Renewable Natural Gas (RNG)

What Is Renewable Natural Gas?

Renewable Natural Gas (RNG) is natural gas or methane produced from renewable resources such as wastewater treatment plants, landfills or by anaerobically digesting organic matter such as agricultural crops.

Renewable Natural Gas is an ultra-clean, low-carbon natural gas alternative. It is not a fossil fuel. Renewable Natural Gas is the naturally occurring gas generated by organic matter
as it decomposes.

When organic matter decomposes or is anaerobically digested, it creates biogas, which primarily consists of approximately 60 percent natural gas and 40 percent carbon dioxide. Today, Hawaii Gas is working to increase the use of renewable natural gas in its business from wastewater treatment plants and landfills and from other renewable resources.

In September 2017, Hawaii Gas received approval from the Hawai‘i Public Utilities Commission (PUC) to begin installing equipment to capture and process biogas from the Honouliuli Wastewater Treatment Plant on O‘ahu. The project is expected to be used and useful by the end of 2018. Hawaii Gas was awarded the contract for capturing and processing biogas at Honouliuli from the City and County of Honolulu in August 2016 after a competitive bidding process.

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Hawaii Gas is working with the City and County of Honolulu Department of Environmental Services to use biogas from the Honouliuli Wastewater Treatment Plant to provide renewable natural gas for our pipeline customers on O‘ahu.

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The machinery to capture and process biogas will be installed on the grass near these two digesters at Honouliuli Wastewater Treatment Plant.

This first-of-its-kind project is equivalent to eliminating the need for nearly 15,000 barrels of oil and reducing greenhouse gases by the amount produced by 400 cars annually. The Honouliuli Wastewater Treatment Plant produces about 800,000 therms of energy per year, which is currently not being utilized. By selling the biogas to Hawaii Gas, the City and County of Honolulu will generate approximately $1.6 million of revenue per year.


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The wastewater feedstock is upgraded through a multi-step process to create renewable natural gas in the form of biomethane.


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Biogas purification equipment similar to the one pictured will process the wastewater gas at Honouliuli Wastewater Treatment Plant.
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Uses Of Renewable Natural Gas

Renewable Natural Gas can be used for many of the same applications as natural gas. Renewable Natural Gas is a cleaner fuel as compared to the 

1) oil and diesel now used to produce electricity  

2) the gasoline and diesel used for ground transportation and 

3) the oil-derived synthetic natural gas distributed on Oahu.  

RNG in its raw form known as biogas can be used for electricity generation. RNG purified to pipeline quality natural gas (greater than 98 percent methane) can be used for ground transportation or injected directly into the existing natural gas pipeline distribution system on Oahu.

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Benefits Of Renewable Natural Gas

Capturing methane from wastewater treatment plants and landfills provides dual environmental benefits by preventing greenhouse gas emissions from entering the atmosphere and using it to displace other higher-emitting fossil-based fuels such as oil and diesel. Renewable natural gas emits approximately 30 percent less carbon dioxide than the oil and diesel now used to produce electricity and for ground transportation.