DC Water’s $470 million waste-to-energy project is now online, producing a net 10 MW of electricity from the wastewater treatment process, which represents about one-third of the Washington, DC Blue Plains plant’s energy needs.
The facilities include a dewatering building, 32 thermal hydrolysis vessels, four concrete 80-foot high anaerobic digesters that hold 3.8 million gallons of solids each and three turbines the size of jet engines.
The project, which broke ground in 2011, uses technology never before used in North America. DC Water brought the Cambi thermal hydrolysis process to the continent, and Blue Plains is now the largest thermal hydrolysis installation in the world, DC Water says.
Thermal hydrolysis uses high heat and pressure to “pressure cook” the solids left over at the end of the wastewater treatment process. This weakens the solids’ cell walls to make the energy easily accessible to the organisms in the next stage of the process—anaerobic digestion. The methane these organisms produce is captured and fed to three large turbines to produce electricity. Steam is also captured and directed back into the process.
Finally, the solids at the end of the process are a cleaner Class A biosolids product that DC Water uses as a compost-like material. Biosolids products are currently being used around the Washington, DC for urban gardens and green infrastructure projects.