Can you link to any information about this process? I would think there's always some byproducts, other than just ash?

https://en.wikipedia.org/wiki/Waste-to-energy_plant

From Wikipedia: "Waste-to-energy plants cause less air pollution than coal plants, but more than natural gas plants."

That sounds, uh, pretty good considering the input is garbage! GIGO doesn't apply when it comes to power generation, apparently.