A plasma-assisted waste gasification system and process for converting waste stream reaction residues into a clean synthesis gas (syngas) is disclosed. The feedstock is fed into a reactor roughly one-third from the bottom through the use of a feed mechanism. The reactor has three zones; a bottom zone where melting occurs, a middle zone where gasification takes place, and a top zone with integrated plasma torches to control the temperature and polish the syngas. The residence times in the three zones are selected to optimize the syngas composition and melted products. The syngas leaves the reactor and is partially quenched with relatively cooler synthesis gas. The partially quenched syngas is further cooled to recover heat for steam generation and/or preheating the waste stream to the reactor. The cold syngas is then processed to remove pollutants. The clean synthesis gas is combusted in power generation equipment to generate electricity, or converted to other fuels by chemical processes.