Humonia and Struvite

[Vlad Jovanovic]

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 calcium...like 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.

 

http://community.theaquaponicsource.com/group/fish-less-systems/for...

http://community.theaquaponicsource.com/group/chemistry-math-and-aq...

 

[Bob Campbell]

What about just letting it dry into a powder?

[Vlad Jovanovic]

Well thats kinda what this is about...that little bit of powder/crystal that forms in the bottle is struvite I believe (well at least some of it)...

I'm not sure if the phosphates in the urine (which are significant) are recovered when it just dries out that way either? 

When urine turns into struvite by itself the limiting factor becomes either the amount of naturally occurring magnesium gets used up, of the amount of phosphate gets used up. So it's not a real efficient 'recovery system' do just let it dry out on its own...and it takes long. I'm sorta looking for minutes or hours, not days or weeks.

I'm not sure, but I suppose any soluble magnesium would do (again not sure on that one, but don't see why not). I may just start pouring Epsom salt in measured amounts into one of the bottles and see what happens...once the reaction stops... add a bit of phosphate rock and see if it picks up again...

Though I really was hoping to have some guidelines to work within first with this one...

[Vlad Jovanovic]

Folks, I hope someone helps out, because I've been in the shop all day fabricating my "struvite reactor"...hope this process doesn't turn out to be too exothermic...in which case a video would be in order...

...according to "the net" struvite should have an NPK value of about 6-29-0(Mg-10)...though I imagine some calcium phosphate to be collected as well?...

[Chris Carr]

The stuvite Wikipedia references have some interesting info. Sorry if you read this already but I will summarize for those too lazy/busy to read more.

Specifically

http://www.ostara.com/technology 

and 

http://www.stormwater.ucf.edu/chemicaltreatment/documents/Burns%20e...

Looks like they do not reference Epsom salt at all but use MgCl (I have this at home for coagulating soy milk into tofu, sold as Nigari) Not sure how effective epsom salt would be as a substitute but worth a try.

Seems the key points are letting it sit bottled up a while as per normal, adding the right amount of Mg to reach 1.6:1 Mg to total P, then raising the pH to 9.0 via sodium hydroxide.

In the experiment documented using pig waste, it seems for them to reach the right Mg to P ratio and the pH levels, the variation from 2 samples was quite a bit. For 400ml samples of waste using 64% MgCl solutions, one sample used ~20ml where the other used 60ml so it would be pretty difficult to say how much one persons humonia would need.

Might be worth doing some tests with your source pee to find a ballpark for optimal amount of Mg. I look forward to seeing your idea for a continuous reactor :)

[Vlad Jovanovic]

Thanks Chris. No, I had not read those...The Ostara reactor looks pretty fancy...mine will be far from a continuous process (I don't pee quite that much hehe)...

My understanding now is that any soluble magnesium will do...it seems that in that study you linked the particular scientist had problems getting MgO into the swine slurry in the past, so they went with MgCl...

Yeah you're probably right, the humonia probably varies quite a bit according to how much water you drank, what you ate etc...but that type of Mg;P ratio is the type of number I'm after. (More as a starting point reference, than any thing). Total phosphate salts in a litr of human urine is about 1.4 grams (yielding 0.11 grams of pure phosphorous). S now I have a starting point .

It's also encouraging to see such small temperature rises in the slurry studied (5 degrees C or so)...

Thanks again...

[Chris Carr]

Not sure if we should punt this over to the other thread or not. (http://aquaponicscommunity.com/group/chemistry-math-and-aquaponics/...)

Since you said you were building a reactor I assumed it wasn't just a bucket :) I was thinking of how you could build one with a 5 gallon bucket but just the reactor volume would be a lot of pee. To run it would be just way too much. I think just manually mixing it and letting it precipitate out in a bucket/barrel would be sufficient.

I don't have any ripe supply laying around at the moment to try it right now.

[Vlad Jovanovic]

I've got most of the galvanized sheet metal and galv pipe I had lying around cut out...next just to rivet and solder/weld, and thread up the pipe on the lathe...(this is actually quicker for me than searching for non-existent PVC parts at horrendously under stocks stores...

It's a pretty simple design...and should hopefully be effective, don't see why it wouldn't be...I'll definitely keep you guys posted...I might actually do a blog on it with pics if I have time...or maybe a video would be quicker...lets just see if it works first...hehe 

[Vlad Jovanovic]

Ok, so while I wait for you smart folks to work out the numbers  I went and did (still doing) a 'trial run'...

1 litre humonia...first added Chris' 4.84 grams of Epsom salt...then after stirring and watching things get cloudy...added another 4.84 grams of Epsom salt to make up the difference because Chris was probably thinking MgSO4 not MgSO4-7H2O...

I went with that number (4.84) wrong or right, it was the only answer I got, so I started from there...stirred and stirred things got cloudy, precipitates formed...anti-climactic...not at all like adding potassium to water....................

Added another (third time) 4.84 grams of Epsom salt...stirred...got sick of watching urine get cloudy after 15 minutes...it's late I'm going to bed...

[Chris Carr]

With the adjustment, should have been 10.5g total, so I think ~15g total sounds perfect to start with. Based on the swine slurry experiments they let it precipitate for 24hours. I guess it takes a while for the crystals to form. Was the urine aged well so you had sufficient ammonia present? Did you pre-dissolve the epsom salt before adding it? I bet you have some salt settle out by tomorrow afternoon. pre-dissolving would just give you a better indication if it actually settle out of solution or not and makes it easier to mix.

Once you pour off the liquid, you should always try again with another 5 or 10g salt to see if you get anymore. Maybe split it in half, try adding more epsom salt to one, in the other test and try upping the pH to 9.0 and see what happens.

[Vlad Jovanovic]

Yes the humonia was very well aged. pH is already near 9.

I just checked on it about an hour ago and there is a nice layer of white fines at the bottom of the container. I will probably filter those out and as you suggest add more Epsom salt to the effluent and see if any more phosphates precipitate out. Then do it all again one more time, and make some decisions about how much Epsom salt to add per litre in the scaled up model...

One thing I'm not sure on is...say there are no more phosphates in the humonia, and I keep adding Epsom salt, what will that look like? I'm thinking of doing it a third time, 15grams Epsom, then filter, then 15grams Epsom, then again, and so on...I sure hope that it doesn't visually look too similar to what I have now...

What has formed now looks like it will be a fine white powder once filtered and dried, not at all 'big-ish' crystals (like the Epsom salt is). But that what I was expecting, white crystalline powder.

I did not pre-dissolved the Epsom, but I could could see the crystals dissolving, then after a couple minutes of stirring, you could see a sort of whisky streaks of cloudy separation starting to happen...like milk in black coffee before it all smooths together, only not as dramatic...So the Epsom appeared at least to dissolve then react...

[Chris Carr]

would be interesting to strain and dry off what you have and see how much it weights anyway.

[Vlad Jovanovic]

Ok, so it seems that the circa 15 grams of Epsom salt was more than enough to completely cause the phosphates to precipitate... When strained off the struvite, I added another 4.84 grams to the leftover effluent, and absolutely nada. The Epsom just dissolved but no reaction ever occurred and the cloudy precipitates did not form this second time around. 

I am also realizing that this is not going to cut down (volume wise) on the space that all this humonia takes up...unless I dump the effluent, which I'm not willing to do.

I need to by a cheap synthetic nylon shirt to try as a filter media on monday. Cotton, or natural fibers seems not good for this ap, and the nylon mesh I used from the (useless) 'dust catcher' on my miter saw is a tad big (mesh wise). So the dry weight might not be truly indicative from this run...