Here’s another big city harvesting “waste” heat from sewage. Milwaukee wants to use sewage to warm buildings at two sewage treatment plants. Even at the below-zero temps of this winter’s polar vortex, sewage flowing beneath Milwaukee streets was a temperate 55° F, so it would not take much additional energy to provide indoor comfort.
“Sewage gets its warmth from all of the water heated in businesses and residences every day — for cooking and showers, as well as washing hands, dishes and vehicles — that is flushed down drains to sewers where it mixes with heated wastewater from industries. The steady flow is carried away to treatment plants,” writes the Milwaukee Journal Sentinel.

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