The Wikipedia page on sewer gas states that
Sewer gas can be used as a power source, thus reducing the consumption of fossil fuels.
However, no references or further details are provided.
So, suppose that a typical modern house had its vent stack replaced by sewer gas burner system. Just how much power could that actually produce?
Addendum: Yes, biowaste is currently used for power generation. And one could set up a bioreactor specifically to produce power from your own local waste. But this is specifically about the power available to a single house via the "natural" gas emissions from an actual sewer. Regardless of how many people live in a house, a modern house (not apartment) most places in the world that have municipal sewer systems will have a single connection to said sewer via pipe of one of a few standard sizes, which is also connected to a vent stack which allows gas to get sucked into the plumbing system when a slug drops through the pipes to avoid accidentally clearing P-traps, and which allows sewer gas to escape out of the house rather than building pressure behind P-traps.
So, how much power could be obtained just by tapping that vent stack to access the gasses coming up from the sewer?
Sewer gas lamps are an (archaic) thing that exists, but they were never used for actual light or power--merely to induce an updraft to force sewer gasses to vent above head hieght and prevent buildups that would be unpleasant if they escaped at ground level.
If that does not represent a reasonable power source, and to grandfather in existing answers, it would also be interesting to know how much power can be supplied per person via small-scale residential bioreactors. And if coupled with a municipal sewer system, could that sort of preprocessing represent a practical method of reducing strain on said municipal sewer and wastewater treatment systems?