In the United States alone, billions of gallons of water flow down the drain to a wastewater treatment plant every day. Approximately 2.5 percent of this water is treated and reclaimed to meet non-potable water needs, such as irrigation of golf courses and public parks. While this treatment is important and helps us conserve water, it’s extremely resource-intensive in other ways.
According to the University of Michigan’s Center for Sustainable Systems, nearly 4 percent of the nation’s total electricity use goes toward moving and treating wastewater. As the population grows, treatment plants are looking for ways to cut their own energy usage, without reducing performance. The city of Ventura, Calif., is experimenting with a self-sufficient system that would allow its wastewater treatment plants to produce all the power they need for operation using something they already have: waste.
Gas is a normal byproduct of the wastewater treatment process, produced by the “sludge” that’s left behind when the water is strained and filtered. Using technology developed by the Pasteurization Technology Group, Ventura is now testing a system that would allow it to capture that gas and use it to generate electricity for the plant. From the project’s page on the city website:
The new technology uses natural gas combined with digester gas (a natural by-product of wastewater treatment) as fuel to drive a turbine (or turbines) to generate electricity. The hot exhaust air from the turbine (energy that is typically wasted) is then passed through a series of heat exchangers that increase the temperature of the wastewater to a level that disinfects the wastewater stream. The disinfected water is then cooled to a safe level by transferring the heat of the disinfected water to the incoming water — reusing the energy over and over.
Right now, the city has only implemented a small evaluation system that can only handle about 5 percent (or 500,000 gallons) of Ventura’s average daily wastewater flow. A full-scale design of the system (7 to 9 million gallons per day) has the potential to generate enough electricity to power the entire facility, which could save the city approximately $450,000 per year. Operational savings are also expected from the reduction of chemical costs, which currently run $250,000 per year. Even with such potential, Ventura is only cautiously optimistic about the system.
“Ventura Water is continually seeking improvement of our treatment and operational processes,” said Ventura Water General Manager Shana Epstein. “We are pleased to be partnering in this important project that is demonstrating effective disinfection without chemicals as well as a potential for significant operational savings, if fully implemented, down the road.”