Lots of things are 'recycled' into energy. I did some work on a wood chip and sawdust fired power plant in Maine. Lots of lumber and paper mills there and they generate a lot of bark, chips, and sawdust. A modern facility with good pollution controls can burn that stuff up just fine. Quite a few odd hydrocarbons (off-spec paint, for example) get blended into No. 6 oil for power plants or cement kilns.
Oddly enough, trash is hard to burn for energy and most places that tried it failed miserably. It's too inconsistent unless it is pre-processed. Monday's trash will have far more grass and leaves than other days of the week. There's an interesting method that separates trash into different components - recovering glass and metals while compiling all the paper, wood, etc. for combustion. Someone tried to build a plant for that near Pittsburgh, but whiny locals shot it down.
Quite a few things - including used cooking oils and fats - can be compounded to make biodiesel. The stuff works pretty well and will clean out the carbon deposits that normal petroleum diesel leaves. Far better energy recovery than making ethanol.