Why is it not used again and wouldn’t it be very efficient to combine with a heat pump for reuse?
Especially since water from shower or sink isn’t usually very dirty, couldn’t it be stored for a while in an isolated tank so that e.g. a heat pump can run more efficient on it than on usually colder air or colder ground water?
In: Engineering
It is in my area! There’s a conversion station nearby in a low elevation area. Warm local sewage flows down, and heat is extracted via a heat pump. The heat is then used to heat a smaller volume of water much hotter (~80C iirc, it’s been a while). This hot water then heats many of the buildings in the area!
This obviously has a pretty big overhead and requires a lot of waste water to be effective – as others have pointed out there isn’t much use to using personal waste water only, there’s just not enough energy. But it’s definitely something that can be done at the municipal level.
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