Could human urine be used on a commercial scale to fertilize the food we eat?
One way to begin to close the fertilizer/food loop could come through using a surprising, yet incredibly common resource, and one that every human on the planet produces daily. However, this resource, human urine, is currently considered to be waste, and we generally flush it (along with gallons of clean drinking water) down the toilet, where travels to the local wastewater treatment plant to be cleaned.
What's wrong with this picture?
Well, aside from the fact that we use large amounts of potable water to remove a relatively small amount of urine from our houses each day, that yellow liquid also happens to be full of nutrients that could be used as fertilizer for crops.
Instead of sending urine, as one component of the treated wastewater, back into local waterways, where it is implicated in the growth of algal blooms due to added nitrogen and phosphorus from the pee, if the urine is separated and diverted from the wastewater, it could help to solve a couple of related issues.
Removing nutrients such as nitrogen and phosphorous from wastewater isn't nearly as easy as removing solids, pathogens, and other pollutants, and most wastewater treatment plants aren't equipped to do so, instead sending those nutrients on downstream, where they can create issues in the ecosystem. According to this article, even though urine makes up just 1% of the wastewater, it contains about 80% of the nitrogen and 45% of the phosphorus, so separating urine from other wastewater sources could allow for recapturing these valuable nutrients, while also cutting the cost of treating the water.
To that end, a group of researchers at the University of Michigan Engineering department are investigating the use of disinfected human urine as fertilizer on a large scale, where it could supply important plant growth nutrients and help to close "the nutrition cycle."
For a more in-depth look at peecycling, the U of M Engineering department has a great Toilet to Table feature. If you just want to start peecycling at home, you can follow Sami's example, or if you're an adventurous home chemist, you can try your hand at making phosphorus from your own pee.