Cities are throwing away a fortune in urine, I learned the other day while visiting Dr. Noemi Stadler-Kaulich, a German agro-forester and long-time resident of Bolivia. The urine from an average person contains $85 dollarsÂŽ worth of phosphorous in one year, Noemi explained. Urine is rich in phosphorous, nitrogen and potassium, the main elements of fertilizer (chemical or organic). A metropolitan area like Cochabamba, with 1,200,000 people, flushes away over $100 million worth every year, Naomi explained, just in the phosphorous from urine, turning the valleyâs main river, the RĂo Rocha, into an open sewer.
Noemi has dry latrines on her farm near the town of Vinto, on the edge of the Cochabamba metropolitan area. If you have never sat a dry latrine it can take some getting used to. There is a large hole for feces and a smaller one, up front, to collect the urine, which can be used right away as fertilizer. After defecating, one walks around to the back of the latrine and adds a handful of wood ash to the deposit, which is composted once the container is full. Dried, composted human feces are an excellent, dry fertilizer with little or no smell.
I used to have a nice dry latrine in Honduras. It used no water and made little odor. But dry latrines do take a little management. At the time I was worried about pathogens and had samples from dry latrines analyzed at a laboratory in Tegucigalpa. The samples were free of the most common parasites and pathogens. Dry latrines compost the night soil for at least six months, which helps to kill pathogens. Still, this demands some competent management.
At our home in Cochabamba, we began recycling urine about a year ago. Urine is easy to collect in a jar or bottle or while sitting on a chamber pot. You can mix urine with water or apply it straight to the soil, near plants. We put most of our urine on the compost pile, where the pee helps to speed up the decomposition of paper and dry plants. Urine in a compost heap has no smell at all; perhaps in part because the nitrogen in urine quickly breaks down into ammonia.
I have not yet been able to confirm Noemiâs estimate of the value of phosphorous in urine, not to mention the potassium and nitrogen, but urine is certainly worth something as fertilizer. Recycling urine also helps to save water. Conventional toilets waste up to six liters of precious water to flush 300 ml of urine.
As it is now, modern conventional agriculture applies nitrogen, phosphorous and potassium (NPK) to crops, and (at least some of) the nutrients become part of the living plants, which are eaten by people and later discarded as human waste. No doubt in the future clever people will find other clean, convenient ways to recycle this NPK, without wasting water. In the meantime, saving urine as fertilizer is a golden opportunity.
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Further reading
Andersson, E. (2015). Turning waste into value: using human urine to enrich soils for sustainable food production in Uganda. Journal of Cleaner Production, 96, 290-298.
