Renewable Natural Gas for Pipeline Injection

(Above Photo) New CMU building, along with hydrogen sulfide removal vessels in large steel tanks and the PSA system outside of the building.

Photo Credit: Benjamin Bosse, MWMC

MWMC is Oregon’s First Public Agency to Create Renewable Natural Gas for Pipeline Injection.

Kennedy Jenks (KJ) and the Metropolitan Wastewater Management Commission (MWMC) charted new territory together during the implementation of KJ’s first Renewable Natural Gas (RNG) project constructed at the MWMC’s Eugene-Springfield Water Pollution Control Facility (WPCF) located in Eugene near the Willamette River. The MWMC is the first municipality in the State of Oregon to treat biogas for injection as RNG into a commercial natural gas pipeline, operated by NW Natural. The Eugene-Springfield WPCF is the second largest wastewater treatment plant (WWTP) in the State of Oregon with a capacity to treat 35 million gallons per day (MGD) and serves the Eugene-Springfield, Oregon area. 

Biogas contains mostly methane and carbon dioxide with trace amounts of other gases and is a byproduct of anaerobic digestion, a wastewater sludge treatment process used to degrade sludge. Prior to the construction of the new biogas treatment system, MWMC used approximately 60% of their biogas to fuel an internal combustion (IC) engine for heat and electricity at the plant, with the remaining 40% flared (burned off through waste methane gas burners) and released into the atmosphere. The IC engine was expensive to maintain and unreliable, and, in 2012, MWMC set out to find a way to use the biogas they were flaring by commissioning assessments for alternative uses of biogas.  

(Above Photo) New CMU building, along with hydrogen sulfide removal vessels in large steel tanks and the PSA system outside of the building 

Photo Credit: Benjamin Bosse, MWMC

KJ was hired in December 2017 for the planning and design of MWMC’s new biogas treatment system. The system consists of hydrogen sulfide vessels to remove hydrogen sulfide from the biogas. A pressure-swing adsorption (PSA) system was constructed to scrub the biogas to a high-BTU, natural gas quality product (RNG), which entails stripping the biogas of carbon dioxide and other contaminants such as volatile organic compounds (VOCs). The RNG is piped to compressors to meet NW Natural’s pressure requirements of 170 psi for injection into their pipeline system. Other ancillary features of the new biogas treatment system include a regenerative thermal oxidizer used to oxidize contaminants removed by the PSA system into carbon dioxide and water before they are released into the atmosphere; a new concrete masonry unit (CMU) building with brick veneer, housing certain components of the treatment system, such as pumps, blowers, compressors, and associated piping; 200 feet of RNG pipeline conveying RNG from the treatment system to NW Natural’s receipt point facility; and associated electrical and instrumentation infrastructure.  

Construction of the biogas treatment system was completed in the summer of 2021, and NW Natural’s receipt point facility, located on the grounds of the WPCF, was completed separately in the fall of 2021. Buried pipeline constructed by NW Natural in the fall of 2020 conveys the RNG from the WPCF to an existing natural gas transmission line operated by NW Natural and located along River Road to the west of the WPCF. Injection of RNG into NW Natural’s pipeline began in November 2021. 

The Pacific Northwest Clean Water Association (PNCWA) selected MWMC’s RNG project for the 2022 Excellence in Resource Recovery Award. This award is presented to agencies that demonstrate outstanding performance in moving the concept of resource recovery forward in the Pacific Northwest region.

MWMC’s RNG project also won a National Environmental Achievement Award (NEAA) in the Water Resources Utility of the Future category from the National Association of Clean Water Agencies (NACWA) in February 2023. The NEAAs recognize outstanding contributions to environmental protection and the clean water community; the Water Resources Utility of the Future category honors water resource recovery facilities for community engagement, watershed stewardship, and recovery of resources such as water, energy, and nutrients.