The ways modern science has harnessed the waste products of the human body for good may surprise, with researchers recently using urine to power mobile phones, hydrogen vehicles and even form biological concrete. Now a team from the University of Cape Town has developed what it says is the world's first biological brick made with human urine, with the strength able to be tweaked to serve a range of needs.
The technology is based on a similar natural process that results in seashells, called microbial carbonate precipitation. Granules of loose sand are colonized with bacteria that produce an enzyme called urease. When confronted with urine, the urease breaks down a compound within it called urea, and it is this chemical reaction that produces calcium carbonate to form the structure.
Over a number of months, engineers at the University of Cape Town have been experimenting with this process to produce materials of differing shapes and tensile strengths. The sand can be coaxed into solid columns and cylinders, but it was the form of a rectangular brick that had the team particularly enthused about their breakthrough.
By testing these different recipes, the teams says it can produce bricks of various strengths, tailor-made to suit a customer's needs. It has significant environmental benefits too because they form in molds at room temperature, whereas regular brick-making involves bringing kilns to temperatures of around 1,400° C (2,550° F), which produces carbon dioxide as a by-product.
"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," says Dr Dyllon Randall, who supervised the research. "The longer you allow the little bacteria to make the cement, the stronger the product is going to be. We can optimize that process."
This technology has the potential to produce more than just environmentally friendly bricks. Describing urine as "liquid gold," the team points to the high amounts of nitrogen, phosphorous and potassium within it that can be captured and used as ingredients for commercial fertilizer, which would essentially equate to a manufacturing process that produces zero waste.
"In this example you take something that is considered a waste and make multiple products from it," says Randall. "You can use the same process for any waste stream. It's about rethinking things."
Source: University of Cape Town
