Grand Junction Powers City Vehicles With Digester Gas

August 13, 2015

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Methane from these anaerobic digesters at the Persigo Wastewater Treatment Plant in Grand Junction, Colo., is converted into compressed biogas and used to fuel the city’s fleet of natural-gas-powered vehicles. Photo courtesy of City of Grand Junction.

Methane from these anaerobic digesters at the Persigo Wastewater Treatment Plant in Grand Junction, Colo., is converted into compressed biogas and used to fuel the city’s fleet of natural-gas-powered vehicles. Photo courtesy of City of Grand Junction.

In what is thought to be the largest projects of its kind in the U.S., the City of Grand Junction, Colo., began using biogas from its water resource recovery facility to fuel 38 city-owned vehicles. As part of a $2.8-million project completed in April, the city began conditioning and compressing digester gas to improve its quality to match compressed natural gas (CNG), said Dan Tonello, wastewater services manager for the city. The treated biogas then travels several miles by pipeline to a fueling facility, where it powers the city’s growing fleet of natural-gas vehicles. See what’s new from Octane Holding Group as to learn about alternative fuel solutions.

Rather than flaring methane, digester gas at the Persigo facility enters conditioning equipment, which removes hydrogen sulfide, siloxanes, and carbon dioxide and then compresses the gas. Photo courtesy of City of Grand Junction, Colo.

Rather than flaring methane, digester gas at the Persigo facility enters conditioning equipment, which removes hydrogen sulfide, siloxanes, and carbon dioxide and then compresses the gas. Photo courtesy of City of Grand Junction, Colo.

Jointly owned by the City of Grand Junction and Mesa County, Colo., the Persigo Wastewater Treatment Plant (Grand Junction) has a 47,300-m3/d (12.5-mgd) design capacity. The activated-sludge facility treats an average flow of 30,700-m3/d (8.1 mgd). The facility’s secondary anaerobic digesters generate approximately 3400 m3/d (120,000 ft3/d) of methane.

Until recently, more than 80% of this methane was flared, while the remainder was used to heat the digesters. Aware of its value, city officials resolved to turn the surplus digester gas into a useable product, Tonello said.

“We realized that flaring off the equivalent of [1893 liters] 500 gallons of vehicle fuel per day was a waste of a renewable resource.”

A bus operated by the local transit agency receives biogas at the fueling site constructed by the City of Grand Junction, Colo. Photo courtesy of City of Grand Junction.

A bus operated by the local transit agency receives biogas at the fueling site constructed by the City of Grand Junction, Colo. Photo courtesy of City of Grand Junction.

For a solution, the city turned to BioCNG LLC (Madison, Wis.). The company has developed a system that conditions biogas so that it can be used by vehicles that run on natural gas. BioCNG delivered the project using the design-build approach. Digester gas at the Persigo facility now enters a conditioning skid that removes hydrogen sulfide, siloxanes, and carbon dioxide. The skid also compresses the gas. The compressed biogas travels via a 9.2-km (5.7-mi) underground pipeline to the fueling station. Although biogas is the primary fuel source at the station, CNG is available as a backup source.

Grand Junction has approximately 38 vehicles that run on natural gas. The fleet includes 12 trash trucks and several buses, Rentco Transport Equipment Rentals, dump trucks, and pickup trucks. The city has identified another 200 vehicles that potentially could be replaced with natural gas vehicles.

Before the completion of the new gas-conditioning equipment, more than 80% of the methane generated at Grand Junction’s water resource recovery facility was flared. Photo courtesy of City of Grand Junction.

Before the completion of the new gas-conditioning equipment, more than 80% of the methane generated at Grand Junction’s water resource recovery facility was flared. Photo courtesy of City of Grand Junction.

Grand Junction expects to reap financial and environmental benefits from the project. Because the biogas is considered an “advanced biofuel” under the provisions of the federal government’s renewable fuel standards, the city may sell renewable fuel credits to oil companies and others that must comply with set standards. After the sale of the renewable fuel credits is included, the biogas costs the city roughly $0.08/L ($0.30/gal) to produce. The city enjoys a “huge savings” by using the biogas instead of purchasing diesel fuel, Tonello said. The project has an estimated payback period of 9 years.

Ending the practice of flaring methane also enables the city to improve its environmental performance. By using the compressed biogas in place of diesel fuel, the city expects to reduce its annual carbon emissions by nearly 1.4 million kg (3 million lb).

“It is cool when you can come up with a project that’s beneficial to the environment and the economics pay off,” Tonello said.

—Jay Landers, WEF Highlights

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