A few posts ago, I joked about installing a paper reactor. Such a device would be a small fireplace that burns paper, and extracts the energy to do useful work or make electricity.
Paper tends to burn very quickly, due to the high surface area and low volume. Still, a large organization could probably provide a constant supply of unwanted paper to keep it going. A single person, such as myself, would quickly run out of such paper and have to supplement with something else, such as wood, or garbage.
The device would consist of a fireplace-like chamber with small holes in the bottom. The holes not only vent air up to provide the oxygen for combustion, they also let the ash from burned paper sink out from the reactor to free up space. Below this should be a ramp to a waste chute. Ash might make good fertilizer, but I doubt anyone will care to collect it.
Above the fireplace chamber will be a chute that unwanted paper enters through and a method to use the heat, of which I know two. One method is to have a tank of water, which boils from the heat, the steam turns a turbine, generating power. The other is the stiller engine, which moves a piston based on the end near the fire being hot and the end far from the fire being cold(er). Either way, wires should then carry the power to the main grid. The burning chamber should also have a vent for the smoke to the outside, because otherwise smoke will escape up the paper-receiving chutes. The turbine method should also have a condenser that cools the steam back into water and bring it back to the tank, since otherwise one would constantly have to vent steam and refill the tank with a hose.
I estimate that a large businesses burned paper would generate about 500 watts of power. They would also appreciate the additional security, since they often destroy papers that could damage them if stolen by shredding, and this would provide a second obstacle to reconstructing the papers. (Yes, one could technically reassemble a shredded paper. It's harder if the paper is cross cut. It's much much harder if the paper is burned. It's nearly impossible if the paper is cross cut and then burned. It's utterly impossible if the waste chute splits between multiple receptacles.)