>energy from treated sewage

wouldn't untreated sewage, still fermenting, be warmer?

Maybe. I guess it's easier to handle in treated form though. At the point where it gets to the facility it's actually not really sewage anymore, it's just clean water, so after passing the heat pumps it's just released into a nearby lake via a small turbine (both the sewage treatment plant and the heating plant ar located above the water level of the lake).