NOVELTY - Processing carbon-containing residues, by working-up of carbon-containing residues incorporating production of hydrogen gas and fermentation to give a biogas so that the aqueous phase is worked up (16) after the fermentation and the water obtained is recycled, especially as process water for the pressure- or steam-reformer (17), is new.    USE - Production of energy from waste materials and recovery of plastics such as PVC.    ADVANTAGE - The environmental problems associated with the process of DE4402559 for conversion of plant material to energy are in part overcome, with the process being simplified and the environmental impact of exhaust gases minimized.    DETAILED DESCRIPTION - Working-up of residues and conversion of the carbon-containing components involves:    (a) separating off the inorganics and metals;    (b) separating off the solids from the aqueous phase and pelletizing them; and    (c) converting the solids in a pressure reactor to an energy-providing hydrogen-containing gas and fermenting the aqueous phase to produce biogas energy, the novel feature being that the aqueous phase is worked up (16) after the fermentation and the water obtained is recycled, especially as process water for the pressure- or steam-reformer (17).    An INDEPENDENT CLAIM is also included for a process in which the process material is sorted (1) and treated (2)-(6) and then subjected to flotation separation (7; Sink-Schwimm-Trennung) with the floating components and a sinking fraction being removed and pelletized or extruded, while simultaneously fermentation to yield the biogas proceeds.    DESCRIPTION OF DRAWING(S) - The block diagram shows the stages of the process in sequence, namely    Pre-sorting/sieving (1)    Shredding (2)    Magnetic separation (3)    Sieving/air separation (4)    Hammer milling (5)    Sieving (6)    Flotation separation (7)    Fine shredding (8)    Plastics classification or sorting (9)    Pelletization (10)    Fine shredding (11)    Sorting (12)    Gas filtering (13)    Biogas storage (14)    Turbine (15)    Water work-up (16)    Steam reformer (17)    Gas filter unit giving pure H2 (18)    Fuel cell (19)