Removing Salt from Urine

This winter, I stumbled on a way to easily remove salt from urine before using it as fertilizer for the garden.

Just put the container of urine in a refrigerator overnight. The salt precipitates out and sticks to the walls of the container. You can then pour out the liquid and the salt will stay stuck to the walls.

I use a wide mouth, roughly 12 cup plastic container (the type used for protein supplements from Trader Joe's). After pouring out the liquid, I've needed to scrub the inside of the container using a rubber glove and dedicated course sponge in order to remove the salt. Tried just pouring in hot water to dissolve the salt. After letting it sit overnight outside in the cold, the salt had not dissolved. Will try letting it sit inside to see if I can get rid of the salt without scrubbing.

Only done this a few times so far. You can really tell if you've been eating salty food, like nachos, by the amount of salt that precipitates. Most times for me it is very little, so this extra effort probably isn't that worthwhile.

Do plan on evaporating some urine after this cold treatment to see if it gets most of the salt out.


http://lowcostvegetablegarden.blogspot.com/2013/03/removing-salt-from-urine.html

Are you sure you're not removing the urea as well?

...

I wonder if there is a viable way to recycle the NaCl back into one's diet.

Two things.

1) housemates.

2) is the urea precipitating out too??  

If this does work, then yay! amazing!  this is a crucial part of the cycle, seems like long-term you'd have an accumulated problem just from peeing.  

At the same time, animals have been peeing for millions of years all over the place, and it hasn't caused a huge problem.  

Do we just eat too much salt?

I like salt.
 
Would love more thinking and info on this!  thanks for this awesome possibility!

...

I wonder if there is a viable way to recycle the NaCl back into one's diet.

OK, this would be waaaaaay on the gross cycle, but "we could pickle with that..."  I'm conjecturing the friendly bacteria outpace the others.  Sandor Katz said that there had been 0 cases of anyone EVER being poisoned by fermented vegetables by WHO or the CDC or something. . .thoughts?

or, do you have a salt water aquaponic pond?

seaweed/algae-growing operation?

scrape it into a big vat in the sun and fill with pure water, then let it evaporate (doesn't work in the city--too much gross black stuff in the air)

OK, according to wikipedia it seems pretty hard to "precipitate" urea out of water.  

On the other hand, I couldn't get clarity about whether the salt precipitates out of the water when it is cooled.  Is there a chemist in the house?

wikipedia:

Urea was first noticed by Hermann Boerhaave in the early 18th century from evaporates of urine. In 1773, Hilaire Rouelle obtained crystals containing urea from human urine by evaporating it and treating it with alcohol in successive filtrations.[59] This method was aided by Carl Wilhelm Scheele's discovery that urine treated by concentrated nitric acid precipitated crystals. Antoine François, comte de Fourcroy and Louis Nicolas Vauquelin discovered in 1799 that the nitrated crystals were identical to Rouelle's substance and invented the term "urea."[60][61] Berzelius made further improvements to its purification[62] and finally William Prout, in 1817, succeeded in obtaining and determining the chemical composition of the pure substance.[63] In the evolved procedure, urea was precipitated as urea nitrate by adding strong nitric acid to urine. To purify the resulting crystals, they were dissolved in boiling water with charcoal and filtered. After cooling, pure crystals of urea nitrate form. To reconstitute the urea from the nitrate, the crystals are dissolved in warm water, and barium carbonate added. The water is then evaporated and anhydrous alcohol added to extract the urea. This solution is drained off and evaporated, leaving pure urea.

Some plants reportedly benefit from some salt, here's an article from NPR (take with a grain of salt):
Salt Water Irrigation Yields Tasty Tomatoes
I've been using my pee in my garden since 2013 and had no issues with salt from urine.

100 ml of urine has about:

2 g urea
0.2 g sodium
0.2 g potassium
0.1 g creatinine

Sodium chloride has approximately the same solubility in refrigerated water as it does in body temperature water (35.7, and 36.4 g/100ml respectively), so I don't think that sodium chloride would be precipitating. Especially considering that the concentration of sodium at 0.2g/100ml is far below the solubility of table salt in cold water.

I couldn't find measured data on the solubility of urea in cold water, but by extrapolating the solubility curve, I estimate that it's about 75g/100 ml at refrigerator temperatures, in other words, about twice as soluble as salt.

creatinine at refrigerator temperatures has a solubility of about 0.6 g/100ml. At body temperature it is described as "slightly soluble". Solubility depends on pH, with normal urine pH levels making it less soluble. So if I were betting on what's precipitating out, I'd guess the creatinine, or other minor components.

Joseph, I agree with you that's it's highly unlikely that the crystals bring observed are NaCl salt. But non-NaCl salt crystals are common in urine. Depending upon the person, crystal production can be high or low, dependent upon the day and diet, depend upon whether the urine is acidic vs alkaline, and depend upon the chemical, health, & genetic make up of the person involved. Plus the longer the urine sits once voided, the more the crystals will precipitate out of it. Refrigeration would also cause crystals to form.

There are numerous types of compounds that form crystals in the urine. Without examining the crystals under a microscope, I couldn't tell you which ones are there in any particular urine sample. During my career I've done thousands of urine slides and have seen numerous very interesting crystals in the samples. But I've never seen NaCl crystals. As I've said, crystals are common enough, so it's no surprise to see them. I just couldn't guess what crystals are in the urine being mentioned.

Personally, I've been using urine on my farm since 2004 and have seen no indication of salt problems. One would be more apt to see salt damage when using commercial fertilizers.....but I don't use them. I should think that if one was concerned about the amount of salt in urine, the easiest approach would be to avoid eating salty foods on a regular basis. The excessive salt in the typical Western diet isn't all that healthy. Another option would be to active enough to build up a good sweat each day. We excrete quite a bit of our salt via sweat. The second best approach would be to simply dilute the urine before using. Most gardeners in my area that are using urine dilute it -- about one cup of urine (or less) to a gallon of water, then use that to water plants that are not drought stressed. If the soil is real dry or the plants are drought stressed, then use half the urine. I'll use diluted urine directly into garden beds that have a good active microbe population. (We collect our urine in a plastic milk jug and then fill the jug with water. One pee per jug.) If I have good microbial action going on the the garden soil, I don't have any odor even when the soil is later tilled or dug. Odor would indicate that I need to get better quality "live" compost into that garden bed.

WOW!  Thank you, once again, amazed at the level of knowledge on this site.

I just love the idea that there's another way to get salt out of the urine.  But sweating is a good one, eating a bit less salt makes some sense too although it's also helpful to put a pinch of sea salt in water if drinking water.  (The Weston A. Price and the herbalist folks say you should drink teas rather than water...but I haven't gotten that habit going.)

Thanks team!

Su Ba wrote:Another option would be to active enough to build up a good sweat each day. We excrete quite a bit of our salt via sweat.

Wouldn't reduce the amount in the soil if I did that - the grey water from the shower goes into the soil the same as the pee does...

I also suspect that a lot of the crystals that form are struvite, which contains a lot of the nitrogen and phosphorus that are the main reason urine is such a good fertiliser.  In fact, a lot of places are deliberately encouraging struvite to form from urine specifically to use as a convenient fertiliser.  I'll post some links later if I have time to hunt some down.

Ok, so that would mean you could scrape the stuff off and use that maybe.

The shower water could maybe be diverted to a part of the garden that is OK with salt, or is more spread out, or has salt-loving marshy plants.  Then dish water and clothing wash water could go to the regular garden.

Joshua, why are you so worried about "salt"? I think that the "salts" you hear about causing problems from soluble fertlizer are various salts, not particularly sodium, and I think Su Ba's experienced advice above sounds great. Urine well diluted and used on soil that has plenty of life, and personally I prefer mulch, seems to work just fine. I've found it only causes problems on 1) already drought-stressed plants, or 2) bare soil, or 3) small seedlings. But diluted urine used into mulch under vigorous plants has worked great in my experience. On bare soil it causes those discolorations of soil that look like "salts." And under seedlings or stressed plants it causes visible damage in my experience.

OMG here's a use for salt--fish, even freshwater fish, need a certain amount of salt, I just learned from someone who has a fish pond in a super-urban setting.  Two biologists next to him seemed to agree or didn't say anything.  And certainly any animal with blood in it needs some salt.

I brush my teeth with salt and baking soda.  maybe this is something i can do with that, or with shower greywater.

We need to know the actual facts about fertilizing with urine.

If you use raw urine in your garden, you are depending on rainfall and irrigation to wash out the sodium salts.
The study below indicates that in ideal conditions of heavy rainfall, something like 5% of salts will remain in the soil after a year.  This sodium does not go away.
Over time this will slowly increase until the soil is no longer tenable, it will be come "sodified," which is the technical term for having too much salt to grow plants.

In areas where there is heavy, dependable rainfall, it would take decades for sodification to occur, but eventually it will be a problem.  It can be mediated by the application of certain calcium compounds.

However, in areas where rainfall is sub-optimum, and regular irrigation is required for plant cultivation, the wash-out does not occur, and sodification can happen much faster.  

So be careful!  Those people who claim that they regularly use urine as fertilizer good results may very well live in a region that has plentiful rainfall, OR, they may have been fertilizing with urine only for a short time.  

Attached is the link to the peer-reviewed paper from 2016 detailing a significant experiment that produced the results I summarize above.  

https://link.springer.com/article/10.1007/s41207-016-0010-9

Never let down your guard against misinformation and disinformation!

Paul, welcome to the forum.

A lot of our members use the urine by diluting it.

Though that is not always an option:

https://permies.com/wiki/113116/pep-greywater-willow-feeders/Give-Urine-Growies-PEP-BB

Here are a couple of threads that others might be interested in:

https://permies.com/t/67128/composting/Fermenting-urine

https://permies.com/t/4876/Urine-fertilizer

I don't dilute urine, I pee straight into my plants, usually a Comfrey plant. I've done it for years. Maybe I'll cause a desert someday.,but I find the idea unlikely. I live in an area with average rainfall.

That's an interesting article and looks impressive, but I'm not convinced it replicates what actually happens in the soil for most gardeners using urine as a fertiliser. Also, it's not arguing against the use of urine, but supporting it, with awareness of the possibility of salt build-up under certain soil and climate conditions.
Final sentence: A supply of 14 g/m2 of calcium led to the full washout of salts that accumulated following previous cultivations of Komatsuna fertilized with human urine, supporting the concept of sustainable cultivation using urine. (emphasis mine)

Reasons I wonder whether this experiment in any way reflects most gardeners real-life experience using urine:
1. They used soil in pots to test for sodium washout, but don't specify what soil they used. What was the microbial and humus content of the soil? It's not stated.
2. They added a LOT of salt to the pots, and as sodium bicarbonate, a different form to most of the salt in urine.
3. The salt-damaged land they refer to is assumed to be due to urine use as fertlliser, but they don't state whether other fertilisers have been used, or how many years it took for the land to become salt affected, or whether the land was also being irrigated with well water. It's also in a more arid area than most Permies will be growing in.
4. They end by saying that adding calcium to the soil enabled complete wash-out of the sodium, suggesting  that salt build-up is more likely to be an issue in semi-arid areas with low calcium soils.

They themselves say "the current finding cannot be transposed directly to the use of urine in real soil in the dry land."