Power Up

The Buses of Tomorrow Will Run on Sewage

Food waste, sewage, and manure are all potent sources of renewable energy

3 min read

Image credit: Gerla Brakkee // CCO

Maybe you haven’t heard of biogas, but it has the potential to replace a quarter of the United States’ annual diesel use. Originating as organic waste, the fuel is not only environmentally efficient, but also proves that one man’s trash really is another’s treasure.

Here’s how it works. Decomposing organic materials like food, crops, animal manure, and even human sewage release methane and carbon dioxide through a process called anaerobic digestion. It’s similar to what goes on in your gut after a meal. When carrying out that process in dedicated tanks, you also end up with digestate, a sludge that’s full of nutrients and can be used as a fertilizer. The gases can be collected at landfills, too.

The biogas is refined to almost pure methane and compressed or liquefied so it can be used as a vehicle fuel that’s resource-efficient and low in emissions. Compared with petroleum-based fuels, combustion of biogas is less polluting. In fact, a report commissioned by the California Air Resources Board (CARB) suggests that, over its entire lifecycle, biogas made from food waste can actually result in net-negative carbon emissions–if it’s assumed that any greenhouse gases produced during the process are reabsorbed when new plants grow. That said, it does contribute to air pollution: Like fossil fuels, it produces nitrogen oxides, sulfur oxides, and health-impacting particulates, although at lower levels. Upgrading the gas to almost pure methane also needs additional water and energy resources.

A bus stopped at a bus stop.
Image credit: Duncan Geere

Refined biogas is called biomethane, and is chemically identical to the natural gas we use for cooking, heating, and transport. That makes it an easy win as a fuel–it can go in any vehicle that already runs on gas, so it’s a proven technology. A bus in Reading, England–powered by biomethane (made from cow manure)–set a land-speed record in 2015 for a service bus when it topped out at 77 m.p.h.

In Indiana, one dairy farm is using its herd’s waste to fuel the 42 trucks that transport its milk across America. Fair Oaks Farm specifically wanted to reduce its environmental impact, and can now produce the equivalent of 1.5 million gallons of diesel every year. Waste power is becoming more popular, according to President of Energy Vision Matt Tomich. He told me, “In 2015, close to 90 million gasoline gallon equivalents of renewable natural gas were produced (mostly from large landfills) for vehicle fuel. In 2012, this volume was effectively zero. [In 2016] that number is expected to approach 150 million.”

More examples can be found across the United States. The Persigo wastewater treatment facility in Grand Junction, Colorado, is the first in the state to operate a biogas-to-vehicle-fuel project. It creates enough biogas to fuel 38 of the city’s municipal vehicles, including dump trucks, pick-ups, and four regional buses. This cuts the requirement for gasoline and diesel by around 168,000 gallons per year. In Sacramento, commercial and household food waste is treated and goes back into fueling the very same trucks it is collected in, creating a perfect closed-loop system.

Large circular tanks with dome roofs.
Anaerobic digestion tanks. Image credit: Jan Nijman // CC0

When can we all expect to be traveling in waste-powered cars? Maybe not just yet: In 2014, the United States consumed nearly 137 billion gallons of gasoline. While biogas does have a place in the future energy mix, it’s tricky to be certain how much, as estimates vary widely. Tomich said that “somewhere between four and 10 billion GGEs of renewable natural gas could be produced annually from biogas.” If production was maximized, the American Gas Foundation reckons that enough gas could be processed to provide as much as 40 percent of the country’s total requirement. The National Petroleum Council is a little more conservative, putting it at 20 percent, based on existing technologies and supply of materials that can be processed.

Money, of course, is a major factor in setting up facilities. At Fair Oaks Farm, it cost US$18.5 million to get the plant installed, and US$2.8 million at Persigo. It is not cheap. Funding often comes from public as well as private cash, with loans and subsidies that support renewable energy projects. In the past the cost advantage of refined biogas versus oil ultimately made it a sound financial investment, but market forces and the dwindling oil price could pose a threat. There’s one key thing that continues to make biogas favorable, though: the race to reduce carbon emissions. There’s enough political will to curb our dependence on fossil fuels, and the Environmental Protection Agency’s Renewable Fuel Standard incentivizes production.

The transport sector is the place where biofuels can make a difference today. Transport is responsible for over one-quarter of the U.S.’s total greenhouse gas emissions, so it makes a lot of sense to power fuel-hungry heavy trucks and public transport on refined biogas. It is particularly beneficial to switch from diesel where there is an existing opportunity–like wastewaster plants, landfills, and dairy farms–because they have the waste to process and vehicles to fuel. It makes financial sense in the long term.

Elsewhere, companies are making commitments to reduce their carbon impacts, with the likes of UPS continuing to invest in less environmentally harmful fleets despite a challenging economic climate. Large firms have the capital to explore alternative fuels, and recognize the commercial value in becoming more environmentally conscious.

Biogas represents a golden opportunity to clean up the transportation sector, and will continue to do so for years to come.


How We Get To Next was a magazine that explored the future of science, technology, and culture from 2014 to 2019. This article is part of our Power Up section, which looks at the future of electricity and energy. Click the logo to read more.