University of Cape Town engineers describe urine as “liquid gold,” given the highly-valuable chemicals such as nitrogen and phosphorus that are found inside it.
Now engineering researchers at the South African university have invented a way to turn that liquid gold into something solid: a bio-brick, which is “grown” by mixing together sand, bacteria and — yes — human urine, researchers said in a news release on Thursday.
“I see so much potential for the process’s application in the real world,” Suzanne Lambert, a master’s student in civil engineering who grew the bricks, said in a statement. “I can’t wait for when the world is ready for it.”
Researchers gathered the key ingredient from urinals. That could change in the future, they said.
“At the moment we’re only dealing with urine collection from male urinals because that’s socially accepted,” Dr. Dyllon Randall, the researchers’ supervisor, said in a statement. “But what about the other half of the population?”
Bio-bricks’ inventors say the creation isn’t just a novelty. It’s a way to harness what’s valuable about a plentiful human waste product and create something useful, all in an eco-friendly way, researchers said. Making a conventional brick requires firing up a kiln to incredibly hot temperatures and releasing planet-warming carbon dioxide emissions in “vast” quantities — while bio-bricks “grow” at room temperature, and are made from largely organic or recycled materials, researcher said.
But how does the process work?
First, researchers need to gather pee — and a lot of it. That’s because researchers say each brick requires 25 to 30 liters of urine, BBC reports. With the average urinal visitor leaving behind 200 to 300 milliliters of liquid waste, it takes roughly 100 bathroom trips to produce enough urine, researchers estimated.
From there, mixing together the ingredients (loose sand, urine and bacteria) unleashes a natural process called “microbial carbonate precipitation,” which unfolds at room temperature.
During the process, the bacteria produce an enzyme called urease, which breaks down the urea from the urine and creates calcium carbonate — a complex reaction that hardens the entire mixture, cementing it into a shape, researchers said. In this case, it’s a brick.
“It’s essentially the same way that coral is made in the ocean,” said Randall, adding that the brick-making process takes four to six days, according to the BBC.
Lambert didn’t come up with the idea of using urea in brick-making herself (it was done in the U.S. years ago using synthetic solutions), but she was the first to use actual human waste in the process, researchers said. Lambert’s bricks also build on the work of a Swiss student who worked with her supervisor last year.
Lambert has also been working on the project with civil engineering honors student Vukheta Mukhari, the university said. Recently, Lambert and Mukhari have been testing various shapes for the bricks.
The bricks can vary in strength, Randall said.
“If a client wanted a brick stronger than a 40% limestone brick, you would allow the bacteria to make the solid stronger by ‘growing’ it for longer,” Randall said. “The longer you allow the little bacteria to make the cement, the stronger the product is going to be. We can optimize that process.”
Creating a bio-brick leaves behind other useful chemicals, too, including nitrogen and potassium, which are valuable as fertilizers, researchers said.
Before the bio-brick is even made, researchers remove carbonate ions and calcium from the liquid waste to make a solid fertilizer, researchers said. What remains goes into creating the bio-bricks, and any liquid left over from the brick-making becomes another fertilizer. That means the entire process creates three different — and useful — products, according to researchers.
“In this example you take something that is considered a waste and make multiple products from it,” Randall said. “You can use the same process for any waste stream. It’s about rethinking things.”
One drawback? The process isn’t easy on the nose, though it does kill all threatening pathogens.
“Say you had a pet and it peed in the corner, and you have that strong smell — that’s ammonia being released,” Randall said, according to the BBC. “This process produces ammonia as a by-product.”