On the Potomac, Egg-Shaped Towers Will Be a High-Water Mark

By Benjamin Forgey
Washington Post Staff Writer
Sunday, March 26, 2006

Washington is about to get a striking new skyline.

Oh, not to worry. We're not talking about changing the profile of the low city, with its hierarchy of heights ranging down from the Capitol dome. Skyscrapers are not about to invade the city's downtown.

Still, if you are standing over in Alexandria's Founders Park and looking north a few years from now, or crossing the new Wilson Bridge, or happen to take the southern approach on a flight into National Airport, you'll notice a dramatic difference.

Lining the Potomac River's eastern shoreline, at the southernmost point in the District, will be two orderly rows of huge industrial structures. Giant egg-shaped sewage digesters, to be precise.

Architecturally, in a city not known for majestic industrial structures, these striking digesters -- each looking a bit like a cocoon from outer space -- will mark quite a change from the norm. They will stretch 303 feet around at their widest point and measure 108 feet from ground level, with sleek elevator towers rising to 120 feet.

They'd be higher still were not the bottoms to be sunk 20 feet into the ground. As the buried bottoms complete the oval form, in full profile the structures look a lot more like giant eggs than the parts that we will see.

Even partially buried, however, these are impressive forms. And there will be eight of them, in two parallel rows of four, plus four additional silolike storage tanks of similar height, though not quite the girth.

Installing the digesters at a cost of $311 million will have significant benefits for the Blue Plains Advanced Wastewater Treatment Plant, the 150-acre facility at the very tip of Southwest Washington that serves more than 2 million folks in the region, and which often bills itself as the largest of its kind in the world. The key word in this boast is advanced. Other, larger sewage-treatment plants do not uniformly carry the processing quite so far; the water that flows into the Potomac from Blue Plains is good for the river.

(The giant containers will process about 350 tons of pre-treated sewage sludge daily -- a feast for the trillions of sludge-loving microbes that actually do the heavy work. Hence the name, digesters. Jerry N. Johnson, general manager of the D.C. Water and Sewer Authority, points out that the efficient digesters will cut odors and reduce the output of sludge -- or biosolids, in today's lingo -- by more than half. This will mean far fewer truck trips to haul the material to Maryland and Virginia farms. As a byproduct, Johnson says, the process will produce enough methane gas to provide 20 percent of the plant's daily power needs.)

In a way, these immense, functional structures resemble the American grain silos that Le Corbusier, the giant of early- to mid-20th-century modern architecture, was so taken with in the 1920s.

Corbusier especially admired the functionality of these buildings, and their sheer massiveness. In "Towards a New Architecture," his important manifesto of 1923, photographs of silos provided background for his famous dictum that "architecture is the masterly, correct and magnificent play of masses brought together in light."

The egg-shape concept actually goes back to the 1920s, when a German engineer discovered the prime advantage of the form -- because it has no angles, it does not provide any "dead zones" where sludge can get stuck. Consequently, the digesters rarely require cleaning. When the Blue Plains structures are fully operational in about four years, Jefferson says, the plant will save about $16 million in annual maintenance.

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