Although waste will be produced, that doesn't mean it's emitted into the air. There is a famous waste burning plant[1] (~6MW) within the city of Vienna, and which is near residential buildings and supplies the nearby general hospital with energy. The waste gases are thoroughly processed and filtered. It emits CO2 of course but it certainly wouldn't be permitted to operate at that location if it produced anything more immediately harmful to the surrounding population.

[1] https://de.wikipedia.org/wiki/Müllverbrennungsanlage_Spittel...

Certainly not!

There are minerals that you can add that cause ash to turn into a glassy slag for later removal. You can also use a cyclonic collector similar to what is used in bagless vacuum cleaners to capture any particle that are contained in the gas, not to mention filters for removing sulfur and any other harmful chemicals that might harm the turbines that burn the resultant syngas as fuel.

There are some technical details here, albeit in an advertorial format: http://www.volund.dk/Waste_to_Energy/References/ARC_Amager_B...

The plant is located very close to downtown Copenhagen, and there is no ash issue.

It's probably plasma gasification plant which produces slag which in turn is used in paving roads, etc.

Personally I've looked what is slag consist of as it doesn't seem like it could be very green, but so far looks like good idea.