Researchers are experimenting with using the same technique for wastewater solids, mainly turning sludge right into a stable product. “If you do pyrolysis—because it’s thermochemical, it’s a heated process—you kill these bacteria, kill these pathogens, kill these viruses. It’s much cleaner,” says engineer Fengqi You, who studies wastewater at Cornell University. In addition, sludge is a heavy, unwieldy liquid to ship from facility to farm. “You transport a lot of water in that, and the density is low. But biochar, it’s light—you can put it in bags—making transport easier.” So producers might ship it off extra simply to faraway farms, but additionally distribute it extra domestically, to city farms nearer to the supply of wastewater.

A wastewater facility may create gasoline in oxygen-free chambers, the place microbes eat the stable waste and launch methane “biogas” as a byproduct. “This biogas can be burned to generate heat,” says You. In Ithaca, New York, that may totally energy a wastewater facility itself, however You has additionally been experimenting with utilizing biogas to warmth close by buildings, together with a medical middle. Heating a constructing with pure fuel provides carbon emissions to the ambiance, however as biogas comes from the crops we eat and poop into the sewer system, which grew by drawing down carbon from the ambiance, so burning it kinds a carbon loop.

Before these microbes create biogas, in addition they generate risky fatty acids. These might be made into jet gasoline, or possibly even a gasoline for fleets of metropolis automobiles, says environmental engineer Sybil Sharvelle, who research wastewater at Colorado State University. “There’s a lot of value in all sorts of those volatile fatty acids,” says Sharvelle.

In addition to utilizing the waste solids as compost, like Epic Cleantec is experimenting with, Sharvelle notes that city farms may benefit from utilizing recycled wastewater that’s been disinfected to be used on crops, however with the nitrogen and phosphorus left in. Those are important vitamins for crops, however are literally troublesome to take away from water. “If you can leave nitrogen and phosphorus in the system, that’s a much more energy-efficient way to just make use of those nutrients directly,” says Sharvelle.

All instructed, the linear path of water—from supply to metropolis to sea—is beginning to curve. The way forward for wastewater is round, recycling again into ingesting water, compost for city farms, and vitality. Far from being unnatural, ingesting repurposed bathroom water is the form of resourcefulness that nature supposed. “Recycling is ubiquitous in nature,” says Kempes. “If there’s an untapped source of energy or nutrients, someone finds a way to use it. If you can create a fertilizer, find a way to clean water, and produce heat and electricity at the same time, that mirrors what we’ve seen biology evolve to do over billions of years.”