Driving Net-Zero at DC Water

DC Water washington, DC, USA

Looking to lower operating costs, reduce its carbon footprint and improve energy efficiency, DC Water implemented a series of innovative projects, including thermal hydrolysis technology.

CDM Smith, in an equal joint venture with PC Construction, partnered with DC Water on the design-build delivery of the biosolids main process train (MPT) project, which incorporates Cambi’s thermal hydrolysis process (THP)—the first facility in the United States to use this technology, and the largest Cambi plant in the world.

The Blue Plains advanced wastewater treatment plant (AWWTP) serves more than 2 million residents in densely populated Washington, D.C., USA, and in surrounding communities in Maryland and Virginia. The 153-acre plant has an average capacity of 370 million gallons per day and a peak capacity of more than 1 billion gallons per day—an expensive, energy-intensive operation.

Incorporating Cambi THP

While DC Water had already developed a successful biosolids reuse program, upgrading the facility provided considerable additional economic and environmental benefits. Originally, the utility pursued a design that used anaerobic digestion—a process that would have required 10 large, egg-shaped digesters—but building the digesters proved expensive, and the utility considered alternative approaches.

Obtaining a fixed price for the $210 million project gave DC Water the certainty to move forward with the detailed design and construction. Another advantage of selecting the CDM Smith/PC team was an alternate approach to design and construction of the digester building, which shaved several months from the delivery schedule. “DC Water was impressed by our commitment to produce the design using VDC technology, and we demonstrated the value of these tools through enhanced visualization of the project at design and operational review meetings,” says David Schwartz, CDM Smith vice president. After thorough evaluation, DC Water settled on a design-build approach to reduce the likelihood of unexpected costs. Using Cambi THP also reduced the size of the digesters needed by 50 percent, lowering construction costs and making the project more affordable. Delivering the project through a design-build approach helped add innovation throughout the project. “Design-build can provide the creativity and flexibility to address challenges that arise, and greater certainty of project costs well before bid day,” notes Schwartz.

reduction in biosolids shipping

50 ^%

reduction in biosolids shipping

less energy purchased from the grid

30 ^%

less energy purchased from the grid

less greenhouse gas produced

41 ^%

less greenhouse gas produced

Building Better Biosolids
The Blue Plains AWWTP previously lime stabilization to treat sludge, producing class B biosolids used for agricultural fertilizer. However, transporting these biosolids to where they can be used was costly—the plant produced 1,200 wet tons of biosolids each day, or about 65 truckloads.

Implementing Cambi THP at Blue Plains AWWTP resulted in an improved, class A biosolid, which DC Water is now providing to soil blenders, landscapers, community groups and governments in DC and Maryland as Bloom. “THP is a digestion preprocessing step that uses heat and pressure to kill pathogens in the biosolids and also breaks down biosolids so they are more readily digested,” says Peter Loomis, CDM Smith project manager. “THP allows higher loading to the digesters, reducing the required retention time and the corresponding digester volume. It also improves the reduction of volatile solids in the digesters, resulting in higher gas production compared to conventional digestion.”

The process reduces the volume of biosolids, produces more biogas to generate more power, and reduces odor issues associated with the transporting and disposing of class B biosolids. These changes are expected to reduce trucking by 50 percent, resulting in less traffic congestion and significantly lower carbon emissions.

THP allows higher loading to the digesters, reducing retention time and resulting in higher gas production compared to conventional digestion.

peter loomis, Discipline Leader –Biosolids

Biogas Fuels Savings
Through a separate project, DC Water is introducing a combined heat and power (CHP) component, which will provide the plant with renewable energy. Capturing and using the biogas created through anaerobic digestion will generate between 8 and 10 megawatts of power, approximately one third of the energy needed to operate the Blue Plains facility. By reducing demand from the electrical grid, the plant will reduce the impact of hot summer days on the mid-Atlantic coast, which can strain the grid and contribute to brown outs. Offsetting the plant’s electricity use now will also help to prevent future rate increases, despite the rising price of power.

Combined, reduced biosolids hauling and onsite power production are expected to reduce the facility's greenhouse gas emissions by 40 percent. And in addition to reducing waste, generating energy and improving air quality, the project will save residents of the district and surrounding metropolitan areas an estimated $20 million annually—$10 million in power savings and $10 million in reduced sludge disposal costs.

The investment in the new MPT has enabled DC Water to expand capacity if necessary and to operate sustainably in the future. “This project brings a new focus on recovering resources,” says George S. Hawkins, DC Water general manager. “The digesters allow us to extract valuable nutrients, energy and carbon from the wastewater and make use of these resources within our service area."