​The Scoop on the Poop Bus: How Human and Animal Waste Might Fuel Our Future

The Bio-Bus, a 40-seat mass transit vehicle that can travel 186 miles on a tank of compressed gas produced from human waste, is a lot less disgusting than you think. It may even be an ingenious, carbon-neutral way to make use of our waste.

One tank of fuel on the Bio-Bus is roughly equal to the waste produced by five people in a year’s time. The exhaust emits about 30% less carbon dioxide than the standard diesel engine of a similarly sized bus. There is an environmental benefit to burning fuel that is generated from human waste: Much of the carbon emissions are carbon neutral, as the CO2 released by the bus was captured from the atmosphere only months or years before, in the food humans consumed to create the waste. By contrast, fuels like oil and coal release carbon into the atmosphere that has been stored in the earth for ages.

If you're worried about the stink, don’t be. Just because cars that run on cooking grease may smell like french fries, it doesn’t mean the exhaust from biomethane smells like a loo. GENeco, the company that produces the fuel captured at the Bristol sewage treatment plant, puts the toilet waste through a process known as anaerobic digestion, in which bacteria consumes the waste and produces a methane, carbon dioxide mixture called biogas. Then the biogas goes through a process, called upgrading, which removes the carbon dioxide molecules and mixes the methane with some propane, so it will burn cleaner. The process removes the impurities that create the odor associated with human waste.

The Bio-Bus has a route of 21 kilometers, or about 13 miles, on a well-traveled loop between Bristol’s airport and Bath’s city center. Some 10,000 passengers take the route each month. But the Bio-Bus might not be such an oddity in the future. Companies that treat sewage water have looked at ways to cash in on the waste that comes their way for some time now.

“Gas-powered vehicles have an important role to play in improving air quality in UK cities,” GENeco’s Mohammed Saddiq told the BBC. "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."

Thinking Outside the Bus

GENeco has also modified a Volkswagen Beetle called the Bio-Bug, which runs on the same fuel. The car can run for a year on the human waste generated from 70 local residences, and it performs, GENeco insists, just like a regular Beetle.

Scientists in the UK say that biogas collected from waste has the potential of replacing around 17% of vehicle fuel there. It can also be easily compressed the same way natural gas is. When it is properly cleaned, like it was for the Bio-Bus, it becomes biomethane, which is a viable replacement for natural gas, clean enough for gas-grid injection and indoor uses such as heating and cooking.

The Bristol sewage plant, which is operated by GENeco, can produce a lot more biomethane than just to run a bus line. The plant processes around 75 million cubic meters of sewage waste and about 35,000 tons of food waste a year. According to the BBC, that is enough waste to produce about 17 cubic meters of biomethane, likely enough fuel to power about 8% of Bristol’s homes.

GENeco is not the only company looking at biogas or biomethane. In countries such as Sweden, Germany and Switzerland, compressed biogas is becoming more common for transportation applications. In Sweden, a train dubbed Biogas Train Amanda has been in service for almost 10 years. And it’s estimated that some 12,000 vehicles, mostly in Europe, run on some form of biogas today.

Here in the U.S., biogas has been slowly making its way into our energy picture. About 0.5 percent of the natural gas we consume as a nation is already biogas, gathered from our landfills. But scientists and environmentalists are pushing for more widespread use of our waste to power our homes and fuel our vehicles. Some even believe it's plausible that agricultural waste can be a big player, like coal, nuclear power and natural gas in generating electricity.

Biogas generated from Vermont dairy farms is already generating power in the Northeast and sold through Green Mountain Power. There are similar biogas energy projects underway in Pennsylvania, New York and Wisconsin, but together these projects only represent a small fraction of what the 8,000 U.S. farms that can create biogas can produce.

Using the Texas Department of Conservation’s estimate that just one cow produces enough manure in a day to generate 3 kilowatts of power, the 87 million cattle in the U.S. could produce some 95 billion kilowatts of electricity, or roughly 4% of the nation’s electricity needs, the amount now produced by the combination of wind and solar.

But it doesn’t stop there; environmental scientists say that biogas production has the potential to remove about 100 million tons of greenhouse gas emissions from the atmosphere, or about 4% of the greenhouse gases produced by the U.S.

“Using biogas as a substitute for other fossil fuels, such as coal for electricity generation, replaces two [greenhouse gas] sources—manure and coal combustion—with a less carbon-intensive source, namely biogas combustion,” says Amanda Cuéllar and Michael Webber of the University of Texas at Austin, who wrote a study on the environmental impact of biogas.

But the world of biogas is less finite than harvesting the energy from our waste. Other sources, such as a seaweed known as sugar kelp and algae, are also being converted into biogas. In Europe and North America, scientists are exploring ways to efficiently harvest and convert sugar kelp into biogas, while others are looking at growing algae in “sporophyte factory farms” to create liquid biofuels, biogas and the refined biomethane.

Like with biogas from waste, biofuels created from algae and seaweed are considered carbon-neutral, sustainable and relatively climate friendly compared to the fossil-fuel alternatives. And unlike using food crops like corn to create biofuels, there is no concern that fuel needs may interfere with food production, which has always been an issue with renewable fuels like ethanol.

It's not often mentioned in the same breath as wind and solar, but when it comes to alternative energy sources, biogas should be more widely considered as an important part of lessening our dependence on carbon-intensive fossil fuel sources like coal, oil and natural gas.