How does a wastewater treatment plant become a power source for thousands of homes? At Honouliuli Wastewater Treatment Plant on Oʻahu, biogas that was once burned off as waste is now captured and turned into renewable natural gas. The facility can produce up to 800,000 therms of energy per year. That’s equal to about 23.44 million kWh, enough to serve thousands of households.
Oʻahu’s Honouliuli plant turns wastewater biogas into renewable energy capable of powering thousands of homes.
The project is a partnership between the City & County of Honolulu and Hawaii Gas. It’s been running since December 2018. Bright green equipment at the plant processes wastewater gases into pipeline-quality biomethane. The biogas starts as roughly 60% methane and 40% carbon dioxide. After upgrading, it’s clean enough to flow through existing gas pipelines.
The contract was awarded in July 2016. The Public Utilities Commission approved it in 2017. Infrastructure took about 12 to 18 months to build. In its first year, the plant produced 381,529 therms of RNG. Production hit 323,128 therms in 2021 and 288,734 therms in 2022. That 2022 output made up 1.3% of Hawaii Gas’s total feedstock. These numbers fall well below the plant’s full 800,000-therm capacity.
The project delivers real economic results. It generates nearly $1.6 million each year for the City’s Sewer Fund. Hawaii Gas invested $5 million in processing equipment and pipeline connections. The original contract runs through December 31, 2024, with an extension to 2034 in process. Since 2018, biogas sales have generated approximately $ 1.85 million for the City and County of Honolulu overall.
On the environmental side, the impact is significant. The RNG displaces about 15,000 barrels of oil annually. It cuts greenhouse gas emissions equal to removing 400 gasoline-powered cars from the road. According to the Argonne GREET model, this RNG is carbon-neutral to carbon-negative. The American Biogas Council recognized the project as its 2019 Project of the Year.
Hawaiʻi relies heavily on imported oil for energy. This project helps the state move toward greater self-sufficiency. Statewide, RNG potential reaches 70.8 million therms per year. Honouliuli’s untapped capacity could play a bigger role as new developments boost biogas production. Hawaii Gas president and CEO Alicia Moy has described renewable natural gas as a key priority for the state’s clean energy future. For now, it stands as proof that wastewater doesn’t have to be waste. It can be fuel.
References
- https://www.hawaiigas.com/clean-energy/decarbonization
- https://www8.honolulu.gov/env/city-hawaii-gas-open-renewable-wastewater-biogas-facility/
- https://www.bioenergy-news.com/news/hawaii-gas-wins-biogas-contract-from-city-and-county-of-honolulu/
- https://www.biocycle.net/anaerobic-digest-77/
- https://puc.hawaii.gov/wp-content/uploads/2022/05/HG-Gas-Co-Renewable-Energy-Report-2021-filed-March-2022.pdf
- https://www.hnei.hawaii.edu/wp-content/uploads/Resources-for-Renewable-Natural-Gas-Production-in-Hawaii.pdf
- https://biomassmagazine.com/articles/hawaii-gas-earns-puc-approval-to-make-rng-from-honouliuli-biogas-14679
- https://puc.hawaii.gov/wp-content/uploads/2023/04/HG-Gas-Co-Renewable-Energy-Report-2022-filed-March-2023.pdf
- https://cleantechnica.com/2026/03/08/biomethane-for-oʻahu-a-small-reserve-with-a-big-reliability-role/?amp=1
