All organic matter contains a lot of Energy that we could release. But it's often not in a very useable form. First organic matter can be hard to move around the place, second it might be wet so wont Combust, and third even it if does Combust it may not do so nicely—it may cause lots of smoke or pollution 1. Finally, depending on where the material comes from, it may contain various infective nasties.
One solution to this is the AnaerobicDigestionPlant. In essence, this is a high tech compost heap. You put all the organic material into a big pot, with some bacteria, seal it away from Oxygen. The bacteria start to rot the material. This generates lots of heat (which so long as it does not get too hot will help the bacteria grow) and as the Oxygen is used up, it will produce Methane and other more complex hydrocarbon gasses. This you can pipe off and use in the NaturalGas infrastructure.
If you use two incubators, the second containing ThermophilicBacteria you can break down a pretty high percentage of organic matter. The high temperature ensures that most of the nasty bacteria or pollutants will be destroyed.
You can this for getting rid of rubbish. It's been mostly investigated for this purpose. Alternatively, you could just use CyanoBacteria or SingleCelledAlgae grown artificially in a BioFuelReactor. In this case, you loose energy, but you end up with Methane, rather than a solid AlgaeCake, which may be more usuable.
The other end product of a AnaerobicDigestionPlant is a slurry of sorts. It should be pretty clean and can be just used as fertiliser, Alternatively, it could be further used in a BacterialFuelCell, to produce Hydrogen.
1. Or much worse, nasty farmyard smells.