By Harrison Suchyta
The Nature Academy is focused on training a new generation of environmental leaders in sustainability, conservation, and ecological restoration. As part of the Nature Academy program, each intern writes a blog post and develops a project. The project provides an opportunity to take on responsibility in an area of interest, contribute to the goals of their team, and develop a skill or area of knowledge that can be added to the intern’s portfolio. The post may reflect the project or be a nature-related topic of personal interest to the intern.
Usually the things that go down the toilet are gone forever. Toilet paper? That goldfish you had in middle school? All lost to a sewer system you will most likely never see. If these other more tangible things are gone then it would make sense that urine, something toilets were built to collect, would be gone forever too. Yet my research challenges that notion and seeks to introduce urine to ecological systems through use as a fertilizer.
Using urine as a fertilizer may seem far-fetched, but the elements found in urine—nitrogen, potassium and phosphorus—match those found in fertilizer, and are required by plants. My work this summer has been split between Dr. Nancy Love’s environmental biotechnology lab for the College of Environmental Engineering and as a summer intern at Matthaei-Nichols.
In the lab I learned several things: what kinds of problems fertilizer and wastewater facilities pose, how urine-derived fertilizers solve environmental issues by preventing certain elements from reaching those facilities, how urine-derived fertilizer is developed, and possible applications for it in the future. I also learned about how fertilizers are used, what types of fertilizers exist and what opportunities exist for urine-derived fertilizers from my work in the botanical gardens.
Curves showing potential phosphorus decline (left) and the growing number of coastal dead zones around the world.
Fertilizer made from urine aims to solve problems with eutrophication, which is nutrient build-up in bodies of water. This build-up cultivates bacterial growth, which draws oxygen out of the water. Most wastewater facilities in coastal cities treat water for both nitrogen and phosphorus. But inland cities, especially those on the Mississippi River, only treat for phosphorus, leading to dead zones in places like the Gulf of Mexico since the excess nutrients travel down the river and culminate in the gulf. Nitrogen and phosphorus are also two of the most energy intensive elements to treat, and by removing them from wastewater plants the energy consumption would drastically decrease.
The extensive use of fertilizer also suggests that phosphorus is abundant. But research in phosphorus mining suggests that supplies will be gone or in strategically difficult-to-access places within the next one hundred years. The limited availability of phosphorus makes collecting urine, an entirely renewable source of the element, much more appealing.
Aside from preventing phosphorus overproduction, urine-derived fertilizer also limits energy consumption in wastewater facilities. The toilets that collect the urine are waterless urinals completely detached from sewage systems. This reduces water consumption and prevents urine from reaching wastewater facilities. One of these toilets is currently in use at the GG Brown building at the University of Michigan. Only a urinal is in use right now because of the difficulty of separating solid and liquid wastes for our current research purposes.
Urine-derived fertilizer is developed in a number of ways, but the lab I’m working with only focuses on freeze-thaw and struvite methods. Before any of these methods can be applied, the urine is heat pasteurized to get rid of any bacteria. The freeze-thaw method works by freezing a large volume of urine. Nitrogen, potassium, and phosphorus’s properties as salts prevent them from freezing, allowing concentrated elements to leak out and leave behind low-nutrient water. If ratios of the elements need to be adjusted, extra nitrogen, potassium, and phosphorus can be pulled from a volume of urine by applying a potassium chloride powder to the urine. The potassium bonds with the nitrogen and phosphorus, creating a powdery substance (struvite) with all three elements.
Urine undergoing the freeze-thaw method. The darker vials are the more concentrated products of the method while the lighter ones are low-nutrient water.
The next step of this project is to apply it to some of the beds in the Nichols Arboretum Peony Garden in summer 2020 and compare it to growth in other peony beds. Getting the word out about this project will help raise public awareness of urine-derived fertilizers and educate people on how they’re made and why they are environmentally friendly. By creating this exposure, we hope to get more people to feel comfortable with urine-derived fertilizers and bring an end to the idea that waste is gone forever once it goes down the drain.