By Heather Knoll

Wastewater serves as a continuous source of energy, available year-round as people clean their homes, do their dishes, and shower.

In the pursuit of a sustainable and energy-efficient future, there are many opportunities to diversify our energy production. One innovative avenue gaining momentum is the harnessing of thermal energy from wastewater, a continuous and largely untapped source that can contribute significantly to reducing energy costs, meeting climate goals, and fostering community resilience. 

Approximately 50% of the energy consumed in buildings goes towards heating and cooling the building and hot water. Wastewater, often overlooked, carries a substantial amount of thermal energy that is currently being sent down the drain. An estimated 350 billion kilowatt-hours of energy flow into U.S. sewers in the form of heat each year according to the Department of Energy. This presents an opportunity to capture and repurpose this heat, turning wastewater into a valuable resource for sustainable energy.

Wastewater serves as a continuous source of energy, available year-round as people clean their homes, do their dishes, and shower. On average, people use 24-30 gallons of hot water per day.  The temperature of this water ranges from 120-140°F. In commercial buildings, the volumes of water are often greater and the amount of water used is typically much higher. Wastewater in underground sewer pipes carries heat that can be repurposed, even during the winter.

Wastewater heat recovery systems integrate well with existing wastewater infrastructure. The technology is simple and low maintenance, offering a cost-effective solution to tapping into this continuous source of thermal energy. The heat within wastewater can either be harnessed within the building through a local system, or carried away from the building and captured later in the sewage system.

To capture energy from wastewater, a system can be set up at a sewer line, or energy can be captured as the water flows into a wastewater treatment plant. Wastewater heat recovery systems essentially transform a sewer into a heat exchanger using pipes and holding tanks. Warm wastewater flows into the heat exchanger that functions as a heat pump, extracting the heat and using it to heat clean water and heat/cool buildings.

One such system being put into place is the wastewater system used to heat the Toronto Western Hospital in Ontario Canada. The hospital will utilize energy captured from the public sewer system to heat and cool the building. The project is estimated to reduce the hospital’s natural gas use by 90%, reducing their carbon dioxide emissions by 8400 tons/year (the equivalent of removing 1800 gas-powered cars from the road).

In Vermont, many opportunities exist to capture the energy from our wastewater at local wastewater treatment plants. An unprecedented amount of government funding through the Inflation Reduction Act is available for energy projects including wastewater energy capture and other thermal energy systems.

Capturing thermal energy from our wastewater treatment plants gives us a stable and low maintenance way to diversify our energy production.  Harnessing energy from wastewater is one way in which we can take the pressure off of our electric grid as our need for clean energy grows.

As our communities embark on wastewater system installations and upgrades, the integration of wastewater heat recovery systems presents an unparalleled opportunity to maximize thermal energy, cut costs of future energy production, and contribute to a sustainable energy transition while alleviating the pressure on our electric grid. By capturing and reusing the heat we already produce, we can lower overall energy consumption, create substantial savings over time, and work towards a greener and more resilient future for our communities.

If you would like to learn more about thermal energy networks and about capturing energy from wastewater, check out the recording of our recent Green Drinks event with the Vermont Community Geothermal Alliance on the Sustainable Woodstock YouTube channel.