No pooh-poohing poo: Researchers envision an extreme circular economy

By Bryn Nelson, CNN

Imagine you’re eating dinner on a ceramic plate and drinking water from a plastic cup while sitting in a brick house — a seemingly ordinary scenario except that your plate, cup, and your home are all fashioned in part from recycled feces.

Now imagine using your poop to propel a spaceship to and from Mars and shield you from cosmic radiation along the way.

In my upcoming book, “Flush: The Remarkable Science of an Unlikely Treasure,” I describe how the misunderstood byproduct of our daily living is a vastly undervalued natural resource.

Poop has power: as medicine, fertilizer, biomethane gas and reclaimed water, among other proven applications. But that’s just scratching the surface of our excremental potential; its biological, chemical and physical attributes have inspired even more wide-ranging and forward-looking brainstorming about what else we can create from our waste.

A hidden asset for space exploration

The extreme limits of space, in particular, have driven scientific innovation toward a more circular economy where nothing is wasted. That invention, in turn, has hinged upon a universal truth: everybody has to go sometime, even astronauts. Among NASA’s poop-themed crowdsourcing challenges, one recent competition sought a new design ideas for a lunar toilet while another — the Waste to Base Materials Challenge: Sustainable Reprocessing in Space — asked the public to help brainstorm how to repurpose both astronauts’ trash and bodily waste.

It’s all about self-sufficient flight: Steve Sepka, project manager for the Trash Compaction and Processing System at NASA’s Ames Research Center in California, said one goal is to create polymers from organic waste that could be used in propulsion systems for spaceflight — as well as planetary surface missions.

For a return flight from Mars, the space agency had initially looked at producing fuel from resources on the red planet, Sepka wrote in an email. But NASA is now considering whether repurposing waste from the crew itself could help the astronauts, well, blast off.

As for protecting crewmembers from dangerously high radiation levels in outer space during an extended voyage, scientists have suggested that the density of molecules in wastewater could offer a solution. One multi-purpose NASA proposal, called “Water Walls Architecture,” envisions a space capsule lined with multiple compartments of water as well as sterilized waste deployed as radiation shielding. The primary ingredient of both urine and feces is water, and the tightly packed atoms of hydrogen and oxygen in water offer a higher density of cosmic ray-blocking nuclei than metals do. Think of it as a doo-doo deflector.

A water-based shield could work well to block radiation particles, said Peter Guida, the liaison biologist for NASA’s National Space Radiation Laboratory and a scientist at its host institution, Brookhaven National Laboratory in New York.

In space, every ounce of cargo — including heavy but necessary water — is precious. “If you have it anyway, can you use it for something?” he said. “In theory, it should work.”

A plastic proposal

Now try to reimagine wastewater treatment plants on Earth doubling as multipurpose resource recovery facilities. As an alternative to plastics made from fossil fuels, for example, researchers are making headway in producing safe and biodegradable bioplastics from existing waste streams.

Creating planet-friendly bottles, containers, and other bioplastic products from what we leave behind is still a work in progress, said Zeynep Cetecioglu Gurol, an associate professor of industrial biotechnology at the KTH Royal Institute of Technology in Stockholm, Sweden. Even so, developing an efficient and affordable method for recovering new products from wastewater could help offset the money, time, and effort spent by treatment plants to meet pollution limits in discharged water. “I think it’s a win-win,” she said.

Many wastewater treatment plants are already using a microbe-dependent process called anaerobic digestion to create biomethane gas, a sustainable fuel alternative, from sewage. Cetecioglu Gurol and other researchers have found that organic compounds created during that biogas production process provide a good source of carbon for creating bioplastics. The goal now is to ramp up production efficiency. “We are still in the baby steps,” she said.

One type of bioplastic called polyhydroxybutyrate, or PHB, is naturally produced by some bacterial species as they feed on organic material. Tests suggest that PHB can replace a variety of petroleum-based plastics and that unlike them, it biodegrades rapidly under normal environmental conditions.

A bacterial strain called Zobellella denitrificans ZD1 has attracted the attention of researchers like Kung-Hui Chu, a professor of environmental, water resources and coastal engineering at Texas A&M University. Chu and colleagues have found that the strain, which normally lives in mangrove wetlands, can also thrive on glycerol (an industrial byproduct), wastewater, and sewer sludge. Its ability to accumulate PHB when grown in such a variety of conditions makes it a promising candidate for transforming waste into bioplastics or into other useful products like fish food.

A lofty load of bricks

Around the world, treated sewage solids are still commonly burned or buried. But incinerating waste creates ash that, while reduced to a fraction of the starting volume, is still often dumped into landfills. Here too, researchers are actively investigating how to convert the solids and ash into useful products.

Such recycling processes could yield a ton of bricks. Engineers at the Royal Melbourne Institute of Technology in Australia have focused on relieving the environmental problem of excavating clay soil for brick production, in part by exploring how to incorporate treated sewage solids, or biosolids, into fired bricks. If making poop bricks seems like an unusual application, consider that animal dung has been used to build homes and produce pottery for centuries.

When fired for 10 hours at nearly 2,000 degrees Fahrenheit, clay bricks with varying amounts of treated biosolids from Melbourne residents weren’t quite as strong as traditional counterparts. But they were lighter and better insulators — and otherwise indistinguishable in both appearance and odor. A 2019 paper from civil engineer Abbas Mohajerani and colleagues at the institute suggested that bricks made with at least 15% biosolids could still meet engineering requirements while theoretically recycling the millions of tons of leftover poop.

A follow-up study by another group of researchers at the Melbourne institute suggested that raw biosolids, biochar (charcoal made from biosolids), and incinerated sewage sludge ash could all be used as cement replacement materials. Other researchers in the United Kingdom have suggested that sewage sludge ash could be feasibly reused in tiles and glass ceramics as well, with the potential for wide-ranging applications in the building industry.

The Museo Della Merda in Lombardy, Italy has, in fact, already created terra cotta tiles, flowerpots, and tableware from a cow pie-and-clay mix. It’s called Merdacotta.

The yuck factor, of course, may be a higher barrier for repurposed-poop consumer products such as bioplastic cups and ceramic plates. But the hostile environment of space and the multiplying challenges of extracting resources on our own planet are helping researchers get behind a wellspring of raw materials that could aid exploration and boost investments in sanitation infrastructure by converting waste streams into revenue. Even better? This particular natural asset will never run dry.

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Bryn Nelson is an award-winning science writer and author of the book “Flush: The Remarkable Science of an Unlikely Treasure.” He lives in Seattle.