A methane flare at the Longmont Wastewater Treatment Plant, where installation of a biogas cleaning system will facilitate turning the methane into usable natural gas. (Adam Butt / Courtesy photo)
Come 2019, Longmont’s trash trucks will be powered by an entirely different kind of waste.
When wastewater (anything that gets flushed down a toilet or washed down a drain) comes into the Longmont Wastewater Treatment Plant, organic material is broken down by microorganisms in a process called anaerobic digestion.
The byproduct of anaerobic digestion is methane gas, 25 percent of which goes back into heating the anaerobic digestion process but the other 75 percent is simply set on fire.
“It’s the natural gas you get out of your home — methane. But there are a lot of contaminants in that gas so we are forced to flare it,” said John Gage, Longmont civil engineer. “If you were to burn it in an engine, it would cause all sorts of problems. So it’s a resource that, right now, is not being utilized.”
Instead, Longmont will install a biogas cleaning system that will turn the methane into usable natural gas by compressing it to 3,200 pounds per square inch.
Once the system construction is completed in 2019, the city will use the biogas to fuel 11 of Longmont’s 16 diesel trash trucks. The 11 trucks will be replaced on the existing replacement schedule. The remaining five trucks will be replaced in 2021.
Longmont received a $1 million grant from the Colorado Department of Local Affairs to offset a portion of the costs required for the cleaning system and a $385,000 grant from the Colorado Regional Air Quality Council to offset costs of the more expensive trucks that run on biogas.
Gage said that the stable and cheaper cost of biogas compared to diesel fuel will save the city money in the long run.
“When you look at gas prices right now at the pump, we are seeing $2 to $2.50 per gallon, something like that … Diesel fuel can get as high as $3 or $4 per gallon,” Gage said. “It costs us to treat biogas the equivalent of $1 per gallon. And we can maintain that for the foreseeable future.”
Longmont would gain additional revenue by selling Renewable Identification Numbers credits to fuel refiners to meet Environmental Protection Agency obligations to reduce the use of fossil fuels. Longmont would generate RIN credits as they produce gallons of biogas.
Gage said the plan to install the biogas cleaning system lines up with Longmont’s sustainability plan by offsetting the use of fossil fuels and beneficially using methane that is currently just being flared.
Gage said there have been discussions with city officials about offering biogas to other entities or to the public in the future.
“What we’ve estimated is that once converted, sanitation will use 50 to 70 percent of the fuel and we’ll still have 50 to 30 percent available,” Gage said. “We have already been talking about a possible expansion to do a public fueling station or reaching out to other government or other interested parties that would be able to use our fuel.”
Longmont is the second city in Colorado to use methane from sewage treatment to fuel government vehicles . Grand Junction implemented its system in 2011.
Gage and other Longmont officials paid a site visit to Grand Junction earlier this year to review the process and make sure there were no issues with either the wastewater treatment plant or the trash truck fleet.
“They haven’t had a day out of service since they started,” Gage said of the Grand Junction fueling station.
Having the fueling station continuously operational is important because biogas stations are few and far between. If Longmont’s station wasn’t working, trash truck drivers can’t just go to the next gas station and get fuel.
Gage said the construction on the cleaning system is estimated to start in February or March and should take about a year.