Well-spotted.
When I take vacations, I try to tour sewage plants in other cities and countries. Germany had closed this loop many decades ago on this opportunity you speak of. In 1990, I was in southern Germany in late fall and on that tour, I saw the treatment plant’s whole building complex (multi-story office buildings, plus some outbuildings and machine sheds) heated by burning methane, with additional methane being used in other applications like electrical generation and keeping the microbes warm (and alive) in the winter. (I can’t find a good source quickly but here’s a start for an overview: https://www.globalmethane.org/expo-docs/canada13/mww_13_Beckmann.pdf and sorry it’s kinda technical.)
Here in Austin, Texas we have the Hornsby Bend Biosolids Management Plant. The old term for this place had been “sewage treatment plant.” The place generates precious clean-ish water and compost (typically used for trees, lawns, and non-food flora) from Austin’s sewage. And in the process of composting the “biosolids” (i.e. sludge), plenty of methane is available to do real work.
http://www.austintexas.gov/department/dillo-dirt-treatment-process
Methane gas, a by-product of the process, is used to power on-site electric generators.
