From what I can recall, landfills produce more methane than any other process. How about we build a carbon capture next to every landfill, divert the methane and burn it to run the DAC?
https://archive.epa.gov/climatechange/kids/solutions/technol...
If the landfill can generate electricity that would otherwise be generated, it will convert the CH4 more efficiently than a bus and you don't expand energy upgrading it.
You can power the bus with the already high quality CH4 you extracted from the ground that you would have otherwise burned in to generate the electricity.
I was reading somewhere that in buses in cold climates, heating is actually what eats up all the energy in an electric bus. ICE buses just use the waste heat from a combustion engine.