Should we try to create a circular urine economy?
Removing urine from wastewater and using it as fertilizer has the potential to reduce nutrient loading in water bodies and enhance sustainability by using a common waste.
Excess nitrogen and phosphorus in our waste streams can stimulate algal blooms and create hazardous conditions for marine and lake ecosystems and human health. According to the website of the Rich Earth Institute, a Vermont-based company that focuses on using human waste as a resource, most of the nitrogen and phosphorus in wastewater comes from human urine, even though it represents only 1% of wastewater. Disposal of urine could remove 75% of nitrogen and 55% of phosphorus from municipal treatment plants. And those nutrients could then be recycled for use as fertilizer.
The catch is against systems that are used to the way things are. Sewage disposal infrastructure is put in place to remove waste from the house, without much thought, using pipes that already exist and toilets that people are used to. Diverting urine would require changing some of these details, while using the diverted material will require greater acceptance of the waste as valuable.
The strength of one
Abe Noe-Hays, co-founder of Rich Earth, said the statistics on urine’s place in wastewater are what got the ball rolling on urine diversion, an attempt to keep it out. of the waste stream in the first place.
A urine-diverting toilet uses the anatomy of the body. When you sit on the toilet, pee naturally goes to the front of the bowl, while feces goes to the back. Therefore, the front half of a split toilet bowl collects urine and can send it to a separate drain for urine only, while the back remains connected to a waste water treatment system such as habit. Separate pipes divert urine to a collection tank. This system may not be perfect – a good lens is a bonus if used while standing and new plumbing is required – but it benefits from modifying the existing infrastructure.
If there is a possibility of fecal mixing, the World Health Organization has (believe it or not) guidelines on how long to store urine before using it as fertilizer. After six months at room temperature, the urine sanitized enough to use on anything, including raw produce, Noe-Hays said.
The key here is that if urine is just urine, it’s ready to serve as nitrogen- and phosphorus-rich fertilizer as soon as it leaves the body. But getting a good separation is important. Feces are the main source of pathogens in collected urine, according to Björn Vinnerås, professor of environmental engineering at the Swedish University of Agricultural Sciences. Urine-diverting toilets aren’t perfect, he said, and some mixing is inevitable.
If it can be separated, the urine can act to partly sterilize itself. Nitrogen in urine leaves the body as urea, a simple organic compound. Bacteria in the pipes usually break down urea into ammonia. When urine sits in a container, the ammonia raises the pH of the solution to around eight or nine. The high pH environment kills any pathogens in the body that might have entered the urine, Vinnerås said.
“It’s like a Twinkie,” Noe-Hays said, referring to the long shelf life of urine.
Ease of transport
Noe-Hays was part of a study looking at drug concentrations in urine. Caffeine and ibuprofen were among the most common and abundant. However, once the urine was applied to the soil, the drug concentration in the crops was extremely low. According to the study, to consume the amount of caffeine in a cup of coffee from urine-fertilized products, a person would need to eat one pound of the product every day for about 2,000 years, Noe-Hays said.
Gardeners often use urine as a fertilizer, and Noe-Hays said it works wonders from personal experience. Noe-Hays said there is no necessary concentration of nutrients for urine to be used as fertilizer. The mass of its components is what matters. If you pour 1,000 gallons of urine on an acre, there are about 50 pounds of added nitrogen. Using a concentrate 10 times stronger than diluted urine, only 100 gallons would need to be applied to achieve the same impact, Noe-Hays said. “Hay doesn’t care if you apply the concentrate or the dilute,” he continued. “What matters is the total number of pounds of fertilizer he gets.”
For urine to be useful as fertilizer for something more than a personal garden, it helps to take advantage of the ability to concentrate it. A Rich Earth spin-off called Brightwater Tools is working on concentrating urine by freezing it, Noe-Hays said.
Freezing the water from the urine leaves behind the nutrients in a slurry that can be used on site or shipped to a farm. The concentration of urine makes the volume more manageable, especially if a urine-diverting toilet is used in a commercial or office building. Instead of requiring multiple visits from urine-specific trucks to empty the tanks, the concentration equipment allows urine to be disinfected, pasteurized and concentrated by freezing on site. In testing, concentration levels reached a factor of 10, meaning trucks could pick up every few months instead of every week.
Vinnerås mentioned dehydration as another method to make urinary fertilizer useful on a larger scale. Some of his research is aimed at stopping the degradation of urea that occurs in pipes. If the urea does not break down, the nitrogen remains solid when dehydrated, creating a dry fertilizer of about 15-20% nitrogen.
The advantage he sees in producing a dry product is the ability to build on existing infrastructure for chemical fertilizer management. There are already machines for applying dry fertilizer, and storing it can be as simple as stacking bags on top of each other.