Thermal plasma treatment
of sludge has a significant benefit in
converting hazardous waste into renewable combustible gas and inert
solid product, which is a workable solution for energy and material
recovery. The advantages of this approach also lie in its flexibility,
smaller installation, greater compactness, fewer contaminant emissions,
and minimization of mass and volume. The present review focuses on
various thermal plasma processes for sludge treatment and co-processing.
The review starts with fundamental aspects of plasma and mechanisms
of thermal plasma sludge treatment and then four basic thermal plasma
systems used in previous studies. Five main thermal plasma conversion
processes of sludge are classified and discussed, namely, plasma combustion,
plasma pyrolysis and vitrification, plasma gasification and vitrification,
plasma co-processing, and pre-processing combined with thermal plasma
unit. Specifically, key parameters influencing thermal plasma treatment
of sludge are distinguished and discussed as well as energy and material
recovery. On these bases, the challenges and future research perspectives
are addressed.