Ameresco natural gas plant

Marking the opening of the new plant are, from left, Scottsdale Water Director Brian Biesemeyer; Tempe Public Works Director–Water Utilities Holly Rosenthal; Ameresco Senior Project Developer Jim Bier; Scottsdale Councilwoman Solange Whitehead; Phoenix Mayor Kate Gallego; Phoenix Councilman Michael Nowakowski; RNG Coalition CEO and Executive Director Johannes Escudero; and Phoenix Water Services Director Kathryn Sorensen shown cutting the ribbon during an April 25 ceremony at the new Ameresco natural gas plant.

The City of Scottsdale and other partners in the Valley recently celebrated the opening of a new natural gas facility at a Valley wastewater plant that could earn the cities money while benefiting the environment at the same time.

Scottsdale, Phoenix, Glendale, Mesa and Tempe are all members of the sub-regional operating group, or SROG, that owns the 91st Ave Wastewater Treatment Plant in Tolleson that cleans wastewater for reuse.

That water is used for a variety of purposes, including irrigating golf courses and cooling the Palo Verde Nuclear Power Plant.

The SROG cities partnered with Ameresco, a Massachusetts-based energy company, to convert the methane gas produced as a byproduct of the water treatment process into usable natural gas, or RNG.

The plant is the largest of its kind in the U.S., according to Arizona Municipal Water Users Association.

The Ameresco RNG plant, which had its ribbon cutting in April, could provide between over $1 million in annual revenue for the SROG cities, said Phoenix Deputy Water Services Director Patty Kennedy. The City of Phoenix operates the jointly-owned facility.

The plant has environmental benefits as well.

Kennedy said that treating wastewater for reuse results in byproducts, including bio-solids and methane gas.

According to an article published by Arizona Municipal Water Users Association, the bio-solids are typically recycled to create fertilizer for non-food crops like alfalfa.

Previously, however, the methane produced at the plant was burned off using flares, which adds carbon dioxide to the atmosphere.

According to Ameresco, the new plant will result in the equivalent of over 44,000 metric tons of carbon dioxide saved per year.

Speaking on the environmental affects of the new plant, Kennedy referred to it as the “third leg” of the stool that already included treating wastewater and reusing the bio-solid byproducts of the treatment process.  

Kennedy said the cities will keep the flares on site as a backup to use if the Ameresco plant goes temporarily offline.

The new plant should also prove to be a financial boon for the cities involved.

Kennedy said the cities explored a number of ways to use the methane byproduct, including using it for energy on site, but ultimately opted to partner with Ameresco, a private company, because of the low risk the proposal posed for the partner cities.

Essentially, the cities are just selling the raw methane gas to Ameresco, which also paid all capital costs to construct the RNG facility at the 91st Ave Wastewater Treatment Plant, Kennedy said.

The company is then responsible for refining that gas to commercial standards at which point it will be put into Kinder Morgan natural gas pipeline network.

Kennedy anticipated the plant will produce over 600,000 mmbtu of methane annually. That raw methane is currently selling at about $1 per mmbtu, equating to $600,000 for the cities.

The agreement with Ameresco also includes a clause that provides for the SROG cities to receive additional royalties if Ameresco reaches a certain amount in sales.

“We estimated that we will also see some royalties, because there is a good market for natural gas,” Kennedy said.

Kennedy said those royalties could boost the cities’ take to around $1.2 million.