Collection and treatment of large quantities of wastewater in cities is a challenging task, especially in megacities. Of course, it is technically, organisationally, and economically feasible. But instead of understanding this issue as a challenge or compelling necessity, it can be seen and used as a renewable energy source. Wastewater is a chance to create an additional mainstay of a sustainable energy supply. Wastewater is classified as a renewable energy source.
On 7 October 2015 DC Water officially unveiled its waste-to-energy project. It provides a net 10 megawatts of electricity from the wastewater treatment process. The clean and renewable energy covers one-third of the Blue Plains plants energy needs. The Blue Plains Advanced Wastewater Treatment Plant is the largest in the world. DC Water distributes drinking water for approximately 600,000 customer and provides wholesale wastewater treatment services for about 1.6 million people in and around Washington, D.C. They operate, among other things, more than 1,300 miles of pipes, five reservoirs and four elevated water storage tanks.
“This is yet another example of the District leading the nation in the adoption and implementation of sustainable practices,” said District of Columbia Mayor Muriel Bowser. “DC Waters Blue Plains facility is converting waste to clean water and a nutrient-rich soil by-product, producing energy and helping to put the District on the path towards a zero waste future.”
DC Water CEO and General Manager George S. Hawkins, said “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.”
The $470 million plant includes 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 5 Megawatt turbines the size of jet engines. The project broke ground in 2011. For the waste-to-energy process, the CAMBI® thermal hydrolysis process is used. It is, according to DC Water, the first in North America and the largest installation in the world.
High heat and pressure to “pressure cook” the solids left over at the end of the wastewater treatment process is used to weaken solids cell walls as well as the structure between cells. In this way the energy is easily accessible to the anaerobic digestion, the next stage of the process. Four digesters with 3.8 million gallons and a dense population of bacteria and archea produce methane. The digesters are able to convert more of the solids into gas, as a result of the hydrolysis process. The gas is captured and fed to three large turbines to produce electricity. Steam is also captured and directed back into the process. All these points make the process highly efficient.