The bio-brick was produced by students from Cape Town, who collected urine from specially designed male urinals at the university’s engineering building and mixed it with sand and bacteria.

Bio-bricks are made in moulds at room temperature, removing the need for high temperature kilns. Nitrogen and potassium, which are crucial for commercial fertilisers, are created as by-products during the process.

“In this example you take something that is considered a waste and make multiple products from it. You can use the same process for any waste stream. It’s about rethinking things,” said Dr Dyllon Randall, a senior lecturer in water quality engineering at the University of Cape Town, who supervised the project.

The idea of using urea to grow bio-bricks has previously been tested in the US using synthetic products, but UCT master’s student Suzanne Lambert is the first to use real human urine to make a brick, according to the university.

Bio-bricks are created through a natural process called microbial carbonate precipitation, said Randall, similar to the way seashells are formed. Loose sand, which has been colonised with bacteria that produces urease, is mixed with the urine. Urease breaks down the urea in the urine, producing calcium carbonate, which cements the sand into shape.

While regular bricks are kiln-fired at temperatures of 1,400C and produce large amounts of carbon dioxide, the bio-bricks do not require heat.

“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,” said Randall.

“The longer you allow the little bacteria to make the cement, the stronger the product is going to be. We can optimise that process,” added Randall.

The urine is collected from fertiliser-producing urinals, which are also used to make a solid fertiliser. The remaining liquid is used to grow the bio-brick.

Randall described urine as liquid gold. By volume, urine accounts for less than 1% of domestic waste water, but it contains 80% of the nitrogen, 56% of the phosphorus and 63% of the potassium found in waste water.

The vast majority of the phosphorus present in the urine can be converted into calcium phosphate, a crucial ingredient in fertilisers, but one that is depleting in supply.

“Given the progress made in the research here at UCT, creating a truly sustainable construction material is now a possibility,” said Vukheta Mukhari, a civil engineering honours student who worked with Lambert.

Rebecca Ratcliffe