NOVELTY - The number of suspension preparation stages selected, is sufficient to generate a given waste portion (5) at their end. This portion has a fibrous content exceeding that which would be generated by an even larger number of stages. The waste portion (5) is devoted to thermal- or electrical energy generation. This energy is partially or entirely supplied: for production of fibrous mixture, to the papermaking machine (14) or to a connected paper finishing plant.    USE - To produce a mixed, recycled fiber suspension for papermaking machine. To operate a papermaking and finishing plant economically, with high energy efficiency.    ADVANTAGE - This method produces papermaking suspension, especially from recycled waste paper, in a more economical manner than in prior art. Natural resources are conserved. The method avoids maximizing papermaking fiber recovery, because the costs rise exponentially as perfection, i.e. 100% recovery of all fibers, is approached. Instead, the waste, or reject portion of the fibers is optimized for energy recovery, in the interests of maximizing overall profitability of the plant. Thermal energy recovery is used with advantage to offset the considerable energy demand of drying operations in papermaking and finishing processes, whilst the electricity generated, is consumed in all stages.    DETAILED DESCRIPTION - A flotation plant (12) is used. The method produces graphic- or packing paper. The portion used for energy production (5) has a fiber content exceeding 8%, 20%, 30% or 50%. At most, only a single stage is used in the sorting plant (10), cleaning plant (11), flotation plant (12) or washing plant. From the waste portion (5) used to produce energy, a fuel is obtained using a biogas plant (13). The fuel recovered is hydrogen, hydrocarbons, methane, alcohols or methanol. It is oxidized or burned to produce thermal and/or electrical energy. Further biological waste is added to the waste portion (5). At least some heat obtained from combustion, is sent to one or more processing stages, the papermaking machine (14) and/or to paper finishing. The fuel may be used in a fuel cell, to produce electrical energy and/or process heat. Heat arising from combustion is converted at least in part, into electrical energy. This is supplied to one or more processing stages, the papermaking machine and/or to paper finishing stages.    DESCRIPTION OF DRAWING(S) - An implementation of the invention is presented in block diagram form.    waste portion (5)    sorting plant (10)    cleaning plant (11)    flotation plant (12)    biogas plant (13)    papermaking machine (14)