“Closing the Poop Loop”

Can human waste composting improve the environment and public health?

“Closing the Poop Loop”

Four-and-a-half billion people around the globe lack access to good sanitation. The methods they typically have access to, such as pit latrines and lagoons, are responsible for widespread illnesses and a portion of the greenhouse gases warming our planet.

In Haiti, only 30 percent of the population has access to sewer sanitation, and less than 1 percent of the human waste there is safely treated. The lack of a better system has led to one of the largest and most virulent cholera epidemics in recent history.

A new study by agro-ecologists Gavin McNicol and Rebecca Ryals, a former professor at CTAHR, shows how off-site composting of human waste is a full-cycle sanitation solution that increases safety, sustainability, even jobs. It also reduces greenhouse gas emissions and waste-borne illnesses—all while producing an effective fertilizer for agriculture.

While at CTAHR, Gavin and Becca worked with Sustainable Organic Integrated Livelihoods (SOIL) Haiti, a nonprofit that designs, tests and implements sustainable, cost-effective solutions to the country’s sanitation crisis.

Their study examined the amount of methane, nitrous oxide, and carbon dioxide emitted during thermophilic composting of human waste. They determined greenhouse gas emission factors—how much source material escapes into the atmosphere as greenhouse gases during the composting process—and found that composting has a much smaller greenhouse gas footprint than any other non-sewer technology used widely today.

“The compost itself becomes a carbon sink,” Becca explains. “We showed that spreading compost on grasslands helps the plants take carbon dioxide out of the atmosphere and increases water retention, and it’s an amazing resource to restore depleted soils.”

Gavin, who was a postdoc in Becca’s lab in CTAHRʻs Department of Natural Resources and Environmental Management when doing the research and is lead author on the paper, said innovative thinking is increasingly important as the world’s resources dwindle and informal settlements increase around the globe.

Becca adds, “While this research was conducted in Haiti, island communities across the world face challenges with safe management of waste. Tackling the public health impact of untreated fecal matter is a priority for sustainability. Closing the ʻpoop loopʻ helps the climate, advances sustainable development, fosters circular economies that recycle waste as resources, improves public health, and improves soil health.”

Read the full article, “Climate change mitigation potential in sanitation via off-site composting of human waste,” in Nature Climate Change.