The different processes within the pulp and paper industry result in the formation of different solid and sludge-like residues. In terms of volume, the largest are those from the deinking of recovered paper and from the treatment of effluents. Wood residues are also produced in large quantities, mainly in the pulp production. Other wastes arising at pulp mills are green liquor, lime sludge and ashes from energy generation and flue gas treatment.
Table 10.1 shows the solid wastes encountered in paper mills. Besides material removed from the pulper or ejected from a drum pulper, solids separated by screening and cleaning are all rejects. Among the sludges encountered there are deinking sludges, solids removed during the mechanical clarification of fresh wa¬ter, process water and wastewater, and sludges from biological effluent treatment plants. Classified as incineration residues are ashes and slags from internal power plants and waste incineration plants including fly ashes. In the category of other waste are chemical residues, used oil, wire and felts and hazardous waste, such as certain laboratory chemicals, batteries or transformer fluids. Wood residues such as bark and sawdust occur where mechanical pulp is also produced at the paper mills concerned.
In Germany the most recent survey on residues from pulp and paper mills dates back to 2001 . According to the data gathered by the German Paper Industry Association a total of 3.6 million tons of residues was produced. This volume re¬fers to the residues in their original state. The calculated mean dry content of all residues was 57 %. Figure 10.5 shows that deinking sludges and sludges from process water and effluent treatment account for the largest proportion of residues with 30 % each. Rejects from recovered paper processing contribute 15 %, followed by incineration residues (11 %) and bark (10 %). Rejects from primary fiber proc-essing and other residues e. g. chemical waste, used wires and felts, and used oil account for only a small share.
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