The paper industry has a high fresh water demand. At the beginning of the 20th century, about 500 to 1000 m3 of water was required for the production of one ton of paper. Today the specific fresh water demand is much lower. The German paper industry, for instance, has succeeded in reducing the specific fresh water consumption to 13 m3 (t paper)–1 which corresponds to a wastewater volume of about 11 m3 (t paper)–1. In an international comparison, the performance in sustainable use of water resources of the German paper mills is very good. In the following mainly data from the German pulp and paper industry is pre¬sented, because of the high technical standard of wastewater treatment in this country.
Characterization of Untreated Wastewater
The pollution in the wastewater of a paper mill depends on the type of raw mate¬rial, the type and amount of fillers and chemical additives applied, and on the degree of circuit closure. Effluents from mills that largely or exclusively process chemical pulps have a lower degree of pollution than those from mills in which mechanical pulp or recovered paper is employed. The use of starch or other or¬ganic additives results in a marked increase in oxidizable effluent compounds, measured as BOD5 (biological oxygen demand) or COD (chemical oxygen de¬mand).
Dyes and fillers can lead to discoloration and/or turbidity of effluents. Effluents from paper mills have a low content of nitrogen and phosphorus compounds. For this reason, these elements must be added as nutrient salts (e. g. urea and phos¬phoric acid) to feed micro-organisms during treatment in biological purification plants. The closure of the water circuit within the mill results in an increase in the concentration of the effluent components. On the other hand, the inorganic and organic load is reduced owing to its partial elimination via the paper produced. For this reason, the specific load in kg per t of paper (specific load = concentration V specific amount of effluent) is a more suitable parameter for quantifying the efflu¬ent pollution. Information on the specific COD and BOD5 loads, classified accord¬ing to product groups, is given in