In the Seventeenth-century, a German alchemist named Hennig Brandt was on a quest to search out the “philosopher’s stone”, a mysterious object that might flip any odd steel into gold. When he realised the golden color of urine, he believed it contained tiny particles of the valuable steel.
Brand then collected urine from himself, his household, and beer drinkers at his native pub and commenced distilling it within the hope of discovering gold on the finish. There was no gold, alas, however the silver lining was that Brandt found the aspect phosphorus.
In truth, some name urine “liquid gold” as a result of it’s loaded with components that vegetation need. The waste product is filled with phosphorus, potassium, and nitrogen within the type of urea, the “Big Three” vitamins that fuel plant progress and type the spine of business fertilisers.
Two birds, one stone
A brand new electrochemical approach revealed within the journal Nature Catalysis now proposes to separate urea from urine in its strong type through a greener, much less energy-consuming process. This methodology converts urea, a nitrogen-rich compound in urine, into a crystalline peroxide by-product referred to as percarbamide.
Thus it strikes two targets without delay: enabling the remedy of urine in city wastewater and reworking it into a helpful useful resource.
Humans get hold of nitrogen from meals, convert it into urea, and excrete it via urine. Since urea is wealthy in nitrogen, it has the potential to be a pure fertiliser. In principle, returning the vitamins to the soil might full the nitrogen cycle, however scientists at present lack environment friendly strategies to extract urea straight from urine, leaving a vital hole on this cycle, Xinjian Shi, a researcher at Henan University, China, and the primary writer of the brand new examine, mentioned.
“Our team’s research fills this gap.”
Pee-cycling to shut the loop
An grownup produces round 450-680 litres of urine, researcher Björn Vinnerås estimated in a 2002 examine. The substance is 95% water but the annual output additionally accommodates round 4 kg of nitrogen and 0.3 kg of phosphorus, sufficient to develop wheat for one loaf of bread each day for a complete yr.
If it’s so worthwhile, why flush it down the bathroom? The reply is that urine is a posh system and lots of of its parts, particularly salts, intervene with processes that may extract urea alone from wastewater, Shi mentioned. The group’s examine claims to have jumped this barrier.
Urea is made up of nitrogen, oxygen, and hydrogen, and is liable to forming hydrogen bonds with different molecules, together with of urea itself. When these bonds type, the compound’s bodily and chemical properties have a tendency to alter. This tendency turned out to be a game-changer within the separation process.
For instance, when urea types hydrogen bonds with hydrogen peroxide, it types percarbamide, a white, crystalline strong that may be precipitated out from urine with excessive purity.
Percabadmide is thought for its capacity to steadily launch energetic oxygen, making it a worthwhile candidate for processes that want to provide oxygen for different chemical reactions. Another key trait of this substance is its capacity to speed up the restoration of urea from urine.
To benefit from this property, the researchers developed an in-situ electrochemical approach that makes use of graphitic carbon-based catalysts to transform urea in urine into percarbamide. Achieving nearly 100% purity, the group used this process to successfully extract percarbamide from each human and animal urine.
While the end result was promising, the true focus of the researchers was one thing else.
A eureka second
At first, the researchers targeted on one downside: preserving hydrogen peroxide steady in liquid type at greater focus. They started exploring whether or not it may very well be solidified straight inside an answer with a appropriate materials. Urea appeared like a promising possibility — however commercially made urea is sort of costly.
“Then, we suddenly thought, if we could use it within the urine system, it would not only achieve the original goal but also address the issues of urine treatment and nitrogen cycling. Wouldn’t that be a win-win?” Shi requested.
With this perception, the researchers designed an activated graphitic carbon catalyst. Graphite is a delicate crystal manufactured from carbon atoms. Activated graphitic carbon is a porous type of graphite subsequently modified to additional improve its floor space, making it extra reactive.
In this case, it was engineered to boost two chemical reactions, or pathways, that produce strong percarbamide.
In pathway I, urea reacts straight with hydrogen peroxide within the presence of a catalyst that facilitates interactions between the 2 molecules. In pathway II, urea binds to a hydroperoxyl (-*OOH) intermediate, a extremely reactive and short-lived molecule. Then it positive factors hydrogen ions (H⁺) and triggers a response to type percarbamide within the presence of a catalyst that enhances hydrogen bonding.
The activated graphitic carbon catalyst was appropriate for each pathways.
Waste is golden?
After a number of rounds of trial and error, the researchers discovered they may maximise percarbamide manufacturing by holding the focus of urea between 15% and 38%. They additionally discovered that sustaining temperatures simply above freezing at a barely acidic pH of round 4 works greatest for the process.
According to the researchers, the pure percarbamide extracted from this new process combines the perfect of each worlds: the nitrogen-rich advantages of urea and the oxidative energy of hydrogen peroxide, unlocking new prospects for sustainable purposes.
“When the solid product is collected and used as fertiliser, nitrogen is slowly released, while also promoting root respiration and facilitating crop growth,” Shi mentioned. “This process fully addresses the missing link in the nitrogen cycle that exists in human society.”
The group has additionally expressed pleasure about bringing collectively resource-recovery and recycling with wastewater remedy in future. They consider this progressive method can change how we take into consideration and use waste.
Sanjukta Mondal is a chemist-turned-science-writer with expertise in writing standard science articles and scripts for STEM YouTube channels.
Published – March 12, 2025 05:30 am IST
