You can actually recover heat from sewers which can heat water or space in nearby buildings. The first example of this (in North America at least) went online i

You can actually recover heat from sewers which can heat water or space in nearby buildings. The first example of this (in North America at least) went online in Vancouver around 2010[1]. > Similar to a geo-exchange (or geothermal) system, heat pumps transfer thermal energy from the warm sewage supply to a higher temperature range that’s effective for residential space heating and domestic hot water. While similar in concept, sewage heat recovery is more efficient and cost effective than typical geo-exchange systems. The heat source (raw sewage) has a higher temperature than ground-source heat (on average 18 degrees Celsius as opposed to 8), so it requires less energy to upgrade. Secondly, accessing the sewer line is less invasive and less capital cost intensive than drilling into the earth to access geothermal heat. It also utilizes a continuous supply of waste heat, closing the loop on a fundamental energy >> waste >> energy stream. [2] [1] http://greenbuildingaudiotour.com/buildings/sefc_neighbourhood_energy_utility http://greenbuildingaudiotour.com/buildings/sefc_neighbourho... [2] http://www.thechallengeseries.ca/chapter-05/neighbourhood-energy-utility/#sewer http://www.thechallengeseries.ca/chapter-05/neighbourhood-en...