Friday, January 2, 2009

Straw Bale Urinal

Well, I admit it's not the usual thing to do on New Year's Day, but I set up a straw bale urinal. Why? Because, quite simply urine is Liquid Gold!

This is what a typical adult produces a day:

Urine produced per adult per day:
Quantity - 1000 - 1,500g/day wet weight
Water Content - 93 - 96%

Contents, Typical daily yield:
Nitrogen (N)- 8g
Phosphorus (P)- 2g
Potassium (K)- 2g
Calcium (Ca)- 2g
Carbon (C):N Ratio - 1:2
Pathogens - None in normal circumstances
(Source: Harper, P. and Halestrap, L. 1999, Lifting the Lid - I've been reading it as part of my MSC)

All that Nitrogen, Phosphorus, Potassium and Calcium is ideal for growing crops. And believe it or not, in healthy people urine is sterile. Plus, pouring that urine down the toilet can cause problems to river water.

Good garden compost needs a ratio Carbon:Nitrogen ratio of about 30:1. You can see from the figures above that urine has more nitrogen than carbon. A straw bale on the other hand is almost all carbon. So the solution is get a straw bale and pour (or directly apply) urine you've collected onto it. The fresher the urine the better - don't let it stand in a container for more than a day. I'm collecting mine in a 6 pint plastic milk container - empty.

I bought a couple of dry straw bales from my local farm shop Hollow Trees in Semer for £2.50 each and a couple of reusable plastic bags to carry them home in. Then I covered one of our small 1 metre by 1 metre raised beds with cardboard, put the straw bale on top and have been generously applying urine on a daily basis. I'm keeping the bale covered with one of the plastic bags between applications.

The straw bale weighed 2.5 stone - just under 16 kilos, with a Carbon:Nitrogen ratio of 80:1. At the moment I don't know how much Carbon by weight. I don't actually know the Nitrogen content of my urine, but as I have a good diet high in protein - plant protein only now of course (except for free range organic eggs and milk) - I should be putting out at least 8g Nitrogen a day. Note: I'm not getting into molar mass stuff here. Carbon's atomic weight is (usually)12 and Nitrogen's is 14 so they pretty close enough for this type of experiment. But I won't always be at home when I urinate, I may be at work or out, and some the nitrogen in the urine can oxidised in ammonia gas and drift away. But as I haven't got figures for the Carbon content of the bale yet I'll continue to pour my urine on the bale and hopefully watch it break down into rich humus that I can spread on my vegetable plot - or maybe grow oyster mushrooms in - but that's another experiment.


  1. Hi Craig,

    You forgot to say that the house is on a water meter. Have you worked out how much water (therefore money) you will be saving?


  2. I came across this blog looking for info on mushroom composting and the possibility of using human urine to break down the straw.

    Mx make a good point on the water meter but because the water disposal charge is made up of 95% of the water meter throughput if you use less water you not only save on paying for the cubic meters of water saved but also on 95% of the sewage charge (as indicated on consumption).
    Catch water from the roof, filter through a sock filter and use it for toilet flushing, clothes washing, etc and you are beginning to save quite a bit. Also because rainwater is soft it uses less detergent or soap (assuming you might be in a hard water area). You can also claim back an allowance each year from the waste sewage/waste water charge if you make sure rainwater is NOT fed into the main sewer.

  3. Where are places to get straw bales then?

  4. Hi Anap
    I got my at a farm shop. You may be able to buy a couple off a local farmer. Or just google "straw bales for sale"