Closing the water-energy loop at Kirie plant

Photo credit: Metropolitan Water Reclamation District of Greater Chicago

By Matt Nichols

In May, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) opened a new energy recycling system at the James C. Kirie water reclamation plant in Des Plaines which will significantly reduce the plant’s heating and cooling bills using a resource already readily available: sewage.

With technical advising from the University of Illinois at Chicago and funding from the Illinois Clean Energy Community Foundation, the Kirie installation becomes one of the first so-called “sewerthermal” energy systems in the country.  The town of Brainerd, Minn. is installing a similar system to capture heat from sewage to heat its schools and municipal buildings. 

Much like geothermal systems which take advantage of the constant temperature below ground, sewerthermal uses a heat exchanger to capture thermal energy from effluent water, which stays at a constant 55 degrees Fahrenheit year-round.  Sewage effluent has useful heat content, even in the winter, because it contains heated water from hot showers and dishwashers.

In winter, cold outside air is passed over coils containing effluent, bringing it most of the way up to the desired indoor air temperature and reducing the need to burn natural gas.  Conversely, in the summer, hot air is cooled down to 55 degrees through contact with the coils, cutting down on electricity use for air conditioning. The addition of heat to waste water effluent is minimal enough that thermal pollution should not affect fish populations downstream from the exit pipe.

All told, the new energy recycling system is estimated to reduce energy use for heating and cooling at the Kirie plant by 40%.  The plant cleans 53 million gallons of water per day and serves 217,000 people in northern Cook County.

Considering the immense energy required to provide clean water – the so-called “water-energy nexus” – and the energy resource present in sewage, expect to see more municipalities retrofit their water reclamation plants with sewerthermal systems.