If we think insulating a single home is bad, image trying to build the infrastructure for that throughout a city.

There's closed loop ground source heat pumps. It's all very situational as to whether they are practical to install. The vertical ones are more expensive but don't need a whole lot of ground area to be installed.

In my city, about 10% of the district heating load is covered by heat pumps where the heat source is municipal waste water.

A similar idea that's somewhat popular in Sweden is to add a heat-exchanger between outgoing sewer water and incoming tap water. You don't need to put fins into the outgoing water, it's simply a piece of regular straight copper pipe, but it's thicker, and the incoming water pipe coils around it a bit.

No need to muck around with fins in the sewage, or trying to convert to electricty, simply heating the incoming water a degree or two saves energy for your water heater.