Researchers in the University of Michigan's Department of Civil and Environmental Engineering are focused on using human urine as fertilizer. A test site? U of M’s beloved peony garden. The project, coming out of the Nutrient-Energy-Water Cycles Group (N-E-W cycles) group led by Dr.Nancy Love, started informally in 2017 and aims to spread awareness of using human urine as a bio-based fertilizer. The urine-derived fertilizer (UDF) contains nitrogen, phosphorus, and potassium, all essential nutrients for plant growth found in synthetic fertilizer. For the past three years, peony beds 24, 25, 26, and 27 have received the UDF treatment, and preliminary results indicate no significant difference between urine-derived and synthetic fertilizers. If you’re thinking “ew!” worry not - the pee goes through a multi-step cleaning process. But the urine is still local, collected nearby at two sites in the GG brown building on North Campus, one a urine-diverting toilet, and another a waterless urinal.
The UDF is pasteurized, so there's no pathogenic or viral content, and pharmaceuticals are removed from the urine. However, Joe Lybik, a third-year PhD student in the lab, explains that “there's still a little bit of a social factor to overcome.” That’s where the peony garden come in. In addition to experimental test plots in the garden, researchers speak to peony garden goers to explain nutrient cycles and gauge their perceptions of UDF, have surveyed attendees in the past, and will provide some UM-generated UDF handouts this year.
The results so far? A general openness to the use of urine as fertilizer. “There is still this initial ick factor, kind of like, 'oh my god, you're using urine as a fertilizer,” Joe explains. “But once you start explaining a little bit more of the process, that it's sanitized, that we run it through processes to remove micropollutants and pharmaceuticals, you start to see a lot more acceptance towards the use of the product.”
To determine the efficacy of UDF, researchers gauge peony growth between the test and control plots for each spring. They measure the circumference of the plants and qualitatively describe how leafy the plants are. Joe explains that this data is key to understanding how the nutrient concentrations in UDF are influencing plant growth. “Urine contains nitrogen, phosphorus, and potassium, which are all key components to fertilizers. And if you want a really leafy green plant, typically you want a lot of nitrogen in your fertilizer. If you want a really nice flower with pretty colors, you tend to want more phosphorus and potassium, and so we need to keep track of what's happening to the peony plant. Is it growing a lot of leaves, or is it growing a lot of blooms and buds and flowers and things like that?”
Pee is for Partnership
The N-E-W Cycles group collaborates with the Rich Earth Institute, a non-profit based in Brattleboro, VT, that champions a community-wide approach to UDF, supporting sustainable agriculture and protecting vital water resources. They also emphasize education, providing free resources for starting your own community-scale urine diversion program, and distilling the science into motivating statistics. For example, did you know that the urine one human produces each day from the food we eat contains these same nutrients, and has enough to grow the wheat for a loaf of bread?
The institute has a for-profit spin-out company called Brightwater Tools that develops the technologies to support community-scale urine diversion. In collaboration with Dr.Love, they completed a research study that resulted in a patented product, a freeze concentrator system, which concentrates the nutrients and urine even further, to a level where it can be a commercial fertilizer product. The first installment of the freeze concentrator system is on U-M’s North Campus.
“We have a research fertilizer license from the Michigan Department of Agriculture, so our product never actually gets classified as waste, which is really important because there are a lot of rules and restrictions around handling waste,” Joe explains.
They can also use magnesium to precipitate the phosphorus from the solution, Joe explains further, resulting in a solid form of phosphorus fertilizer and a more concentrated liquid nitrogen fertilizer.
“Sometimes you want more phosphorus, and sometimes you want more nitrogen. And so we were really doing a lot of work on trying to figure out what the best fertilizer composition is for a given plant. How can we create custom fertilizers? How can we create fertilizers in either liquid or solid forms that farmers may prefer to apply?”
We’re in climate trouble, and urine is a solution.
Synthetic fertilizers for agricultural production are created using energy-intensive, polluting methods. 2% of global carbon emissions come just from ammonia production, one of the biggest fertilizer products. Research suggests that worldwide wastewater holds enough nutrients to offset 13% of global fertilizer demand.
However, despite decades of research focused on trying to recycle nitrogen and phosphorus from wastewater treatment plants, the retrieval rate is still hovering around 10 to 15% for the nitrogen that gets sent to a wastewater treatment plant, and 20 to 25% for phosphorus. Instead, through source separation, we could harness these nutrients before they leave the bathroom.
“The idea is, instead of mixing all of your waste together, diluting those nutrients into the regular wastewater, and then sending it to the wastewater treatment plant where they have to spend a lot of energy to separate those really dilute concentrations of nitrogen and phosphorus, we can just go upstream to the source,” Joe shares.
‘Flush and Forget’ to ‘Flush and Fertilize’
Will there be a future where all of our toilets will be urine-diverting? Perhaps. Until then, Joe is focused on reaching a more attainable goal. Currently, UDF can’t compete at a cost level with synthetic fertilizers that carry a high environmental cost, but are cheap to produce. Instead, Joe sees the winning game on the treatment plant side, where removing nitrogen and phosphorus and reducing the use of potable water for flushing is one of the biggest drivers of energy costs and GHG emissions. “I think if we can get to a point where there are enough people doing urine diversion, to where we can have downstream impacts on the wastewater treatment plant, where they're not accepting as much volume of wastewater so they don't have to spend a lot of capital costs to expand their treatment plant with growing populations. And if we can help them reduce their energy usage through decreasing the amount of nutrients that are getting sent to the wastewater treatment plant, we can do that.” A study out of Melbourne suggests that those impacts require just 5% of the total urine that a municipality creates to be diverted.
Joe’s call to the broader population is to consider that urine is valuable and to be open to changes that are working for a sustainable future. “Our current systems are not set up to be efficient and are set up to be circular. Being more comfortable with the change that it's going to have to take to improve, to improve our waste systems and our food systems, I think will be really important, and to lean into solutions that will help the world in the long run.”
