Researchers say they have developed the world's first bio-brick grown from human urine, an advance with significant consequences for waste recycling and upcycling.
The bio-bricks are created through a natural process called microbial carbonate precipitation, said researchers from the University of Cape Town (UCT) in South Africa.
Loose sand is colonised with bacteria that produce urease enzyme which breaks down the urea in urine while producing calcium carbonate through a complex chemical reaction.
This cements the sand into any shape, whether it is a solid column or the rectangular building brick described in the Journal of Environmental Chemical Engineering.
Suzanne Lambert and Vukheta Mukhari from UCT tested various bio-brick shapes and tensile strengths to produce an innovative building material.
The development is also good news for the environment and global warming as bio-bricks are made in moulds at room temperature, researchers said.
Regular bricks are kiln-fired at temperatures around 1400 degrees Celsius and produce vast quantities of carbon dioxide.
The strength of the bio-bricks would depend on client needs, the researchers said.
"If a client wanted a brick stronger than a 40 per cent limestone brick, you would allow the bacteria to make the solid stronger by 'growing' it for longer," said Dyllon Randall, a senior lecturer at UCT.
"The longer you allow the little bacteria to make the cement, the stronger the product is going to be. We can optimise that process," Randall said.
The concept of using urea to grow bricks was tested in the US some years back using synthetic solutions, but Lambert's brick uses real human urine for the first time, with significant consequences for waste recycling and upcycling.
The bio-brick process produces as by-products nitrogen and potassium, which are important components of commercial fertilisers.
Chemically speaking, urine is liquid gold, according to Randall.
Some 97 per cent of the phosphorus present in the urine can be converted into calcium phosphate, the key ingredient in fertilisers that underpin commercial farming worldwide.
This is significant because the world's natural phosphate reserves are running dry, according to the researchers.
The fertilisers are produced as part of the phased process used to produce the bio-bricks.
First, urine is collected in novel fertiliser-producing urinals and used to make a solid fertiliser. The remaining liquid is then used in the biological process to grow the bio-brick.
"What we do last is take the remaining liquid product from the bio-brick process and make a second fertiliser," Randall said.
The overall scheme would effectively result in zero waste, with the urine completely converted into three useful products.
"No-one's looked at it in terms of that entire cycle and the potential to recover multiple valuable products. The next question is how to do that in an optimised way so that profit can be created from urine," Randall added.