Environmental groups are applauding the city’s latest effort to reuse a byproduct from its Honouliuli Wastewater Treatment Plant.

The city recently awarded a contract to Hawaii Gas to capture and process biogas there and turn it into renewable energy.

“We congratulate both Hawaii Gas and the mayor and the city for making this happen, essentially taking this waste product, which is methane that’s produced as they clean up the sewage. Instead of just releasing it into the atmosphere, they’re going to capture that and use it as the natural gas supply,” said Jeff Mikulina, executive director of Blue Planet Foundation. “This is a really exciting step toward our 100-percent renewable energy future.”

Currently, the Honouliuli Wastewater Treatment Plant produces the equivalent of 800,000 therms of biogas each year, which is then flared, or burned.

The new contract will allow Hawaii Gas to remove impurities and produce a ready-for-market renewable natural gas (98% methane and 2% carbon dioxide) that can be blended with the synthetic natural gas in its pipeline.

“What’s sort of unique about this is they can take that gas, clean it up a little bit and inject it directly into their existing supply line,” Mikulina explained. “Instead of using a fossil fuel that they need to import from elsewhere, we’re going to use a local renewable sustainable energy source.”

The City and County of Honolulu can then sell the biogas to generate revenue.

Terms of the contract are still being negotiated, but the city says the price Hawaii Gas pays the city will be scaled to the quality of the biogas, which will be determined when it is extracted. Depending on these factors, it is estimated that the contract could bring the city in the range of $1 million or more annually, along with the environmental benefits.

“As the State’s gas utility, Hawaii Gas was the most qualified to partner with the City to develop this resource, which was previously unutilized. The capturing and processing of biogas is done across the nation as one of the most efficient ways to develop renewable natural gas,” said Honolulu Mayor Kirk Caldwell.

“Incorporating cost-effective renewable natural gas as part of our fuel mix is a key priority as we continue to advance Hawaii’s clean energy future,” said Alicia Moy, Hawaii Gas president and CEO. “We look forward to working with the city on this project and other projects like it, so that we can provide renewable fuels for our customers, and provide the City with a steady stream of revenue.”

The awarded contract expires on Dec. 31, 2024, with a provision to extend the term.

Hawaii Gas will invest in the infrastructure to process the raw biogas for use and to connect the Honouliuli Wastewater Treatment Plant to the company’s existing pipeline.

The project is estimated to take between 12 to 18 months to become operational, subject to the permitting process and approval by the Hawaii Public Utilities Commission.