We’re hitting peak P! Forget about fossil fuels, we are running out of phosphorus, shown in the periodic table with the symbol ‘P’. P is important: it is literally in our DNA. While there are alternatives to energy from fossil fuels, there is no alternative for phosphorus. 
Even worse: P pollution is messing up our water bodies. We really need to prevent nutrients like Nitrogen (N) and P getting into water bodies in the first place.
About 16% of all mined phosphorus enter wastewater treatment plants with about 8% being discharged to the environment. That’s approximately 1.5 million tonnes of P  and 7.4 million tonnes of N  that are released into surface water each year.
Energy is expensive. It takes about 45 MJ to remove 1kg of N, and about 49 MJ for every kg of P removed. All this energy to take something out that should not have been there in the first place.
Consider this: Pee = P.
Urine is a major source of P. Urine makes up less than 1% of domestic wastewater by volume, but it contains about 80% of the nitrogen, 56% of the phosphorus and 63% of the potassium of this wastewater. On the other hand, urine has very few pathogens, so it makes sense to keep urine separate from other wastes!
The University of Cape Town is doing research on how best to recover urine. We need your help. More immediately, we need your urine. And hey, seeing that it’s a great idea to let it mellow if it’s yellow, let us have your mellow yellow for a great cause!
D. Cordell, S. White, Life's Bottleneck: Sustaining the World's Phosphorus for a Food Secure Future. Annu Rev Env Resour 39, 161 (2014).
B. E. Rittmann, B. Mayer, P. Westerhoff, M. Edwards, Capturing the lost phosphorus. Chemosphere 84, 846 (2011).
G. Van Drecht, A. F. Bouwman, J. Harrison, J. M. Knoop, Global nitrogen and phosphate in urban wastewater for the period 1970 to 2050. Global Biogeochem Cy 23, (2009).