People have been looking to turn municipal sewage into useful things like electricity, biochar or biofuels for many years.
Often biofuels require a blend of feedstocks, but a UK firm, Firefly Green Fuels, has just produced a jet fuel from 100% human poo with a near identical chemical compositions as A1 (fossil) jet fuel. And while not a zero-emission option, it does have a carbon footprint 90% less than conventional jet fuel, it doesn't require additional land use to grow the biofuel stock and its already pretty abundant!
https://www.bbc.com/news/uk-england-gloucestershire-67771640