drying (which is also pretty quick depending on the weather)

There are some pics and descriptions in that link. There certainly seems like a bunch of ways you could go about this, and right now I'm happy with the 'reactor''s pretty simple and clean. No clogging issues, splashing, (or siphoning with the mouth hehe...) 

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