Sewage-Source Heat Pumps Turn Wastewater to Warmth

Every time hot water goes down the drain from showers, sinks, dishwashers, clothes washers, and yes, even toilets, energy is wasted—to the tune of about 350 billion kWh, according to the U.S. Department of Energy.

A few wastewater treatment plants have started recovering some of that energy by using heat pumps to deposit excess heat in the summer or extract heat in the winter from the effluent in their holding pools, but much of the heat energy dissipates as the water is pumped to the facility. Individual buildings can employ small drainwater heat exchangers to take advantage of the hotter water before it enters the sewer, but as they’re incapable of handling chunky solids, any heat energy contained in the building’s blackwater is lost, and the gadgets are dependent on relatively high flows.