PURPOSE: To provide a waste treatment method including the formation of a substantially continuous curtain of plasma and directing the material to be treated so as to pass this curtain.

CONSTITUTION: An electric arc 6 is formed between two electrodes 1 and 2 which are separated by an annular space 5 and the arc column is rotated about the axis of the annular space 5 so that a substantially uninterrupted curtain of plasma bridges the space and extends around the circumferential extent of the space. The direction of rotation of the arc column is approximately transverse to the direction in which the column extends between the two electrodes. The material to be treated is fed through the curtain in a direction which is transverse to both the rotational direction and the direction of longitudinal extent of the arc column. One of the electrodes may be of cylindrical tube form, in which the material to be treated is fed in the region of the arc through the axial bore of the electrode. The other electrode may have a cavity in alignment with the adjacent end of the tubular electrode which serves to direct the material in a direction such as to pass through the plasma curtain.