Last month, the District of Columbia Water and Sewer Authority, or DC Water, unveiled its $470 million waste-to-energy project that is producing a net 10 megawatts of electricity from the wastewater treatment process, while providing renewable energy to power about one-third of the Blue Plains Advanced Wastewater Treatment Plant’s energy needs.
“This project embodies a shift from treating used water as waste to leveraging it as a resource. 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,” says DC Water CEO and General Manager George Hawkins.
The plant serves the District of Columbia in wastewater treatment, in addition to Montgomery and Prince George’s counties in Maryland and Loudoun and Fairfax counties in Virginia. The plant also serves more than 2 million people.
DC Water conducted more than a decade of research before bringing these facilities online.
“We began the process with research back in 1999. Our board of directors approved the project in 2009 and we broke ground in 2011,” says Hawkins. “The facilities were nearly complete in 2014 and we have been in commissioning mode for most of 2015.”
The facilities include a dewatering building, 32 sleek 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.
According to Hawkins, the Blue Plains Advanced Wastewater Treatment Plant can treat 370 million gallons a day.
“In wet weather, it can rise to 1 billion gallons per day. We average about 300 million gallons per day,” he says.
The project, which broke ground in 2011, was only viable through the use of technology never before used in North America—the CAMBI thermal hydrolysis process.
“Now that we have added thermal hydrolysis to our solids processes, we are also unique in that we are the largest thermal hydrolysis plant in the world. We are the first in North America to use thermal hydrolysis,” says Hawkins.
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.
Matthew Brown, DC Water Board chair said in a statement, "The board of directors approved this voluntary investment to create a better class of biosolids and generate 10 MW of power to cut the electricity bill at the Blue Plains plant, which is the single largest consumer of electricity in the District. Additionally, the cleaner biosolids can be applied locally, saving millions of dollars in hauling costs."
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.
Hawkins says this is what makes the project unique.
“Blue Plains discharges to the Potomac River, a tributary of the Chesapeake Bay, which has a very delicate ecosystem. Because of this, our effluent has to be superclean. We have one of the most stringent EPA permit limits in the country,” he says. “Many plants only treat to secondary treatment, but Blue Plains does tertiary treatment or nitrification-denitrification. Our extra treatment steps classify us as an advanced wastewater treatment plant.”
The project received the 2012 Grand Prize in Planning Award from the American Academy of Environmental Engineers and Scientists, the 2012 Global Honour Award in Planning from the International Water Association, as well as one of two WERF Excellence in Innovation Awards, first presented at WEFTEC 2011.
“This is yet another example of the District leading the nation in the adoption and implementation of sustainable practices,” District of Columbia Mayor Muriel Bowser said in a statement. “DC Waters Blue Plains facility is converting waste to clean water and a nutrient-rich soil byproduct, producing energy and helping to put the District on the path towards a zero waste future.”