Phoenix, Ariz.: Biogas-to-renewable natural gas plant

The 91st Avenue Renewable Natural Gas (RNG) Plant in Phoenix is the United States’ largest biogas-to-RNG plant located at a wastewater treatment plant. It is a multi-million dollar project that is expected to reduce the equivalent of 44,671 metric tons of CO2 each year — the equivalent of taking 70,452 cars off the road for one year.

Part of the plant’s innovativeness comes from it harnessing a previously wasted by-product of wastewater treatment: raw biogas. The plant uses anaerobic digesters to generate biogas, which is then processed in a pressure swing adsorption system to become RNG. The RNG is then injected into the country’s natural gas pipeline grid — the plant’s first RNG entered the grid in December 2018.

RNG has many applications as a substitute for natural gas — it can be used for vehicle fuel, as a bio-product feedstock, in electricity generation and for thermal purposes, according to the U.S. Environmental Protection Agency.

Building the facility is part of a goal Phoenix set in 2016 to be 100 percent carbon-neutral by 2050.

However, multiple parties worked together to make this project happen.

Energy efficiency and renewable energy solutions provider Ameresco entered into a 20-year contract with Phoenix to design, build, own, operate and maintain the plant. Numerous local contractors were hired to build the plant. Ameresco also has a 20-year agreement with Phoenix to purchase the biogas generated at the plant and to occupy city-owned land.

Phoenix operates the wastewater treatment plant, which is owned by a sub-regional operating group (SROG) consisting of the Arizona cities of Phoenix, Glendale, Mesa, Scottsdale and Tempe. The city councils and attorneys of these five cities had to review and approve the agreements. However, Ameresco is giving the cities base royalty payments for the purchase of biogas at the site.

Mike Bakas, EVP of distributed energy systems at Ameresco, admits that working with five cities on a project like this can be a challenge.

“You’re dealing with a number of different cities… all with their own legislative bodies, all with their own mayors. So, just the political process was time consuming — not anyone’s fault; it’s just the nature of the beast. But it’s a process,” Bakas says.

“The good thing is, you have a lot of cities that want to do something good for the environment,” he adds, calling the five cities, “forward-thinking communities.”