Description of waste pyrolysis and gasification:
Pyrolysis is thermal decomposition at about 400 C and higher without the addition of oxygen or air. Proponents claim pyrolysis takes place without oxygen but medical or municipal solid waste will always contain some oxygen. Gasification, which is considered combustion by EPA and therefore covered under EPA's medical waste incinerator rule, is thermal decomposition at about 400 C and higher with the addition of a limited amount of air or oxygen. Both pyrolysis and gasification plants are in effect incinerators since their gas products are subsequently burned. For this reason, both are considered incineration by the European Union. Depending on the composition of the waste and operating conditions, they release dioxins and furans, mercury and other metals, particulate matter, carbon monoxide, hydrogen chloride, sulfur dioxide, etc. as well as toxic contaminants in the char or ash residues.
Health Care Without Harm's short explanation on pyrolysis and gasification is at:
http://www.noharm.org/library/docs/Update_on_Pyrolysis.pdf