The U.S. Department of Energy defines as a "pipeline-quality gas that is fully interchangeable with conventional natural gas." The difference between it and its fossil fuel derived cousin is that RNG is a filtered byproduct of organic decomposition sourced from landfills or livestock or鈥� well, let's just say you and me.
Every day, 8 million gallons of what the people of Grand Junction have flushed down their drains flows into the Persigo Wastewater Treatment Plant. The water coming out the other end is cleaner than the Colorado River it flows back into. The organic solids strained from that water are now serving a new purpose -- producing fuel for city vehicles.
Grand Junction has been replacing an aging fleet of garbage trucks and city busses with compressed natural gas vehicles, fueled mostly by the human-sourced gas from the treatment plant. The city's wastewater services manager, Dan Tonello, said Grand Junction is the first city in the nation to do so.
"We're looking at hundreds of thousands of dollars a year being saved by implementing this process," Tonello said, "and for a utility our size that's significant money."
The waste solids at Persigo have been processed for decades so they can be safely dumped at a landfill. That processing produces methane, which the plant used to just burn off into the air. By further refining that methane, they end up with natural gas that's chemically identical to what's drilled from underground.
Joanna Underwood, the president of Energy Vision, a nonprofit dedicated to expanding the use of renewable natural gas, applauds the Grand Junction project as a common sense way to both save money and lower greenhouse gas emissions.
"That's a model for small wastewater treatment plants anywhere in the country," she said.
Underwood points out there are other sources for RNG beyond human waste. Natural gas can be made from food waste too.
Right now, food scraps from restaurants are being collected along with that from grocery stores and large food manufacturers all over Colorado's densely populated Front Range. In a few weeks it will all be heading up to Northern Colorado, where the Heartland Biogas Facility is in final stages of construction. It basically does the same thing that the Persigo treatment plant does with solid waste, but on a much larger scale.
A1 Organics is partnering with the Heartland facility to coordinate all the arriving food waste. Bob Yost, the company's and chief technical officer, said the facility is unique and "one of the largest in North America."
There could soon be 25 to 30 semi loads of food waste making its way to the plant, where it is then mixed together with manure from a local dairy. It turns out the best way to get the most natural gas from waste is to process a balanced diet of both food scraps and animal waste.
After the facility extracts the RNG from the waste, it's injected into a pipeline along with fossil derived natural gas, feeding a nationwide delivery system.
Joanna Underwood of Energy Vision, said that if all the organic waste in the country was gathered, current technologies could produce enough natural gas to replace about half of the diesel fuel used in the U.S. transportation sector.
It's not a replacement for traditional oil and gas by a long shot, but Underwood argues practical solutions to climate change have to be assembled piece by piece.
"One thing isn't gonna do it," she said. "But for this sector, which in and of itself is big, it's not a small piece."
Inside Energy is a public media collaboration, based in Colorado, Wyoming and North Dakota, focusing on the energy industry and its impacts.
