Human waste: Unlikely climate change hero?

Surprisingly, it doesn’t smell that bad.

During a tour on a recent spring afternoon, King County analyst Jim Pitts navigated his way through a network of open-air scaffolds and underground tunnels at one of the county’s wastewater treatment plants in Renton. Despite processing up to 200 million gallons of sewage, runoff and gray water per day, the plant is surprisingly clean and free of offensive odors or waste — even as tons of sludge, garbage and human feces are efficiently processed on the 80-acre site.

On top of cleaning water and returning it to Puget Sound through pipes thousands of feet from shore, the King County South Treatment Plant also produces a product called Loop. Loop is a concentrated and sanitized form of human waste that is used as a highly potent fertilizer for agriculture and forests. It also has the consistency of cake, an observation Pitts was quick to point out as he molded a handful of the treated brown fertilizer into something resembling an animal before dropping it back into a machine.

While this process may seem gross, nearly all pathogens have been removed from the finished Loop, and it is safe to use for many commercial uses across the state, including a collection of farms in Eastern Washington. On top of this, Loop and the wastewater plant are playing a role in a process that is already needed if the planet is to avoid the worst effects of climate change.

Loop is so rich in carbon, it offsets the carbon that’s expended to process the plant’s wastewater. Loop also returns carbon to farmland, allowing crops to grow larger and soak up more carbon.

There are several ways to remove carbon dioxide (CO2) from the atmosphere, many of which are outlined in a report from the Intergovernmental Panel on Climate Change. The report presents a case for keeping global temperatures from rising more than 1.5 degrees Celsius above pre-industrial levels — and if that fails, the need to keep the increase below 2 degrees.

Agriculture, water access and heat-related deaths will be lower at 1.5 degrees. Even still, in areas around the equator, hot days have the potential to be up to 3 degrees Celsius warmer than now with 1.5 degrees of total warming.

In order to stay at or under 1.5 degrees, the world would need to reach net zero emissions by 2050, and for limiting warming below 2 degrees, net zero would need to be met by 2070.

This will require stopping the use of fossil fuels, but also removing carbon from the atmosphere, which will require large investments. James Mulligan is a senior associate with the World Resources Institute, which published a post detailing several techniques to remove carbon from the atmosphere.

“It would be really great to have the technologies available by 2040,” Mulligan said.

Several of these options can be implemented fairly cheaply, but there is a trade-off between cost and effectiveness and feasibility. For example, reforesting is an option. Healthy forests are good at removing CO2 from the atmosphere and storing it in wood and soil. Every acre of restored forestland can rake in around 3 metric tons of CO2 annually.

A recent article in Science Magazine said the U.S. is the largest cumulative emitter of CO2 from fossil fuels, but reforestation has the potential to offset around 20 percent of net annual emissions.

Expanding and enhancing farmland can help store carbon. Farmland is expensive to acquire and maintain and would likely require government subsidies to help landowners. Composting and using products such as Loop can additionally boost carbon storage in farm and forest soils. However, these may not solve global warming on their own, Mulligan said.

“If you think about how much we might be able to get out of those options globally, it’s meaningful,” he said. “It also falls well short of what we need globally.”

Other techniques require more research and development, including using bio-energy like old wood or trash to power energy plants. However, this also requires the plants to actually capture the emissions and store the carbon either underground or use it to make long-lasting products such as concrete.

Other methods can more directly remove large amounts of CO2 from either the air or seawater. Direct air capture involves sucking air into large scrubbers, where it is run through a solution that binds with carbon and removes it. From there, the carbon is turned into pellets and can be stored. Since cleaning units can be stacked, direct air capture provides another major benefit over more natural methods.

“Direct air capture is kind of scalable in a way that none of these other options are,” Mulligan said.

The technology to do this is still expensive. But three companies have already developed systems, and as more join, the price should begin to drop. One recent study cited in the World Resourses Institute’s post found it would cost between $92 to $232 per metric ton to operate direct air capture, and to work as it’s supposed to, it would require using green energy for power. This is still much lower than the $1,000 per cubic ton that was projected around eight years ago, Mulligan said.

It would also require a lot of energy. One of the existing types of direct air capture was estimated to require around 7 percent of all energy in the U.S. But deep decarbonization will require massive penetration of the global energy grid, Mulligan said. Another form of the same idea would scrub seawater of CO2, allowing it to soak up even more from the air. This would require more energy than air scrubbing, but the U.S. Navy already has a prototype in hopes that the captured CO2 could be turned into hydrogen and fuel for vessels.

Some effort like this will likely be necessary in coming years unless the world somehow transitions entirely to clean energy and does away with industries like raising cattle for beef, Mulligan said.

“It would be really great to have the technologies available by 2040,” Mulligan said.

This would allow them to be scaled up by 2050. While a rollout date of 2040 may feel distant, investments should be made now into research and development because there’s up to a 15-year lag between those initial investments and rollout for not only direct air capture, but for forest and soil alternatives as well as seawater capture.

“You’ve got to start doing those now,” Mulligan said.

Air capture alone would require up to $70 million in investments each year, which would scale up to around $250 million annually, according to the institute. This would allow the development and testing of direct air capture systems. Once research and development is done, then it would require public investment to build the required amount of scrubbers.

And unlike other green technology, such as solar panels, which provide a distinct benefit to the private companies building them, technologies like direct air capture of CO2 likely won’t be rolled out en masse by the private sector, according to the institute, because they provide a global public good.