You probably didn’t think poop. But poop is one of the most popular forms of biofuel today. From street lamps in Malvern Hills, England, to heaters and cooktops in Kenya, to trucks in the city of Portland, Oregon, waste is the hottest thing in fuel. And because this biomass is a renewable resource and consuming it means working with carbon that’s already circulating in the atmosphere, many argue that sewage is a net-zero emitter. Poop is the green energy fuel of the future.
“People have been thinking about waste to energy for a long time. And it used to be a joke, but when I go into a room with other people in my field I open a conversation with: ‘How many of you have played with poop?’” says Corinne Drennan, a scientist that leads the biofuels research program at the Pacific Northwest National Laboratory (PNNL).
Her question isn’t a joke anymore: “I think now we’re realizing there are technologies that are really viable and that are able to convert the sludge into very high-quality fuels.”
These technologies are especially useful in addressing the growing waste problem the agriculture community now faces. To an extent, waste from animals produced on farms could be used a fertilizer in soils. But, says Drennan, “there’s only so much land application you can do before you saturate the ground with phosphorus and nitrates and other nutrients that are in these materials. You don’t want to over-fertilize or put pathogens on the ground. Raw sewage has potential for disease or over-fertilizing that runs off into streams.”
As a result, she says, most farmers are shoveling it into ponds, destroying it, or paying to have it trucked to landfills. “Farmers or dairy operations, they’re struggling right now. They’ve pretty much saturated the land around them with raw manure as much as they can.”
Using biomass from these sources is going to solve a series of problems. And, while in the past the best methods to turn poop into fuel were focused on incineration (which is still used), new technologies have figured out how to turn it into liquid fuel that can be stored for later use.
At PNNL, they accomplish this by pushing sewage slurry through a tube at extremely high pressure (3,000 PSI) and at a high temperature (about 660 degrees Fahrenheit). That pressure cooking changes the sewage into different phases. At the solid stage it can be used for fertilizer. But it also goes through two liquid phases, one of which is oil rich.
This oil rich phase, says Drennan, might actually be able to power a diesel engine on its own. But, more realistically, it can be compared to crude oil—meaning it can be refined into a liquid fuel that can power all sorts of motors.
Though the process itself isn’t energy neutral, it looks a lot different when compared to the standard method of harvesting crude oil. When you turn sewage into fuel, she says, you don’t have the environmental consequences of drilling and extracting the oil. Sewage, she says, is “like recycling, working with carbon that’s already in play.”
And it’s not just farmers that are trucking their manure to landfills. Wastewater treatment plants have to get rid of the sewage they collect as well. They are using different methods, but all of them are expensive. So PNNL and Drennan are taking advantage of the need to more efficiently dispose of poop. They’re currently working in California with Contra Costa County to design and build a demonstration facility that will capture sewage and convert it into fuel on the site of a wastewater treatment facility.
Drennan says that Vancouver is also planning a similar pilot program, and they have partners at oil refineries looking at ways to process the crude that’s produced there along with petroleum. PNNL is also looking at setting up these types of facilities at farms. But it will be more difficult, she says, because the raw materials there have to be shoveled.
They’ll figure it out eventually. Poop is gaining traction.