Reclaimed water could help power plants run more efficiently, study finds
By Liz Ahlberg
The water going down the drain could help keep the lights on, according to a new study showing that reclaimed water – municipal wastewater that has been treated or cleaned – could be more efficient for cooling power plants than water taken from the local environment.
University of Illinois assistant professor of civil and environmental engineering Ashlynn Stillwell and graduate student Zachary Barker published their analysis of cooling water sources for thermoelectric power plants in general, and the costs and benefits for the Chicago area in particular, in the journal Environmental Science and Technology.
Generating electricity also produces an immense amount of heat, so most thermoelectric power plants use large volumes of water for cooling to keep the machinery running.
“Power plants are very large water withdrawers. In the United States, about 45 percent of our total water goes just to thermoelectric power plants,” Stillwell said. “That means a lot of fresh water is going toward electric power generation that could go to other uses.”
Many thermoelectric plants withdraw water from the local environment – streams, rivers, aquifers or other local supplies – then return that water to the environment, to be withdrawn again downstream by other power plants, irrigators or water treatment facilities.
However, there are some challenges inherent in using natural water sources, Stillwell said. For example, when a power plant draws large volumes of water from a river, it also draws in whatever is in the water – including fish, other wildlife and pollutants. Along with the subsequent discharge of hot water back into the river, the process stresses the river ecosystem.
A big disadvantage to the power plant itself is the variability in the river water. Spring rains can provide plenty of water, but a warm, dry summer can cause river levels to drop and the water to warm, making the plant less efficient and reducing its capacity, Stillwell said.
While looking at a map of Chicago-area power plants and wastewater treatment facilities, Stillwell and Barker realized that a number of thermoelectric plants were downriver from the Stickney water reclamation facility, one of the largest-volume water reclamation operations in the world.
“That’s what led us to ask, what if we built a pipeline to directly transfer the water instead of using the river as a conduit?” Stillwell said.
They looked at thermoelectric power plants in the Chicago area and compared the costs and benefits of withdrawing cooling water from the river with piping it in from local water reclamation facilities.
“We found that using reclaimed water was actually more advantageous to the power plant in terms of cooling efficiency than relying on a natural river water source,” Stillwell said. “Yes, the cost of the pipeline is expensive, but because we can more efficiently cool the power plant using water at a relatively constant temperature and quality, the avoided losses at the power plant can offset the pipeline cost.”
Another advantage is that reclaimed water is a drought-resistant source, Stillwell said. While natural water supplies may dwindle in a drought-stricken area, municipal supplies still flow, though the volume may decrease somewhat as residents take measures to conserve water.
“In just the Chicagoland area, there’s more than 1.8 billion gallons per day of reclaimed water, in a tiny geographical area,” Stillwell said. “That is an immense supply of reclaimed water in this area that can support a lot of water-intensive industry like power generation or other industries that don’t require drinking-quality water. We’ve been treating it as waste, but it’s not waste – it’s a resource.”
The Illinois Water Resources Center supported this work.
To reach Ashlynn Stillwell, call 217-244-6507, email: firstname.lastname@example.org.
Photo: L. Brian Stauffer