Driving Net-Zero at DC Water
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.
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."
Design-build can provide creativity and flexibility to address challenges, and greater certainty of project costs.
The Value of Net-Zero
This project is estimated to save DC residents $20M annually: $10M in energy savings and $10M in sludge disposal costs.