August 31, 2021 | AD & Biogas, Facilities

Colorado Cities Fuel Fleets With RNG From WRRFs

Top: The City of Longmont has five bays and 16 fueling positions for its current fleet of RNG-fueled collection vehicles. Photos courtesy of City of Longmont.

In 2018, the City of Longmont, Colorado began construction of a renewable natural gas (RNG) project at its Water Resource Recovery Facility (WRRF) to make fuel to utilize in the City’s fleet trash trucks. The project was completed in late 2019. Prior to building the RNG pipeline, 75% of the biogas produced by the WRRF was flared; only a small portion was needed for heat at the wastewater treatment facility. A biogas treatment skid was installed to remove contaminants in the biogas. The pressure of the clean biogas is about 100 psi. To use the fuel in vehicles, compressors boost the pressure of the biogas to over 4,000 psi.

The Waste Services facility consists of a 22,680-square-foot building encompassing five bays and 16 fueling positions (or posts). Eleven of Longmont’s 21 diesel collection trucks were replaced with compressed natural gas (CNG) trucks capable of using RNG fuel. The trucks connect to the fueling posts at the end of their shifts. They are filled with RNG overnight and ready for drivers to begin collection routes by the next morning. The fleet change out aligned with the existing replacement schedule for those trucks. The remaining diesel trucks are expected to be replaced in 2024. The Waste Services division anticipates using about 50% to 70% of the biogas produced at the WRRF.

The City of Boulder’s WRRF completed its Biogas Use Enhancement Project in 2020, producing RNG from the treatment plant’s biogas. The RNG is sold to Western Disposal, the city’s franchised waste hauler; Western can fuel up to 38 trucks in the fleet it uses for the city’s trash collection. Tetra Tech provided the engineering, procurement and construction (EPC) services to the City of Boulder. The facility installed Tetra Tech’s proprietary BioCNG™ gas conditioning system.

The Biogas Use Enhancement Project replaced the WRRF’s cogeneration system, which was at the end of its useful service life. The RNG is injected into the Public Service Company of Colorado’s pipeline. The City sells the natural gas to Western for a rate that’s published in a monthly energy index, with a 5% discount, according to an article in the Daily Camera, which equated to about $0.75/diesel gallon in 2020. Boulder also is capitalizing on the sale of RIN credits in the federal Renewable Fuel Standard marketplace.

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