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Poop Bricks and Other Ways Our Waste is a Renewable Resource

by Lynne Peskoe-Yang
March 15, 2019 | Our Future

Why do we love to read about new ways to work with waste? It might have to do with the guilt we feel over the waste we produce as the most immediately tangible (and frequently, the most viscerally unpleasant) evidence of our negative impact on the environment.

But the way we think about waste might be changing. In one sense, 2018 was a great year for our garbage, maybe the greatest we’ve ever seen.

Our task is humongous: To truly mitigate any of the impending effects of climate change, the species as a whole will have to shift its paradigm around what we use — and what we waste.

But to the most creative minds of the engineering world, this global challenge looks and smells like a golden opportunity to reinvent our relationship with the natural world and reexamine the cycles of use and waste that led us to this crisis in the first place.

We're still figuring it out

New methods for shrinking the volume of trash, throwing it farther away so we don’t have to think about it so much, and treating it to at least remove the biohazardous threats it contains have been tested, used and rejected on a regular basis since the pre-Industrial era.

Illustration of liver being examined by medical professionals. Renewable Resource pbs rewire
Most animals, like humans, use the same chemical reactions to convert food and oxygen into energy, producing body waste and carbon dioxide as part of the process. But what if we tried to hack that cycle?

These solutions, while sometimes necessary, frequently involve a compromise: Comfort, convenience and cleanliness in the present come with negative costs in the form of loss of space, safety risks and logistical problems in the near and distant future.

Recently, though, scientists and engineers have taken a fresh look at the rotten stuff we’d rather not think about.

They're doing more than proposing new ways to hide, compress or eject waste from our consciousness. They're suggesting new ways of thinking about it altogether.

Thanks to this kind of bold thinking, the future of waste may be far less shameful than you’d think. Here are some of the ways researchers are shifting the paradigm of waste as a social phenomenon.

The house that waste built

It’s no surprise that talking about human waste involves dancing around the subject matter. In fact, there may be a strong evolutionary explanation for our aversion to dealing directly with the contents of our toilets.

Unfortunately, the scale of human waste production in the modern era means it’s no longer feasible to politely ignore its existence.

For some enterprising engineers, this is actually good news. Instead of expending all their energy and creativity on devising new ways to push waste into the ocean or hurl it into space, these researchers are turning the prevailing cultural norms around waste upside down.

Two new projects are taking on these norms in an attempt to turn social stigma into social good – by making bricks out of poop and pee.

After you flush, your waste typically travels to a nearby water treatment plant. There, sewage sludge is chemically disinfected and becomes the slightly less off-putting substance engineers call biosolids.

Though biosolids already have well-known applications as a kind of fertilizer that can help rehabilitate poorly-managed farmland, most of the United States' wind up in landfills.

According to research led by civil engineer Abbas Mohajerani of the Royal Melbourne Institute of Technology in Australia, biosolids have a lot more to offer than just taking up space.

Mohajerani and his research team have spent the past five years collecting biosolids from water treatment plants in Melbourne, mixing them with soil, and firing them for over 10 hours at nearly 2,000 degrees Fahrenheit.

The resulting bricks are sturdy, odorless and better insulators than traditional clay bricks. Even more exciting: Mohajerani’s team found that a well-planned switch to bricks made of a biosolid-clay hybrid could eventually rid the world of biosolid waste – and provide building materials that require only half the energy it takes to make clay bricks.

Can urine help us get to net zero?

At the University of Cape Town in South Africa, civil engineering students Suzanne Lambert and Vukheta Mukhari are also thinking about the future of bio-waste in building: they produced usable bricks made from human urine.

Funnily enough, Mukhari and Lambert looked to seashells as their inspiration.

Seashells are produced when bacteria colonizes loose sand and produces the enzyme urease, which breaks down urine and releases calcium carbonate as a byproduct. Calcium carbonate is what makes seashells hard.

The researchers can use the same method to create customizable bricks according to the specific needs of a building project. The density of the bricks depends on how long bacteria are allowed to grow in the brick-shaped sand mold.

While traditional clay bricks must be fired at extreme temperatures and produce harmful carbon dioxide as a byproduct, the “bio-bricks” made from urine are grown at room temperature. They leave behind only nitrogen and potassium as byproducts, both of which make excellent fertilizers. The leftover calcium from the urine is converted to calcium phosphate, another fertilizer.

At maximum efficiency, the process is effectively a zero-waste equation. Lambert’s supervisor, engineer Dyllon Randall, is optimistic about the bio-bricks’ potential.

“No one’s looked at (urine) in terms of that entire cycle and the potential to recover multiple valuable products,” he said in an interview. “The next question is how to do that in an optimized way, so that profit can be created from urine.”

Taking cues from other organisms

Most animals, like humans, use the same chemical reactions to convert food — proteins, fats and carbs — and oxygen into energy, producing body waste and carbon dioxide as part of the process. But what if we tried to hack that cycle?

The idea of offsetting waste and consumption patterns with non-animal organisms that get their energy differently is familiar to anyone who has heard of efforts to improve air quality by planting new forests.

But, as we know from the urine bricks, the life cycles of certain types of bacteria offer even more creative ways to combine chemical processes to create something brilliant.

Purple phototrophic bacteria, or PPB, are particularly inventive when it comes to extracting food from their environment. Like plants, these tiny organisms are photosynthetic: they use light energy from the sun to turn their surroundings into chemical energy, which can become food for other life forms.

Purple phototrophic bacteria are especially particular about the kind of light they use: they absorb the longer wavelengths in the electromagnetic spectrum, including infrared, which gives them their purplish-brown color.

Daniel Puyol, a postdoctoral researcher at King Juan Carlos University in Spain, noticed something even more unusual about PPB’s special kind of photosynthesis. It is anaerobic, which means it works efficiently even without the presence of oxygen.

That feature makes PPB the perfect candidate to solve a problem civil engineers have worried over for decades: how to minimize the waste in contaminated water.

When humans consume water, whether in an industrial setting or in their own homes, they introduce a variety of organic material – including food waste, toilet waste, dirt, dead skin and anything that can be washed down the drain – into the water cycle.

The possibility of making this wastewater potable again is especially exciting for anyone paying attention to the dangerous shortages of clean drinking water in cities around the globe. When Puyol and his team released the water-loving PPB into vast stores of wastewater, they found that it was able to efficiently metabolize the organic material, producing only hydrogen gas – itself a valuable resource – as a byproduct.

That could mean more clean water and less waste with only the help of friendly bacteria.

Lynne Peskoe-Yang
Lynne Peskoe-Yang is a freelance science and tech journalist who dabbles in science fiction and social justice. Find more of her writing about telecom monopolies, ethical artificial intelligences and nuclear pasta on or on twitter @lynnepeskoe.
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