Are we talking about classic incinerators (simply burn stuff) or plasma arc (gasification)incinerators? With plasma arc gasifications the temperatures are so high (2,200 to 13,900 °C) that all the waste and any resulting toxic byproducts, the very molecules themselves, are broken down to individual atoms. There are no toxic compounds left.

All that remains at the end is ash that contains various metals and syngas that is produced in the process. Which can be used for generating electric power.

I hope plasma arc gasification becomes the standard for managing and disposing municipal solid waste. It really works. But you do need a certain scale (enough waste) for it to be effective.

https://en.wikipedia.org/wiki/Plasma_gasification

http://www.waste-management-world.com/articles/print/volume-...