At the University of Cape Town (UCT) in South Africa, contributing to a sustainable future might be as easy as using the men's bathroom.

Dyllon Randall, a senior lecturer in water quality engineering at UCT, has been leading an effort to turn human urine into the zero-waste building material of tomorrow. While about 90 percent of urine is made of water, the remainder contains vital nutrients — like phosphorous, nitrogen and potassium — for anyone brave enough to retrieve them. And that's just what Randall and his team did: They placed portable urinals in men's rooms around the campus to capture pee. [The 7 Biggest Mysteries of the Human Body]

Using the collected urine, Randall and his students recently demonstrated novel ways of turning that human waste into sustainable fertilizers, and even sturdy, limestone-like "bio bricks" that can be molded into any shape within just a few days.

"The ideal future for the bio bricks is to create a more sustainable society," Randall told Live Science in an email. "I want us to rethink typical 'waste' streams rather as resources and to develop innovative processes to recover these."

Liquid assets

Turning pee into bricks is a three-phase process.

First, urine is collected in special urinals connected to plastic containers filled with calcium hydroxide powder (also known as lime). Over time, this pee-lime pie mixture naturally combines to form calcium phosphate — a common fertilizer. This phase also kills any harmful pathogens and bacteria living in the pee, Randall said.

Once the fertilizer is removed from the urine, a liquid component remains. In step two of the process, this liquid is mixed into a separate vessel containing sand and bacteria. These bacteria react with the urine to produce calcium carbonate, which effectively cements the sand into any shape. Put the ingredients into a rectangular mold and in two to six days, you've got a bio brick. The longer the mixture is left to grow, the sturdier the brick becomes.

The house that "liquid gold" built

When completed, bio bricks are gray and rock-hard (about as hard as limestone bricks, Randall told the BBC). And, unlike kiln-fired bricks that need to be heated to about 2,550 degrees Fahrenheit (1,400 degrees Celsius), they produce no carbon dioxide while they set at room temperature.

"What we do last is take the remaining liquid product from the bio-brick process and make a second fertilizer," Randall said in a statement.

The entire process is novel, sustainable, and, unsurprisingly, really stinky. A single bio brick takes about 25 to 30 liters of urine to grow, according to Randall, which is the equivalent of about 100 bathroom trips for the average person. Randall told the BBC that the partially formed bricks produce a smell akin to a pet peeing in a corner. However, within about 48 hours, the smell dissipates.

The bio-brick project is still in its infancy, but Randall believes the material "could definitely be used to construct buildings" in the future. In addition to lots of further testing on the bricks, turning pee into what Randall dubs "liquid gold" will also require navigating some logistical hurdles, such as developing sustainable methods of collecting and transporting human urine to production plants en masse. (Randall and his students have already started looking into this.)

Encouraging public acceptance of bricks that used to be human pee will be another challenge, but that's a worry for another day. Perfecting the bricks themselves is, you could say, the number one concern.

Originally published on Live Science.