This might work, but in a city, a large centralized system might be more effective.

I already have a septic tank, but I think the tiny amount of human waste that goes in it in one day wouldn't produce much methane fuel. I do know that hog-farms utilize these systems for heating, etc, but they have much more waste. The Mad Max Beyond Thunderdome movie had this too.

I think you'd be suprised how much methane a full septic tank might produce. Have you ever opened it up and taken a whiff? lol The biggest problem I see is getting wastes into it without losing all your methane that you've produced. A person can also up methane production by putting more anaerobic bacteria into the system.

Methane is odorless. The gasses you are smelling are mostly sulfur compounds that are not suitable as fuel.