Cleantech
The US Has a Low-Carbon Vehicle Fuel — But It's Being Thrown Away

The United States generates millions of tons of food scraps; inedible fats, oils and greases; sewage and manure. Some of this organic waste is used for energy or fertilizer, but most of it — around 50 million tons a year — is sent to landfills, incinerated or otherwise left to decompose.

But this trash doesn’t have to be wasted. New WRI research finds that turning certain types of organic waste into renewable natural gas (RNG) could provide trucks and other heavy-duty vehicles with a fuel that avoids more greenhouse gas (GHG) emissions than it creates over its lifecycle.

How does waste become RNG?

“Wet” organic wastes, as they are called due to their moisture content, are typically turned into RNG through a process known as anaerobic digestion. As the waste breaks down, it produces biogas, a mixture of carbon dioxide, methane and other trace components, which is then refined into RNG, essentially pure methane that can be used in the same ways as conventional natural gas. RNG is then liquefied or compressed and used in any vehicle with a natural gas engine — typically garbage trucks, freight haulers and buses.

When wet organic wastes decompose in their typical management facilities — food scraps in a landfill or dairy manure in an open lagoon, for example — they produce methane, a greenhouse gas that’s 28 times as potent as carbon dioxide. Landfills, livestock and wastewater treatment facilities contribute around 30 percent of all U.S. methane emissions.

When RNG is made from waste that would otherwise lead to methane emissions, it can have a much lower lifecycle carbon footprint than conventional natural gas, diesel and other fuel options. RNG from food scraps and dairy manure are considered carbon-negative under California’s low-carbon fuel standard, meaning the emissions avoided from RNG production and use completely outweigh the emissions it causes when it’s produced, transported and burned in a vehicle. RNG from food scraps and yard trimmings is 120 percent less carbon-intensive than fossil fuels under California’s low-carbon standard; RNG from dairy cow manure is 400 percent less carbon-intensive.

RNG is already being produced and used around the country

Cities, towns and businesses from Louisiana, Indiana, Michigan and several other states around the country are already using RNG to more efficiently manage local waste and power vehicle fleets such as garbage trucks, city buses and freight vehicles. A dairy farm in Fair Oaks, Indiana found that powering its milk delivery trucks with RNG made from cow manure saves them $2.5 million in fuel costs each year while reducing methane emissions by the CO2 equivalent of 24,000 tons. Private companies with large vehicle fleets such as UPS are using RNG as one low-carbon fuel option to meet corporate sustainability goals. RNG is part of California’s plan to reduce emissions 40 percent below 2020 levels by 2030.

These early adopters represent just a fraction of RNG’s potential. The 50 million tons of unused organic waste that the United States produces every year is the energy-content equivalent of 6 billion gallons of diesel — 15 percent of the diesel consumed by the country’s heavy-duty trucks and buses last year. Due to technical and economic limitations, actually converting 50 million tons of waste into RNG would produce roughly 6 billion gallons of fuel, but the comparison provides a sense of RNG’s potential.

With growing interest in RNG, its production is likely to continue to grow. RNG that meets the conditions described in our research could help states, cities, universities and companies cut GHG emissions and meet their climate goals.