Turning Wastewater Emissions into RNG and Local Art


Southwest Gas, Arizona’s largest natural gas utility, has connected its system to Pima County’s Tres Rios Wastewater Reclamation Facility in Marana, Arizona as a renewable natural gas plant (GNR).

Pima County has consumed raw biogas to power the engines used at the Tres Rios Wastewater Treatment Plant for many years. A 2014 study concluded that it would be more economical to refine raw biogas from Tres Rios into salable RNG, and construction of the plant was subsequently approved. The county signed an agreement with a biogas joint venture to build the RNG processing facility and market the gas. Eventually the joint venture stalled, but Pima County decided to move forward by building the plant on its own and partnering with Southwest Gas.

In an effort to help the local community achieve energy sustainability with reduced emissions, Southwest Gas is acting as a catalyst to bring RNG sources to consumers. Southwest Gas’s plans for a sustainable energy future and Pima County’s decision to market the highest quality gas led to the finding of a company specializing in gas quality evaluation to enable the marketability of the Tres product. Rios. Mustang Sampling was chosen to provide a turnkey solution, Analytically Accurate® to ensure a verifiable supply of sustainable, clean and safe GNR.

Wastewater treatment plants typically produce methane-rich gas from the anaerobic breakdown of solid waste, sludge, or biosolids in municipal wastewater. Constituents of Concern (COCs) such as metals, sulfur compounds and siloxanes may be present in the gas as these materials are present in waste streams. With treatment to increase methane content, reduce water and remove COCs, wastewater treatment plants are able to produce RNG that meets tariff requirements for injection into gas pipelines. Continuous monitoring thereafter and periodic on-site sampling prior to injection into the pipeline ensures reliable future supply.

Final gas quality is measured at the interconnection between the RNG plant and the Southwest Gas pipeline. Continuous monitoring begins with the extraction of an RNG sample through a probe housed in the Pony® heated probe enclosure. The extracted gas is transferred via the patented Mustang® heat-tracing tube bundle to a Mustang P53® sample conditioning system, which maintains the sample temperature well above the hydrocarbon dew point. The representative sample is distributed using a Mustang Modular Sample Control Panel to various analyzers in an industrialized Mustang Sampling building. The GNR supply is typically continuously monitored for CH4, CO2, H2S, Nitrogen and Oxygen to ensure it meets the rate parameters set by Southwest Gas. Safety mechanisms at the interconnect allow the pipeline to reject any substandard RNG into the pipeline.

The artist behind the evolution of energy

Pima County commissioned a locally renowned muralist and public artist, Ignacio Garcia, to adorn the highly visible installation. Garcia is best known throughout Arizona and California for his 3D chalk and large photorealistic murals. The commissioned mural wraps the building at the RNG Interconnection between the Tres Rios Wastewater Reclamation Facility and Southwest Gas, capturing a variety of energy-related themes in a style only Garcia could offer.

Through Garcia’s work, he offers an innovative and unique point of view that challenges the emotional and physical reaction of the viewer. He believes that the research, reflection and exploration of the subject before creating the finished piece will invoke an authentic, unpredictable and organic response from each individual viewer. Using this belief system, Garcia was able to facilitate an engaging brainstorming session with the sewage treatment plant team, which ultimately led to the evolution of energy through their eyes.

“It was the wastewater management team, the people who actually work there. They had this idea of ​​how our energy evolved,” Garcia said. “How it evolved so far, into the future, through wildlife. We went back and forth and then they mentioned a dinosaur. At first I was like, ‘really?’ and then I knew exactly what to do with it. The whole mural came together and, in the end, I linked it with an artist’s perspective.

For more information, visit www.mustangsampling.com or call (713) 482-6930.


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