Biochemistry/soil science of collected urine

Hello!

We're currently in the process of planning a new permaculture-ey life and are doing a lot of the thinking about the practicalities. One of the these is obviously composting toilets; over the last year of travelling we've used a lot of different types, and picked up a fair few ideas about how we'd like to make it work for us.

Now I know that people are divided on the benefits of urine-diverting toilets, and obviously a lot of it comes down to what you can make work effectively for you - it's clear people have had success with both approaches. But one thing we really noticed is that if handled badly, the urine is *by far* the nastiest bit of the process (whether separated or not). Emptying a bucket of urine that has sat open in the sun for two days is one of the most retch-inducing things I've done in a long time. On the other hand, for an indoor bucket toilet, separating out the urine really cuts down on the emptying, and an "unseparated" bucket where the urine has gone ammonia-ey can be even nastier than the stale urine on its own.

But the thing that worries me most is that there seems to be disagreement about the ecological benefits of the separating systems. A lot of people seem to think that it's fine to divert the urine off and store it in closed containers for later use, diluted, as a fertiliser, and we've seen this system in use at various places, including at least one big, well-established project.

Other people, however, raise questions about these systems. In particular this website claims that separation misunderstands the biochemistry of both the manure composting process and the urine breakdown. The solids dry out too quickly, aren't completely broken down into humus, and if stored in closed containers, often decompose anaerobically, losing nitrogen in the process. And the urine, even in a closed container, will inevitably start to decompose into ammonium within a few hours. By the time one starts using it as a fertiliser, it is essentially the same as using standard chemical fertilisers. In particular, it will be rich in nitrates which leach out of the soil very readily rather than being bound into the humus in a slowly-releasing form.

Does anyone have any definitive information about the biochemistry/soil science side of this? Although I'd like to make the system as convenient and inoffensive as possible, I'd like to be sure that we're not undermining the nutrient-cycling value.

Cheers,

Lucian

Welcome to Permies, Lucian!

Here's a thought on how you can keep the nitrogen from leaching while making it less offensive to handle -- chelate it. Or rather use it to chelate other minerals that your plant will be needing. Chelation is the process of forming an ion complex where the nitrogen in the ammonia (or urea) bonds to metal ions. While bonded, the nitrogen isn't going anywhere, up into the air, or leached out with the next heavy rain. It also makes the metals more available for plants, because chelated metal complexes are slightly soluble, not insoluble, like a lot of metal sulfides that just sit in the soil, unavailable for plants to use.

I talk a little about chelation in my post on composting alkaline batteries. This process requires a fair amount of urine and you can do it as a batch process. If you are thinking of a continuous process that will chelate the urine as it is produced (and flushed), then you might want to set up a trickle bed of rusty iron. I say 'rusty', because metallic iron will be slow to react with urine and you need to give it a kickstart with some type of acid that can be forming iron(II) ions. But that is real easy, since even rainwater is acidic enough to get iron started rusting. If you set your trickle bed up with an eye to what mineral deficiencies there are in your soil, you can solve that mineral problem as you solve your collected urine problem.

John Elliott wrote:Here's a thought on how you can keep the nitrogen from leaching while making it less offensive to handle -- chelate it.

Wow - that's a really fascinating idea. I'd love to give that a go at some point. I'm wondering what else one might use to absorb the urine in ways that might help fix it more permanently. I know that people make simple urinals out of straw bales, which seems to be closely related to the role of sawdust/shavings/peat moss/etc in the traditional humanure system. If one takes fresh urine (before it starts to break down into ammonium etc) and soaks it into carbon-rich organic matter, what happens? Is the chemistry of that process any more conducive to the nutrients not being leached out than storing the urine and applying to the soil later?

Sorry, that's a lot of questions! I guess the permaculture spirit tends to be more "give it a go and see if it works", but I'm concerned that it would be very easy for it to seem like it was working great, but was actually setting up hidden problems for the future because I just wasn't observing all the outputs accurately. I guess that's kind of how we got ourselves into the mess we're in today with soil fertility in the first place!

Sorry, I'm not a scientist. We've been using the bucket system for a few years now and we don't separate all #1 from #2. When going #2 we go #1 but when just going #1 we have an RV/marine toilet that uses just a few fl oz to flush. This makes the buckets much more manageable. Not so heavy or stinky yet the mix is not totally dry and by the time the buckets are rinsed with the rinse liquid being dumped on the pile, it's about the right moisture for a compost pile. We have saved urine in the past and yup, it gets nasty quick. I did read somewhere that saving it for a couple of days is desirable because the changing towards ammonia kills the nasty bacteria (if there is any). Of course I've read, use it right away, use it in a couple of days or save it as long as you like. That's the problem and how we got here. Waiting for the scientific community to make up their mind and agree on something. In the end, it's whoever has the best funding and political/business connections that wins the argument publicly. Isn't Florida supposed to be underwater soon. 30+ years to decide agent orange was bad. By that time most of the vets were dead. Yeah, I trust the scientific community and business/government. Another problem. Most science is theory and there always seems to be someone else who has a different theory. I think the "permaculture spirit" is more like, if it already happens in nature, then it's probably ok. and look where science and progress and regulation has gotten us. That would be why a lot of folks just "go" outdoors and not in the same spot every time. It's just natural.
I have just been moving the outlet to our pee toilet and not aiming it anywhere that we'll be growing food. It's winter and we've only been on our property a year so we haven't gardened yet and I haven't had time to set up a collection/dispersal/distribution system. I'm not sure what we'll do with the urine yet. I do know we won't be hanging on to it for long and I see it's usefulness as a fertilizer and compost activator. I just need to come up with a system to dilute and disperse. If I want some to use for a special purpose outside of the system, it's easy enough for me or my son to collect a bit in a bottle. I'll probably use it very quickly because I don't see any urine in nature being saved or collected.
My initial low tech system will probably be a 5 gal bucket to catch the urine from the RV toilet and dump it daily. I'll have to figure out how long to hold the flush to get a good dilution. Of course I've also read that by diluting immediately, you lose the benefit of the ammonia change killing bad bacteria but hopefully we don't have too much of that.

And that was probably no help at all.

John Pollard wrote:Waiting for the scientific community to make up their mind and agree on something. In the end, it's whoever has the best funding and political/business connections that wins the argument publicly.

Yeah, I'm not really talking about waiting for the scientific community to pronounce on compost toilets, that's likely to be a long wait. But I'm guessing that the basic biochemistry of urine decomposition and it's relationship to bio-available nitrogen in compost/soil may well already be quite well understood, and I figure that's a good place to start in making decisions about this stuff. If the knowledge is already out there it makes sense to use it..

John Pollard wrote:
I think the "permaculture spirit" is more like, if it already happens in nature, then it's probably ok.

Agreed. The tricky bit is identifying what "happens in nature". It involves a whole lot of assumptions about what is "natural" and also a lot of presumptions about our ability to identify the salient features of natural systems when trying to replicate them (because we never replicate them completely). That's where the skill in observation comes in. We can get over-confident about our abilities to take apart natural systems and understand how they work (that's Fukuoka's whole gripe, as I read it); but equally if we go too far the other way, we deny ourselves the tools to make meaningful observations, because we can't distinguish what is relevant information from what isn't. My preference is probably further over to the analytic end of the spectrum than most, but I recognise that it's a balance.

John Pollard wrote:
And that was probably no help at all.

Not at all, it's always good to hear other people's experiences and perspectives. It may not be the way I'd approach it but it's still a data point!

Analysis Paralysis. Sure there's information out there but there's always tendency to over analyze things and a decision is never made due to differing theory and/or variables. It's pee not rocket science. Scatter it here-n-there and don't aim into the wind. It'll be fine.

Good topic. I wish we had more information.

FYI, urine from a healthy person is sterile. No pathogens to worry about. A person would have to have an active urinary tract infection.

As for parasite eggs in urine, those parasites have to go through an intermediary host before they could reinfect a person. So it's best not to pee into a pond or river.

John, a question about chelating. We presently collect some urine in a bucket of biochar which gets added to the compost every three days or so. What's your take in putting rust nails in the bottom of the bucket? I have access to plenty of rusty metal.

Su Ba wrote:
John, a question about chelating. We presently collect some urine in a bucket of biochar which gets added to the compost every three days or so. What's your take in putting rust nails in the bottom of the bucket? I have access to plenty of rusty metal.

I give two thumbs up to that idea -- that's how I dispose of little scraps of iron.

The problem with burying the iron as is and letting it rust is that it turns into iron(II) oxide in the soil, which is still a little difficult for plants to digest. It needs some chloride or ammonium or urea to come along to make it a little easier for the cell to absorb. That's why blood meal makes such good fertilizer, the iron is still sitting in its heme cages ready to be cycled into biochemical pathways.

Chelation sounds interesting. Unfortunately my knowledge of chemistry is a bit lacking, but two other possibilities I have heard of but don't fully understand is lactofermentation of urine, and producing struvite.

Here's my understanding:

When we collect urine and don't treat it but just let it sit for a few months, the natural process is that at some point, the pH will get really HIGH, rendering it pathogen-free. The problem with this is that the urea hydrolyzes and off-gases CO2 and NH3 or NH4, don't remember which. CO2 is a greenhouse gas and Ammonia/Ammonium is taking your much-desired nitrogen off into the atmosphere, leaving a less potent fertilizer.

BUT, lactofermented urine sidesteps this process because instead of going HIGH, the pH goes LOW, creating pathogen-free fertilizer while keeping the nitrogen content.

•••

Struvite is made when you add magnesium and stir for about 10 minutes.  Something apparently coagulates and can be filtered out from the liquid effluent as a sort of paste which can contain up to 90% of the phosphorus from the urine in the crystals which can be dried into an odor/pathogen/hormone/pharmaceutical-free powder with far less volume and therefore easily transportable fertilizer. The effluent still can be used and still contains many of the other nutrients.

This is my understanding, but I may have gotten some of the technical terms wrong.

Is this also a form of chelation?

Also, can anyone tell me if the two processes I described are mutually exclusive? Or is there any benefit to fermenting urine AND extracting struvite? And if both can be done, in which sequence is best?