In the United States it is estimated that heat and embedded energy extracted by clean water agencies contain enough energy to meet up to 12% of U.S. electricity demand. In addition to providing revenue from surplus energy, the extraction/conversion of energy at wastewater treatment plants (WWTP) contributes to overall energy independence, smaller community carbon footprints and saves ratepayers money.
Aloha to biogas in Hawaii
In Hawaii, the City of Honolulu has recently awarded a contract to Hawaii Gas – a state utility – to capture and process biogas at the Honouliuli Wastewater Treatment Plant and turn it into renewable energy. Previously, the WWTP flared the equivalent of 80,000 therms of biogas annually into the atmosphere. The new contract will allow Hawaii Gas to remove impurities from the raw biogas to produce a ready-for-market renewable natural gas (98% methane and 2% carbon dioxide), which Hawaii Gas will then blend with its synthetic natural gas.
The price Hawaii Gas will pay to 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 will generate for the city $1 million or more annually, along with environmental benefits. Overall, the project is estimated to take between 12-18 months to become operational.
WWTPs of the future will provide renewable energy to local communities, which will not only create additional revenue streams for the utility but also reduce carbon emissions.
*Robert C. Brears is the author of Urban Water Security (Wiley). Urban Water Security argues that, with climate change and rapid urbanization, cities need to transition from supply-side to demand-side management to achieve urban water security.