The District of Columbia Water and Sewer Authority's wastewater treatment plant is going green in a big way. The authority, known as DC Water, is in the early stages of projects that will help meet stringent regulatory requirements for nitrogen as well as make improvements primarily aimed at improving water quality in the Chesapeake Bay.

One of the projects is to reduce total nitrogen in the plant system to under 4 milligrams per liter (mg/l) from current levels of about 5 mg/l. The second approach will build a system of tunnels to accommodate and store peak water flows so the plant can fully treat more of the water that currently overflows the plant's capacity during heavy storms.

However, it is the third leg of these project that is leading innovation in water treatment. The Cambi thermal hydrolysis process will be used to “cook” sludge material under high pressure and steam to generate a better class of biosolids as well as about 13 MW of power at the plant. Blue Plains will be the first plant in North America to use the process, according to DC Water.

All told, the $4-billion projects are making the 153-acre site more energy efficient and sustainable. The projects are the culmination of years of planning and will help Blue Plains reduce the plant's carbon footprint, DC Water officials say.

“This is about as green a project as you can get,” says Dave Schwartz, vice president with Cambridge, Mass.-based Camp, Dresser & McKee and project manager for the biosolids project.

Nitrogen Reduction Costs Nearly $1 Billion

Tough new federal limits for nutrients, particularly nitrogen, in effluent are driving the enhanced nutrient- removal facilities project, especially given its significance to the Chesapeake Bay Program, whose plan to restore the watershed back to health includes one of the most aggressive total maximum daily load (TMDL) standards in the nation. Blue Plains surpassed the requirements under the 2000 Chesapeake Bay agreement between several states and the District of Columbia and wants to beat the new 4-mg-per-liter limit now, says George Hawkins, DC Water's general manager.

Under its new federal operating permit, by Jan. 1, 2015, Blue Plains will need to reduce the amount of nitrogen in effluent to levels under 4 mg/l from current levels of about 5 mg/l, which is lower than what is now required.

The nitrogen portion of the project, valued at $950 million, will expand the capacity of the nitrogen removal by adding more tankage, says Hawkins. This feature is key. Currently, the nitrification and denitrification processes occur within the same set of tanks. Those processes will be split up, and eight new reactor tanks with a total capacity of 40 million gallons will be built specifically for denitrification. Contractors will also enhance existing tanks for nitrification as well as build an 890-million-gallons-per-day (mgd) pump station, post-aeration facilities, new channels and conveyance structures.

Los Angeles-based AECOM is the program manager, and Englewood, Colo.-based CH2M Hill is the professional design engineer.


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