About 25 million people visited Chicago's World Columbian Exposition in 1893. They streamed in from around the world, arriving by ship, locomotive, and "El" train. Because of the city's dubious drinking water and fear of a dysentery outbreak, their water was piped in from a Wisconsin spring.

Chicago still faces its share of water woes more than a century later.

The Metropolitan Water Reclamation District of Greater Chicago serves more than three million people with a combined sewer system. Rain water and the sanitary sewer share a single set of pipes, tunnels, reservoirs, and treatment plants. Though the facilities can treat about two billion gallons of water a day, a single large rainstorm can produce more than five billion gallons before a single sink is turned on or toilet is flushed, according to data from the water reclamation district.

On the wettest days, the treatment plants can't keep up. Sewage is diverted into the area's waterways, and the Environmental Protection Agency levies fines. People go home to flooded basements. To avoid these problems, the U.S. Army Corps of Engineers and the water reclamation district are building a pair of reservoirs that will bring the district's total storage capacity to 15.6 billion gallons. (A third reservoir, with a capacity of more than 325 million gallons, is already complete.)

The plan certainly holds water. But it's not without drawbacks, especially in a metropolis with an average of 12,000 people per square mile. "The reservoirs are in residential areas," says Heather Henneman, a Corps of Engineers hydrologist working on the project. "Can't be helped. Everything's populated in Chicago."

The longer the water sits in open reservoirs, the more it begins to smell. Aeration systems, not unlike the one in your aquarium, can be used to oxygenate standing water and reduce odor. But an 87-acre reservoir is no mere fish tank.

"Aeration at this scale is not common," says Fabián Bombardelli.

As part of his PhD work at the University of Illinois at Urbana-Champaign, Bombardelli used NCSA's Titan cluster to model the plumes of air bubbles produced by aeration systems. The models are the first of their kind to consider not only the physics of aeration but also the amount of oxygen consumed by organic particles in the wastewater. It is used in conjunction with an existing Corps of Engineers model to help the Corps make decisions about the final design of the reservoirs.

Bombardelli worked with Marcelo García, the Chester and Helen Siess Professor of Civil and Environmental Engineering at the University of Illinois, and Professor Gustavo Buscaglia of the Instituto Balseiro and Centro Atómico Bariloche in Argentina. An early description of the model can be found in the November 2002 edition of the International Journal of Multiphase Flow.

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Access Online | Posted 3-9-2004

Snapshots of velocity magnitude in the aeration simulations.
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Snapshots of gaseous oxygen concentrations in the aeration simulations.
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