Seattle's Biosolids Reuse Plan Closes 'Loop'

A wastewater treatment plant serving Seattle and other communities in King County, Washington, is moving sustainable reuse practices forward with a product that it calls “Loop.”

“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,”Seattle Weekly reported. “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.”

Turning the byproducts of wastewater treatment into fertilizer for reuse in agricultural operations is not exactly novel, but it is certainly a practice that environmental groups and wastewater advocates alike want to expand.

“Once the wastewater reaches the plant, the sewage goes through physical, chemical and biological processes which clean the wastewater and remove the solids,” according to the U.S. EPA. “If necessary, the solids are then treated with lime to raise the pH level to eliminate objectionable odors. The wastewater treatment processes sanitize wastewater solids to control pathogens … and other organisms capable of transporting disease… By treating sewage sludge, it becomes biosolids which can be used as valuable fertilizer.”

Biosolids products like Loop are utilized by nearby farms, often to the profit of the municipalities that produce them, and can be key in reducing the atmosphere’s carbon and combating climate change.

“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,” per Bellevue Reporter. “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.”

Of course, for a biosolids reuse plan to be effective, the product has to reach nearby farms. Usually this isn’t an issue, but earlier this month, it was.

“Cars traveling east on Interstate 90 outside Seattle on Sunday morning found themselves backed up for nearly four miles in bumper-to-bumper traffic after a truck filled with human waste flipped over and spilled poop all over the place,” Thrillist reported. “The truck, operated by the biosolids company Loop, was hauling a bunch of soil made from literal crap when its driver allegedly fell asleep and caused the rig to overturn.”

To read more about how wastewater treatment operations reuse their byproducts, visit Water Online’s Sludge And Biosolids Processing Solutions Center.