The University of Cape Town in South Africa has developed the world’s first bio-brick made using human urine.
The team—civil engineering master’s student Suzanne Lambert and civil engineering honors student Vukheta Mukhari—has been perfecting the process behind turning liquid gold into something that’s a little more marketable. The finalized bricks are created through an organic process called microbial carbonate precipitation, the same process that creates the hard elements of coral.
First, the researchers collect the urea from human urine, and mix it with loose sand. After packing the sand into a mold, they colonize the sand with bacteria that produce the enzyme urease. The urease breaks down urea to produce calcium carbonate, the compound that strengthens eggshells. Over time, the calcium carbonate cements the bricks into the shape of the researchers’ mold.
The team found that the longer the bacteria are allowed to break down urea, the stronger the bricks become. “If a client wanted a brick stronger than a 40 percent limestone brick, you would allow the bacteria to make the solid stronger by ‘growing’ it for longer,” said supervisor Dyllon Randall. “The longer you allow the little bacteria to make the cement, the stronger the product is going to be. We can optimize that process.”
But the ability to control how strong the bricks are isn’t the only remarkable thing about this process: it’s as environmentally friendly as it is chemically interesting. While typical bricks need to be baked at 1,400°C (2,552°F), which produces significant carbon emissions, the bio-bricks actually function as a carbon sink.
Additionally, the other by-product of the urea-harvesting process is a solid mixture that is rich in nitrogen and potassium. While urea is used as a “liquid fertilizer” for the bacteria that create the bricks, this solid mixture can be used to help grow more traditional crops. “No one’s looked at it in terms of that entire cycle and the potential to recover multiple valuable products,” said Lambert. “The next question is how to do that in an optimized way so that profit can be created from urine.”
When asked whether she thinks the urine-derived bricks will find a place in mainstream construction, Lambert was cautiously optimistic. “First, these kinds of things require putting an idea into people’s brains, and showing them that the bricks don’t smell,” she said. “It may be a little while until it’s something that can be applied in our real world, but it’s not that far away. Maybe it can absorb some of the market. I’m not sure. You can only hope.”