Removing urine from wastewater and using it as a fertilizer has the potential to reduce the nutrient load in water bodies and promote sustainability by using a common waste material.
In excess, the nitrogen and phosphorus in our wastewater can encourage algae blooms and create dangerous conditions for marine and lake ecosystems and human health. According to the website of the Rich Earth Institute, a Vermont-based company focused on using human waste as a resource, most of the nitrogen and phosphorus in wastewater comes from human urine, even though it only makes up 1 percent of wastewater. Removing urine can remove 75 percent nitrogen and 55 percent phosphorus from municipal wastewater treatment plants. And then those nutrients can be recycled for use as fertilizer.
The rub is against systems that are used to the way things are. Wastewater infrastructure is set up to take the wastewater out of the house, without much thought, to people using pre-existing pipes and toilets. Urine diversion would require changing some of these details, while using the diverted material would require accepting the waste as valuable.
the power of one
Rich Earth co-founder Abe Noe-Hayes said the place urine in wastewater has figures that spin the ball on urine diversion, an attempt to keep it out of the waste stream in the first place.
The toilet diverting urine uses the anatomy of the body. When sitting in the toilet, urine naturally moves to the front of the bowl, while stool moves to the back. Therefore, the front half of the split toilet bowl captures the urine and can only send it to a separate drain for urine, while the rear part remains connected to the wastewater treatment system as usual. Separate pipes divert urine to a collection tank. This system may not be perfect – good purpose is a bonus if it is used while standing, and requires some new plumbing – but it benefits from replacing existing infrastructure.
If there is any possibility of fecal mixing, the World Health Organization has (believe it or not) guidelines on how long urine should be stored before it can be used as a fertilizer. After six months at room temperature, the urine has been sufficiently sanitized to be used on anything, including raw products, Noe-Hays said.
The key here is that if urine is only urine, it is ready to go the moment it leaves the body as a fertilizer containing nitrogen and phosphorus. But having a good separation is important. According to Björn Viners, professor of environmental engineering at the Swedish University of Agricultural Sciences, the main source of pathogens in collected urine is feces. That said, toilets that divert urine are not perfect, and some mixing is inevitable.
If it can be separated, the urine may act partially to dehydrate itself. Nitrogen in urine leaves the body as urea, a simple organic compound. The bacteria in the pipe usually break down the urea into ammonia. When urine is sitting in a container, ammonia raises the pH of the solution to about eight or nine. The high pH environment kills any pathogens from the body that may have entered the urine, Viners said.
“It’s like a Twinkie,” Noe-Hays said, referring to the urine’s long shelf-life.
ease of transport
Noe-Hays was part of a study that looked at the concentrations of pharmaceuticals in urine. Caffeine and ibuprofen were the most common and abundant. After the urine was applied to the soil, however, the concentration of the drug in the crops was extremely low. In order to consume the amount of caffeine in a cup of coffee from a urine-fertilized product, according to the study, a person would have to consume a pound of produce every day for about 2,000 years, Noe-Hays said.
Gardeners often use urine as a fertilizer, and No-Haze said it works wonders from her personal experience. Noe-Hayes said there is no required concentration of nutrients for urine to be used as fertilizer. The mass of its components matters. If 1,000 gallons of urine are added to one acre, about 50 pounds of nitrogen are added. Noe-Hays said that using concentrations 10 times stronger than diluted urine, only 100 gallons would need to be applied to achieve the same effect. “The grass doesn’t care whether you’re concentrate or thin,” he continued. “It just matters how many pounds of fertilizer he gets in total.”
More than the personal garden, it is helpful to take advantage of its ability to concentrate, to be useful as a fertilizer for urine. Noe-Hayes said a spinoff of Rich Earth called Brightwater Tools is working on focusing on freezing urine.
Freezing water from urine releases nutrients into the solution that can be used onsite or sent to the field. Concentrating the urine makes the volume more manageable, especially if urine diversion toilets are used in a commercial or office building. Instead of requiring multiple trips from urine-specific trucks to empty the tanks, the concentration hardware allows the urine to be cleaned, pasteurized and freeze-concentrated on site. In tests, concentration levels reached a factor of 10, meaning trucks could assemble every few months instead of every week.
Viners brought in dehydration as another method to make urine fertilizer useful on a large scale. Some of his research is looking at preventing the breakdown of urea in pipes. If urea does not break down, nitrogen remains solid when dehydrated, making a dry fertilizer of about 15 to 20 percent nitrogen.
The benefit he sees with dry product production is a chance to piggyback on existing infrastructure for chemical fertilizer management. The machinery for applying dry fertilizer already exists, and storing it can be as simple as stacking the bags on top of each other.
(This story has not been edited by seemayo staff and is published from a rss feed)