Using treated municipal wastewater could help improve the overall efficiency of local thermoelectric power plants according to Professor of Civil and Environmental Engineering Ashlynn Stillwell and graduate student Zachary Barker in their new study of the Chicago-area. Their findings were published this month in the journal titled “Environmental Science and Technology”.

Thermoelectric power plants generate heat (for example, by burning coal or natural gas or through nuclear fission) to boil water in order to produce steam. This steam is then used to spin a turbine in order to generate electricity. This process also results in a significant amount of excess heat that cannot be efficiently converted into electricity, but is still too hot to directly release into the environment where it could harm local plants and animals. In turn, thermoelectric power plants use large amounts of water to remove the excess heat.

According to a 2014 report from the U.S. Geological Survey, thermoelectric power plants withdrew an estimated 161 billion gallons of water per day for cooling, representing 45% of total water withdrawals across the country (more than the total amount of water used for irrigation). The majority (73%) of these withdrawals were from freshwater sources and almost all (99%) of this water was from surface water sources (e.g. rivers and lakes).

Given the dependence of thermoelectric power plants on freshwater resources in order to operate, water availability from season to season is a primary concern for power plant operators. Furthermore, during the summer months when water temperatures rise, power plant operators rely on increased amounts of water to keep their power plants cool.

With all of these factors in mind, Stillwell and Barker looked at a map of Chicago-area power plants and wastewater treatment facilities. They were struck by how many thermoelectric power plants were located downriver from the Stickney Water Reclamation Plant. This facility is one of the largest wastewater treatment facilities in the world, serving 2.38 million people over a 260 square mile area. Stickney is designed to treat up to 1.2 million gallons of wastewater per day in its two plants, which have been in operation since the 1930s.

Photo of Stickney Water Reclamation Plant by brewbooks (CC2.0)

In turn, Stillwell and Barker decided to examine the possibility of piping in water from Stickney Water Reclamation facilities instead using local fresh river water. They considered both hydrologic and economic conditions in order to see where it might make sense to use reclaimed water instead of local river water. Overall, according to Stillwell:

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…Yes, the cost of the pipeline [to move water from the wastewater treatment facility to the power plant] 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.”

The full results of their analysis - including details on their full methodology - can be found here.