The District of Columbia Water and Sewer Authority (DC Water) unveiled its $470 million waste-to-energy project that is producing a net 10 MW of electricity from the wastewater treatment process, providing clean, renewable energy to power about one-third of the Blue Plains plant’s energy needs.
The facilities include a dewatering building, 32 thermal hydrolysis vessels, four concrete 80-ft-high anaerobic digesters that hold 3.8 million gal of solids each and three turbines the size of jet engines.
The project, which broke ground in 2011, was only viable through the use of technology never before used in North America. DC Water not only brought the CAMBI thermal hydrolysis process to the continent, in addition Blue Plains is now the largest thermal hydrolysis installation in the world. 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 and the structure between cells 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 District for urban gardens and green infrastructure projects. DC Water is also working to bring a compost-like product to market.
“This projects embodies a shift from treating used water as waste to leveraging it as a resource," said DC Water CEO and general manager George S. Hawkins. "We are proud to be the first to bring this innovation to North America for the benefit of our ratepayers, the industry and the environment.”
DC Water selected the PC/CDM Joint Venture, which brings together the expertise in water treatment facility design and construction of PC Construction and CDM Smith, to utilize the design-build delivery method to build the Cambi thermal hydrolysis process at the Blue Plains facility.
“This massive design-build project boasts significant environmental benefits, including creating 10 MW of renewable electric energy, capturing steam heat to efficiently run the anaerobic digesters, and producing cleaner Class A biosolids that can be used as compost rather than being hauled away,” said Mike Angeli, construction executive at PC Construction and the construction project director for the PC/CDM Joint Venture. “The PC/CDM Joint Venture team is proud to work with DC Water to introduce innovative thermal hydrolysis technology to North America.”
Source: PC Construction
