Hawkins says, “DC Water is the largest consumer of electricity in the [Washington, D.C.] area, and the digesters should cut our consumption by a third. We're also saving $10 million in trucking costs and reducing our carbon emissions by cutting the amount of solids at the end of the process in half.” Moreover, the authority will save nearly $5 million by not having to use lime to treat the sludge, Schafer says.
All those savings “go a long way toward paying for the bonds and the capital [used to fund the program], so it's a project and a program that essentially pays for itself, which is kind of unheard of in our industry,” Schafer adds.
The projects and engineering for the biosolids program will total about $400 million, DC Water says.
To date, most of what has been done has been site preparation work, some concrete construction of the slurry wall and some foundation work. Bohdan Bodniewicz, program manager at AECOM Water, says he expects the projects to ramp up over the next year.
Hawkins says other water utilities are watching the progress of the biosolids program at Blue Plains “with great interest.” He says, “If the Cambi system works and [if] it works at this scale, I suspect we'll see a lot of installations of Cambi-like processes with digestion to generate energy.” The project will reduce the plant's carbon footprint, an important consideration during the planning process, he says.