I have no resources to offer you but it sounds like a very interesting project. Please keep us posted on your progress!

I would assume that this needs to be an aerobic system so that nitrogen is not lost. Urea breaks down into ammonia and CO2, so the trick is to capture the ammonia and oxidize it to nitrate before it is lost to the air.

This sounds like the attempt to isolate nitrate from organic sources (such as urine). Nutrient isolation defeats the main purpose of composting cuz the "taken as a whole" thing is just what composting really are. If organic nutrients are to be isolate and made into specified fertilizer then why bother with compost when one can always buy factory manufactured urea or compound ferts(which in the process consumes great amount of fossil fuel ) conveniently?

I don't know if this would help, but I do know that in the process where they convert chicken manure into a nitrogen-rich cattle feeding supplement, they have to dry out the chicken manure very quickly or the nitrogen is lost.

So they have a series of wooden baffles under the chicken coops/cages so that when the droppings fall, they get spread out / break up into small bits and dry quickly.

So I'd hazard a guess that you'd want to find some method of spreading the urine on something that would dry quickly, which is far from the world of composting where moist heat is used to break stuff down.

ceth makes a good point. The 'traditional' low-tech way to capture those nutrients is to mix the urine with a dry brown such as sawdust, shredded leaves or paper, etc. and compost it aerobically.

I will guess that the answer to 'why not just buy it' is the usual one: it's cheaper, recovers nutrients otherwise lost, avoids the env. cost of fertilizer production, etc.

It may be a crazy idea, but that's not necessarily a bad thing.

Wow, what a great bunch of responses. I hope we can get somewhere from here.

The short version of the reason that I'm doing this project is: I have a stream (no pun intended) of urine on the order of 10-100L per day, and I'd like to turn it into something useful rather than dumping it down the drain.

Ammonia is one possibility: Drop in some urease from soybeans and capture the ammonia via air-stripping. Simple, but there are two downsides: First, the volume doesn't change much (urine -> NH4(aq)) Second, leaks are smelly.

On the other hand, if I can further bioconvert the urine/ammonia to nitrates, those can be dried and transported easily, and have no odor in the case of a leak in the system or the transport.

Please keep the ideas coming! I'm open to any suggestions out there, in terms of chemistry, physical setup, "right" compost mix, temperature, etc.

All help welcomed thankfully

What exactly did you want to do with this urine?
If you just want to use it add some water to dilute it and go apply it to where you want it. You can probably even "stream" it right to where you want. Just not in the same place to often or where the neighbors can see.
But it kind of sounds like you are looking for something on a more industrial level, and that I can't help you with.

Why not evaporate all the water and turn it into a dry fertilizer? The conversion process can take place in the soil after it's applied.

I hope you don't mind my asking, but I can't help being curious...can you reveal where your 10-100L of urine, per day, comes from? What line of work are you in?

Since I'm asking a question, maybe I can also help with an idea. This is just a thought that occurred to me, I know nothing about how this might work in practice...

In addition to your urease, add some vingar so that once evolved, ammonia will be converted to its salt, ammonium acetate, a solid (in pure form, it will still be dissolved in the urine solution). You will not have to worry about smell or capturing gaseous ammonia. You can evaporate down your product to capture a more concentrated form which of ammonia which should be relatively stable.

Interesting idea with the vinegar. One would have to look at the chemistry of the ammonia/ammonium equilibruim with respect to pH to see how that would work, how much vinegar is required, etc.

And what about all the inorganic salts in urine? Do you plan - or even need to - remove them?

The source is both animal (mammal) and human. 10-100L per day is a lot to flush down the drain, and the solids are already taken care of, so I was looking for some efficient way to recover the useful components. I posted to composting forums expecting "merely" recipes and setups to convert it into nitrates, but happily the responses have been far broader than that.

One person has suggested mushroom farming/growing... apparently mushrooms can take in a substantial load of ammonia directly, unlike other plants for which substantial amounts of ammonia can be toxic. Likewise the suggestion above for just pooling it and adding vinegar, producing ammonium acetate which could be crystallized and removed. Either method would be aided by the addition of some soy based urease.

On the other hand, if there's a good way to take the urea->ammonia->nitrite->nitrate path to its normal biological terminus, I'm all ears.

-Riventree