I'm not claiming to have good ideas, just brainstorming.
Once you got the methane, you could store it in solution (in diesel fuel or some other liquid with a low vapour pressure which dissolves methane). I expect it would be difficult to store in a gaseous state and the flow may not be sufficient for continuous burning.
If you could digest your waste with water and no oxygen you could make ethanol instead of methane which you could add to gasoline.
Alternatively, passing an electric arc through a mixture of methane and oxygen might produce some more useful hydrocarbons and water.