How many times did you flush a toilet today?
It’s a query most of us never consider. Going to the bathroom is a frequent enough exercise that it tends to be void of any distinguishing memory. But it’s a surprisingly important question for two important reasons: Water is a natural resource that is being rapidly depleted, and nutrients that are flushed down the toilet contribute to water pollution.
Now, back to that initial question. The average person flushes five times a day, according to the American Water Works Association. While newer toilets use 1.6 gallons of water per flush, older models can require up to four gallons. The Environmental Protection Agency estimates that toilet flushing constitutes 27 percent of the average person’s water consumption. That adds up to 1.2 trillion gallons annually.
But water isn’t the only resource being flushed away. Nitrogen and phosphorus — two nutrients essential to plant growth — are also being squandered. Negating that waste is the goal of Abraham Noe-Hays and Kim Nace, co-founders of the Rich Earth Institute, a pioneer in developing ways to convert human urine into plant fertilizer. The Institute runs the country’s first community-scale urine-diversion-to-soil-fertilizer program.
Each person’s urine emits, on average, 4,000 grams of nitrogen and 365 grams of phosphorus every year. When urine is flushed it goes to a sewage treatment plant, which does little to remove nutrients. The nutrient-rich effluent, containing nitrogen and phosphorus, is then discharged into lakes and rivers. Both nutrients support the growth of algae and plants, which provide food and habitat for marine life. But too much nitrogen and phosphorus accelerates the growth of algae, which causes significant harm to marine and aquatic ecosystems. The resulting algal blooms can produce elevated toxins that can be harmful to humans. Likewise, nutrient pollution in groundwater can be detrimental, according to the EPA, even at low levels.
Of all the nitrogen flowing into wastewater treatment plants, 75 percent comes from urine; of all the phosphorus, that figure is 55 percent. (Wastewater plants in large urban areas typically have systems for removing the nutrients, but those systems represent a huge capital investment; plants in smaller communities often can’t afford to install the systems.) Not only can the traditional method of flushing and treating human waste be harmful to the environment, it leaves the nutrient cycle broken, in turn necessitating the use of synthetic fertilizer to return those same nutrients to the soil.
“There’s a constant flow of nutrients out of soil and into food crops, off the farm to our plates, through our bodies, into our toilets and then lost,” Noe-Hays says.
The impetus for his research began in 2000, while he was a senior at the College of the Atlantic in Maine, studying human ecology.
For his senior thesis, Noe-Hays installed two waterless toilets in the university library, collected the human waste, and composted it in a container that controlled air flow and monitored composting temperature and oxygen levels.
The conventional way to replace the discarded nutrients is through the use of synthetic fertilizers, which contain nitrogen and phosphorus. Phosphorus is mined from rock phosphate, and nitrogen is produced through a process using natural gas and nitrogen gas from the atmosphere.
“It’s this big open loop — capturing human waste, reclaiming nutrients, and getting them back to farms — that really stood out to me as a critical missing piece,” Noe-Hays says. “No one was really looking at how to do a complete recycle of those nutrients on a community scale.”
By the time he met Nace, at a friend’s potluck dinner the following year, he was designing and building composting toilets. Nace, who had made a film about composting toilets for her graduate thesis and was concerned about the foolish waste of water inherent in flushing toilets, tucked Noe-Hay’s name in the back of her mind. After subsequently spending two years in Chennai, India, where several million had limited or no access to toilets, her passion about the importance of sanitation was rekindled. She returned home in 2010 a year after that, and quickly called up Noe-Hays. By 2012, the Rich Earth Institute was formed.
“We founded the Institute with the goal of pushing the envelope on the issue and moving the agenda forward for a sustainable solution,” Nace says. “We started with urine-diverting toilets, and that’s what we stuck with.”
A urine-diverting toilet separates urine from feces. Noe-Hays and Nace have developed a method of pasteurizing the urine by heating it to 80 degrees Celsius for two minutes, which sanitizes the urine but retains the nutrients.
Since 2012, Nace and Noe-Hays have operated on minimal funding provided by small grants (working for little or no pay). In September, the Institute received $830,000 in research funding from the National Science Foundation, as part of a larger $3 million grant awarded to the University of Michigan to further the study of Innovations at the Nexus of Food, Energy, and Water Systems. (The Rich Earth Institute, the University of Buffalo, and New Water Resources are all collaborators.)
The Institute, which relies on urine donation for its work, has enlisted the participation of businesses and residents in the nearby community. There are over 100 participants (donating 5,000 gallons of urine annually) using some type of urine-collecting toilet or device, and delivering it to a “Urine Depot” (a tank and self-service pump) located at the Institute. Participants can also opt to install a urine-diverting toilet connected to a tank, which is emptied by a local septic company in partnership with the Institute.
For the last few years, the Institute has run field trials with three local farms. Researchers applied 1,000 gallons per acre of urine-derived fertilizer (both diluted and undiluted) and synthetic fertilizer to hay once over the growing season. (They also used fertilizer-free hay as a control.) The yield among the fertilized crops was roughly 1,400 pounds per acre, without significant difference between the treatments. The unfertilized field produced about half as much. Not having to dilute the urine-derived fertilizer makes it more cost- and labor-effective for farmers.
In partnership with the University of Michigan, the Institute has also conducted a study to determine the level of pharmaceutical residuals — including caffeine, antibiotics, and anti-anxiety and anti-inflammatory medications — remaining in the urine after pasteurization. The results found caffeine to be the most prevalent residual in urine. (You’d need to eat a salad made with urine-derived fertilizer every day for a thousand years to get the equivalent of a single cup of coffee.)
“If the Rich Earth Institute didn’t exist we would not be having this conversation,” says Nancy Love, a civil engineering professor at the University of Michigan. “They are the trailblazers of taking this concept and putting it into practice. Getting as far as they have allowed us to get as far as we have.”
Coupled with the scientific research is the need to get people past what Noe-Hays calls the “ick factor.” That makes public outreach an equally significant part of their work.
“We’ll be developing educational communication tools that will be available to the public,” Nace adds, “and we will also be finding the best pathway to explain the science and bring it out to people so they can make informed choices about what they want to do.”
Nace and Noe-Hays recently met with town officials in Brattleboro, Vermont, to discuss making urine-diversion part of the town strategy to meet new nitrogen emission limits imposed on the wastewater treatment plant.
“That’s an area that’s just starting to go forward and it’s exciting because part of the reason we’re doing this is we wanted to do the legwork that enables municipalities and other groups to use urine diversion as a tool to meet their nutrient control strategies, and to create more sustainable systems on a broad scale for managing human waste,” Noe-Hays says.
Neither Nace nor Noe-Hays advocate replacing the current national bathroom infrastructure with urine-diversion toilets. Rather, they view the technology as just one solution to the challenges of nutrient cycling and water conservation, to be used not only in forward-thinkinghousing developments and smaller communities in the United States, but also in developing nations that currently lack sanitation infrastructure.
“We don’t want to just be scientists doing our own experiments and publishing in journals,” Noe-Hays says. “We also want to be enabling the adoption of these technologies to solve real-world problems.”
