What happens when human urine ferments?

January 21, 2012 4:08 PM

What happens when urine ferments? I am interested in the chemical formulas, health effects, and agricultural fertilizer applications. More specifically: one gallon of human urine stored for 7 days in a plastic milk jug at room temperature.
posted by gray17 to grab bag (19 answers total)

Urine comes out sterile, but immediately attracts microbes (the result of which is the smell). I've heard the best practice for fertiliser use is to store it in an air-tight container for several weeks or months to allow the microbial blooms to run their course, and also allow the high nitrogen content to reduce (it'll burn most plant roots if applied undiluted). After this period the n/p/k ratio should settle to around 1:1:1, which safe for pretty much everything.
posted by Kandarp Von Bontee at 4:20 PM on January 21

Usually if you let urine sit undisturbed you will get a precipitate of Tamm-Horsfall proteine, in amounts that vary, depending on the individual source, and this is part of the cloudiness you notice at the beginning. I really do not thinks it ferments in the sense of alcohol fermentation, just that urea is converted to carbonate of ammonia.

Disclaimer: I'm not a chemist, just a lab peon who has learned odd factoids here and there.
posted by francesca too at 4:39 PM on January 21

Are there adverse health effects from being exposed to the vapors if the milk jug is indoors?
posted by gray17 at 5:16 PM on January 21

It'll fill the room with a miasma so bad you might puke, and it may attract flies, but you're not going to get poisoned or diseased from it unless you drink it.
posted by Kandarp Von Bontee at 5:26 PM on January 21 [1 favorite]

I am am microbiologist who likes to garden but I am not your microbiologist and this does not constitute microbiological advice.

So long as you use decent aseptic technique, a reasonably sanitized milk jug, and a collection of healthy sterile bladders fed by reasonably standard diets, after 7 days you will likely get a largely unchanged gallon of piss.

If what you are looking for is an exhastive report of what is in urine and what it could do to you, then you want to crack open NASA Contractor Report No. NASA CR-1802, D. F. Putnam, July 1971(PDF). Its pretty comprehensive.

Urine from a perfectly healthy adult aught to be sterile, though it isn't always, and so is still worth handling with respect, especially in terms of exposing folks who didn't produce the piss. This is a great guide to best practices for safe storage of urine for agricultural purposes. Here is their small scale agricultural guide Urine can be a great and safe way to fertilize your garden, but only if you understand the safety risks, make sure you do.

This is a great practical guide if you want to actually go ahead and do it:

"Keep in mind that urine is very high in nitrogen. You may need to pee daily, but your plants don’t need your daily pee. Choose plants that need lots of nitrogen, such as corn and squash, tomatoes and cucumbers during their fruit-bearing stage, and older plants that need a boost. Signs of nitrogen deficiency include yellow or pale green leaves, and some plants have key signs, like pointed cucumbers. Don’t overdo it at the beginning of the season, as excess nitrogen can lead to bushy, leafy plants that bear little fruit. Signs of excess nitrogen include curled leaves, and these plants may also attract aphids. For garden plants in need of a genuine nitrogen boost, once or twice a month is generally fine, though some people will add highly diluted pee a couple of times a week. If you have more pee to give, try your lawn, trees and bushes.

As a basic premise, the urine must be mixed with carbon-rich materials in order for the nitrogen to become accessible to the plants. Carbon-rich materials can include leaves, straw, or just good quality earthy soil. The nitrogen in urine is in the form of urea, creatine, and ammonia; when mixed with carbon-rich materials, the aerobic bacteria convert it into nitrates, which the plants can then uptake.

Here are a few possible ways to use pee in your garden or landscaping.

Recipe 1: Watered-down pee
For soil with good drainage that is crumbly and earthy-smelling. Also works well for container gardens.

Grab a reclaimed plastic container and take a pee. Dilute it with eight to ten parts water, and apply it to the soil. Easy peesy. Working the urine into the soil or applying the urine under the top layer of soil would ensure that less nitrogen is lost due to conversion to ammonia gas, and the presence of soil organisms would help neutralize the (rare chance of) pathogens, though just pouring it on the soil works okay too. After applying the pee, water the plant.

Recipe 2: Straight up pee
For soil with a thick layer of carbon-rich mulch, like wood chips and leaf mulch.

This is the easiest method. Just pee on the mulch. The mulch will stop the plants from receiving an overly-concentrated blast of urine, as well as helping to break down the nitrogen into a source the plants can use. Peeing between two layers of mulch will lessen nitrogen losses from conversion to ammonia gas.

Recipe 3: Compost pee
Urine can be composted. It’s very high in nitrogen, so it counts as a "green" in the compost, and shouldn’t be added to a compost bin that is already high in nitrogen-rich materials like food scraps. Be sure to add plenty of carbon-rich materials, like dry leaves, sawdust, straw and cardboard. Urine can act as a starter for a compost, encouraging the decomposition process, such as adding urine to a pile of leaves.

Recipe 4: Straw bale bathroom
You can urinate directly on a bale of straw until the straw decomposes, and this compost can later be added to your garden. We’ve even met a gardener from Montreal who plants directly in the decomposing straw bales to create a new garden.

Recipe 5: Greywater with a hint of yellow
Greywater is the waste water from showering, doing dishes, etc, and urine can be added to a greywater system. The greywater provides some carbon and significantly dilutes the urine. Ideally this should drain into an aerobic greywater system with natural filters like plants and gravel. Instructions for installing such a system can be purchased from the EcoWaters Project in the guide How to Build a Washwater Garden Plan.

Keep in mind: Urine is high in salt. This is one reason why it needs to be properly diluted. Not all plants respond well to high salt content. Reducing the salt in your diet can be helpful to your own health and improve the salt ratio in your urine."

Also of interest,
Human urine harvesting and utilization as an organic fertilizer(PDF)
Guidelines on the use of urine and faeces in crop production(PDF)
WHO: Urine Diversion: Hygienic risks and microbial guidelines for re-use(PDF)
posted by Blasdelb at 7:09 PM on January 21 [105 favorites]

urine must be mixed with carbon-rich materials in order for the nitrogen to become accessible to the plants. Carbon-rich materials can include leaves, straw, or just good quality earthy soil.

That explains why the first gunpowder recipes required scraping the aged and dried residue of horse urine from the walls of straw-lined stalls.
posted by StickyCarpet at 7:41 PM on January 21 [7 favorites]

Kandarp: After this period the n/p/k ratio should settle to around 1:1:1

Waitaminute. Don't you end up with the same proportions of N/P/K as you started with?
posted by exphysicist345 at 8:46 PM on January 21

IIRC it comes out of most healthy people at about 20:1:2 (though obviously this can vary a great deal, e.g. if you've eaten a lot of protein, resulting in more urea). I've seen a few sources report that the longer it's aged, the closer the ratios tend to level out. I guess the nitrogen evaporates and/or is metabolised by microbes.
posted by Kandarp Von Bontee at 10:01 PM on January 21

Don't you end up with the same proportions of N/P/K as you started with?

If it's stored in an unsealed container, a lot of the nitrogen will evaporate in the form of ammonia. But really, as a gardener, storing urine in liquid form at room temperature is just making a large collection of rods for your own back (as is storing greywater likewise). Listen to Blasdelb.
posted by flabdablet at 2:27 AM on January 22

Blasdelb's answer is fantastic. As you can see from the links given, the real research and how-to guides for this are mostly found in international development water and sanitation manuals. Knowing this will help your online and library searches; do be aware, though, that most of these manuals are written for hot-weather places, and if you are in the US or Europe you will have the winter storage issue. There has been a lot of work in Sweden especially on urine separation on a large scale (example, another), and you may be able to learn from those experiences.
posted by Forktine at 5:58 AM on January 22

I am a dyer, but I'm not your dyer, and this does not constitute dyeing advice.

Humans have been collecting and storing urine for thousands of years, for use in dyeing textiles. When you allow a few gallons of urine to ferment undisturbed in a sealed container for a week or so (preferably in a very warm place, like a slow oven) you are creating the kind of alkaline, deoxygenated solution that is necessary for use in indigo dyeing. Add your indigofera tinctoria and off you go.

(If you have a lot of protein in your diet, you'll want to carefully siphon off the liquid at the top of your urine fermentation container and leave the sediment behind - it'll make the resulting dye clearer and brighter.)

I have studied many, many historic accounts of indigo dyeing in various cultures, and I have yet to see mention of any dangers in storing large amounts of fermenting urine. I don't know if that means there are no health effects, or if the recorders simply didn't see it as worthy of notice compared to the financial value of the trade in indigo-dyed cloth.

(Personally, I use a different method to produce an indigo vat, as I cannot generate enough urine on my own and my family & friends decline to cooperate.)
posted by Mary Ellen Carter at 6:47 AM on January 22 [8 favorites]

Blasdelb Recipe 4, with modifications: Urine collected in a urinal or porta-potty dumped into a plastic barrel with holes drilled in the bottom and top (and screened against flies). Barrel is kept full of hay, added as it concentrates down. Containers are rinsed with water, that's added. Works fine summer of winter. No issues with odors (nice grassy smell) or freezing.
posted by RichardS at 12:34 PM on January 22

I gave this book on watering your plants with pee as a Secret Quonsar gift in 2010. I can't vouch for its effectiveness but it is full of beautiful watercolor illustrations.
posted by Tesseractive at 12:43 PM on January 22

If you are on the bed any medications, you should be wary of concentrating them and their byproducts in your food supply.
posted by fake at 12:48 PM on January 22 [1 favorite]

"If you are on any medications"...
posted by fake at 12:49 PM on January 22

There's more than one reason the chemical symbol for phosphorus is P.
posted by Sys Rq at 2:23 PM on January 22 [1 favorite]

I haven't read it myself, but Cool Tools recently recommended Liquid Gold: The Lore and Logic of Using Urine to Grow Plants.
posted by gwint at 6:11 PM on January 22

Whoops, sorry Tesseractive.
posted by gwint at 6:12 PM on January 22

I've used my urine in my garden and I can tell you that it kind of smells if you use a lot on container plants.
posted by latkes at 7:39 PM on January 22