On November 20, 40 unassuming tourists boarded a bus at the Bristol Airport bound for the historic city of Bath in southwest England. The markings on the bus, however, might have tipped them off that something was different here: One side of the vehicle depicted people dumping food scraps into food-recycling bins (standard waste-disposal in the United Kingdom), while the other side displayed a row of citizens perched atop toilets.

The vehicle was the Bio-Bus, the first bus in the U.K. powered by fuel derived from sewage and food waste. Built by biogas plant GENeco, a subsidiary of the local water department, the bus can run for about 186 miles on a single tank of fuel, which is derived from the annual sewage and food waste of five people.

Locally, it’s a big step towards sustainable, low-pollution transportation. “Gas powered vehicles have an important role to play in improving air quality in U.K. cities, but the Bio-Bus goes further than that and is actually powered by people living in the local area, including quite possibly those on the bus itself,” GENeco general manager Mohammed Saddiq said in a statement. “Using bio[gas] in this way not only provides a sustainable fuel, but also reduces our reliance on traditional fossil fuels.”

Despite the unappealing origins of its power source, the bus is a breath of fresh air on the roadways. According to a report in Fast Company, nixing the standard diesel fuel cuts pollutants, such as benzene and arsenic, by 97 percent. GENeco also claims that the bus puts out 20 to 30 percent less carbon dioxide than a diesel model would.

In addition to refueling the Bio-Bus, the GENeco biogas plant pumps enough electricity into the grid to power 8,500 homes.

Biogas (often referred to as “biomethane” across the pond) is created through a process called anaerobic digestion. In an oxygen-less tank, called a digester, microorganisms break down organic material. The process nets two products: biogas (methane and carbon dioxide) and fibrous byproducts that are repurposed into things like animal bedding and fertilizers. Methane then passes through an upgrading process to concentrate it to the levels necessary to be a viable replacement for fuel or to power the electrical grid.

There isn’t a single waste source for this process. Biogas can be rendered from landfills, wastewater, manure and agricultural waste (think stripped sugar cane), among other sources. The GENeco plant, for example, converts more than 2.6 billion cubic feet of sewage and upwards of 38,000 tons of food waste. It’s the first and largest plant in the U.K. to use those sources to deliver energy to the grid.

If implemented worldwide, the impact of biogas would be sizeable. The EPA’s National Renewable Energy Laboratory estimates that biogas—should it be gathered from all available U.S. sources—could offset 46 percent of natural gas consumption for electricity and replace natural gas in transportation entirely. In fact, if all sources were tapped, it would produce the biogas equivalent of 35 billion gallons of gasoline. There are currently more than 1,500 biogas digesters at wastewater treatment centers in the U.S., some of which produce enough electricity to go entirely off-grid.

Using biogas for transportation is still new, although several similar projects have sprung up across Europe in the past several years, spurred by aggressive renewable-energy legislation in some countries. Sweden, for instance, runs a fleet of more than 36,000 vehicles, including trucks and buses, using waste-derived biogas. And Oslo, Norway, has about 80 poo-powered buses on the road.

In 2010, GENeco debuted a proof-of-concept for sewage-derived transportation, the Bio-Bug, before taking on the larger task of revamping public transit. The Bath Bus Company, whose route the Bio-Bus currently follows, also runs tour buses in popular U.K. destinations, but hasn’t committed to expanding beyond this initial offering.