How Much Energy Exists in Wastewater?

Through technologies like anaerobic digestion, wastewater treatment plants can make use of wastewater’s latent energy.

The energy potential of untreated wastewater has been widely discussed, but is there any reliable measure of how much energy is available in effluent?

In the United States alone, wastewater holds enough energy potential to generate 851 trillion BTU of energy annually, according to the American Biogas Council. This is enough to heat 13 million homes (almost all the homes in California).

The American Biogas Council observed:

Wastewater is a renewable resource. […] Wastewater contains nearly five times the amount of energy needed for the wastewater treatment process — the majority in the untapped area of thermal energy.

The organization estimates roughly 80 percent of the latent energy is thermal; 20 percent is chemical; and less than 1 percent of the potential exists in hydraulic generation.

Net Energy Production

To be fair, treating wastewater consumes a great deal of energy, but what would happen if more organizations produced as much or more power than they consumed? If $4.8 billion were invested in energy-recovery technologies for the 100 largest wastewater treatment facilities in the U.S., the plants could offset 17 percent of the energy use in the nation’s wastewater industry, according to American Biogas Council estimates.

In addition to producing clean water and energy, adding waste-to-energy technologies to water treatment plants creates other benefits for the environment, such as reducing greenhouse gas emissions and carbon sequestration. It also could create new jobs.

Some regional and municipal governments in the U.S. are taking steps toward energy production. For example:

• In Washington’s King County, the wastewater treatment plant uses digester gas onsite.
• The East Bay Municipal Utility District in Oakland converts 20 to 40 tons a day of restaurant food scraps into electrical power, saving approximately $3 million a year it otherwise would be spending on conventional electricity to power its facilities.
• The city of Ithaca, New York, is collecting and making biogas from food waste collected from the Cornell University dining facilities.

Energy Recovery Outside the U.S.

There is increased interest in this type of technology outside North America. In Europe, the city of Aarhus, Denmark, is now operating what is purported to be the first energy neutral wastewater treatment facility in the world. The plant in Marselisborg, operated by Aarhus Water, serves 200,000 local residents. It produces both electricity and thermal heat, 40 percent more power than needed for its operations. The 2.5 GW of thermal heat it generates is used by the city’s district heating system.

The energy potential within wastewater is waiting to be fully exploited using proven technologies such as anaerobic digestion. Adopting them can help organizations create reliable, renewable energy and become net-zero energy consumers. There also is the potential to create a new revenue stream from selling excess energy.

Anaerobic Digestion Solutions

RWL Water Group offers a wide range of anaerobic digestion solutions for waste-to-energy conversion, drawing from its decades of experience across a wide range of industries and applications.