Cities Built of Bone and Sewage Could Be Our Future Homes

Mankind may need to move away from steel and concrete to build cities for our future population boom. gremlin/Getty Images Mankind may need to move away from steel and concrete to build cities for our future population boom. gremlin/Getty Images
Mankind may need to move away from steel and concrete to build cities for our future population boom. gremlin/Getty Images

How do we plan for our dystopian future? First, we need to get the aesthetic right, and "Mad Max: Fury Road" seems as good a place to start as any. Obviously, the cities of the future will need to be made of bone and sewage. But don't worry, we've got some legit researchers working on that.

The United Nations predicts that by the year 2100, the world's human population will reach 11.2 billion (we hit 7.4 billion back in March of this year). The UN also estimates that because human population growth has been so aggressive over the past couple of hundred years, more than half of the people in the world now live in urban areas — and that number will continue to grow as we keep making human babies at this breakneck pace. And hey, those babies gotta live somewhere.

There are a lot of questions about where the food and water will come from to run these megacities, how they'll be powered, and how we'll deal with their waste products, but one of the more immediate questions is: How will we build them?

These days, the world's cities are mostly made of concrete and steel, two extraordinarily energy-intensive materials. In fact, about a tenth of the world's carbon emissions comes from manufacturing and then transporting these two energy gluttons alone.

Bone Machines for Real

Bioengineer Dr. Michelle Oyen of Cambridge's Department of Engineering is leading research to develop more sustainable materials for building future cities, and she's got her sights set on some surprising substances: bone and eggshell.

"The great biomimetics expert Julian Vincent made the point that engineers tend to throw energy at problems, while nature throws information at problems," says Oyen, referencing biomimicry, in which human technology takes inspiration from nature. "In the case of bone and eggshell, the information is the sequences of amino acids in DNA that give rise to the structural protein collagen, on which most natural materials in humans are based."

Structures like bone and eggshell are composites of minerals and proteins (mostly collagen); bone is made of about of equal parts of each, while eggshell is about 95 percent mineral and 5 percent protein. Though bone and eggshell grow differently, they both form strong internal lattice structures that grow quickly and at room temperature, requiring less heat to manufacture and manipulate them, making them lower in carbon emissions caused compared with steel and concrete.

Oyen's lab at Cambridge synthesizes bone and eggshell using animal-derived collagen in a process that could be enlarged to a scale suitable for construction materials. Before this technology can be taken to the streets, however, a synthetic collagen has to be developed so we're not making our new gigacities literally out of animals. (Where would our vegan friends live?)

Building from the Bowels Up

Sewage might get a better reputation once it becomes the building material of choice for the cities of the future. A research team in Malaysia has developed a process for drying and grinding sewage sludge into a powder that can be mixed with cement to make concrete. As the human population grows, sewage disposal will become a bigger problem — it can't be responsibly buried due to its high heavy metal content, because there's a potential it could seep into and contaminate groundwater.

The Malaysian researchers are currently working on creating higher-quality sludge powder that will make strong, lasting building material. And if the sludge of the future could be locked up in mortar or concrete to help build the massive gigacities looming on the horizon, that's one less thing our poor great-great-great grandchildren Will have to worry about. Even if their vegan friends won't come for a visit.