RNG 101: the basics of Renewable Natural Gas

Northern Colorado Clean Cities recently interviewed CGRS and City of Longmont, Colorado, representatives about the ins and outs of constructing a system that converts biogas at a wastewater treatment plant to Renewable Natural Gas (RNG). The goal: provide useful information about the decision-making and construction processes so other jurisdictions can determine if a similar project is right for their facilities and their communities. The following article is based on the content of those interviews.

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800.288.2657

Cory Kahler
Water/Wastewater
Operations Manager
Mobile: 720.537.9387

Unlike the petroleum that fuels most vehicles, renewable natural gas (RNG) is a treated or purified gas product from the decomposition of organic matter, such as that found at a wastewater treatment plant (WWTP).

The City of Longmont’s John Gage, P.E., Public Works and Natural Resources Civil Engineer, and Cory Kahler, CGRS Water/Wastewater Operations Manager and an expert in RNG/Compressed Natural Gas (CNG) systems, explain how the City uses this valuable resource to fuel its Waste Services fleet.

With CGRS as the general contractor and Kahler overseeing the RNG/CNG portion of the project, the City’s new Biogas Treatment and RNG Fueling Station began operating at its Wastewater Treatment Plant (WWTP) this spring.

Gage explained that before the RNG system was built, the City’s WWTP used anaerobic digestion to turn its biogas into concentrated methane, and then flared it off. The addition of an RNG system treats or purifies the methane so that it can be used as fuel for a wide variety of engines including vehicles, combustion engines and more.

Treating the methane and using it as fuel has a positive effect on the environment, Kahler explained. “There’s been a lot of advancement in cleaning up the methane and using it as renewable natural gas, RNG.

“Basically it offsets the greenhouse gas, obviously, and we’re using it, so it helps with carbon impact,” Kahler said. “If you take into consideration the amount of carbon produced by a diesel-burning vehicle and you eliminate that diesel-burning vehicle and start burning renewable natural gas, it can be carbon negative.”

He used Waste Services fleets, which stop and start often, as an example of how CNG vehicles can have a visible impact on a community’s environment.

“Every time they step on the throttle on the old trash trucks, you would see black puffs of smoke coming out of the exhaust,” he said. “It’s dirty, it’s not appealing.”

Gage noted some WWTP operators treat their biogas to a lower-quality RNG to fuel combustion engines that provide electricity and heat.

If RNG is treated to meet higher specifications, the jurisdiction can inject it into a pipeline where other end users across the country can access it, Kahler said.

In Longmont’s case, the ability to fund the RNG system and its fleet replacement cycle aligned so the City could not only build an RNG system at its WWTP, but also pipe it to a new Waste Services facility where it is turned into CNG and fuels the City’s new CNG trucks.